Geochemical Methods of Prospecting and Exploration for Petroleum and Natural Gas [Reprint 2020 ed.] 9780520346079

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GEOCHEMICAL METHODS OF PROSPECTING AND EXPLORATION FOR PETROLEUM AND NATURAL GAS

A. A. KAPLIEB, 3. A. TABACAPAHCKHft, M. M. CyBBOTA, F. A. MOrK/IEBCKHfl

rEOXHMHMECKHE METOflbl nOHCKOB H PA3BEÄKH HETHHbIX M TA30BbIX

MECTOPOÄÄEHHPI

rOCyAAPCTBEHHOE HAyMHO-TEXHHMECKOE H3iXATEJIbCTBO HETHHOFl H rOPHO-TOn/IHBHOPl JIHTEPATyPbl M o c KBa

1954

A. A. KARTSEV, Z. A. TABASARANSKIT, M. I. SUBBOTA, and G. A. MOGILEVSKII

GEOCHEMICAL METHODS OF PROSPECTING AND EXPLORATION FOR PETROLEUM AND NATURAL GAS English Translation Edited by PAUL A. WITHERSPOON and WILLIAM D. ROMEY

BERKELEY AND LOS ANGELES

UNIVERSITY OF CALIFORNIA PRESS 1959

UNIVERSITY OF CALIFORNIA PRESS B E R K E L E Y AND LOS ANGELES, CALIFORNIA CAMBRIDGE U N I V E R S I T Y PRESS LONDON, ENGLAND © 1959, BY T H E REGENTS OF T H E UNIVERSITY OF CALIFORNIA LIBRARY OF CONGRESS CATALOG CARD N U M B E R : 5 9 - 1 1 3 1 3 PRINTED B Y O F F S E T IN T H E UNITED STATES OF AMERICA

Prefaces EDITORS' PREFACE California Research Corporation, a subsidiary of Standard Oil Company of California, became interested in this book because of its excellent and comprehensive coverage of the subject of geochemical prospecting f o r petroleum in the Soviet Union. After making a complete English translation, they decided that the petroleum industry in America and elsewhere would be interested in the many concepts presented and in the detailed descriptions of methodology and results. Accordingly, they kindly turned the translation over to the Minerals Research Laboratory of the Department of Mineral Technology, University of California, Berkeley. This translation is an accurate reproduction of the authors' original and has been carefully checked for its scientific exactness. In several chapters, where sections seemed obscure, the original Russian has been retranslated. In this connection, we gratefully acknowledge the excellent work of Dr. W. D. Rosenfeld of California Research Corporation in editing Chapter XIII, "Microbiological Methods." His valuable assistance on this important chapter is especially deserving of recognition. In some places, however, it was not feasible to redraft the entire text into literary English. Thus, although the translation is a faithful reproduction of the original, the reader may occasionally find the phraseology somewhat unfamiliar because of the differences between English and Russian syntax. Some unfamiliar data or terminology, however, is merely a reflection of the differences between petroleum technology in the Soviet Union and in the United States. Most of the illustrations were adapted from the original publication, and the legends translated into English. A number of illustrations, however, could not be handled in this manner, and it was necessary either to eliminate them or to obtain the original drawings and photographs. When the authors were informed of this, they immediately provided all necessary materials through the Soviet agency, Mezhdunarodnaya Kniga, and thus made it possible to include illustrations that could not otherwise have been published. We should like to thank Mezhdunarodnaya Kniga and the authors for this generous assistance. As might be expected in a technical translation, some words in Russian do not have exact equivalents in English. For example, "neftyanoe mestorozhdenie" has been translated as "petroleum formation" or "petroleum deposit" and has a much more general meaning than "neftyanaya z a l e z h ' , " which has been translated as " o i l pool". As used by the authors, " p e t r o leum formation" means a group of " o i l pools" below a single region of the surface plus all intervening and overlying beds. Thus, a " f o r m a t i o n " may include both productive and non-productive sections of strata. The authors also distinguish between the use of " p o i s k o v , " which has been translated as "prospecting," and " r a z v e d k a , " which has been translated as [ix]

PREFACES

X

" e x p l o r a t i o n . " " P r o s p e c t i n g " f o r p e t r o l e u m should be understood to i n clude the use of methods that a r e r e s t r i c t e d to the e a r t h ' s s u r f a c e and a r e l a r g e l y c a r r i e d out in undrilled a r e a s . " E x p l o r a t i o n " f o r p e t r o l e u m , on the other hand, should be understood a s the work that is done a f t e r " p r o s p e c t i n g " is finished, such a s the examination of b o r e holes f o r evidences of oil or g a s . The work " p o r o d , " which h a s been t r a n s l a t e d a s " r o c k , " is a n o t h e r t e r m that has a m o r e g e n e r a l m e a n i n g in this book that it n o r m a l l y h a s in English. As used by the a u t h o r s , " r o c k " includes both consolidated and unconsolidated f o r m s . The work " g l i n a , " which h a s been t r a n s l a t e d a s " c l a y , " a p p a r e n t l y can a l s o s o m e t i m e s m e a n " s h a l e , " a s will be evident to the r e a d e r in Chapter VI. A n u m b e r of o t h e r such t e r m s o c c u r at v a r i ous p l a c e s in the text. T h e s e a r e usually used only in a single c h a p t e r , and, t h e r e f o r e , explanatory footnotes have been added at a p p r o p r i a t e points. The r e a d e r will a l s o encounter a n u m b e r of geologic n a m e s that a r e used to d e s c r i b e the s t r a t i g r a p h y of t h o s e p a r t s of the Soviet Union where oil is produced. F o r those who a r e not f a m i l i a r with this s t r a t i g r a p h y , a g e n e r alized geologic column is included a s an Appendix. The original t a b l e of contents of the R u s s i a n edition has been g r e a t l y expanded, and it is hoped that it will s e r v e a s a guide to the d e t a i l s of the s u b j e c t m a t t e r . We should like to thank the a u t h o r s f o r t h e i r g r e a t i n t e r e s t in this t r a n s l a t i o n . In addition to supplying the i l l u s t r a t i v e m a t e r i a l mentioned above, they have a l s o contributed a p r e f a c e to this edition. The e m p h a s i s in g e o c h e m i c a l p r o s p e c t i n g in the Soviet Union h a s changed somewhat s i n c e 1954, when this book was f i r s t published. As the a u t h o r s indicate, h o w e v e r , the f u n d a m e n t a l i d e a s and techniques have not changed. C e r t a i n l y , nothing c o m p a r a b l e to t h i s t r e a t m e n t of the subject has yet a p p e a r e d in the English language. Finally, we want to e x p r e s s our s i n c e r e a p p r e c i a t i o n to P r o f e s s o r H. E. Hawkes, University of C a l i f o r n i a , f o r s u g g e s t i n g that we u n d e r t a k e the publication of this t r a n s l a t i o n . As d i r e c t o r of a l i t e r a t u r e r e v i e w p r o j e c t on g e o c h e m i c a l p r o s p e c t i n g , P r o f e s s o r Hawkes was quick to a p p r e c i a t e the value of this book and urged that it be published. Berkeley M a r c h 1, 1959

P a u l A. Witherspoon William D. Romey

AUTHORS' P R E F A C E TO AMERICAN EDITION The R u s s i a n edition "of t h i s book was published in 1954. Naturally a g r e a t many new developments have o c c u r r e d in the field of g e o c h e m i c a l p r o s pecting and exploration f o r p e t r o l e u m during the past f o u r y e a r s . F o r the m o s t p a r t , however, t h e s e changes have not affected the f u n d a m e n t a l methods o r techniques d e s c r i b e d in this book. R a t h e r , they have been concerned with the ways in which v a r i o u s geochemical p r o c e d u r e s have been applied. The p o s s i b i l i t i e s of the v a r i o u s m e t h o d s and logical ways of combining t h e m have been made c l e a r e r through p r a c t i c a l applications. It has been found that g e o c h e m i c a l investigations involving h o r i z o n s close to the s u r f a c e a r e e f f e c t i v e in geologic p r o v i n c e s where the r o c k s a r e considerably d i s t u r b e d . Under s o m e other conditions, they a r e r e l a t i v e l y ineffective. G e o c h e m i c a l investigations of h o r i z o n s that have been cored have been found to be p a r t i c u l a r l y advantageous. Combining t h i s type of

PREFACES

xi

investigation with the d r i l l i n g of shallow geologic s t r u c t u r e t e s t s is u s e f u l . The combined use of w a t e r - g a s , h y d r o c h e m i c a l , and b a c t e r i a l s u r v e y s in studying a q u i f e r s h a s been widely developed. Consequently the r e l a t i v e significance of v a r i o u s p a r t s of the book h a s changed s o m e w h a t . We a r e g r e a t l y pleased that our work will be a c c e s s i b l e to E n g l i s h speaking r e a d e r s . We would like to e x p r e s s o u r s i n c e r e g r a t i t u d e to the people and institutions who have contributed to the t r a n s l a t i o n and publication of this book in E n g l i s h , and e s p e c i a l l y to the w o r k e r s at the M i n e r a l s R e s e a r c h L a b o r a t o r y of the University of C a l i f o r n i a and to P r o f e s s o r P a u l A. Witherspoon. Moscow J a n u a r y 10, 1959

A. Z. M. G.

A. A. I. A.

Kartsev Tabasaranskii Subbota Mogilevskii

AUTHORS' P R E F A C E TO RUSSIAN EDITION All of the g e o c h e m i c a l m e t h o d s used in p r o s p e c t i n g and exploration f o r p e t r o l e u m and n a t u r a l gas a r e d e s c r i b e d in this book. T h e o r e t i c a l p r i n c i p l e s , field m e t h o d s , and techniques of geological i n t e r p r e t a t i o n a r e s e t f o r t h . The g e o c h e m i s t r y of p e t r o l e u m and n a t u r a l g a s f o r m a t i o n s is a l s o p r e s e n t e d . The book is intended as a text f o r s t u d e n t s of p e t r o l e u m s c i e n c e and f o r p e t r o l e u m geologists in t h e i r p r a c t i c a l work. The introduction and c h a p t e r s I, II, VII, VIII, IX, XI, XII, and XIV w e r e w r i t t e n by A. A. K a r t s e v . Z . A. T a b a s a r a n s k i i w r o t e chapter VI; M. I. Subbota, c h a p t e r s III, IV, V, and X; and G. A. Mogilevskii, c h a p t e r XIII. The m a n u s c r i p t was r e a d e n t i r e l y o r in part by s e v e r a l people whose c o m m e n t s the a u t h o r s g r e a t l y a p p r e c i a t e d . The a u t h o r s a r e e s p e c i a l l y g r a t e f u l to the Head of the C e n t r a l P e t r o l e u m and G a s E x p l o r a t i o n Division (Glavneftegazrazvedka) G. L. G r i s h i n , P r o f e s s o r M. V. A b r a m o v i c h , P r o f e s s o r A. F. Dobryanskii, P r o f e s s o r S. I. Kuznetsov, Doctor of G e o l o g i c a l M i n e r a l o g i c a l Sciences L. A. Gulyaeva, V. N. F l o r o v s k a y a , L e c t u r e r B. I. Sultanova, L e c t u r e r B. S. Moldavskii, Candidate of G e o l o g i c a l - M i n e r a l ogical Sciences E . A. B a r s , and Candidate of P h y s i c a l - M a t h e m a t i c a l Sciences P . L. Antonov. The a u t h o r s a l s o e x p r e s s t h e i r thanks to D o c t o r of Biological Sciences S. V. Viktorov, who contributed a s h o r t s e c t i o n on geobotanical i n d i c a t o r s of p e t r o l e u m - b e a r i n g f o r m a t i o n s to the book.

Contents INTRODUCTION I

xxi

THE GEOCHEMISTRY O F P E T R O L E U M FORMATIONS

. . . .

Properties of Petroleum The physical state of petroleum, 2; State of knowledge on the composition of petroleum, 3; Elemental composition, 4; Hydrocarbon composition, 4; Acids, 6; Compounds of sulfur and nitrogen, 6; T a r s and asphaltenes, 6; Elements of the ash, 7; Specific gravity, 7; Optical activity, 7; Physiological activity, 8; Regularities in the chemistry of petroleum, 8.

2

Physical and Chemical Conditions in Petroleum Formations . . . Temperature, 11; P r e s s u r e , 12; Motion of subterranean waters, 12; Physicochemical and chemical properties of rocks and waters, 12.

11

Geochemical Processes in Petroleum Formations Metamorphism of petroleum, 13; Oxidation of petroleum, 16; Consequences of the oxidation of petroleum by sulfates, 19; Paragenesis of petroleum and sulfur, sulfuring of petroleum, 20; Physical processes, 21.

13

Causes of Petroleum Variability Role of initial composition, 23; Significance of physical processes, 24; Significance of geochemical transformation of petroleum, 24; Conclusions, 27; Practical importance of the question, 28.

22

Geochemical Peculiarities of the Gases, Waters and Rocks of Petroleum Formations Natural gases, 29; Waters, 33; Changes of properties of waters in oil-bearing strata, 35; Organisms, 36; Rocks, 37. Bibliography

II

1

28

37

CLASSIFICATION OF GEOCHEMICAL METHODS Geochemical Indices of Petroleum

[xiii]

PROSPECTING 42 42

xiv

III

IV

CONTENTS C l a s s i f i c a t i o n of G e o c h e m i c a l Methods A c c o r d i n g to Indices Used

44

C l a s s i f i c a t i o n of G e o c h e m i c a l Methods by Objective and by O r g a n i z a t i o n

44

THE GEOCHEMISTRY O F GASES

47

Introduction G a s e o u s m i n e r a l s , 47; G a s e o u s a s s o c i a t i o n s , 48.

47

P r o p e r t i e s of G a s e s D e t e r m i n a t i o n of g a s e s , 50.

48

T y p e s of G a s e s G a s e s in the a t m o s p h e r e , 50; G a s e s in the h y d r o s p h e r e , 51; G a s e s in the l i t h o s p h e r e , 52.

50

Origin of G a s e s and t h e i r G e n e t i c C l a s s i f i c a t i o n N a t u r a l g a s e s of p u r e l y g a s e o u s f o r m a t i o n s , 58; G e n e s i s of purely g a s e o u s f o r m a t i o n s , 60; Change in the composition of n a t u r a l gas within a f o r m a tion, 61; Dissipation of g a s a c c u m u l a t i o n s , 62.

53

Bibliography

62

GAS SURVEYS

64

Brief H i s t o r y of G a s Surveying

64

T h e o r e t i c a l B a s i s of the G a s Survey Migration of g a s , 66; P h y s i c a l f o r m s of g a s m o v e ment through r o c k s , 68; A l t e r a t i o n of a gas d u r i n g the p r o c e s s of m i g r a t i o n , 71; Composition of the g a s detected in the gas s u r v e y , 73.

66

V a r i o u s Types of Gas Surveys

75

Methods of Field Work A r r a n g e m e n t of s a m p l i n g points, 76; Drilling b o r e h o l e s , 76; Taking gas s a m p l e s , 77; S e a s o n a l f l u c t u ations of gas content, 82; C a u s e s of v a r i a t i o n s in gas concentration, 85.

76

G a s Analysis T o t a l a n a l y s i s of n a t u r a l g a s in the VTI a p p a r a t u s , 87; Analysis of h y d r o c a r b o n g a s e s in the Sokolov a p p a r a t u s , 90; A n a l y s i s of m i c r o c o n c e n t r a t i o n s of h y d r o c a r b o n s in s t a t i o n a r y m e r c u r y a p p a r a t u s , 90; Stationary m e r c u r y a p p a r a t u s , m o d e l No. 3, 90;

87

CONTENTS

V

VI

xv

G a s A n a l y s i s (Cont'd.) Stationary c i r c u l a t i v e m e r c u r y a p p a r a t u s , 92; A n a l y s i s of m i c r o c o n c e n t r a t i o n s of h y d r o c a r b o n g a s e s in the TG-5A a p p a r a t u s and the c h r o m a t o g r a p h i c a p p a r a t u s , 93.

87

I n t e r p r e t a t i o n of Gas Survey R e s u l t s P r e s e n t a t i o n of s u r v e y r e s u l t s , 96; Compilation of m a p s , 98; F o r m s of gas a n o m a l i e s , 101; Evaluation of the s u r v e y r e s u l t s , 106.

96

Bibliography

107

CORE-GAS SURVEYS

109

Introduction P r o b l e m s of the method, 109; Origin and development of the method, 110.

109

T h e o r e t i c a l B a s i s of the C o r e - G a s Survey.

110

Methods of Field Work Coring o p e r a t i o n s , 116; E f f e c t of s t o r a g e t i m e on c o r e s , 116; Depth of s a m p l i n g , 117; Fluctuation in the gas content of r o c k , 120.

116

Method of Degassing C o r e s Degassing at elevated t e m p e r a t u r e s , 122; D e g a s s i n g under v a c u u m at elevated t e m p e r a t u r e s , 122; D e g a s sing by d i s a g g r e g a t i o n of the r o c k under vacuum, 126; Degassing in boiling w a t e r , 128; G a s a n a l y s i s , 130.

122

I n t e r p r e t a t i o n of C o r e - G a s Survey R e s u l t s

131

O t h e r Methods of Studying the G a s Content of C o r e s The " t h e r m o b i t u m e n " s u r v e y , 132; Change of p a r a m e t e r s of m o n t m o r i l l o n i t e a s an index of h y d r o c a r b o n m i g r a t i o n , 134.

132

Bibliography

134

OIL AND GAS LOGGING

136

T h e o r e t i c a l B a s i s of Oil and G a s Logging

139

Methods and A p p a r a t u s Used in Oil and Gas Logging Mud logging, 143; I n t e r m i t t e n t d e g a s s i n g of d r i l l i n g m u d s , 144; Continuous d e g a s s i n g of d r i l l i n g m u d s , 146; Analysis of combustible g a s e s r e c o v e r e d f r o m d r i l l i n g m u d s , 151; Oil and gas logs based on a n a l y s e s of cuttings

143

xvi

CONTENTS Methods and A p p a r a t u s Used in Oil and G a s Logging (Cont'd.) . . and c o r e s , 155; Method of l u m i n e s c e n c e logging with drilling muds and cuttings, 156.

143

Automatic and S e m i a u t o m a t i c Logging Equipment

158

Method of Calculating Lag of the D r i l l i n g Mud

164

F a c t o r s Affecting R e s u l t s of Oil and G a s Logging G a s - o i l r a t i o and c r u d e oil composition, 167; F o r m a t i o n p r e s s u r e s , 168; Influence of w a t e r b e a r i n g l e v e l s , 169; Method of mud d e g a s s i f i c a t i o n , 169; D r i l l i n g p r o c e d u r e , 171; Clays used in p r e paring d r i l l i n g mud, 173; Addition of c r u d e oil and p e t r o l e u m p r o d u c t s to d r i l l i n g mud, 173; E f f e c t of higher productive zones on p e n e t r a t i o n of lower i n t e r v a l s , 173; Change in physical p r o p e r t i e s of d r i l l i n g mud, 175.

167

I n t e r p r e t a t i o n of Oil and G a s Logs I n t e r p r e t i n g manually r e c o r d e d data, 175; I n t e r preting oil and gas logs of single and m u l t i l a y e r f o r m a t i o n s , 177; Distinguishing between oil and gas zones, 181; I n t e r p r e t i n g automatically r e c o r d e d data, 183; Data n e c e s s a r y in oil and gas logging, 185; I n t e r p r e t i n g m e c h a n i c a l logs, 186; I n t e r p r e t i n g l u m i n e s c e n c e logs, 189; C h a r a c t e r i s t i c s of well logs f r o m v a r i o u s t y p e s of r o c k s , 191; C o r r e l a t i o n of oil and gas logs, 194.

175

Bibliography

196

VII BITUMEN METHODS

198

B a s i c Information on Bituminology Definition of the " b i t u m e n c o n c e p t , " 199; C l a s s i f i c a t i o n of b i t u m e n s , 201; C h a r a c t e r i s t i c p r o p e r t i e s of b i t u m e n s , 203; F r a c t i o n a l composition of b i t u m e n s , 206; Bitumens d i s p e r s e d in r o c k s , 207; Bound b i t u m e n s , 210.

199

Methods of Quantitative Analysis D e t e r m i n a t i o n of organic c a r b o n , 211; D e t e r m i n a tion of nitrogen, 211; D e t e r m i n a t i o n of b i t u m e n s by the weight method, 212; D e t e r m i n a t i o n of b i t u m e n s by the c o l o r i m e t r i e method, 212.

211

Application of Bitumen Methods P r o s p e c t i n g f o r o i l - b e a r i n g s t r a t a , 213; B i t u m e n a r e a s u r v e y s , 214.

213

CONTENTS Bibliography VIII BITUMEN-LUMINESCENCE METHODS

IX

xvii 217 219

B a s i c I n f o r m a t i o n on L u m i n e s c e n c e of B i t u m e n s L u m i n e s c e n c e , its m a i n f o r m s and s o m e p r o p e r t i e s , 220; P r i n c i p l e s of l u m i n e s c e n c e a n a l y s i s , 221; L u m i n e s c e n c e of b i t u m e n s , 222; L u m i n e s c e n c e of b i t u m e n f r a c t i o n s , 222.

219

L u m i n e s c e n c e Analysis of Bitumens Equipment, 224; Drop a n a l y s i s , 225; T e s t tube a n a l y s i s , 226; c a p i l l a r y a n a l y s i s , 226; A d s o r p t i o n a n a l y s i s , 227; Quantitative f r a c t i o n a l a n a l y s i s , 227; L u m i n e s c e n c e - e x t r a c t i o n a n a l y s i s , 227; M i c r o s c o p i c l u m i n e s c e n c e d e t e r m i n a t i o n s , 229.

223

Application of B i t u m e n - L u m i n e s c e n c e Methods Route s u r v e y s , 230; A r e a s u r v e y s , 230; Study of c o r e s f r o m deep w e l l s , 232; L u m i n e s c e n c e logging, 233; C o r r e l a t i o n of well s e c t i o n s , 235.

230

Bibliography

235

HYDROCHEMICAL METHODS

237

D i r e c t H y d r o c h e m i c a l I n d i c a t o r s of P e t r o l e u m Dissolved b i t u m e n s (soaps), 238; I m p l i c a t i o n s of p r e s e n c e or a b s e n c e of dissolved b i t u m e n s , 240; Phenols and t h e i r d e r i v a t i v e s , 241; Iodine, 242; Ammonia, 243.

238

I n d i r e c t H y d r o c h e m i c a l Indicators of P e t r o l e u m H y d r o s u l f i d e s and other reduced compounds of s u l f u r , 244; a b s e n c e of s u l f a t e s , 246; Soda (alkalinity), 248; C a l c i u m c h l o r i d e , 249; B r o m i n e , 249; G e n e r a l c h a r a c t e r i s t i c s of the salinity of b r i n e s , 250; Use of combined h y d r o c h e m i c a l i n d i c a t o r s , 251; C o n s i d e r a tion of hydrogeological data, 252.

244

Water Analyses L a b o r a t o r y d e t e r m i n a t i o n of f u n d a m e n t a l ions, 253; D e t e r m i n a t i o n of dissolved b i t u m e n s , 254; D e t e r m i nation of iodine, 255; D e t e r m i n a t i o n of a m m o n i a , 256; D e t e r m i n a t i o n of h y d r o s u l f i d e s and other r e d u c e d compounds of s u l f u r , 256; D e t e r m i n a t i o n of b r o m i n e , 256; F i e l d l a b o r a t o r i e s , 256; D e t e r m i n a t i o n of pH of w a t e r , 257.

253

xviii

X

XI

CONTENTS Application of H y d r o c h e m i c a l Methods Route s u r v e y s , 258; H y d r o c h e m i c a l p r o s p e c t i n g , 260; H y d r o c h e m i c a l i n v e s t i g a t i o n s in exploration w o r k , 263; H y d r o c h e m i c a l investigations in p r o duction work, 264.

258

H y d r o c h e m i c a l I n d i c a t o r s of S t r u c t u r e T h e o r e t i c a l concepts of s t r u c t u r e s u r v e y s , 266; O r g a n i z a t i o n and methodology of s t r u c t u r e s u r v e y s , 268; I n d i c a t o r s used and t h e i r i n t e r p r e t a t i o n , 268; C o r r e l a t i o n of r e s u l t s with s t r a t i g r a p h i e d a t a , 271.

266

Bibliography

272

WATER-GAS SURVEYS

274

B a s i c Information on W a t e r - G a s Surveys History of the method, 276; P u r p o s e of the w a t e r g a s s u r v e y , 277.

274

Methods and A p p a r a t u s used in W a t e r - G a s S u r v e y s Methods of field work, 277; Sampling w a t e r s f o r d e g a s i f i c a t i o n , 279; R e c o v e r y of g a s f r o m w a t e r , 281; G a s a n a l y s i s , 283.

277

W a t e r - G a s Survey R e s u l t s and t h e i r I n t e r p r e t a t i o n P r e s e n t a t i o n of r e s u l t s , 285; Oil and gas i n d i c a t o r s , 286; I n t e r p r e t a t i o n of w a t e r - g a s s u r v e y d a t a , 287.

285

Bibliography

288

SOIL-SALT METHODS

290

V a r i o u s T y p e s of Soil-Salt Methods The c h l o r i d e method, 291; The iodine method, 293; The g y p s u m method, 293; The c a r b o n a t e - s i a l l i t e method, 294.

291

Application of Soil-Salt Methods

296

Radioactivity S u r v e y s

296

Bibliography

298

XII THE OXIDATION-REDUCTION P O T E N T I A L METHOD

299

Application of the Method

299

Bibliography

301

CONTENTS XIII MICROBIOLOGICAL METHODS T h e o r e t i c a l B a s i s of the Microbiological Method G e n e r a l i n f o r m a t i o n on m i c r o o r g a n i s m s , 304; Role of m i c r o o r g a n i s m s in the f o r m a t i o n of g a s e s , 307. Indicator and Control M i c r o o r g a n i s m s in P r o s p e c t i n g f o r Oil and G a s S u l p h a t e - r e d u c i n g b a c t e r i a , 310; H y d r o g e n - o x i d i z i n g b a c t e r i a , 312; M e t h a n e - p r o d u c i n g b a c t e r i a , 312; B a c t e r i a which d e c o m p o s e c e l l u l o s e , 313; B a c t e r i a which oxidize g a s e s and v a p o r i z e d h y d r o c a r b o n s , 313; Conditions limiting the propagation and u s e of i n d i c a t o r m i c r o o r g a n i s m s , 317.

xix 302 304

310

Main V a r i e t i e s of the Microbiological Method T h e s o i l s u r v e y , 319; The w a t e r s u r v e y , 323; Biologging, 327; The b a c t e r i a l g a s - o u t p u t s u r v e y and o t h e r analytical m e t h o d s , 329.

319

M i c r o b i o l o g i c a l R e s u l t s and t h e i r I n t e r p r e t a t i o n T r e a t m e n t of f a c t u a l data, 331; Evaluation of b a c t e r i a l a n o m a l i e s , 332; E x a m p l e s of the i n t e r p r e t a t i o n of m i c r o b i o l o g i c a l data, 333.

330

Geobotanical I n d i c a t o r s

340

Bibliography

342

XIV THE ROLE O F GEOCHEMICAL METHODS IN P E T R O L E U M PROSPECTING APPENDIX

345 349

Introduction Geochemical methods are one of a group of ways of prospecting and exploring f o r petroleum and natural gas formations. Among these methods is the chemical analysis (as well as the physico-chemical and microbiological study) of gases, waters, rocks, and soils. The purpose of these analyses is to determine: (a) the presence of dispersed petroleum substances (petroleum, hydrocarbon gases, bitumens), (b) traces of the influence of petroleum substances on gases, waters, rocks, soils, and organisms, (c) substances or conditions which customarily accompany oil and gas pools. Most geochemical methods of prospecting and exploration for petroleum are direct methods. 1 They directly indicate the actual presence of oil and gas. This is the main difference between geochemical and geophysical methods. The latter indicates only the presence of conditions favorable f o r petroleum accumulation. Herein lies the great value of geochemical prospecting methods. They are especially useful in the following two cases: (1) prospecting for stratigraphic and lithologic pools which are not associated with local structural features, (2) deciding whether a previously discovered structural trap contains petroleum or is " d r y . " Geochemical exploration methods are also effective in determining the presence of natural gas and petroleum in strata which have been drilled (geochemical well-logging). Among geochemical methods there are indirect as well as direct methods of prospecting for petroleum. The problems posed by the indirect methods are similar to those in geophysical prospecting. Structural hydrochemical surveys are an example of the indirect approach. Direct geochemical prospecting for petroleum is analogous to the oldest geological method which consisted of searching for and investigating oil and gas seeps. The difference between geochemical and geological methods is that the former are concerned with micro-concentrations of petroleum substances and microseeps, while the latter seek traces that are visible to the naked eye. None of the direct geochemical methods, however, can tell the investigator whether or not oil and gas pools are present. (Even less are they able to tell whether a pool is of economic proportions.) They can only v e r i f y the presence of petroleum hydrocarbons which may be present in a dispersed form. Geochemical methods are used in prospecting and exploring for deposits of other useful minerals (especially ore deposits) as well as f o r petroleum. There are great differences between the methods used in petroleum work and the methods used in prospecting for ore deposits. These differences result basically from the peculiarities of petroleum and natural

^Using the t e r m " e x p l o r a t i o n " in its strictest sense, exploration methods (not prospecting methods) can only be direct ones.

[xxi]

xxii

INTRODUCTION

gas as minerals. The singularity of oil and gas is that the bond between them and the surrounding and containing rocks is weaker than it is for ores. Furthermore, tectonic factors play a decisive role in the formation of oil and gas pools. In prospecting and exploration for ore deposits, geochemical methods are so closely bound up with geological ones that it is practically impossible to separate them. On the other hand, in prospecting for petroleum, geological and geophysical methods may be separated from the geochemical ones to a large degree. 2 For this very reason, geochemical methods long occupied a subordinate place in searching for petroleum and natural gas formations. The presence of structure was considered decisive in prospecting for petroleum for a long time. Recently, various other methods have come to be used more often, although structure still remains the most important feature in petroleum prospecting. Among these, geochemical methods occupy a larger and larger place. In the first stage of prospecting work (the finding of petroleum-bearing strata in a new district), geochemical methods play a very important role. This is also true in the last stage of exploration work — the discovery of productive horizons during drilling. These methods, however, are not being put to their fullest use at the present time. Geochemical methods of prospecting for petroleum should be used only in close connection with the other prospecting work. The results should then be evaluated in the light of all available geological and geophysical data. The geologist examines the sum total of all facts obtained by the various methods and makes the final decision. The use of geochemical methods separately from other methods and evaluation of geochemical results without reference to geological data leads to incorrect conclusions. Credit for the development of geochemical methods of prospecting for petroleum goes to Soviet scientists. The first development of such methods began in 1929 when V. A. Sokolov worked out and proposed the gas survey method. This method received extensive development and notoriety and also served as the basis for development of other geochemical methods. To V. A. Sokolov goes credit for development of the theory of movement of gases in the earth's crust which is the theoretical foundation for many other geochemical methods. He also developed methods of microanalysis of gases. The core-gas survey and geomicrobiological method were first proposed by G. M. Mogilevskii in 1935 and 1937 respectively. Oil and gas well-logging, which at present is one of the most important geochemical methods, was proposed by M. V. Abramovich in 1933. All of these methods are based on the gas survey. Bituminological r e s e a r c h also was first developed in the USSR (in 1925). "Bituminology" is greatly developed in our country. N. A. Shlezinger and others in the USSR were the first to use luminescent-bituminous methods starting in 1939. Nowhere have luminescent-bitumenous methods received such development as in our country. V. N. Florovskaya's services in this field must be mentioned. Starting in 1940, work on dissolved gases also began in the USSR.

^This does not mean that they should or can be used completely separately from geological and geophysical methods (see below).

INTRODUCTION

xxiii

Other m e t h o d s which have been highly developed in the Soviet Union a r e h y d r o c h e m i c a l methods (V. A. Sulin and o t h e r s ) , s o i l - g e n e t i c m e t h o d s (V. A. Kovda), and the oxidation-reduction potential method f i r s t p r o p o s e d by V. E . Levenson in 1936. The P e t r o l e u m - G a s - S u r v e y Bureau ( " N e f t e g a z o s ' e m k a " ) and, s i n c e 1950, the g e o c h e m i c a l division of the G e o c h e m i c a l and Geophysical Explor a t i o n Scientific R e s e a r c h Institute (NIIGGR) of the M i n i s t r y f o r the P e t r o l e u m Industry have played an important r o l e in the development of g e o c h e m i c a l m e t h o d s of p r o s p e c t i n g f o r p e t r o l e u m and n a t u r a l g a s . The f o l lowing other o r g a n i z a t i o n s should a l s o be mentioned: The P e t r o l e u m I n s t i tute ( f o r m e r l y the Institute of Combustible R e s o u r c e s ) of the A c a d e m y of Sciences of the USSR has played an important r o l e in the development of h y d r o c h e m i c a l , bituminological, and oxidation-reduction potential m e t h o d s . The Soils Institute of the Academy of Sciences of the USSR h a s p a r t i c i p a t e d in the development of s o i l - s a l t methods and s o i l - b i t u m e n s u r v e y s . T h e All-Union Geological E x p l o r a t i o n Scientific R e s e a r c h Institute (VNIGRI) has f u r t h e r developed bituminological and other methods. As shown above, insufficient u s e is being m a d e of g e o c h e m i c a l m e t h o d s in the p e t r o l e u m i n d u s t r y . Most of t h e s e methods r e q u i r e f u r t h e r r e f i n e m e n t . T h e r e is still not sufficient c o r r e l a t i o n between g e o c h e m i c a l and other types of p r o s p e c t i n g work. Not a l l p e t r o l e u m g e o l o g i s t s have a c o m plete and c o r r e c t understanding of the v a r i o u s g e o c h e m i c a l m e t h o d s of s e a r c h i n g f o r oil and g a s . T h e s e d e f i c i e n c i e s m u s t be o v e r c o m e in the n e a r f u t u r e . The goal of this book is to help in that d i r e c t i o n .

CHAPTER ONE

The Geochemistry of Petroleum Formations The geochemistry of petroleum formations is concerned with processes of chemical interaction between oil pools* and the medium surrounding them— gases, waters, rocks, organisms—and such chemical properties of crude oils, waters, gases, and rocks as are factors and consequences of these processes. The geochemistry of petroleum is part of the geochemistry of oil f o r mations and is concerned only with one aspect, the transformations and properties of crude oils themselves. The geochemistry of oil deposits, which encompasses these questions, also deals with another aspect, the environment of the oil pools. Oil pools, together with the medium surrounding them form polyphase systems. Among the phases of these systems, and also among the components of different chemical nature within the separate phases, chemical interaction takes place. Interchange of substances among phases also occurs as a result of physical and physicochemical processes (evaporation, adsorption, etc.); this also leads to chemical changes. As a result of all these processes, both the oils and the gases, waters, and rocks associated with them acquire new properties (which are subsequently changed). The study of this entire, very involved complex of phenomena constitutes the task of the geochemistry of oil f o r mations . The geochemistry of petroleum deposits is closely associated with questions of the origin of oil (oil genesis) and the formation of oil deposits (oil accumulation). Oil accumulation does not entirely end with the development of pools; it may proceed in several stages. Those chemical transformations of oils which proceed in the pools constitute the object of study of the geochemistry of oil formations. Herein lies its fundamental theoretical significance. In the present work, however, the exposition of the fundamentals of the geochemistry of petroleum deposits mainly serves other purposes of a practical character. Some of these practical applications are described below. 1. The most important practical application of the geochemistry of oil formations is the use of the geochemical peculiarities of the environment of oil pools (gases, waters, rocks, organisms) as indices of oil-bearing character in exploration and prospecting. In this scheme, the geochemistry of oil formations provides the general theoretical basis of geochemical methods of exploration and prospecting for mineral resources of this type. The exposition of the fundamentals of the geochemistry of oil formations in the present work is primarily determined by these problems.

^By the w o r d " p o o l " is here understood a single m a s s of oil; the w o r d s " f o r m a t i o n " and " d e p o s i t " r e f e r to a group of pools situated below a single region of the s u r f a c e together with the n o n - o i l - b e a r i n g rocks lying under, o v e r , and between these pools.

[1]

2

GEOCHEMICAL PROSPECTING FOR PETROLEUM

2. An important application of the geochemistry of petroleum formations is the use of its data for the prognosis of the quality of oil and in prospecting for oil of predetermined quality. As yet, this problem can only be indicated; its solution is a matter for the future. Nevertheless, it would be improper to avoid all mention of this problem. Therefore, questions of the relation of the properties of crude oil to geological conditions are briefly stated below. 3. Data on the geochemistry of oil formations may also be used: (a) for the correlation of geologic strata (according to the properties of oils, waters); (b) for secondary methods of exploitation of oil pools (choice and preparation of water and gas for pumping into the reservoir); (c) in prospecting for several other mineral resources (ozokerite, iodine, sulfur, etc.). In relation to all that has been stated, the present chapter is arranged in the following manner. Since the main fluid in the reservoir is oil, the characteristics of some crude oils are given at the beginning. Then, after a brief discussion of the external conditions affecting geochemical processes in oil formations, the character of these processes is given. After this, a summary is provided of conclusions on the relation of the properties of crude oils to the geological conditions of their deposition. Finally, those peculiarities of the environment of oil pools which are the consequences of the reaction of oil with the environment are characterized. This is followed by transition to the problem of geochemical indices of oil-bearing character. Of necessity, all questions are stated as briefly as possible. This chapter does not by any means attempt to give a complete account of the geochemistry of petroleum formations. The geochemistry of natural gas formations is difficult to separate from that of oil formations; not only formations, but also individual pools usually have a "double content", i.e., oil and gas. Nevertheless, the geochemistry of purely gaseous formations has its special features. In this chapter only the geochemistry of oil formations is considered. Natural gases are included in the following manner: (1) as component parts of oil pools and (2) as part of the medium surrounding oil pools (gases in gas caps, marginal waters, etc.).^ PROPERTIES OF PETROLEUM In this section are considered only those properties of crude oils which are important from the geochemical point of view. Before proceeding with the discussion of this problem, it is necessary to dwell briefly on the physical properties of petroleum. The Physical State of Petroleum The basic mass of petroleum in the usual conditions of oil pools consists of a mixture of liquid substances, normally containing a significant quantity of soluble gases (up to several hundred cu. m. of gases per ton of oil) and colloidally dissolved solid substances: tars, paraffins, etc. (up to 40%). The liquid substances are characterized by widely different boiling points.

The elements of the general geochemistry of gases and of natural gas formations are given in Chapter III.

3

GEOCHEMISTRY OF PETROLEUM FORMATIONS

The physical state of the individual components may be changed under the conditions usual for pools. At pressures above 200 - 300 atm. under conditions of saturation by gas, oils may pass over into a single-phase state (so-called retrograde vaporization): in this case, however, solid substances separate. T A B L E 1. Fractional Composition of Petroleum Boiling range at normal pressure, *C

Content, %

below 200

0-80

Gasoline^ } (to 150°) 1 (light) Ligroin )

200-300

5-50

Kerosine

300 - 5 5 0

0-80

Lubricating oils

above 550

0-70

Tar

Technical names of fractions

Light oils Distillate

Fuel oil

Residue

A representation of the quantitative relations between the physically different components of oils gives their fractional composition (Table 1). This representation, however, is not exact, since gases are not represented therein. The temperature fractions, although they are of arbitrary, technical significance, are also essential for the evaluation of the composition of crude oils. State of Knowledge on the Composition of Petroleum The chemical composition of petroleum has not been adequately studied. Only the elementary composition has been completely studied. The group composition, i.e., the content of different groups (classes) of chemical compounds, has been studied only for the light fractions comprising on the average 15% of the oil mass. The group composition of kerosine and lubricating oil fractions is only approximately known, while that of the heavier fractions is practically unknown. The individual composition, i.e., the content in petroleum of individual chemical compounds, is known only for the gasolines. The unsatisfactory state of knowledge of the heavy, high-molecular fractions is explained by the character of the method of analysis. At present, the separation of crude oil into fractions, necessary for analysis, is accomplished primarily by distillation and purification. The high t e m peratures used in these operations (for the higher fractions) destroy the natural compounds; the substances determined in this manner are newly formed in the analysis. Furthermore, the presence in the middle fractions of crude oils of an enormous number of compounds, isomers having nearly identical properties, makes it practically impossible at the present time to investigate the individual composition of any fractions, except the light ones. " B e n z i n e " in o r i g i n a l R u s s i a n h a s b e e n t r a n s l a t e d a s " g a s o l i n e . "

Ed.

4

GEOCHEMICAL PROSPECTING FOR

PETROLEUM

Elemental Composition The limits of variation of the elemental composition of petroleum are given in Table 2. 4 T A B L E 2. Elemental Composition of Petroleum^

%C

%H

%o

%S

83 - 8 7 . 5 11 - 14.5 0 - 2.5 0 - 5

%N

C H

0 - 1 5.7-7.7

Generally, C value (O+S+N) (C+H)> 96%, content 1 2 - 8 7 0 0 20 %

II

10- 20 %

II

o

Q

EMBA-JURASSIC

O o ©

o




1 %

SULFUR

>

1 %

ROMAN NUMERALS CORRESPOND TO CLASSES OF PETROLEUM.

Geochemical classification of p e t r o l e u m .

slight i n c r e a s e sometimes o b s e r v e d in the percent of p a r a f f i n s on transition to lubricating oils is explained by the peculiarities of transition f r o m liquid to solid hydrocarbons.

10

GEOCHEMICAL PROSPECTING FOR P E T R O L E U M

The following c h a r a c t e r i s t i c p a r a g e n e t i c c o r r e l a t i o n s between the d i f f e r e n t c h e m i c a l p r o p e r t i e s of oils m u s t be s t a t e d . 1. The m o r e p a r a f f i n h y d r o c a r b o n s in t h e light f r a c t i o n s of an oil: (a) the m o r e a r o m a t i c s t h e r e a r e ; (b) the l e s s b r a n c h e d - c h a i n p a r a f f i n s ( i s o m e r s ) ; (c) the m o r e naphthenes with f i v e - m e m b e r e d r i n g s ( d e r i v a t i v e s of cyclopentane) in c o m p a r i s o n with naphthenes with s i x - m e m b e r e d r i n g s (derivatives of cyclohexane); (d) finally, t h e m o r e solid h y d r o c a r b o n s (waxes) in the l u b r i c a t i n g oil f r a c t i o n s . Consequently, t h e r e is a definite r e l a t i o n between the v a r i o u s h y d r o carbon g r o u p s : The content of one of the g r o u p s in a c r u d e oil is r e l a t e d not only t o the content, but a l s o t o the s t r u c t u r a l type of the o t h e r g r o u p s .

100 % PARAFFINS

El'

mm*

Fig. 3. Relation between the hydrocarbon c o m p o s i t i o n of p e t r o l e u m and i t s other c h e m i c a l p r o p e r t i e s . 1 — w a x content over 1%; 2 — t a r content, 10-20%; 3 — t a r content over 20%; 4 — s u l f u r content o v e r 1%.

The p a r a g e n e s i s of a r o m a t i c and p a r a f f i n h y d r o c a r b o n s in light f r a c tions is of p a r t i c u l a r i n t e r e s t . T h e s e s i m p l e a r o m a t i c h y d r o c a r b o n s (homologs of benzene) a r e genetically distinct f r o m the m o r e complex m a i n body of a r o m a t i c h y d r o c a r b o n s c o n c e n t r a t e d in higher f r a c t i o n s . They a r e c h a r a c t e r i s t i c f o r the most p a r a f f i n i c m e t h a n i c oils. 2. The m o r e t a r t h e r e i s in a c r u d e oil: (a) t h e m o r e a r o m a t i c h y d r o c a r b o n s t h e r e a r e ; (b) the m o r e poly cyclic l u b r i c a t i n g oil f r a c t i o n s t h e r e a r e ( r e g a r d l e s s of the c h a r a c t e r of the light f r a c t i o n s ) . Consequently, a definite r e l a t i o n e x i s t s between the h y d r o c a r b o n and n o n - h y d r o c a r b o n

GEOCHEMISTRY OF PETROLEUM FORMATIONS

11

portions of p e t r o l e u m . ^ Thus, the differences among crude oils are not determined by their fractional composition alone. Fractions with the same boiling range may be chemically different in different oils. According to the geochemical classification of petroleum suggested by A. A. Kartsev (Fig. 2), two basic classes of oils are recognized: (1) aromatic paraffinic, waxy, tarry, sulfurous oils (typical representatives, the paleozoic oils of the Ural-Volga region); (2) aromatic-naphthenic, nonwaxy, non-sulfurous oils (typical representatives, the majority of the Baku oils). The relation between the hydrocarbon composition and other properties of oils is shown schematically in another diagram (Fig. 3). PHYSICAL AND CHEMICAL CONDITIONS IN PETROLEUM FORMATIONS In this section are considered only those conditions which exist in formations independently of petroleum; i.e., conditions which are not due to reaction of the crude oils with the surrounding medium, but may in themselves be important factors of geochemical processes. Temperature Measured temperatures in oil beds vary from 10 to 180°C. It is quite possible, however, that lower temperatures as well as much higher ones exist: at a geothermal gradient of 1° per 20 m., usual for many formations, the temperature at a depth of 5 km. must reach 250°C. The geochemical effect of temperature in oil formations appears in the following form. 1. As the temperature increases, decomposition of some components of petroleum may occur. F o r example, several complex sulfur compounds in oils break down at a temperature below 100°C, forming hydrogen sulfide and mercaptans; several nitrogen compounds break down at a temperature below 200°C, forming quinolines and the like. Several other chemical processes are accelerated.^^ 2. Elevated (and also, possibly, reduced) temperatures may a r r e s t biochemical processes which lead to oxidation of the oils; even at 70°C, bacterial activity in oil-bearing strata ceases. 3. Temperature affects the physical state of the oil components, thus changing the composition of petroleum, f o r example, at temperatures below 30 - 40°C solid paraffins may separate out as a precipitate, etc.

1 ' The r e l a t i o n s between the content of naphthenic h y d r o c a r b o n s and the a c i d content, b e t w e e n the a r o m a t i c i t y of the l u b r i c a t i n g oils and the sulfur content of the crude o i l s , e t c . , m a y be m e n t i o n e d . ^ B e s i d e s the s u b s t a n c e s m e n t i o n e d above and the w e l l - k n o w n p o r p h y r i n s , the c o r r e l a t i o n among s e v e r a l h y d r o c a r b o n s m a y be u s e d a s " g e o c h e m i c a l t h e r m o m e t e r s " in the opinion of S . N. Obryadchikov ( 1 1 ) and A. V. F r o s t (12). A c c o r d i n g to t h e s e a u t h o r s , the r a t i o of c y c l o p e n t a n e to m e t h y l c y c l o h e x a n e in oil i n c r e a s e s a s the t e m p e r a t u r e at which the oil h a s b e e n m a i n t a i n e d d e c r e a s e s . T h e s e i d e a s , h o w e v e r , a r e not in a c c o r d with g e o l o g i c a l f a c t s : it i s known that o i l s f r o m a p l a t f o r m , a s a r u l e , have undergone h i g h e r t e m p e r a t u r e s than o i l s f r o m folded r e g i o n s ( s e e the t a b l e at the end of the a r t i c l e by F r o s t (12)).

12

GEOCHEMICAL PROSPECTING FOR PETROLEUM Press' re

Hydrostatic pressure in the strata is also a geochemical factor. For oil formations its magnitude may lie between a few units and several hundred atmospheres. When the pressure exceeds 200 - 300 atm. and the strata are saturated with gas, evaporation of liquid hydrocarbons (the so-called retrograde vaporization) is observed. This sometimes extends down to the lubricating oil fractions, which results in a change in the composition of the crude oils. In the presence of a hydraulic connection between an oil-bearing stratum and another natural reservoir (particularly, the atmosphere), the pressure drop leads primarily to removal from the crude oil of gases and the lightest fractions. Motion of Subterranean Waters The rate of motion of water in oil-bearing strata may be extremely variable: from 10 m. per year with significant water exchange (for example, in the Grozny r e g i o n ) ^ to 10"^ m. per year in a static regime (for example, in parts of the Ural-Volga region according to the calculations of A. I. SilinBekchurin (13)). As a geochemical factor, the velocity of subterranean waters is important because it insures the entry of a greater or lesser quantity of substances which react with oils (primarily sulfates). Therefore, the greater this quantity is, the more change in the composition of the oil there may be as a result of reaction with substances dissolved in the water. Physicochemical and Chemical Properties of Rocks and Waters The properties of rocks, as collectors of hydrocarbons and as rocks constituting the roof and floor of oil-bearing reservoirs, may have a substantial effect on geochemical processes in petroleum formations. These include sorption, catalytic, and reactive properties. The sorption and catalytic properties of rocks are closely related. Rocks may adsorb primarily asphaltenes and tars from crude oils. The sorption capacity of rocks is usually the greater, the more colloidal f r a c tions they contain and the more hydroaluminosilicate minerals of the type of montmorillonite, etc., there are in the composition of these fractions. Hence the greatest sorption capacity (except for coals) is found in several fine clays such as Fuller's earth and bentonites, while the least is found in quartz gravels and coarsely crystalline rocks. First of all, these minerals may have a catalytic effect on some of the chemical transformations of hydrocarbons and other components of petroleum: redistribution of hydrogen, hydrogenation, and the like. Very great catalytic activity is also found in rocks of the type of bentonites. There are no systematic investigations of these properties of the rocks of oil formations on record. Therefore, it is impossible at the present time to characterize either the activity of natural catalysts, or the specific effects of various representatives thereof.

^ U n d e r natural conditions; that i s , b e f o r e p r o c e s s i n g .

GEOCHEMISTRY O F P E T R O L E U M

FORMATIONS

13

The effect of sorption and c a t a l y s i s on the properties of crude oils is apparently v e r y great. F o r example, on the one hand, in the formation of Kettleman Hills (California), oil consisting entirely of c l e a r f r a c t i o n s is found in thin, sandy beds in a stratum of nearly pure bentonites (14). On the other hand, an oil of very uncommon type, consisting of heavy, black oil r e s e m b l i n g petroleum residue, is found in the purely siliceous Athabaska (Canada) sandstone (15). Apparently, an effect s i m i l a r to that of aluminosilicates may r e s u l t f r o m the radioactivity of r o c k s . The radioactivity of sedimentary r o c k s is a s s o c i a t e d with the finest fragmented p a r t i c l e s thereof. T h e r e f o r e , the most radioactive r o c k s a r e a l s o fine c l a y s . The reactivity of r o c k s toward crude oils amounts mainly to their oxidizing action. The main m a s s of oxygen in sedimentary r o c k s ( s i l i c a , s i l i c a t e s , and carbonates) is inert. Only the oxygen of sulfates, f r e e oxides of iron, and s o m e r a r e r m i n e r a l s can be active. In the c a s e of l a r g e a c cumulations of these s u b s t a n c e s , crude oils may acquire particular propert i e s . F o r instance, very t a r r y oils a r e found in the gypsum-bearing Kungurian stratum. Much m o r e important is the oxidizing action of the sulfates dissolved in subterranean waters. It i s , however, very difficult to estimate the effect of the sulfate content of the waters, since values of the sulfate content of waters may be " s e c o n d a r y " , i . e . , they t h e m s e l v e s may depend chiefly on the reaction of petroleum with the waters. Also important a r e such physicochemical quantities as the pH of the water. According to the data of S. G. Movsesyan, alkaline waters have the ability to penetrate oil deposits in depth, so that t h e i r effect on crude oil is increased. The alkalinity of the w a t e r s , however, may i t s e l f be changed by the reaction with oil. GEOCHEMICAL P R O C E S S E S IN P E T R O L E U M

FORMATIONS

Of the geochemical p r o c e s s e s occurring in petroleum formations, only those will be considered in this section in which e i t h e r the oils t h e m s e l v e s or substances derived from them take part. The m a j o r i t y of these p r o c e s s e s have not been sufficiently studied up to the present time. T h r e e kinds of p r o c e s s e s may be distinguished: (1) m e t a m o r p h i s m of crude oils, proceeding p a r a l l e l to the metamorphism of sedimentary r o c k s and subterranean w a t e r s ; (2) oxidation of crude o i l s ^ with accompanying p r o c e s s e s having the c h a r a c t e r of consequences; (3) p r o c e s s e s of a physical c h a r a c t e r (evaporation, sorption) leading to changes in the c h e m i s t r y of petroleum. Metamorphism of P e t r o l e u m P r o c e s s e s which occur when crude oils m i g r a t e to a g r e a t e r depth with i n c r e a s e of t e m p e r a t u r e and p r e s s u r e a r e called m e t a m o r p h i s m of petroleum. T h e s e p r o c e s s e s a r e very little known. The metamorphism of

l ^ F o r r o c k s , a s well a s s u b t e r r a n e a n w a t e r s , oxidation and, in g e n e r a l , p r o c e s s e s r e l a t e d to i n f l u e n c e s " f r o m a b o v e " (the e a r t h ' s s u r f a c e ) m a y not be c a l l e d " M e t a m o r p h i s m " ; the l a t t e r concept p r e s u p p o s e s the a c t i o n of plutonic f a c t o r s .

14

GEOCHEMICAL PROSPECTING FOR

PETROLEUM

petroleum may be considered the direct continuation of the process of its formation: the general tendency is toward reduction of the original subs t a n c e s . ^ The chief factors in the metamorphism of crude oils are temperature and catalysis. The process of metamorphism consists of r e distribution of hydrogen among the components of oil according to the following scheme: Cm+nHp

A

CmHq

B

+

CnHp-q;

[q > (p-q)]

d)

C

Here substance B may finally pass over to the gaseous phase (in the limit m = O; i.e., B is pure hydrogen), while substance C may go over to the solid phase (in the limit p = q; i.e., C is pure carbon), and in the end, liquid oil ceases to exist. The chemistry of these processes was investigated by A. F. Dobryanskii. He showed that the redistribution of hydrogen within a crude oil is basically tantamount to the accumulation in the oil of low-molecular weight paraffins (B) and (in lesser quantity) low-molecular weight aromatic hydrocarbons (C) as a result of decomposition of high-molecular aromatic, naphthenic, and naphtheno-aromatic hydrocarbons (A). Complex molecules are broken down into simple ones; the detachment of side-chains gives paraffinic hydrocarbons, thus converting isomeric hydrocarbons to simple forms. Poly cyclic groups are broken down into separate rings of the benzene type. Thus, the lower fractions of crude oils originate from the higher fractions (and, in the final analysis, from complex non-hydrocarbon compounds). On the basis of these processes a number of regularities observed in the composition of petroleum may be explained: the concentration of paraffin hydrocarbons in the low fractions, their paragenesis with the simplest aromatic hydrocarbons and gasolines, the paragenesis of paraffinic hydrocarbons with naphthenes, etc. The explanation of the second phenomenon is especially important. The overall results of the conversion of large molecules into smaller ones are depolymerization and decrease of the specific gravity of crude oils. A. F. Dobrysnskii and co-workers were able artificially to produce similar conversions of petroleum in 20 hours at a temperature of 250°C and in a longer time at 175°C, using natural clays as catalysts (16). These experiments show that the given processes are possible in nature. The actual occurrence of the conversions described above are not disputed by anyone. Up to the present time, however, they have received little attention. In view of this, it is in order to point out several facts which can only be explained by processes of the metamorphism of petroleum. Besides purely chemical facts such as the previously mentioned paragenesis of saturates and aromatics in gasoline, geological facts are also important. Thus, on the Apsheron peninsula according to data from

^ M e t a m o r p h i s m of crude oils ought not, h o w e v e r , to be called the p r o c e s s of their reduction: during the main stage of existence of oils in deposits true reduction, i . e . , l o s s of oxygen and gain of hydrogen, is not an essential part of the p r o c e s s of m e t a m o r p h i s m of oils.

GEOCHEMISTRY O F P E T R O L E U M FORMATIONS

15

the investigations of A. A. K a r t s e v , the v e r t i c a l distribution of the p r o p e r t i e s of c r u d e oils in individual pools can be explained only by m e t a m o r p h i s m (changes f r o m one f o r m a t i o n to another a r e not included h e r e ) . With inc r e a s e in depth (consequently, with i n c r e a s e of t e m p e r a t u r e ) , the s p e c i f i c g r a v i t y r e g u l a r l y d e c r e a s e s and the content of light f r a c t i o n s i n c r e a s e s . The effect of o t h e r f a c t o r s (oxidation, evaporation) is excluded, b e c a u s e the effect should d i f f e r with change in depth, w h e r e a s a c c o r d i n g to o b s e r vations, t h e s e f a c t o r s r e m a i n the s a m e throughout the e n t i r e section. F o r the K u l s a r a f o r m a t i o n (Emba), c o m p a r i s o n of the detailed c h a r a c t e r i s t i c s of the oils with geological conditions l e a d s to the s a m e conclusion (17). S i m i l a r f a c t s m a y be pointed out in connection with A m e r i c a n f o r m a t i o n s (18, etc.). In T u i m a z y , a s the c a l c u l a t i o n s of A. F . Dobryanskii (2) indicate, the quantity of lighter a r o m a t i c h y d r o c a r b o n s i n c r e a s e s r e l a t i v e l y with depth; in C a r b o n i f e r o u s oils the r a t i o of a r o m a t i c s boiling at t e m p e r a t u r e s over 400° to a r o m a t i c s boiling at t e m p e r a t u r e s below 250° (a > 4 0 0 ° / a < 250°) is above 4, while in Devonian oils t h i s quantity is l e s s than 2. T h e s e c o r r e l a t i o n s , i.e., the m a j o r r o l e of the s i m p l e s t a r o m a t i c s in the lower s t r a t a , indicate the conversion of the s i m p l e s t a r o m a t i c h y d r o c a r b o n s f r o m h e a v i e r ones in the deepest f o r m a t i o n s . In an analogous way, the content of a r o m a t i c h y d r o c a r b o n s in the light f r a c t i o n s a l s o i n c r e a s e s with depth in the f o r m a t i o n s of Yablonov Ravine, Z o l ' n o e , and K r a s n o k a m s k . The s c h e m e of A. F . Dobryanskii given above a p p a r e n t l y does not e n t i r e l y c o r r e s p o n d to the actual c o u r s e of m e t a m o r p h i s m of p e t r o l e u m . Thus, the lower a r o m a t i c h y d r o c a r b o n s a r e probably not the only " r e s e r v o i r of c a r b o n " (as A. F . Dobryanskii e x p r e s s e d it) taking part in the r e d i s t r i bution of e l e m e n t s among the components of the oils. Among the h y d r o g e n poor s u b s t a n c e s f o r m e d (in equation (1)) m a y a l s o be high m o l e c u l a r c o m pounds such a s a s p h a l t e n e s . P o s s i b l y , p a r t of the a s p h a l t e n e s w e r e f o r m e d by the decomposition of t a r s a c c o r d i n g to the s c h e m e of equation (1) (if p r o c e s s e s of p o l y m e r i z a t i o n occur s i m u l t a n e o u s l y ) . T h i s is c o n f i r m e d by the high content of a s p h a l t e n e s in many " p a r a f f i n i c " oils (e.g., in h i g h - w a x Grozny oils, up to 2%) and the l i n e a r r e l a t i o n between the solid p a r a f f i n content of the oils and the value of the r a t i o of a s p h a l t e n e s to t a r s ( s i l i c a gel type) contained in t h e m (Fig. 4). T h i s p r o b l e m m u s t be studied v e r y c a r e f u l l y . A s p h a l t e n e s may r e a d i l y be deposited f r o m solution (in c r u d e oils) and s o r b e d by r o c k s . In t h i s c a s e a g e n e r a l e n r i c h m e n t of the oils in hydrogen o c c u r s , i.e., reduction. At the s a m e t i m e , the m e d i u m s u r r o u n d ing the deposit will be enriched by new components.*® Unfortunately, e s t a b l i s h m e n t of the p r e s e n c e of t h e s e p r o d u c t s of decomposition of p e t r o l e u m in r o c k s is hindered by t h e i r s i m i l a r i t y to o r g a n i c s u b s t a n c e s s y n g e netic to the r o c k s . T h e r e f o r e , t h e r e a r e no f i r m l y e s t a b l i s h e d f a c t s in this field at the p r e s e n t t i m e . It is quite possible that the c o u r s e of the c o n v e r s i o n of p e t r o l e u m under the influence of t e m p e r a t u r e , c a t a l y s i s , and t i m e m a y be qualitatively dependent on the m a n n e r in which t h e s e t h r e e b a s i c f a c t o r s a r e combined. T h i s question is quite o b s c u r e . T h e question of i s o m e r i z a t i o n is a l s o o b s c u r e .

l ^ T h i s e n r i c h m e n t of the m e d i u m m a y a l s o o c c u r a s a r e s u l t of the e v o l u t i o n of g a s e s (CH^, C J H J , H 2 S , N H 3 , N £ , e t c . ) upon d e c o m p o s i t i o n of the m o r e c o m p l e x c o m pounds.

16

GEOCHEMICAL PROSTPECTING FOR PETROLEUM

PARAFFIN F i g . 4.

WAX, %

R e l a t i o n b e t w e e n the wax content of c r u d e o i l s and the r a t i o of a s p h a l t e n e s to s i l i c a - g e l t a r s .

F o r example, A. S. Velikovskii assumes that isomerization of hydrocarbons proceeds under the catalytic influence of aluminosilicates; hence, in limestones, where there is l e s s of the latter than in sandstones, crude oils are l e s s isomerized (19). This point of view does not agree with the aforementioned arguments of A. F . Dobryanskii on the conversion of isoparaffin hydrocarbons to simple forms by decomposition. Finally, the possibility of hydrogenation of oils by free hydrogen should be mentioned. The latter is formed upon decomposition of water under the influence of radioactivity in the rocks (20). In this case the process consists of the migration into the crude oils of substances from the surrounding medium and, consequently, leads to the absolute enrichment of the oils in one of the elements. The extent of this process and the part played by it, however, are in all probability insignificant. Oxidation of Petroleum In contrast to the conversions discussed above, oxidative processes in petroleum formations have attracted attention for a long time. Even today, however, much in this field is not clear. Important features distinguishing oxidation from the processes considered above include: (a) the participation in them of organisms, and (b) significant changes in the medium surrounding the oil. The latter circumstance is of great significance in prospecting for petroleum. The oxidation of petroleum within the reservoir occurs because of bound oxygen. The role of free oxygen (in the form of gaseous O2 dissolved in water) can only be appreciable in the immediate vicinity of the earth's surface and, consequently, is important only in those r a r e cases where an

GEOCHEMISTRY OF PETROLEUM FORMATIONS

17

oil pool still exists at very shallow depths. 1 "* Salts dissolved in water, primarily sulfates, 1 ® are of basic significance. Such components of rocks are sulfate minerals and those of the limonite group may have some effect. The effect of water is pronounced owing to its mobility, which sharply inc r e a s e s the amount of reacting substance. There is no doubt as to the actual occurrence of the process of interaction of crude oils with the sulfates in water: the well-known fact of the absence of sulfates in water in contact with oil pools is sufficient evidence of this. Also, the participation of microbes in this process is not disputed by anyone today. The question as to the possibility of nonbiochemical oxidation of oil in strata remains open. The basis of the process, regardless of its biochemical or nonbiochemical character, is the reaction expressed by the following scheme: C m H p + RSO4

( C m + n H p + q ) + ( C m + n H p + q O r ) + C 0 2 + H 2 0 + RS r m + n >-s. m ! I p+q - p J

^

The parentheses enclosing the substances Cm_j_nHp_|_ and Cm-(-nHp-|-qOr indicate that these compounds are intermediate products of the reaction and may also be converted in the end of CO2 and H2O. This means that the given process can completely destroy the oil. In reality, however, the reaction does not always go to completion. The chemistry of the entire oxidation transformation is more complex than that expressed by equation (2), and many aspects of it are still obscure. The oxidation of crude oils by free 0 2 has been studied experimentally. Anaerobic oxidation was experimentally investigated by V. A. Uspenskii and co-workers (21); thermodynamic calculations were performed by V. O. Tauson (22). Taking into account the data obtained by them, microbiological observations (23, etc.), several facts related to the distribution of the properties of crude oils in formations, and finally, several facts related to the oxidation of oils by free 0 2 (3, 24), it may be concluded that in the oxidation of petroleum by sulfates the following phenomena occur. 1. Several hydrocarbons, mainly paraffinic (and including solid paraffins), are immediately oxidized to C 0 2 and H 2 0 . In this case, owing to the elimination of paraffin hydrocarbons, the oils are relatively enriched in cyclic components. 2. Other hydrocarbons, mainly cyclic, yield on oxidation oxygen compounds of the type Cm+nHp-i-qOr. These are mainly acids and t a r s . Naphthenic hydrocarbons on oxidation form more acidic products, largely naphthenic acids, while aromatics form products of less acidic nature, chiefly t a r s . As a result of true oxidation crude oil is enriched in t a r s and acids. 3. True oxidation of hydrocarbons is accompanied by their dehydrogenation and polymerization, as well as cyclization to some extent. The hydrocarbon Cm-|-nHp-(-q in equation (2) is one product of the oxidative

' ^ F o r e x a m p l e , in such e x p o s e d f o r m a t i o n s a s M i r z a a n i . ^ A p p a r e n t l y , n i t r a t e s a l s o play s o m e p a r t .

18

GEOCHEMICAL PROSPECTING FOR P E T R O L E U M

dehydrogenation and p o l y m e r i z a t i o n of the h y d r o c a r b o n C m H p : its m o l e c u l a r weight is g r e a t e r than that of C m H p (polymerization), ana the C / H r a t i o is a l s o g r e a t e r (dehydrogenation). Naphthenes on dehydrogenation m a y give a r o m a t i c h y d r o c a r b o n s , p a r a f f i n h y d r o c a r b o n s , and a p p a r e n t l y , naphthenes (i.e., cyclization o c c u r s ) . The o v e r a l l r e s u l t of dehydrogenation and p o l y m e r i z a t i o n m u s t be the e n r i c h m e n t of crude oil in h e a v i e r c o m ponents. It is possible that in a n a e r o b i c p r o c e s s e s , dehydrogenation and polym e r i z a t i o n of oils play an even g r e a t e r part than t r u e oxidation. It m a y be that a v e r y i m p o r t a n t p a r t is played by r e a c t i o n s following t h i s s c h e m e : C m H p + RSO4

C

m + n

m-t-n . [ FTq

H

p + q

+ 4 H 2 0 + RS

(3)

m P ]

4. Oxidation, dehydrogenation, and the like, a r e accompanied t o s o m e extent by antagonistic p r o c e s s e s : a s a r u l e oxidation l e a d s to the f o r m a tion of the lightest h y d r o c a r b o n — m e t h a n e . It is t h i s product (along with w a t e r ) to which the hydrogen goes upon complete dehydrogenation of c r u d e oil. 5. The s u b s t a n c e of b a c t e r i a a l s o t a k e s part in the r e a c t i o n s . To a c e r t a i n extent, the r e m a i n s of dead b a c t e r i a combine with t h o s e t a r r y s u b s t a n c e s which a r e the chief p r o d u c t s of oxidation. S u m m a r i z i n g the above d i s c u s s i o n , it m u s t be concluded that the r e s u l t of the action of s u l f a t e s is the e n r i c h m e n t of p e t r o l e u m in heavy, m o r e p o l y m e r i z e d , mainly cyclic components, e s p e c i a l l y t a r s ; at the s a m e t i m e , h o w e v e r , n a t u r a l gas is f o r m e d . The r e a l i t y of t h e s e t r a n s f o r m a t i o n s in n a t u r e is shown by the e x i s t e n c e in oil pools of zones of r e l a t i v e l y heavy oils in t h o s e regions which a r e in contact with w a t e r . This is a well known phenomenon. The m e c h a n i s m of propagation of the p r o c e s s throughout the r e s e r v o i r is not e n t i r e l y c l e a r . The possibility that alkaline w a t e r p e r c o l a t e s to the depths of the oil pool in a d i s p e r s e d s t a t e should be c o n s i d e r e d . The l i m i t s of b i o c h e m i c a l oxidation of c r u d e oils a r e d e t e r m i n e d by the t e m p e r a t u r e conditions. T h u s , a c c o r d i n g to data f r o m the i n v e s t i g a tions of V. M. Nikolaev in the G r o z n y f o r m a t i o n s in s t r a t a with t e m p e r a t u r e s over 70°C the w a t e r contains s u l f a t e s , while in s t r a t a with l o w e r t e m p e r a t u r e s the w a t e r is p r a c t i c a l l y f r e e of s u l f a t e s . T h e r e f o r e , in the f i r s t c a s e reduction p r o c e e d s m u c h l e s s vigorously. V e r y low t e m p e r a t u r e s , a p p a r e n t l y , a l s o inhibit b a c t e r i a l activity. Thus, a c c o r d i n g to the data of N. T. Lindtrop, in one of the f o r m a t i o n s of the Second Baku the w a t e r underlying the o i l - b e a r i n g s t r a t u m at t e m p e r a t u r e s u n d e r 15°C contains s u l f a t e s (25). It is quite probable that the r e a c t i o n between c r u d e oils and s u l f a t e s can go to a c e r t a i n extent even without the participation of o r g a n i s m s . Indirect c o n f i r m a t i o n of the o c c u r r e n c e of t h i s p r o c e s s is f u r n i s h e d by c a s e s in which the w a t e r is f r e e of s u l f a t e s at high t e m p e r a t u r e s . F o r e x ample, on the Apsheron peninsula, a c c o r d i n g to D. V. Z h a b r e v , t h e r e is no SO4 in the w a t e r s adjacent to oil pools (though SO4 is p r e s e n t at a s u f f i c i e n t d i s t a n c e f r o m the pool in the s a m e s t r a t u m ) , even in t h o s e s t r a t a in which the t e m p e r a t u r e r e a c h e s 100°C. The n o n - b i o c h e m i c a l p r o c e s s may be

GEOCHEMISTRY O F P E T R O L E U M FORMATIONS

19

catalyzed by such s u b s t a n c e s a s the s a l t s (soaps) of naphthenic a c i d s in an alkaline m e d i u m (as in the i n d u s t r i a l oxidation of h y d r o c a r b o n s (26, 27). If the s u l f a t e s a r e solid m i n e r a l s , the p r o c e s s a p p a r e n t l y o c c u r s in the s a m e way a s it does when the s u l f a t e s a r e in solution. T h e r e f o r e , t h e r e a r e no p a r t i c u l a r d i f f e r e n c e s in this c a s e . The c h a r a c t e r of the oxidation of p e t r o l e u m is not fully e s t a b l i s h e d , and the c o u r s e of the p r o c e s s may v a r y depending on conditions. In s o m e c a s e s the oxidation of s a t u r a t e d h y d r o c a r b o n s m a y go p r e f e r e n t i a l l y to CO2 and H2O, while in o t h e r s , the chief product m a y be t a r s , etc. T h e s e q u e s tions s t i l l r e q u i r e c l a r i f i c a t i o n . Consequences of the Oxidation of P e t r o l e u m by Sulfates T h e r e a c t i o n s d i s c u s s e d above may be a c c o m p a n i e d by a n u m b e r of p r o c e s s e s in the m e d i u m s u r r o u n d i n g the p e t r o l e u m . F i r s t of all, the following kinds of s u b s t a n c e s may be evolved f r o m the crude oils: (a) t a r s 1 ^ f o r m e d upon oxidation and deposited f r o m solution or s o r b e d by r o c k s ; (b) a c i d s , a l s o f o r m e d upon oxidation and dissolved in w a t e r ; (c) m e t h a n e , obtained upon dehydrogenation of oil h y d r o c a r b o n s and f o r m i n g a gas phase. B e s i d e s t h i s a n u m b e r of additional r e a c t i o n s m a y o c c u r . The c h a r a c t e r of t h e s e depends in part on the kind of s u l f a t e taking part in the b a s i c r e a c t i o n . In alkaline w a t e r s , where the given p r o c e s s e s a r e usually obs e r v e d , t h i s will be sodium s u l f a t e (the l a t t e r is not limited to alkaline w a t e r s ) . In t h i s c a s e the c o u r s e of the r e a c t i o n s will be a s follows: CnHm + Na2S04 H20

Na2S20 + C02 +

(4)

N a H C 0 3 + H2S ( + C 0 2 + H 2 0 )

As a r e s u l t , soda a p p e a r s , dissolved in the w a t e r , and consequently, the alkalinity of the w a t e r i n c r e a s e s ; the g a s e s H 2 S and C 0 2 a l s o a p p e a r and may r e m a i n in solution. In alkaline w a t e r s the evolution of a c i d s f r o m the p e t r o l e u m m a y play a significant r o l e . They f o r m alkali m e t a l s a l t s (soaps) a c c o r d i n g to the reactions: 2 C n H m C O O H + Na2S —» 2 C n H m C O O N a + H2S , CnHmCOOH + NaHC03

(5)

C n H m C O O N a + CO2 + H2O

(5')

^ T h e s e ( s e c o n d a r y ) t a r s m u s t be distinguished f r o m " p r i m a r y " t a r s p r e s e n t in t h e o i l s . T h e c h a r a c t e r of t h e d i f f e r e n c e i s a s y e t o b s c u r e . ^®The i n t e r m e d i a t e p r o d u c t s i n c l u d e ^ ¿ S O j a n d N a ; > S 0 4 . In a l k a l i n e w a t e r s N a H S i s a r e l a t i v e l y s t a b l e c o m p o u n d . A c c o r d i n g t o t h e d a t a of S. A . S h c h u k a r e v t h e c o n t e n t of HS i o n s m a y e x c e e d t h a t of f r e e H 2 S (28). T h e c o n t e n t of h y d r o s u l f i d e s i n t h e w a t e r s of oil-bearing r e s e r v o i r s has r e c e i v e d little attention. ^ I n t h e c a s e of o x i d a t i o n of c r u d e o i l s a s a r e s u l t n o t of s u l f a t e s , b u t of n i t r a t e s , the p r o c e s s a p p a r e n t l y follows this c o u r s e : CnHjn + 2 N a N 0 3

2NaHC03 + N2.

O w i n g t o t h e i n e r t n e s s of n i t r o g e n , t h i s r e a c t i o n d o e s n o t o c c u r . as an intermediate product.

N 2 0 may appear

20

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These sodium soaps a l s o e n t e r into the composition of the alkalinity of water. Sometimes they accumulate in water in such quantities that they may be used in industry (29). If the water is hard owing to contact with gypsum, the reduction of sulfates may lead to r a t h e r different r e s u l t s . When the reaction o c c u r s with the participation of calcium sulfate, it may be e x p r e s s e d by the following s c h e m e : CnHm + CaS04

CaS + CO2 + H2O

(6)

C a C 0 3 + H2S ( + CO2+ H2O)

In this c a s e the difficultly soluble calcium carbonate appears as a p r e c i p i tate and, consequently, enters into the composition of the r o c k s . Thus, depending on the reacting sulfate, changes occur in the water, e i t h e r alone or in the p r e s e n c e of r o c k s . The simultaneous action of Na and Ca sulfates is a l s o possible in sodium sulfate-type w a t e r s . The carbon dioxide gas formed in every c a s e may r e a c t with s e v e r a l rock components. S e v e r a l investigators (D. V. Zhabrev et al.) believe that under the influence of CO2 in o i l - b e a r i n g s t r a t a , even s i l i c a t e s may decompose; this effect is s i m i l a r to the weathering of the e a r t h ' s c r u s t . T h e r e a r e , however, no f i r m l y established f a c t s known at present which prove the o c c u r r e n c e of these p r o c e s s e s . P r e s e n t knowledge of the action of hydrogen sulfide, to which is related the formation of sulfur and the sulfuring of oil, is more r e l i a b l e . P a r a g e n e s i s of P e t r o l e u m and Sulfur. Sulfuring of Petroleum Hydrogen sulfide is usually found in o i l - b e a r i n g s t r a t a , in which is appears as a r e s u l t of reduction of sulfates. It may a l s o be formed in s e v e r a l other ways. Thus, at high t e m p e r a t u r e s (above 100°C) some sulfurous components of crude oils may decompose. It is possible that formation of hydrogen sulfide a l s o o c c u r s as a result of hydrolysis at normal t e m p e r a tures (30). Hydrogen sulfide is a very active reducing agent. In o i l bearing r e s e r v o i r s it must act p r i m a r i l y on f e r r i c oxide m i n e r a l s . The c o u r s e of these reactions is represented by the following s c h e m e : H2S + F e 2 0 3

S + 2FeO + H2O ,

(7)

2H 2 S + F e 2 0 3 - 4

F e S 2 + FeO + 2H20

(8)

The substances f o r m e d — s u l f u r , pyrite, f e r r o u s o x i d e — r e m a i n in the r o c k s , a l t h o u g h crystallization of pyrite in oil pools has never been recorded (32). Usually, the relations between H2S and F e 2 0 3 a r e c h a r a c terized by an e x c e s s of the f i r s t substance; hence, the reaction proceeds according to equation (8), and H 2 S may continue to be present in the g a s e s . Sulfur is formed on a l a r g e s c a l e in the p r e s e n c e of f r e e oxygen by the reaction: 2H2S + O 2 2S + 2H2O (9)

^ F e r r o u s oxide m a y f o r m s i d e r i t e under the i n f l u e n c e of c a r b o n i c a c i d . ations of this m i n e r a l have b e e n o b s e r v e d in oil d e p o s i t s (31).

Agglomer-

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21

T h i s p r o c e s s o c c u r s n e a r the s u r f a c e of the e a r t h , w h e r e O2 is d i s s o l v e d in the w a t e r s . It m a y r e s u l t in the f o r m a t i o n of i n d u s t r i a l s u l f u r d e p o s i t s . In t h e s e c a s e s s u l f u r t a k e s the f o r m of the " c a p " of an oil f o r m a t i o n (33). The s u l f u r (and hydrogen sulfide) f o r m e d m a y a l s o r e a c t with h y d r o carbons : CnHm + S CnHmS (10) In t h i s way a n u m b e r of s u l f u r compounds m a y be f o r m e d and t h i s l e a d s to s u l f u r i n g of p e t r o l e u m . The s u l f u r m a y a l s o act a s a c a t a l y s t , p r o m o t i n g p o l y m e r i z a t i o n and t a r f o r m a t i o n . According to A. S. Velikovskii (19), V. A. U s p e n s k i i , and O. A. Radchenko (34), the s u l f u r i n g of c r u d e oils is closely r e l a t e d to t h e i r oxidation. According to U s p e n s k i i and Radchenko, the s u l f u r i n g of oils o c c u r s only in c a r b o n a t e r e s e r v o i r s , s i n c e in s a n d s t o n e - c l a y r o c k s a l l of the H2S f o r m e d in the oxidation of the c r u d e oils is bound with i r o n to f o r m p y r i t e . T h i s c o n f i r m s the following h y p o t h e s e s : (a) in the w a t e r s or c a r b o n a t e r e s e r v o i r s hydrogen sulfide is c o m m o n , while in b r e c c i a t e d r e s e r v o i r s it is r a r e ; (b) s u l f u r o u s oils, a s well a s m a s s e s of s u l f u r , a r e e n c o u n t e r e d a s a r u l e in l i m e s t o n e s and d o l o m i t e s but not in b r e c c i a t e d rocks. The h y p o t h e s i s of the g r e a t r i c h n e s s in i r o n of b r e c c i a t e d r o c k s in c o m p a r i s o n with c a r b o n a t e r o c k s , based on the data of F . C l a r k c o n c e r n ing total F e content (including s i l i c a t e F e ) and applied to the phenomenon d e s c r i b e d above, is not proved. The f a c t of the m a t t e r is that to speak of the r e d u c t i o n of i r o n s i l i c a t e s by hydrogen sulfide is i n a d m i s s i b l e . Only reduction by the l a t t e r of f r e e oxides and h y d r o x i d e s is conceivable and t h e r e a r e hardly any data on the content of t h e s e in r o c k s . The i n v e s t i gations of A. A. K a r t s e v and V. N. Kholodov f o r the West F e r g h a n a f o r m a t i o n s r e v e a l that t h e r e is no d i f f e r e n c e in n o n - s i l i c a t e i r o n content between the s a n d s t o n e and c a r b o n a t e r e s e r v o i r s t h e r e . At the s a m e t i m e , the d i f f e r e n c e s in the s u l f u r content of the c r u d e oils in t h e s e s t r a t a and the hydrogen sulfide content of the w a t e r s a r e quite m a r k e d . Taking t h e s e f a c t s into account, it m u s t be concluded that the question of the s u l f u r i n g of p e t r o l e u m is not fully c l a r i f i e d a s yet. It may be that the s u l f u r content of the oils of c a r b o n a t e r o c k s is partly explained by p r i m a r y f a c t o r s , a s V. A. Sokolov (20) s u g g e s t s . In t h i s c a s e the a c c u m u lation of H2S in c a r b o n a t e r o c k s is partly r e l a t e d to its evolution f r o m s u l f u r o u s oils. It m a y a l s o be that c e r t a i n o t h e r , unknown c a u s e s a r e acting here. Physical P r o c e s s e s One of the most common physical p r o c e s s e s a f f e c t i n g the p r o p e r t i e s of c r u d e oils is g r a v i t a t i o n a l d i f f e r e n t i a t i o n . T h i s phenomenon was i n v e s t i gated in g r e a t detail by M. V. A b r a m o v i c h (35). As s e p a r a t i o n of g a s , oil, and w a t e r o c c u r s in a s t r a t u m , s o s t r a t i f i c a t i o n a c c o r d i n g to s p e c i f i c gravity t a k e s place in an oil pool. The g r e a t e r p a r t of the d i s s o l v e d gas c o l l e c t s in the u p p e r p a r t s of the r e s e r v o i r , while the h e a v i e r portion of the d i s s o l v e d t a r s a c c u m u l a t e s in the lower p a r t s . The g r e a t e r the height of the r e s e r v o i r , the m o r e s t r a t i f i c a t i o n o c c u r s . When the height of a pool is a m a x i m u m , v e r y light d i s t i l l a t e s m a y f o r m at the t o p — f r o m s o m e light f r a c t i o n s . T h i s phenomenon i s a p p a r e n t l y o b s e r v e d in the Kympin

22

GEOCHEMICAL P R O S P E C T I N G F O R

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formations in Rumania (36) and those at Ventura in California (37). When the height of the r e s e r v o i r s is s m a l l , differentiation is slight. Thus, in the formations of Tuimaz and E a s t T e x a s , the oils in these fields a r e v e r y homogeneous in spite of their great s i z e . Another physical p r o c e s s which is important in the g e o c h e m i s t r y of petroleum is the partial evaporation of crude o i l s , which is e s p e c i a l l y rapid when there is a hydraulic outlet f r o m the deposit to the atmosphere. At f i r s t , dissolved gases a r e evolved f r o m the o i l s ; they a r e followed by all the light f r a c t i o n s . The remaining crude oil is enriched in heavy c o m ponents, ^ and these oils a r e e x t r e m e l y common. The light f r a c t i o n s may migrate not only to the atmosphere but a l s o t o other r e s e r v o i r s . Then either new deposits of very light oils a r e formed, or t h e s e light " d i s t i l l a t e s " a r e mixed with other crude oils. It is not as yet possible to develop s i m i l a r c a s e s with confidence. At very great depths ( g r e a t e r than 3,000 m . ) s e p a ration of heavier fractions f r o m the oils may a l s o o c c u r . Filtration fractionation of crude oils upon t h e i r passage through a l a y e r of clay was long ago pointed out as a p r o c e s s leading to great changes in the properties of the oils. Here adsorption of the heavy components by the r o c k s plays the chief r o l e . N. A. E r e m e n k o attaches great importance to this p r o c e s s (38). In the opinion of most investigators, however, this phenomenon is not widespread. Most of the c a s e s in which it has been suggested can be explained in other ways. F o r example, on the Apsheron peninsula, according to data from the investigations of A. A. K a r t s e v , f i l tration fractionation of the oils did not play any substantial part. Among other physical p r o c e s s e s , deposition f r o m petroleum of solid paraffins and c e r e s i n s on d e c r e a s e of t e m p e r a t u r e is worthy of note. T h i s phenomenon is related to the formation of o z o k e r i t e s . The problem of the formation of ozokerites is s t i l l far f r o m solution. Apparently, the f o r m a tion of ozokerites is not purely a physical p r o c e s s but a l s o involves c h e m i c a l changes of solid hydrocarbons (39). Such a r e the fundamental geochemical p r o c e s s e s taking place in p e t r o leum formations. It should be kept in mind that different p r o c e s s e s can occur in a given place simultaneously. It is even possible that t r a n s f o r mations, opposite in kind, may occur simultaneously. Such is the c a s e for metamorphism and oxidation. Oils contain chemically different s u b s t a n c e s , susceptible to change in different d i r e c t i o n s . CAUSES O F P E T R O L E U M

VARIABILITY

In t h e i r composition and properties crude oils a r e very d i v e r s e , b e c a u s e petroleum is not a single m i n e r a l f o r m but an entire family of m i n e r a l s related by gradual transitions. The diversity of crude oils is of t h r e e kinds: (1) the difference among oils of various geological provinces, usually of different age; (2) the d i f f e r e n c e s between oils of various levels within the boundaries of a single formation; (3) the differences within the individual pools. T h e s e d i f f e r e n c e s often have a r e g u l a r c h a r a c t e r . T h e s e r e g u l a r i t i e s were f i r s t noticed by A. K. Sorokin in Baku (40). T h e

2^ " T h i s p r o c e s s i s not in i t s e l f r e l a t e d to oxidation. o i l s o x i d i z e d , a s i s often done, i s quite i n c o r r e c t .

T h e r e f o r e , to c a l l a l l h e a v y

GEOCHEMISTRY O F P E T R O L E U M FORMATIONS

23

explanation of t h e s e r e g u l a r i t i e s and t h e i r c a u s e s is v e r y i m p o r t a n t f o r the u n d e r s t a n d i n g of the g e o c h e m i c a l p r o c e s s e s o c c u r r i n g in p e t r o l e u m f o r m a t i o n s and f o r the development of a method of p r o g n o s i s of the quality of c r u d e oils. The t h i r d kind of d i f f e r e n c e s in the p r o p e r t i e s of o i l s — w i t h i n pools — is chiefly explained by g r a v i t a t i o n a l d i f f e r e n t i a t i o n . T h i s phenomenon is s u f f i c i e n t l y c l e a r and is not c o n s i d e r e d below. It r e m a i n s t o d i s c u s s the f i r s t two kinds of d i f f e r e n c e s . The p r o c e s s e s d i s c u s s e d above can g r e a t l y change c r u d e oils and c r e a t e s h a r p d i f f e r e n c e s in t h e i r p r o p e r t i e s . It m a y be, however, that the n a t u r e of the original s u b s t a n c e s a l s o a f f e c t s t h e s e properties. Role of the Initial Composition T h e r e a r e s e v e r a l quite c o n t r a d i c t o r y viewpoints on the evaluation of the r o l e of the initial composition on the p r o p e r t i e s of p e t r o l e u m . T h u s , A. F . Dobryanskii, V. A. Uspenskii, and o t h e r s deny the i m p o r t a n c e of the n a t u r e of the initial s u b s t a n c e s and c o n s i d e r that the o b s e r v e d d i f f e r e n c e s among c r u d e oils a r e wholly d e t e r m i n e d by t h e i r r e c e n t h i s t o r y . A n u m b e r of i n v e s t i g a t o r s , g e n e r a l l y a d m i t t i n g that the initial composition p^ays s o m e p a r t , r e l e g a t e it to quite an insignificant place (15, 16). Sharply d i f f e r i n g views w e r e developed by H. Hlauschek (41, 42), V. A. Sokolov, and s e v e r a l other a u t h o r s . H. H l a u s c h e k , p r o c e e d i n g f r o m the p r e v i o u s l y o b s e r v e d r e l a t i o n between the c h a r a c t e r of c r u d e oils and the age of the s u r r o u n d i n g r o c k , attempted to e s t a b l i s h the p r e s e n c e of evolution, r e l a t e d to the evolution of the o r g a n i c world. However, the f a c t u a l foundation f o r t h i s hypothesis is v e r y weak. A m o r e plausible hypothesis was advanced by V. A. Sokolov (20). T h i s was b a s e d on the d i f f e r e n c e s between the Baku and Second Baku c r u d e s (see above). T h e a s s o c i a t i o n of U r a l - V o l g a oils with c a r b o n a t e r e s e r v o i r s , and Baku oils with b r e c c i a t e d ones is r e l a t e d by V. A. Sokolov to the e n v i r o n m e n t a l c h a r a c t e r of the p e t r o l e u m f o r m a t i o n . In c a r b o n a t e e n v i r o n m e n t s , w h e r e the land h a s contributed little, the m a i n s o u r c e of p e t r o l e u m c o n s i s t s of the albumins and f a t s of plankton, which gives l a r g e a m o u n t s of s a t u r a t e s , p a r a f f i n , s u l f u r , and n i t r o g e n ; w h e r e a s , in sandy, a r g i l l a c e o u s e n v i r o n m e n t s , w h e r e the land h a s f u r n i s h e d a l a r g e amount of lignin and humus r e s i d u e s f r o m s u r f a c e vegetation, the initial m a t e r i a l i s d i s t i n guished by its high cyclicity and low s u l f u r content. V. A. Sokolov a d m i t s that t h i s hypothesis cannot lay c l a i m to u n i v e r s a l i t y . Its inadequacy is shown by the following. In the f i r s t place, a v e r y g r e a t n u m b e r of p a r a f f i n i c oils lie, not in c a r b o n a t e r e s e r v o i r s , but in s a n d s t o n e ones. At the s a m e t i m e , a s the author h i m s e l f o b s e r v e s , t h e r e a r e c r u d e oils of the m o s t s a t u r a t e d c h a r a c t e r (in f a c t , n o n - s u l f u r o u s ) lying in s a n d s t o n e s ; i . e . , Pennsylvania oils. In the second place, V. A. Sokolov h a s only taken into account the composition of the light f r a c t i o n s . If the l u b r i c a t i n g oil f r a c t i o n s a r e a l s o c o n s i d e r e d , t o say nothing of the t a r s , it is s e e n that the c r u d e s of the Second Baku, a s a r u l e , a r e not l e s s but m o r e cyclic than the oils of Baku and s i m i l a r ones. In g e n e r a l , it a p p e a r s that oils in l i m e s t o n e a r e distinguished by s o m e w h a t g r e a t e r t a r r i n e s s ; t h i s phenomenon has n e v e r been r e c o r d e d . T h u s , the hypothesis of the p r i m a r y e n v i r o n m e n t a l n a t u r e of oil h y d r o c a r b o n s (in the f o r m advanced by V. A. Sokolov) p r o v e s on c l o s e r

24

GEOCHEMICAL PROSPECTING F O R

PETROLEUM

examination of the facts to be untenable. The p r i m a r y nature of the sulfur content in petroleum is m o r e probable. But even h e r e , possibly, it i s not the nature of the initial m a t e r i a l that is playing a part but the c h a r a c t e r of the evolution of the crude oils; the l a t t e r may not be the s a m e in l i m e stones and sandstones (owing to differences in the catalytic and oxidative properties of r o c k s , and the like). " P r i m a r y " hypotheses promoting the idea of d i f f e r e n c e s in composition of the initial substances have r e c e n t l y been widely disseminated abroad (42, 43, e t c . ) . However, not one authentic instance can be adduced of the evident influence of the initial composition of crude oils on the observed differences in their p r o p e r t i e s . This does not mean that such influence cannot exist in general, but it does mean that all " p r i m a r y " hypotheses a r e at present devoid of any solid foundation. T o promote the f i r s t plan, and t h e r e f o r e , to deny the p r o c e s s e s of change in petroleum and to admit that crude oils a r e completely stable and immune to changes by other s u b s t a n c e s , is t h e r e f o r e impossible. This road will lead to the r e a l m of speculation and to the negation of p r o g r e s s . F o r an explanation of the diversity of crude oils in nature, let us turn to the phenomena of transformation of petroleum. Significance of P h y s i c a l P r o c e s s e s The effect of evaporation of light f r a c t i o n s is apparently v e r y substantial. It especially affects the distribution of properties v e r t i c a l l y in the section. In the upper s t r a t a , where t h e r e is insufficient thickness of c o v e r , the oils a r e often impoverished in the light f r a c t i o n s in comparison with oils f r o m lower l e v e l s . Evaporation may a l s o have taken place during the ancient epochs of denudation. The relation between crude oils that have lost the light fractions and the discontinuities and unconformities in the section was established and studied in detail by Z. A. T a b a s a r a n s k i i in the Western Kuban. T h i s has a l s o been noted by A. A. K a r t s e v in Western Azerbaijan. A s i m i l a r , but more pronounced phenomenon, o c c u r s at the P a l e o z o i c Mesozoic boundary in the Rocky Mountains (44). However, neither the physical p r o c e s s e s nor the natural fractionation of crude oils can explain the differences in the chemical composition of narrow fractions of the s a m e boiling range f r o m different oils. Y e t , such differences a r e observed not only for different provinces but a l s o for different levels of individual formations. T h i s inevitably leads to the concept of the great significance of chemical p r o c e s s e s in the g e o c h e m i c a l t r a n s formation of petroleum. Significance of Geochemical T r a n s f o r m a t i o n s of P e t r o l e u m The decisive significance of g e o c h e m i c a l p r o c e s s e s of change in petroleum is acknowledged today by the m a j o r i t y of investigators working in this field. On the question of the c h a r a c t e r of these p r o c e s s e s , however, opinions

^ P r o c e s s e s of m i x i n g of c r u d e o i l s cannot e x p l a i n the o b s e r v e d f a c t s of r e g u l a r d i s t r i b u t i o n of the p r o p e r t i e s of the o i l s in the depths. They c a n only l e a d to s p e c i a l c a s e s of deviations f r o m t h e s e r e g u l a r i t i e s .

GEOCHEMISTRY OF PETROLEUM FORMATIONS

25

sharply differ. Thus, A. F . Dobryanskii favors the first plan of metamorphism, denying the role of oxidation (2, 45, 46, et al.)2*> V. A. Uspenskii and O. A. Radchenko adhere to a contrary position, considering that the main process of change of petroleum is biochemical, anaerobic oxidation at the expense of sulfates iij the waters (34, 50, et al.)? 6 According to the first point of view, light oils are formed from heavy ones, while lower fractions of oils are formed from higher fractions and t a r s . According to the second point of view, heavy crudes are formed from light oils, while higher fractions and tars are formed from lower fractions. Identical regularities in the distribution of the properties of petroleum in formations are explained in each hypothesis by contradictory assumptions. Thus, the most common of these regularities in formations containing many strata are the decrease in specific gravity of crude oils and the decrease in their t a r r i n e s s with depth. According to data from the investigations of A. A. Kartsev on 250 formations in various countries of the world, decrease in specific gravity and t a r r i n e s s with depth are observed in 172 c a s e s , while the opposite phenomenon is seen in only 30 cases (changes with depth in the remaining cases are absent or irregular). A. F . Dobryanskii explains this by the assertion that the crudes at lower levels are more metamorphosed on account of their greater age and higher t e m peratures. V. A. Uspenskii and O. A. Radchenko explain the same phenomenon by the assertion that the oils lying at l e s s e r depths are more oxidized on account of the greater activity and higher sulfate content of the waters of the upper strata. The one-sided character of any given point of view was pointed out by V. A. Sulin, A. A. Kartsev, and Acad. S. I. Mironov (52). If one adheres to the theory of metamorphism consistently, one will be obliged to acknowledge as accidental coincidences the many cases of regular relation between the properties of oils and waters, i.e., between the quantities that characterize the activity of the waters (the total mineralization 2 and the indicators of metamorphism, which are the secondary salinity S2 and the primary alkalinity A^) and the specific gravity and t a r r i n e s s of the oils. Cases are known in which these and other quantities are not related to depth or are anomalously related thereto. Examples of this relation are given in diagrams (Fig. 5). Besides this, regular diminution in the specific gravity of crude oils with depth is often observed with such slight differences in the ages and temperatures of the strata and at such low temperatures that to speak of the effect of metamorphism is impossible [e.g., the formations at Dossor, Tschiebii, and Witze in Germany (53) and at Sansa-Santa in Borneo (41)]. Finally, within the limits of the theory of A. F . Dobryanskii, the existence of crude oils which are high in t a r s and also high in paraffins, such as the typical oils of the Second Baku, cannot be explained. Thus, the theory of A. F . Dobryanskii cannot be considered universal. Still less can the universality of the oxidation theory be admitted. Besides the facts given above in this connection, the following should be

^ S i m i l a r views have b e e n e x p r e s s e d by a n u m b e r of a u t h o r s ( 4 7 , 4 8 , 4 9 , et a l . ) in l e s s developed f o r m . ^ S i m i l a r views have a l s o b e e n e x p r e s s e d by o t h e r a u t h o r s ( 3 8 , 5 1 , et a l . ) .

26

GEOCHEMICAL P R O S P E C T I N G F O R

PETROLEUM

pointed out. If one consistently applies the b a s i c concept of the oxidation theory one is obliged to a s s u m e that all components of petroleum a r e derivatives of paraffinic hydrocarbons. This conclusion is completely ina d m i s s i b l e . It leads to an improbably high e s t i m a t e of b a c t e r i a l activity, because all nitrogen compounds in petroleum can be regarded in this c a s e as conversion products of the substance of b a c t e r i a . This conclusion c l e a r s the way for a perfectly a d m i s s i b l e inorganic theory of oil f o r m a tion, i . e . , that in the final reckoning the formation of paraffinic hydrocarbons may r e s u l t in the simplest of t h e s e — m e t h a n e . Thus, the consistent development of one oxidation theory leads to a geochemical and geological absurdity. Today the authors of this theory admit that it is i m possible to explain the origin of all oil t a r s by the oxidation of hydrocarbons (55). Consequently, here again one must deal with the problem of the heterogeneity of t a r s . This problem is very s e r i o u s in petroleum geoc h e m i s t r y , but it cannot be solved owing to the lack of adequate methods.

Ü LOK-BATAN

IL SHORSU

HL OKHA

F i g . 5. R e l a t i o n b e t w e e n the p r o p e r t i e s of c r u d e o i l s and w a t e r s ( d i s t r i b u t i o n within the f o r m a t i o n c r o s s - s e c t i o n ) . 1 — p r o p e r t i e s of o i l s ( s p . g r . , Yjj); 2 — p r o p e r t i e s of w a t e r s ( 2 - I; S 2 - II; A j - III).

If it were possible to s e p a r a t e " p r i m a r y " and " s e c o n d a r y " t a r s , the investigation of the causes of diversity among crude oils would take a long step forward. Valuable a s s i s t a n c e can be rendered h e r e by a detailed investigation of the c h e m i c a l composition of oils in t h e i r changes within the bounds of particular formations. Such data a r e very m e a g e r at present. Thus, it must be concluded that the role of the different geochemical p r o c e s s e s that cause the natural variations in petroleum is e x t r e m e l y i m portant, but it is evidently not possible to attribute all differences to any .one of t h e s e p r o c e s s e s .

27

" T h e h y p o t h e s i s , a d v a n c e d by s e v e r a l a u t h o r s , that n i t r o g e n o u s s u b s t a n c e s , i n cluding p o r p h y r i n s , in c r u d e o i l s a r e a c c i d e n t a l a d m i x t u r e s , should be c o n s i d e r e d i n v a l i d : the r e g u l a r r e l a t i o n b e t w e e n t h e s e s u b s t a n c e s and the r e m a i n i n g p o r t i o n s of the o i l s , a s well a s the type of o i l s ( s e e a b o v e , and a l s o ( 2 ) , e s p e c i a l l y the s e c t i o n on p o r p h y r i n s (54). Note that d i s t i l l a t e s , which a r e r e g a r d e d a s " f i l t r a t e s " and t h e r e f o r e m u s t e x t r a c t p o r p h y r i n s f r o m the r o c k s , a r e devoid of t h e m .

GEOCHEMISTRY OF PETROLEUM FORMATIONS

27

Conclusions Consideration of the entire complex of facts related to the geochemistry of petroleum in the light of the methodology of dialectical materialism leads to the following conclusions. The diversity in the properties of crude oils in nature is mainly the result of geochemical transformations of petroleum under the influence of external conditions. The observed properties of every oil are the result of its history. The composition of the initial substances probably has some effect, but this is only a minor influence which cannot be demonstrated as yet.

8

-«j o

£* 0

1 I£

g Ul (s

£

S c h e m e of the f u n d a m e n t a l g e o c h e m i c a l t r a n s f o r m a t i o n s of p e t r o l e u m .

Of the geochemical processes leading to conversions of crude oils, two groups, which are oppositely directed for the most part, are of decisive importance. This is determined by the close relation between the history of the oils and the general manner of " l i f e " on the earth's crust. The metamorphism of petroleum is related to the settling and metamorphism of rocks. Oxidative transformations, the epigenesis of oils, are related to rising and epigenesis. The decomposition of oils may be the final result of both processes, upon the passage of the crude oils beyond the limits of the " f i e l d " of their geochemical being. A scheme of the fundamental directions of the conversions of petroleum on the background of general geological processes is shown graphically (Fig. 6 ) . T h i s scheme reveals that in nature at least two genetically distinct forms of heavy tarry oils are encountered (the residues from evaporation constitute a third). Unfortunately, the state of knowledge concerning the composition of crudes in relation to the conditions of their deposition

^®This s c h e m e i s s i m i l a r to that s u g g e s t e d b y D. I. V y d r i n ( 5 6 ) , but was d e v e l o p e d independently. R e c e n t l y , N. B . V a s s o e v i c h and G. A. A m o s o v ( 5 7 ) a r r i v e d at the s a m e conception.

28

GEOCHEMICAL PROSPECTING FOR P E T R O L E U M

does not p e r m i t an a c c u r a t e elucidation of the g e o c h e m i c a l h i s t o r y of p a r t i c u l a r oils. The given s c h e m e c h a r a c t e r i z e s only the m o s t f u n d a m e n t a l f e a t u r e s of the g e o c h e m i c a l evolution of p e t r o l e u m . In r e a l i t y , t h e r e a r e a n u m b e r of c o m p l i c a t i o n s , which have been d e s c r i b e d above in d i f f e r e n t connection. B r i e f l y , the b a s i c hypotheses on t h e s e complicating f a c t o r s m a y be s u m m a r i z e d in the following f o r m . 1. The c h a r a c t e r (and t h e r e f o r e , r e s u l t s ) of m e t a m o r p h i s m a s well a s oxidation m a y v a r y in dependence on a combination of such conditions a s t i m e , t e m p e r a t u r e , c a t a l y s t s , f o r m of r e a g e n t , and the like. 2. M e t a m o r p h i s m and oxidation m a y p r o c e e d s i m u l t a n e o u s l y and in the s a m e place, s i n c e c r u d e oil contains c h e m i c a l l y d i s s i m i l a r components. 3. In the c o u r s e of geological h i s t o r y one d i r e c t i o n of t r a n s f o r m a t i o n m a y shift to the r e v e r s e d i r e c t i o n a s a r e s u l t of changes in sign of f l u c t u ating m o v e m e n t s of the e a r t h ' s c r u s t of g r e a t amplitude. 4. On c h e m i c a l p r o c e s s e s m a y be s u p e r i m p o s e d physical o n e s ; t h e combination of evaporation of light f r a c t i o n s and oxidation is e s p e c i a l l y probable. As a r e s u l t t h e o v e r a l l p i c t u r e b e c o m e s v e r y complex. I n t e r p r e t a t i o n of the e n u m e r a t e d c o r r e l a t i o n s r e q u i r e s c a r e f u l study of many geological and c h e m i c a l i n d i c e s f o r each p a r t i c u l a r c a s e . P r a c t i c a l I m p o r t a n c e of the Question Elucidation of the r e l a t i o n between the p r o p e r t i e s of c r u d e oils and the geological conditions of t h e i r e x i s t e n c e should m a k e p o s s i b l e the solution of the p r o b l e m of p r o g n o s i s of t h e quality of p e t r o l e u m ; it m a y m a k e s u c h a p r o b l e m a s p r o s p e c t i n g f o r oil of d e f i n i t e quality the o r d e r of the day. T h e s e p r o b l e m s a r e e x t r e m e l y i m p o r t a n t , s i n c e the e c o n o m i c value of v a r i o u s c r u d e s m a y be d i f f e r e n t , f o r e x a m p l e , f o r oils without gasoline and t h o s e high in t h i s component. T h e r e f o r e , a t t e m p t s at predicting the quality of c r u d e oils have been m a d e f o r a long t i m e , but they b o r e a p r i m i t i v e l y e m p i r i c a l c h a r a c t e r . M o r e s c i e n t i f i c w e r e the p r o g n o s e s of B. M. S a r k i s y a n f o r the Apsheron peninsula (58). It is c h a r a c t e r i s t i c that a l l t h e s e p r o g n o s e s depend on the p r e v i o u s l y noted predominant r e g u l a r i t y , i.e., the i n c r e a s e in gasoline content of p e t r o l e u m with the depth of the d e p o s i t . H o w e v e r , t h i s r e g u l a r i t y is not u n i v e r s a l . F u r t h e r m o r e , b e s i d e s the g a s o l i n e content, the p r i m a r y i n t e r e s t l i e s in the prediction of s u c h p r o p e r t i e s a s the h y d r o c a r b o n composition of the light f r a c t i o n s (which d e t e r m i n e s t h e i r octane n u m b e r ) and the like. T h e r e f o r e , it m u s t be admitted that no method of p r e d i c t i n g t h e quality of c r u d e oils h a s been developed a s yet. The n e c e s s i t y of work in t h i s d i r e c t i o n should be p e r fectly obvious. A f t e r gaining an acquaintance with the changes in c r u d e oils t h e m s e l v e s , it is in o r d e r to p r o c e e d t o the e f f e c t s of t h e s e p r o c e s s e s on the surrounding medium. GEOCHEMICAL PECULIARITIES O F THE GASES, WATERS, AND ROCKS O F P E T R O L E U M FORMATIONS The environment of oil pools c o n s i s t s of g a s e s , w a t e r s , and r o c k s . As a s p e c i a l f a c t o r of t h e e n v i r o n m e n t o r g a n i s m s m a y be distinguished, s u c h

GEOCHEMISTRY OF PETROLEUM FORMATIONS

29

as bacteria living in the waters. The geochemical peculiarities of gases, waters, and rocks of petroleum formations are of three kinds. To the first kind belongs the content in the gases, waters, and rocks of the products of the direct dispersion of the main substance of the oil pool: hydrocarbon gases, bitumens, and the like. To the second kind belong those properties which are the result of chemical reactions between hydrocarbons and the surrounding substance (for example, soda formed in the oxidation of oil). Finally, the third kind of peculiarity has no direct, genetic relation to petroleum. An example is the phenomenon of the presence of calcium chloride in reservoir waters, which is characteristic for certain formations only because of a combination of conditions favoring the simultaneous accumulation of the crude oils and these substances. The relation between oil pools and the associated geochemical peculiarities of gases, waters, and rocks is paragenesis. In accordance with the preceding statements, three kinds of paragenesis are distinguished. Natural Gases The natural gases of oil formations are, in part, a transitional link between the crude oils and the surrounding medium; the gases dissolved in oil constitute a part of the oils themselves, and it is impossible to draw a sharp line between them and the free gases. According to the conditions of their location in petroleum formations, the following forms of gases may be distinguished: (1) dissolved in oils; (2) free (in gas caps); (3) dissolved in waters; (4) sorbed by rocks. Transition from one of these forms to another is relatively easy. This transition is a physical process. In the latter a decisive role is played by pressure, especially the correlation between the pressure of the gas and the hydrostatic pressure in the reservoir. The chemical properties of the gases, oils, waters, and rocks themselves are also important. The composition of each of the four forms also depends on the solubility of particular kinds of gases; in a gas cap, gases of much lower solubility (e.g., CH^, Ng) will predominate, while in the waters, the role of the most watersoluble gases (CO2) will become more important, etc. In Table 4 data are given on the composition of the natural gases of oil formations, i.e., the composition of f r e e gases, as well as those partly dissolved in oils and waters (that portion of them which is evolved upon penetrating the strata).30 in this table C2H5+ refers to hydrocarbons from ethane up; C5H12+ refers to hydrocarbons from pentane up. The most abundant gases of oil formations, as Table 4 reveals, are methane, the heavier gases as a group, carbon dioxide, and nitrogen. These four components can therefore be used as a basis of classification.

oq The following f a c t o r s may be distinguished by their spatial relation to the oil pool: (1) internal factors of the e n v i r o n m e n t — o i l - s a t u r a t e d rocks with bound water occluded therein; (2) external f a c t o r s of the environment—the outer portion of the r e s e r v o i r , s a t u rated with g a s e s and w a t e r s , basement and cap r o c k s , etc. 30 It should be kept in mind that data on the CO2 content of f r e e l y evolved g a s e s a r e not entirely indicative, owing to its great solubility.

30

GEOCHEMICAL PROSPECTING FOR

PETROLEUM

T A B L E 4. Composition of Natural Gases f r o m Petroleum

%

CH 4

% C2H6

%

C3H8

%

%

C4H10 C5H12+

CH 4

%

C2H6+

% total Cn*m

%

co 2

%

%

N2 H 2 S

1 - 9 9 0.2 - 3 4 0.01 - 35 0 - 1 8 0.2 - 15 1 - 6 6 0 . 2 - 9 9 5 - 1 0 0 0 - 9 5 0 - 6 0 0 - 1 2 The geochemical classification of the natural gases of oil formations must be compatible with chemical as well as geological characteristics. An example of such a classification is presented here. For the preparation of this classification, a double trigonogram (Fig. 7) similar to that suggested by S. A. Durov for waters (59) is used. The upper triangle gives the total composition of the natural gas; and its vertices correspond to values of the total gas content (comprising hydrocarbons, carbon dioxide, and nitrogen) equal to 100%. The triangle to the left gives the composition of the carbonaceous part of the gas; and its vertices correspond to values of the gas content (comprising methane, the heavier hydrocarbons, and carbon dioxide, computed on the basis of these three components without N2, etc.). The triangle to the left is necessary f o r the development of a correlation among hydrocarbons that is of great significance. The data of both triangles are projected onto a square. A point on the square shows the classification position of the gas f r o m a given pool. T A B L E 5. Geochemical Classification of Natural Gases f r o m Petroleum Composition Class

% total

% CH 4

% C2H6

CnHm

%

%

co 2 N 2

Geological region of origin of typical representatives

1. Hydrocarbon, dry

>95

>75

O vß H fi H (M I I I I I co co ^ ^ co »n -H

o l i l i

I S ö I

e •s o e

e v u a

X

u w J m
»

Yes »1 t »

-

No10 Yes11 No11 No11

Temp. °C

-

70 >70

Conclusion: Oil and/or Gas Yes ) ?

? ? ?

No

)

Remarks It is important to consider the presence or absence of HS1 and HS 2

In some cases it seems possible to give an approximate estimate of the distance from the r e s e r v o i r in a given stratum to the sample point by using the SO4 content. Thus, in the reservoirs of the Apsheron Peninsula, according to the date of V. A. Sulin, D. V. Zhbrev, A. Ya. Gavrilov, and others, oil-bearing strata contain sulfates in small quantities at a distance of several hundred meters f r o m the boundary of the r e s e r v o i r ; but closer than that, there are no sulfates. Soda (Alkalinity) Soda (sodium bicarbonate) can be formed by oxidation of hydrocarbons by sulfate (see Chapter I). Therefore, the presence of soda in water (which makes the water of the alkaline sodium bicarbonate type) may under certain conditions be considered a criterion of the presence of oil. Alkaline waters are characteristic of numerous oil-bearing strata. Apparently, most of the soda in waters of oil-bearing sediments was formed by oxidation of oil substances. However, soda can occur in natural waters in other ways, unrelated to petroleum. Alkaline waters are also characteristic of regions where sodium-rich magmatic, metamorphic, and some sedimentary (arkosic sandstone) rocks occur. Secondly, they occur also in zones of solonetz development. Finally, alkaline waters can also be connected with volcanic regions where the soda is formed by CO2 coming from the depths. It is relatively simple to distinguish alkaline waters of the weathering zone draining salt-free rocks from alkaline waters of oil-bearing strata. The former are fresh and calcium carbonate is the most abundant salt they contain. The latter are salty and sodium chloride is the principal salt present. The alkaline waters of the solonetz can usually be distinguished by the conditions of their occurrence. They can be only surface or groundwaters. However, ambiguous cases are possible. This is particularly true of waters in volcanic, or primarily volcanic, regions (for instance, Borzhomi). Whether or not soda may form by oxidation of coal and similar caustobiolites (compare the hydrosulfides and others, above) is also unclear. In

sulfates, even if d i s p e r s e d , a r e included, " w e

consider h e r e m a j o r m a s s e s of gypsum and anhydrite

HYDROCHEMICAL METHODS

249

the upper zones of coal deposits, alkaline waters apparently are not found, and if found, their alkalinity is of inorganic origin (17, 18, and others). However, alkaline waters are known to occur in deep coal-bearing sediments, for instance in the Donbass (16). There the soda apparently is formed by reduction of sodium sulfate by methane. Thus, soda in waters can be considered an indicator of oil and gas (including gas-bearing coal beds?) providing the waters are not from the weathering zone, the Solonetz, or do not have a volcanic origin. The absence of soda in waters is of no value in estimating oil potential. If one considers springs, the soda can be displaced by sulfates in the weathering zone. According to A. A. Kartsev, the oil-bearing Maikop deposits of Transcaucasia contain only alkaline waters at great depths. At the same time, springs at the surface, which originate from those deposits, do not contain soda. In considering oil formations, not only alkaline waters but also waters of the calcium chloride type are c h a r a c t e r i s t i c . ^ Calcium Chloride Calcium chloride in the water is the final product of metamorphism of the salt composition of subsurface waters. It forms by cation exchange between the water and the rocks. The process of metamorphism of brines leading to the formation of calcium chloride proceeds further the more stagnant the hydrogeological conditions. This stagnancy (hydrogeological closure) favors the preservation of the oil r e s e r v o i r s . Thus, the most favorable conditions for oil deposits and dissolved calcium chloride coincide. T h e r e fore, the presence of calcium chloride in waters (i.e., calcium chloride type of water) is an indirect indicator of possible oil and gas. In contrast to the indicators considered above, calcium chloride never has any direct connection with petroleum. Therefore, the presence of calcium chloride does not indicate the presence of oil itself but only favorable conditions for oil accumulation (hydrogeologic stagnancy). The existence of such conditions does not necessarily imply the presence of r e s e r v o i r s . Other factors are necessary for this (the processes of oil formation, traps, etc.) Waters containing calcium chloride have, as a rule, a very high mineral content. If the presence of calcium chloride is established in highly mineralized waters at considerable depths (or emerging from such depths) it may be concluded that stagnant conditions occur. If calcium chloride is detected in weakly mineralized groundwaters (or in r a r e cases, surface waters), there must be an inflow of water from depth, or from other horizons, and mixing of waters must occur. It is not always possible to determine the horizon from which the calcium chloride originates, in such c a s e s . The absence of calcium chloride in water does not indicate unfavorable conditions for preservation of oil accumulations. As is known, alkaline waters are also characteristic of oil-bearing strata. Bromine Bromine is present in natural waters in the form of bromides and especially as sodium bromide. Bromine has no direct connection with petroleum. t h e s e and in h a r d w a t e r s , c a l c i u m c a r b o n a t e i s f o r m e d during the o x i d a t i o n of h y d r o c a r b o n s i n s t e a d of s o d a ( s e e C h a p t e r I).

250

GEOC HEMIC A L PROSPECTING FOR PETROLEUM

The value of bromine in oil exploration is due to the fact that it is found in high concentrations in waters containing calcium chloride. Thus, the role of bromine as an oil indicator is essentially analogous to that of calcium chloride. Large amounts of bromine indicate a high degree of metamorphism of the brines that are characteristic in particular for rocks containing commercial accumulations of oil. In some cases, the bromine content exceeds 1000 mg/l, a concentration high enough f o r commercial production of bromine. However, a high concentration of bromine (even high enough to be commercially valuable) occurs also in some salt lakes and has a purely surface origin. Moreover, in many alkaline waters of oil-bearing strata, the bromine content is small. The CI/Br ratio is of considerable interest. In ocean water it equals 292. In metamorphosed brines (subsurface as well as surface, i.e., lakes) the ratio Cl/Br

> '

-

\ r*

>y

S\ \

^ M

1

I ,?

s

^

311

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F i g . 132. B a c t e r i a which reduce sulfates. 1 — V i b r i o desulfuricans (x800); 2 — V i b r i o rubentschikii (xl200).

F i g . 133. Sulfate-reducing bacteria of o i l - b e a r i n g w a t e r s . V i b r i o d e s u l f u r i c a n s , v a r . g r a n u l a r i s . V i b r i o s and r o d shaped f o r m s (x2000).

oil formations in their ability to develop in a medium in which heptane is the only source of hydrocarbon nourishment.* No common desulfurizing microspira with this ability is known (17). Sulfate-reducing bacteria developing in a medium which contains heptane are the only oil-indicating microorganisms for waters containing hydrogen sulfide, since bacteria which oxidize hydrocarbons in an atmosphere containing hydrogen sulfide cannot exist.

A controversial claim. Some w o r k e r s b e l i e v e that sulfate r e d u c e r s g r o w only on aliphatic hydrocarbons of g r e a t e r m o l e c u l a r weight than decane. Ed. ( W D R )

312

GEOCHEMICAL PROSPECTING FOR PETROLEUM Hydrogen-Oxidizing B a c t e r i a

As s t a t e d above, the ability to produce w a t e r by decomposition of o r g a n i c m a t t e r i s p o s s e s s e d by many a n a e r o b i c m i c r o o r g a n i s m s . At the s a m e t i m e , b a c t e r i a which oxidize hydrogen a r e quite widely d i s t r i b u t e d in soil and s u b s o i l d e p o s i t s . H y d r o g e n - o x i d i z i n g b a c t e r i a a r e encountered in g r o u n d - and s t r a t u m - w a t e r s , and a l s o in s e d i m e n t a r y l a y e r s containing gas pockets or oil pools. The oxidation of m o l e c u l a r hydrogen to water is a b a s i c e n e r g e t i c p r o c e s s f o r the development of hydrogen b a c t e r i a . Hydrogen b a c t e r i a u s e f r e e oxygen to oxidize hydrogen. Under c e r t a i n conditions they m a y a l s o utilize the combined oxygen of n i t r a t e s and s u l f a t e s , and even r e d u c e c a r bon dioxide with the f o r m a t i o n of m e t h a n e . Typical and non-typical f o r m s of hydrogen-oxidizing b a c t e r i a a r e d i s tinguished (28). F o r non-typical f o r m s of hydrogen-oxidizing b a c t e r i a , t h i s p r o c e s s is incidental. Noticeable growth of t h e s e b a c t e r i a o c c u r s only in the p r e s e n c e of a l r e a d y - f o r m e d organic m a t t e r , which is utilized by t h e m a s a s o u r c e of c a r b o n . In c o n t r a s t to t h i s , typical f o r m s of hydrogen b a c t e r i a oxidize hydrogen under autotrophic conditions. F o r t h e s e the s o u r c e of c a r b o n is c a r b o n dioxide. As is known, the r e l a t i o n of hydrogen to oil pools and h y d r o c a r b o n g a s e s is not s u f f i c i e n t l y c l e a r a s yet (29). In biologging work the p r e s e n c e in the c o r e s of hydrogen-oxidizing b a c t e r i a is usually c o n s i d e r e d to be one of the i n d i r e c t i n d i c a t o r s of the o i l - b e a r i n g n a t u r e of the d e p o s i t s . Methane-Producing Bacteria As investigations of s u b t e r r a n e a n w a t e r s conducted in the c o u r s e of a q u e o u s b i o c h e m i c a l s u r v e y s have shown, b a c t e r i a which produce m e t h a n e f r o m fatty a c i d s a r e widely d i s t r i b u t e d in ground w a t e r s lying at l e s s e r d e p t h s , and a l s o in the w a t e r s of polluted wells and s u m p s . M e t h a n e - f o r m i n g or methane-producing bacteria are strictly anaerobic. T h e r e a r e about ten d i f f e r e n t kinds of b a c t e r i a capable of causing m e t h a n e f e r m e n t a t i o n , i . e . , producing m e t h a n e f r o m the s a l t s of fatty a c i d s and v a r i o u s alcohols by the r e d u c t i o n of carbon dioxide to m e t h a n e in the p r e s e n c e of hydrogen (30). The m o s t c h a r a c t e r i s t i c p r o d u c e r s of m e t h a n e a r e the f o u r kinds of n o n s p o r e - f o r m i n g b a c t e r i a given below: 1. M e t h a n o s a r c i n a m e t h a n i c a , known mainly b e c a u s e of the work of Sohngen; it is c h a r a c t e r i z e d by g r e a t s i z e and the f o r m a t i o n of s a r c i n o u s packets; it does not f e r m e n t alcohol; 2. Methanococcus, which c a u s e s m o r e v i g o r o u s f e r m e n t a t i o n than s a r c i n a ; usually a p p e a r s in the lower s t a g e s of f e r m e n t a t i o n of ethyl and butyl a l c o h o l s ; 3. r o d - s h a p e d b a c t e r i a ; t h e r e a r e two morphologically s i m i l a r f o r m s , M e t h a n o b a c t e r i u m Sohngenii and M. O m e l a n s k i i , which have the a p p e a r a n c e of long, twisted t h r e a d s c o n s i s t i n g of s e p a r a t e r o d s . In t h e i r physiological p r o p e r t i e s , h o w e v e r , the two f o r m s d i f f e r s h a r p l y f r o m one a n o t h e r : one f e r m e n t s acetic acid with f o r m a t i o n of m e t h a n e , while the other f e r m e n t s ethyl alcohol. The two f o r m s of m e t h a n e - p r o d u c i n g b a c t e r i a , s e p a r a b l e in B a r k e r m e d i a with alcohol and with s o d i u m a c e t a t e , a r e e x t r e m e l y i m p o r t a n t cont r o l m i c r o o r g a n i s m s . C a s e s of c o n t e m p o r a r y f o r m a t i o n of m e t h a n e in

MICROBIOLOGICAL METHOD

313

u n d e r g r o u n d w a t e r s through decomposition of v a r i o u s o r g a n i c r e s i d u e s or through r e d u c t i o n of CO2 by hydrogen a r e quite definitely e s t a b l i s h e d by their presence. B a c t e r i a which Decompose Cellulose The n o n - n i t r o g e n o u s m a t t e r r e m a i n i n g a f t e r d e c o m p o s i t i o n of a l b u m i n s is usually b r o k e n down to c a r b o n dioxide and w a t e r by m i c r o o r g a n i s m s u n d e r a e r o b i c conditions. A f t e r this other compounds which m a k e up p a r t of the r e m a i n s of a n i m a l s and plants ( s u g a r , s t a r c h , c e l l u l o s e , and other c a r b o h y d r a t e s ) a r e d e c o m p o s e d . The m o s t s t a b l e of t h e s e is c e l l u l o s e . Its d e composition under a n a e r o b i c conditions l e a d s to the f o r m a t i o n of m e t h a n e , carbon dioxide, and w a t e r (31, 32). The c a u s e of a n a e r o b i c decomposition of c e l l u l o s e i s a c y l i n d r i c a l rod which f o r m s s p o r e s . It is o b s e r v e d in the ground by use of O m e l y a n s k i i solution. Decomposition is a p p a r e n t l y due to two m i c r o o r g a n i s m s , one of which p r o d u c e s hydrogen and c a r b o n dioxide, while the other b r i n g s about the c h e m o s y n t h e s i s of t h e s e g a s e s with f o r m a t i o n of m e t h a n e . C e l l u l o s e - d e c o m p o s i n g b a c t e r i a a r e used a s control o r g a n i s m s in s u r v e y s in the zone of s u b s o i l d e p o s i t s . If c e l l u l o s e - d e c o m p o s i n g b a c t e r i a a r e found t o g e t h e r with methane-oxidizing b a c t e r i a in the s o i l p r o f i l e , ground s a m p l e s m u s t be taken at a g r e a t e r depth in o r d e r to avoid the zone of c o n t e m p o r a r y f o r m a t i o n of combustible g a s e s . B a c t e r i a which Oxidize G a s e o u s and V a p o r i z e d H y d r o c a r b o n s H y d r o c a r b o n - o x i d i z i n g b a c t e r i a a r e of the g r e a t e s t i n t e r e s t in oil p r o s p e c ting, s i n c e t h e s e b a c t e r i a a r e d i r e c t i n d i c a t o r s of the c o r r e s p o n d i n g hyd r o c a r b o n s . However, not all m e m b e r s of t h i s w i d e s p r e a d g r o u p a r e s u f ficiently s p e c i f i c with r e s p e c t to t h e i r function — oxidation of h y d r o c a r b o n s . In p a r t i c u l a r , b a c t e r i a which oxidize v a p o r i z e d and liquid h y d r o c a r b o n s a r e h e t e r o t r o p h i c o r g a n i s m s , i . e . , they can utilize a l r e a d y - f o r m e d o r g a n i c m a t t e r . A s t r i c t e r s e l e c t i v i t y in relation to the s o u r c e of c a r b o n n o u r i s h ment is p o s s e s s e d by b a c t e r i a which oxidize g a s e o u s h y d r o c a r b o n s . The oxidation of h y d r o c a r b o n s s e r v e s a s a s o u r c e of e n e r g y , while carbon dioxide s e r v e s a s a s o u r c e of c a r b o n . Thus, they may be included among the autotrophic o r m e s o t r o p h i c b a c t e r i a . The o c c u r r e n c e in n a t u r e of p r o c e s s e s of biological consumption of m e t h a n e was e s t a b l i s h e d in 1905 by K a z e r e r . At the s a m e t i m e Sohngen d i s c o v e r e d b a c t e r i a r e q u i r e i n g m e t h a n e f o r t h e i r development. B a c t e r i a which oxidize m e t h a n e (according to Sohngen, Bacillus m e t h anicus), have the a p p e a r a n c e of s h o r t , thick r o d s having a s h a p e i n t e r m e d i a t e between an ellipsoid and a cylinder. The b a c t e r i a v a r y in length f r o m 2 - 3 to 4 - 5 n and a r e about 1.5 - 2 n thick (Fig. 134). Methaneoxidizing b a c t e r i a r e l a t e d to the type Methanomonas m e t h a n i c a a r e v e r y widely d i s t r i b u t e d in n a t u r e in c o m p a r i s o n with o t h e r f o r m s of b a c t e r i a which oxidize g a s e o u s h y d r o c a r b o n s . Methane-oxidizing b a c t e r i a a r e found in s u r f a c e d e p o s i t s and in deep-lying ones, a s well a s in ground and s t r a t u m waters. A c c o r d i n g to the findings of Miinz (33) the m e t h a n e b a c t e r i a isolated by him developed not only in the p r e s e n c e of m e t h a n e , but a l s o with o t h e r o r g a n i c s u b s t a n c e s (sodium a c e t a t e , g l y c e r o l , mannitol, glucose). H o w e v e r ,

314

GEOCHEMICAL PROSPECTING FOR PETROLEUM

F i g . 134.

C e l l s of m e t h a n e - o x i d i z i n g bacteria.

in this case the development of the methane-oxidizing bacteria proceeded much more slowly. It has been shown that the ability of methane-oxidizing bacteria to assimilate methane after cultivation with other sources of organic matter usually diminishes or even vanishes. The investigations of G. P. Slavnina (34, 35) showed that the properties of methane-oxidizing bacteria stated above are associated with the presence of the oxidative enzyme peroxidase. This enzyme is absent in other forms of bacteria which oxidize heavier hydrocarbons. Bacteria which oxidize ethane were isolated from Tambukanian mud by Gubin in 1923. Ethane-oxidizing bacteria have the appearance of moving, sporeless rods measuring 1.5x0.5 . Ultimately, bacteria utilizing ethane as a source of energy were isolated in a number of regions in the course of oil-prospecting work. However, in the examination en masse of ground samples from known oil-bearing regions, ethane-oxidizing bacteria are found relatively rarely. It may be that these bacteria require special conditions for development. F o r these reasons ethane-oxidizing bacteria are not now used as indicating organisms in oil-prospecting work. Ethane-oxidizing bacteria are identified as Mycobacterium perrugosum var. ethanicum. They are not able to assimilate methane, but can develop in an atmosphere of propane and other heavier hydrocarbons mixed with air (36). Bacteria which oxidize propane were first isolated in 1939 in the Maikop region in the course of microbiological prospecting for oil and gas (37)y At present propane-oxidizing bacteria are used as very c h a r a c t e r i s tic indicator organisms in oil-prospecting work. According to the data of E . N. Bokova (36), propane-oxidizing bacteria belong to the type Mycobacterium rubrum var, propanicum (Fig. 135). They possess an oxidative enzyme, or catalase (35), and are unable to assimilate methane or ethane, but can utilize hydrocarbons heavier than propane (butane, pentane, hexane, etc.). As experiments have shown, most

MICROBIOLOGICAL METHOD

F i g . 135.

315

C e l l s of p r o p a n e - o x i d i z i n g bacteria.

varieties of Mycobacterium rubrum utilize only molecular oxygen and cannot subsist by reduction of the oxygen of sulfates and nitrates. Bacteria which oxidize butane and do not utilize propane are not described in the literature and have not been studied. Attempts to isolate these bacteria from samples of oil-bearing regions were made by using a propane-butane mixture. Therefore, clear results were not obtained. The question of the existence of butane-oxidizing bacteria as organisms having distinct physiological properties remains open. Bacteria which oxidize vaporized hydrocarbons. It has been established that vaporized and liquid hydrocarbons are accessible to a relatively large number of heterotrophic microorganisms. In particular, it has been shown that paraffin hydrocarbons with 1 0 - 1 6 carbon atoms are more easily oxidized by bacteria than those of lower molecular weight (21). Therefbre, bacteria developed in an atmosphere of vaporized hydrocarbons cannot always be considered indicators of the corresponding hydrocarbons. This group of microorganisms is less significant in the examination of surface deposits. However, as the depth from which samples are taken is increased, the finding of bacteria which oxidize vaporized hydrocarbons acquires definite significance in prospecting. Bacteria which oxidize the first homologs of liquid hydrocarbons (pentane and heptane) are of great interest. Different varieties of these, isolated from deep-lying deposits, are able to utilize the bound oxygen of nitrates. Hexane-oxidizing bacteria belong to the type Bact. aliphaticum liquefaciens. As stated above, one of the theoretical foundations of the microbiological method of prospecting is the specificity of the bacteria used as indicators. If prospecting for oil and gas pools is to be on the basis of microbiological indicators, it is necessary to know how widespread within the bacterial world is the ability to oxidize methane, propane, and higher homologs and to what extent indicator microorganisms possess the ability to assimilate different hydrocarbon homologs, as well as other organic compounds.

316

GEOCHEMICAL PROSPECTING FOR

PETROLEUM

The great m a s s of experimental m a t e r i a l accumulated during the y e a r s of application of the method shows that r e l a t i v e l y few groups of m i c r o organisms have the ability to oxidize methane and especially propane. In the examination of ground and water s a m p l e s containing methane- or propane-oxidizing b a c t e r i a , the b a c t e r i a could only develop in an atmosphere Of the corresponding gas mixed with a i r or oxygen. The indicated f o r m s of m i c r o o r g a n i s m s a r e e a s i l y distinguished in cumulative cultures by the c h a r a c t e r of the f i l m s they form and a l s o m o r phologically. Methane-oxidizing b a c t e r i a in a l a t e r stage of development f o r m a brownish, wrinkled film, while propane-oxidizing b a c t e r i a form an e l a s t i c , sagging film, usually white or light yellow ( F i g . 136). The s p e c i ficity of methane-oxidizing b a c t e r i a , in particular, is confirmed by the fact that, a f t e r cultivation in media containing prepared organic substances instead of methane, they lost peroxidase. Propane-oxidizing b a c t e r i a have been only r a r e l y observed beyond the boundaries of oil- and g a s - b e a r i n g r e g i o n s . Thus, data on b a c t e r i a which oxidize gaseous hydrocarbons show that they p o s s e s s sufficient s p e c i a l i zation to permit t h e i r use as indicators of the corresponding g a s e s . Vaporized and liquid homologs of methane, beginning with pentane, a r e available X

F i g . 1 3 6 . F i l m s of b a c t e r i a which oxidize m e t h a n e and p r o p a n e , a — m e t h a n e - o x i d i z e r s ; b — p r o p a n e - o x i d i z e r s (view f r o m a b o v e )

317

MICROBIOLOGICAL METHOD

to many microorganisms, and hence, the determination of these hydrocarbons in the microbiological way is possible, but without their subdivision into separate fractions. Table 36, compiled on the basis of the investigations of E. N. Bokova (38), shows the difference in selective ability among the various microorganisms which oxidize hydrocarbons. T A B L E 36. Utilization "of Gaseous and Liquid Hydrocarbons by Bacteria Bacterial cultures

Hydrocarbon methane ethane propane butane pentane hexane heptane

Methane oxidizers . . . .

+

_

Ethane oxidizers . . . .

_

+ -

Propane oxidizers . . . . Oxidizers of pentane and higher homologs . . . .

-

_

+

+

+

+

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+

+

+

+

+

+

+

+

+

+

+

Conditions Limiting the Propagation and Use of Indicator M i c r o organisms Bacteria which oxidize methane and its homologs (propane, butane, and hexane) require atmospheric oxygen, moisture, and sources of mineral nourishment containing nitrogen, phosphorus, potassium, and magnesium besides the hydrocarbons in order to develop. The growth of the bacteria is substantially affected by temperature, hydrogen-ion concentration, and several other environmental conditions. The correlation of the physicochemical conditions enumerated above changes, upon transition f r o m one climatic or geographical zone to another, and also with change of depth of the layer being studied. Let us consider the change of these conditions with depth. The earth's crust may be divided into three microbial zones which differ in the nature and abundance of their bacterial populations, and in the peculiarities of biochemical activity of these bacteria. This division, which is somewhat provisional in character, is as follows: 1. The zone with the greatest bacterial population and variety of morphological and physiological groups of bacteria is the soil zone. The thickness of this first zone is very slight in comparison with the other zones distinguished by us. Depending on soil-climatic conditions it varies for specific regions and areas from 0.5 to 1.5 m., or slightly more in a few cases. The soil zone from the viewpoint of bacterial investigations is characterized by the presence of biochemical processes of decomposition of soil organic matter now taking place. As a rule, these processes occur slightly below the soil layer itself. 2. Below the soil zone lies a zone of subsoil deposits which, in a number of cases, is associated with Quarternary deposits. It coincides with the so-called zone of erosion. The peculiarity of this zone is the greater

318

GEOCHEMICAL PROSPECTING FOR PETROLEUM

or l e s s e r d e g r e e of a e r a t i o n of its constituent r o c k s . Thus, the b a c t e r i a l population of t h i s zone is c h a r a c t e r i z e d by the development of a e r o b i c f o r m s along with a n a e r o b i c and f a c u l t a t i v e o n e s . The t h i c k n e s s of t h i s zone is m e a s u r e d in t e n s , and s o m e t i m e s h u n d r e d s of m e t e r s . 3. Below the zone of s u b s o i l d e p o s i t s l i e s the zone of d e e p - l y i n g d e p o s i t s , which is c h a r a c t e r i z e d by the p r e s e n c e of poorly a e r a t e d and slightly p e r m e a b l e , m a i n l y bedrock d e p o s i t s . H e r e a r e e n c o u n t e r e d only s e l e c t e d f o r m s of m i c r o o r g a n i s m s , the f u n c t i o n s of which a r e d e t e r m i n e d by the c h a r a c t e r of the v a r i o u s o r g a n i c compounds buried in the depths or d i f f u s i n g through a s e d i m e n t a r y l a y e r and by the p r e s e n c e of n e c e s s a r y mineral substances. The p r a c t i c a l s i g n i f i c a n c e of t h e s e zones is that: 1. not all f o r m s of h y d r o c a r b o n m i c r o f l o r a have the ability t o utilize the combined oxygen of n i t r a t e s and s u l f a t e s ; hence, t h e i r propagation is l i m i t e d in depth; 2. s p e c i f i c m i c r o o r g a n i s m s used a s b a c t e r i a l i n d i c a t o r s of oil and combustible g a s e s a r e not good i n d i c a t o r s through the full t h i c k n e s s of a s t r a t u m b e c a u s e , a s the s u r f a c e is a p p r o a c h e d , p r o c e s s e s of c o n t e m p o r a r y gas f o r m a t i o n r e s u l t i n g f r o m t h e decomposition of organic r e s i d u e s o c c u r . F o r t h e s e r e a s o n s , n e i t h e r b a c t e r i a which oxidize m e t h a n e n o r those which develop in an a t m o s p h e r e of v a p o r i z e d h y d r o c a r b o n s can be i n d i c a tive in oil and gas p r o s p e c t i n g within the l i m i t s of the soil zone. Such a d ditional i n d i c a t o r s a s h y d r o g e n - o x i d i z i n g and d e s u l f u r i z i n g m i c r o o r g a n i s m s a l s o l o s e t h e i r s i g n i f i c a n c e h e r e . Only p r o p a n e - o x i d i z i n g b a c t e r i a m a y be used to s o m e extent within the soil zone. H o w e v e r , the t h e o r e t i c a l l y a d m i s s i b l e possibility of f o r m a t i o n of heavy h y d r o c a r b o n s f r o m o r g a n i c c o m pounds in the soil m u s t a l s o be kept in m i n d . The s o i l l a y e r can be significant in m i c r o b i o l o g i c a l s u r v e y i n g if the r e l a t i o n s h i p s between m o r p h o l o g i c a l g r o u p s and the total n u m b e r of m i c r o o r g a n i s m s a r e taken into account. In t h i s way the total i n c r e a s e of biogenic activity of the s o i l s o v e r oil and gas pools m a y be d e t e r m i n e d . In the s u b s o i l zone the m a i n i n d i c a t o r s of h y d r o c a r b o n g a s e s a r e b a c t e r i a which oxidize m e t h a n e and p r o p a n e . H e r e b a c t e r i a which develop in an a t m o s p h e r e of v a p o r i z e d h y d r o c a r b o n s a r e l e s s r e l i a b l e . Within the l i m i t s of the zone of d e e p - l y i n g d e p o s i t s , the m o s t i m p o r t a n t i n d i c a t o r o r g a n i s m s a r e a n a e r o b e s or f a c u l t a t i v e a n a e r o b e s which can utilize the combined oxygen of highly oxidized m i n e r a l s o r o r g a n i c compounds. Among the e n u m e r a t e d f o r m s of m i c r o o r g a n i s m s , those which fully s a t i s f y t h i s r e q u i r e m e n t a r e the b a c t e r i a which oxidize v a p o r i z e d h y d r o c a r bons and the d e s u l f u r i z i n g b a c t e r i a . Methane-oxidizing and h y d r o g e n oxidizing b a c t e r i a a r e d e t e c t e d in well b o r e s to a l e s s e r depth. P r o p a n e oxidizing b a c t e r i a a r e e n c o u n t e r e d in s m a l l n u m b e r s , even in deep-lying d e p o s i t s . Thus, in d e e p - l y i n g d e p o s i t s , b a c t e r i a which oxidize m e t h a n e and p r o p a n e play a m i n o r r o l e in oil- and g a s - p r o s p e c t i n g work in c o m p a r i s o n with b a c t e r i a which oxidize v a p o r i z e d h y d r o c a r b o n s . E x i s t i n g data on the o c c u r r e n c e of a h y d r o c a r b o n m i c r o f l o r a f o r a g r e a t v a r i e t y of g e o g r a p h i c a l points show that d i f f e r e n t c l i m a t i c conditions do not h i n d e r the development of the m i c r o o r g a n i s m s named above, although they do a f f e c t the total n u m b e r and r a t e of growth during s p e c i f i c p e r i o d s of the y e a r . The p r e s e n c e of b a c t e r i a which oxidize m e t h a n e , p r o p a n e , and v a p o r i z e d h y d r o c a r b o n s in s u b s o i l d e p o s i t s h a s been e s t a b l i s h e d in the north, p a r t i c u l a r l y in the p e r m a f r o s t zone, and in the s o u t h e r n r e g i o n s of

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the Soviet Union, p a r t i c u l a r l y in the d e s e r t zone. The lithological composition of the r o c k s a l s o h a s a c e r t a i n e f f e c t on the development of a h y d r o c a r b o n m i c r o f l o r a . It has been e s t a b l i s h e d that the m i n e r a l compounds n e c e s s a r y for the growth of the h y d r o c a r b o n m i c r o f l o r a e x i s t in a wide v a r i e t y of c o n t e m p o r a r y d e p o s i t s a s well a s in ancient r o c k s . Relatively r a r e l y , c a s e s a r e o b s e r v e d in which given clay i n t e r b e d s do not contain the m i n e r a l s a l t s n e c e s s a r y f o r the growth of b a c t e r i a or prove unsuitable f o r t h e i r v i t a l activity owing to the acid r e a c t i o n of the m e d i u m . C o r r e l a t i o n of the lithology of r o c k s with the population density of the h y d r o c a r b o n m i c r o f l o r a shows that, other conditions r e m a i n i n g equal, i n c r e a s e in p o r o s i t y f a v o r s g r e a t e r development of the b a c t e r i a l population. An e x t r e m e l y i m p o r t a n t e l e m e n t f o r the m e t a b o l i s m of b a c t e r i a is m o i s t u r e . It has been e s t a b l i s h e d that in the s o u t h e r n r e g i o n s the d r y i n g out of the r o c k s in c e r t a i n p e r i o d s of the y e a r m a y lead to a pronounced diminution of the h y d r o c a r b o n m i c r o f l o r a . H o w e v e r , the s e a s o n a l d e c r e a s e of m o i s t u r e in r o c k s of the c e n t r a l zone of the Soviet Union h a s no e f f e c t on i n d i c a t o r s f o r m i c r o b i o l o g i c a l s u r v e y i n g . T h u s , if the u n f a v o r a b l e conditions e n u m e r a t e d above a r e a b s e n t growth of the h y d r o c a r b o n m i c r o f l o r a will be d e t e r m i n e d m a i n l y by the p r e s e n c e of a s o u r c e of h y d r o c a r b o n n o u r i s h m e n t and the qualitative c o m position of the h y d r o c a r b o n s . It h a s been shown that the quantity of gas needed to i n s u r e the growth of a h y d r o c a r b o n m i c r o f l o r a is on the o r d e r of 1 - 1 0 p a r t s p e r million (39). S i m i l a r c o n c e n t r a t i o n s of h y d r o c a r b o n s , a c cording to g a s - s u r v e y data, a r e usually found over oil and gas pools. As a r e s u l t of t h i s , h y d r o c a r b o n g a s e s m i g r a t i n g f r o m the depths m a y be c o m pletely oxidized in the p r e s e n c e of a sufficiently developed b a c t e r i a l f i l t e r . MAIN VARIETIES O F THE MICROBIOLOGICAL METHOD Microbiological s e a r c h e s f o r oil and gas m a y be conducted by examination of s u b t e r r a n e a n w a t e r s and ground s a m p l e s f r o m v a r i o u s depths below the s u r f a c e . The following m e t h o d s m a y be used: 1. m i c r o b i o l o g i c a l soil s u r v e y s when the s a m p l e s being examined a r e taken f r o m s u b s o i l d e p o s i t s ; 2. r o c k s u r v e y s in depth, w h e r e s a m p l e s a r e taken f r o m r o t a r y drilled wells; 3. biologging w h e r e m i c r o b i o l o g i c a l a n a l y s i s is applied to c o r e s f r o m c o r e - d r i l l e d wells; 4. w a t e r s u r v e y s , w h e r e f o r m a t i o n a l w a t e r s and ground w a t e r s a r e studied. E a c h of t h e s e v a r i e t i e s of the method c o v e r s a d i f f e r e n t a r e a . The amount of detail in the o b s e r v a t i o n s a l s o v a r i e s . H i s t o r i c a l l y , the ground s u r v e y c a m e into use f i r s t ; it was followed by biologging and finally the w a t e r s u r v e y . At p r e s e n t , the w a t e r s u r v e y i s the m o s t widely u s e d . The Soil Survey The m a i n type of detailed m i c r o b i o l o g i c a l p r o s p e c t i n g work is the soil s u r vey, which is b a s e d on the collection and s u b s e q u e n t a n a l y s i s of s a m p l e s of s u b s o i l d e p o s i t s f o r m e t h a n e - and p r o p a n e - o x i d i z i n g b a c t e r i a . Two s t a g e s of t h i s s u r v e y consist of the s e a r c h f o r and s u b s e q u e n t localization of the h y d r o c a r b o n a u r e o l e s which accompany oil and g a s pools. H e r e the s a m p l e s

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may be taken f r o m shallow, s p e c i a l l y d r i l l e d wells of 2 - 3 m . depth, and a l s o f r o m pits, c l e a r i n g s , and t r e n c h e s . Another type of detailed s u r v e y c o n s i s t s of s a m p l i n g m a n y l e v e l s in r o t a r y - d r i l l e d wells to a depth of 15 - 30 m . in c o n f o r m i t y with individual geological p r o f i l e s . The " d e e p " s u r v e y c o n s i s t s of d e t a i l e d qualitative and quantitative a n a l y s i s of g a s o b a c t e r i a l e f f e c t s t h r o u g h the well s e c t i o n . Soil s u r v e y s a r e u s e f u l when the geological s t r u c t u r e of the r e g i o n h a s been studied to a c e r t a i n extent and the r e s u l t s obtained can be c o m p a r e d with p r e v i o u s l y obtained d a t a f r o m geophysical or geological s u r v e y i n g work. Field method of s o i l s u r v e y i n g . The points w h e r e s a m p l e s a r e to be taken in detailed work a r e usually chosen on individual p r o f i l e s at i n t e r v a l s of 100 - 200 m . and 200 - 300 m . in a r e c o n n a i s s a n c e s u r v e y . The d i s t a n c e between p r o f i l e s c o r r e s p o n d i n g l y v a r i e s f r o m 400 - 500 m . to 1 - 2 k m . The depth of s a m p l e - t a k i n g a s s u m e d f o r s o i l - s u r v e y wells m a y change depending on s o i l - lithological conditions. In r e g i o n s with highly developed t e r r a c e and alluvial d e p o s i t s it m u s t be not l e s s than 3 - 4 m . In a r e a s of high r e l i e f the depth of s a m p l i n g m a y be d e c r e a s e d to 2.5 - 3 m . In stony ground, and a l s o at points w h e r e b e d r o c k r e a c h e s the s u r f a c e , it is p e r m i s s i b l e to take s a m p l e s f r o m about 2 m e t e r s . F o r wells d e e p e r than 2 m . , a s a r u l e , two s a m p l e s a r e taken at an i n t e r v a l of 0.5 m . In conducting field work, g e o m o r p h o l o g i c a l and soil conditions u n f a v o r a b l e f o r m i c r o b i o logical s u r v e y i n g m u s t be taken into account. The m a i n c o n t a i n e r s used to hold soil s a m p l e s a r e p a p e r c o n t a i n e r s or g l a s s j a r s . The p a p e r c o n t a i n e r s have a double bottom and a r e shipped to the working s i t e a l r e a d y s t e r i l i z e d in shipping boxes. The s i z e of the soil s a m p l e put into a c o n t a i n e r m u s t be not l e s s than 250 g. Knives u s e d in taking soil s a m p l e s a r e s t e r i l i z e d in the f l a m e of an alcohol b u r n e r . The s o i l s a m p l e is brought to the s u r f a c e by m e a n s of s p e c i a l c o r e l i f t e r - s t e r i l i z e r s (Fig. 137). The c o r e l i f t e r - s t e r i l i z e r c o n s i s t s of a c o r e s e p a r a t o r (1) which is a hollow tube with an i n t e r n a l d i a m e t e r of 35 m m . and a length of 250 m m . , a c o r e e x t r a c t o r (2), a w o r m (3), which, when the handle (7) is t u r n e d , e j e c t s the c o r e f r o m the c o r e s e p a r a t o r t h r o u g h the s t e r i l i z e r of the c i r c u l a r c u t t e r (4); the l a t t e r cuts away the o u t e r s u r f a c e of the extruded r o c k . The a p p a r a t u s is r e i n f o r c e d by a c o l l a r (6), f a s t e n e d to a hollow s h a f t (5). The s h a f t is d r i v e n into the ground b e f o r e h a n d . The s e q u e n c e of o p e r a t i o n s in w e l l - s a m p l i n g with the aid of the c o r e l i f t e r s t e r i l i z e r is shown in the d i a g r a m (Fig. 138). In the a b s e n c e of a c o r e - l i f t e r and a l s o in c a s e s when the r o c k is s o d e n s e that it cannot be t r i m m e d by the c u t t e r of the s t e r i l i z e r , a hollow cylinder with a s h a r p outer edge is u s e d . Microbiological a n a l y s i s of soil s a m p l e s . The p u r p o s e of m i c r o b i o logical a n a l y s i s is to e s t a b l i s h the p r e s e n c e and abundance in the soil s a m p l e of m e t h a n e - o x i d i z i n g and p r o p a n e - o x i d i z i n g b a c t e r i a . S a m p l e s in which m e t h a n e - o x i d i z i n g b a c t e r i a a r e found a r e f u r t h e r analyzed f o r c e l l u l o s e - d e c o m p o s i n g b a c t e r i a . The s a m e e x p e r i m e n t a l conditions a r e used f o r the isolation of b a c t e r i a that ozidize m e t h a n e or propane. A liquid m i n e r a l m e d i u m is inoculated with a portion of the r o c k being studied and the h y d r o c a r b o n content of the gas m i x t u r e is v a r i e d depending on the p a r t i c u l a r type of b a c t e r i a that is to be i s o l a t e d . F o r development of the h y d r o c a r b o n m i c r o f l o r a , the s o - c a l l e d e l e c t i v e m e d i a , which a r e m o s t f a v o r a b l e (specific) f o r a given type of b a c t e r i a and do not s e c u r e the growth of o t h e r t y p e s , a r e u s e d . The liquid m i n e r a l p a r t

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F i g . 1 3 7 . C o r e l i f t e r - s t e r i l i z e r c o n s t r u c t e d by G. A. M o g i l e v s k i i and M . V. V e l e m i t s y n . a — i n dismantled form; b — i n assembled form. 1 — c o r e separator; 2 — c o r e e x t r a c t o r ; 3 — w o r m ; 4 — c i r c u l a r cutter; 5 — h o l l o w shaft; 6 — c o l l a r ; 7 — h a n d l e .

of this medium (for the f i r s t two groups of b a c t e r i a in general and, with slight changes, for cellulose-decomposing b a c t e r i a ) contains nitrogen, phosphorus, potassium, and magnesium sulfate. The only s o u r c e of energy and hydrocarbons provided f o r methane-oxidizing b a c t e r i a is methane; for propane-oxidizing b a c t e r i a , propane is used; and for cellulose-decomposing b a c e r t i a , cellulose is used. F u r t h e r m o r e , the oxygen content must be different for each group, i . e . , a e r o b i c for methane and propane b a c t e r i a and anaerobic for cellulose-decomposing b a c t e r i a . B a c t e r i a l analyses consist of three s t e p s : (1) preparation cultures, (2) incubation of cultures, and (3) analysis of c u l t u r e s . The technique of making b a c t e r i a l cultures is described in the following paragraphs ( F i g . 138): E a c h s o i l - s a m p l e studied is introduced c o l l a t e r a l l y into five s m a l l glass b e a k e r s supplied with c o v e r s . Correspondingly, five cultures a r e made of each type of b a c t e r i a , i . e . , methane- and propane-oxidizing b a c t e r i a . The s i z e of the portion of s o i l - s a m p l e may vary for each individual beaker between 5 and 7 g. The portion may be measured by the volume method. After the b e a k e r s a r e loaded with sample m a t e r i a l , a thin l a y e r of m i n e r a l medium is poured into them. Recently, a method of preliminary

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HHHSB

F i g . 1 3 8 . D i a g r a m of p r o c e d u r e s in t h e s o i l s u r v e y . I — f i e l d w o r k : a — e x t r a c t i o n of s o i l - s a m p l e f r o m w e l l by c o r e l i f t e r ; b — s t e r i l e s e p a r a t i o n of s o i l - s a m p l e with the a i d of c o r e l i f t e r ; c — p a c k i n g of s a m p l e s into shipping b o x e s f o r t r a n s p o r t a t i o n to l a b o r a t o r y ; d — f i e l d k i t with a c c e s s o r i e s f o r taking s o i l s a m p l e s . I I — l a b o r a t o r y w o r k : a — putting s o i l - s a m p l e into b e a k e r s ; b — p o u r i n g m i n e r a l m e d i u m into b e a k e r s ; c — c h a r g i n g b e l l j a r , f i l l e d with c u l t u r e s , with g a s m i x t u r e ( 1 / 3 m e t h a n e + 2 / 3 a i r o r 1 / 5 p r o p a n e + 4 / 5 a i r ) ; d — i n c u b a t i o n of c u l t u r e s in t h e r m o s t a t ( t i m e of i n c u b a t i o n 14 d a y s ) .

aqueous dispersion of samples has been introduced into laboratory practice. This increases the accuracy of determinations. Cultures prepared in this manner (observing the requirements of sterility) are placed in groups of 60 - 80 in several layers on a metal platform with a stopcock and covered with a bell j a r , the ground base of which is fitted to the platform and sealed with vacuum cement. At f i r s t the air under the bell j a r is evacuated to a residual pressure of 40 mm. Hg; then it is filled with a gas mixture containing 1/3 methane and 2/3 air (in analyses for methane-oxidizing bacteria, or correspondingly, 1 / 5 propane and 4 / 5 air (in analyses for propane-oxidizing bacteria). The filled bell j a r s are kept in a thermostat at a temperature of 32° C for 14 days. At the end of the allotted time each beaker is examined. In those cultures in which the soil contained hydrocarbon microflora, a bacterial turbidity or film, quite distinctive in form, appears on the surface of the culture medium (see Fig. 136). The results of bacterial growth a r e evaluated according to the thickness of the film formed by the bacteria and the area of the beaker surface to which this film adheres. The intensity of formation of the film and its thickness are evaluated according to the following five-point s c a l e : 1. Turbidity of medium, bacteria observable only with microscope 2. Thin, transparent film 3. Semitransparent, weakly pigmented 4. Dense, opaque, smooth, pigmented 5. Dense, opaque, wrinkled, pigmented

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The fraction of the beaker surface covered by the film is also measured. The percent of the beaker surface which is attached to the film is multiplied by its thickness as evaluated by the five-point system. The size of the films in arbitrary units of intensity of growth bears a definite relation to the quantity of hydrocarbon-oxidizing bacteria in the in the groundsamples. In order to determine what quantity of bacteria can produce a film of given thickness in a given time, E . V. Dianova and L . I. Tarkovskaya conducted special investigations with artificial introduction into experimental beakers of methane-oxidizing bacteria in quantities varying from 2 billion to a few individuals in each culture. As a result of these experiments it was established that the size of the films developed varies directly with the initial quantity of bacteria and the time of incubation (Fig. 139). 500

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I

1/

1

1

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2210' 2-nf 2-I0 3 2-10" 2-W s 2-l(f 2-W 7 2-Vf NUMBER OF BACTERIA INTRODUCED F i g . 1 3 9 . D i a g r a m of i n t e n s i t y of g r o w t h of c u l t u r e s o f m e t h a n e oxidizing b a c t e r i a in r e l a t i o n to the i n i t i a l quantity of the l a t t e r and t i m e of i n c u b a t i o n . 1 — i n c u b a t i o n t i m e 5 d a y s ; 2 — i n c u b a t i o n t i m e 10 d a y s ; 3 — i n c u b a t i o n t i m e 12 d a y s .

Soil-samples in which methane-oxidizing bacteria have positively been shown to be present must be subjected to a control analysis for bacteria which decompose cellulose. Cellulose-disintegrating bacteria are detected with the aid of a glass test tube into which the ground-sample being tested and a piece of filter paper are placed (Fig. 140). After the test tube has been filled with mineral medium, it is closed with a rubber stopper containing a glass tube. Liquid raising into the tube establishes anaerobic conditions within the test tube. When cellulose bacteria are present in the soil-sample, the filter paper in the test tube begins to decompose with the formation of gas bubbles after two or three weeks of incubation. Anaerobic conditions in the test tubes may be established by the use of 0.75% agaragar. The Water Survey The main type of microbiological work of a reconnaissance nature is the water survey, usually conducted in conjunction with gas and hydrochemical investigations of underground waters. Investigating the bacterial m i c r o -

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PETROLEUM

F i g . 140. D e t e c t i o n of b a c t e r i a which d e c o m p o s e c e l l u l o s e , a — f i l t e r p a p e r a t beginning of e x p e r i m e n t ; b — f i l t e r p a p e r d i s i n t e g r a t e d by b a c t e r i a .

flora of underground waters f o r oil and gas prospecting, a l s o called hydrom i c r o b i o l o g i c a l surveying, was developed at the VSEGINGEO Institute during the period f r o m 1944 to 1946 by G. A. Mogilevskii and Z. I. Kuznetsova (17). The e s s e n c e of the method c o n s i s t s in collecting and analyzing s t e r i l e water s a m p l e s at points of discharge f r o m aquifers. Springs, fountains, and sumps, as well as a r t e s i a n wells and other water wells a r e investigated. The advantage of the gasomicrobiological survey of waters as a r e c o n n a i s sance method is that aquifers encounter a c u r r e n t of migrating h y d r o c a r bons at a much g r e a t e r depth than s o i l - s u r v e y b o r e - h o l e s . Underground w a t e r s , which dissolve migrating hydrocarbon g a s e s contain t h e s e g a s e s in g r e a t e r quantity and with m o r e uniform distribution in the a r e a of the investigations than subsoil deposits situated at l e s s e r depths. W a t e r - b e a r i n g s t r a t a thus s e e m to have a check on any given part of the current of migrating hydrocarbons on its way to the s u r f a c e . Hency, hydrocarbon g a s e s that can be detected by the water survey may in a number

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of c a s e s e s c a p e notice in s u b s o i l s u r v e y s . F u r t h e r m o r e , b a c t e r i a l oxidation of h y d r o c a r b o n s is e x t r e m e l y active in underground w a t e r s . T h e r e f o r e , a n a l y s i s f o r d i s s o l v e d h y d r o c a r b o n s should include not only gas a n a l y s i s , but a l s o a n a l y s i s of the w a t e r s f o r a m i c r o f l o r a which oxidizes t h e s e g a s e s . The i n d i c a t o r m i c r o f l o r a f o r oil and gas in h y d r o m i c r o b i o l o g i c a l investigations a r e : (1) b a c t e r i a which oxidize m e t h a n e ; (2) b a c t e r i a which oxidize p r o p a n e ; (3) b a c t e r i a which d e velop in an a t m o s p h e r e of one of the v a p o r i z e d h y d r o c a r b o n s , such a s pentane, hexane, or heptane. In conducting a water s u r v e y the s a m e m e t h o d s a r e used f o r the d e t e r mination of h y d r o c a r b o n m i c r o f l o r a a s in the s o i l s u r v e y . A m o r e c o n c e n t r a t e d Munz (2x) m i n e r a l m e d i u m is used, and instead of a portion of a s o i l s a m p l e , 3 - 4 m l . of the w a t e r being t e s t e d a r e put into the m e d i u m . F o r w a t e r s a s s o c i a t e d with oil and gas f o r m a t i o n s , and containing s i g n i f i c a n t c o n c e n t r a t i o n s of hydrogen s u l f i d e , the b a c t e r i a l i n d i c a t o r s mentioned above cannot be u s e d . The i n d i c a t o r s used in t h e s e c a s e s a r e d e s u l f u r i z i n g b a c t e r i a , which develop u n d e r l a b o r a t o r y conditions in a m e d i u m containing heptane which is a s o u r c e of c a r b o n f o r t h e m . D e s u l f u r i z i n g b a c t e r i a a r e r e c o v e r e d f r o m the w a t e r s by p r e l i m i n a r y concent r a t i o n of the b a c t e r i a on m e m b r a n e f i l t e r s . The w a t e r being t e s t e d is f i l t e r e d through an u l t r a f i l t e r with the aid of a Seitz funnel, while the b a c t e r i a suspended in the w a t e r a r e r e t a i n e d on the f i l t e r . In o r d e r to e s t a b l i s h the p r e s e n c e of b a c t e r i a which oxidize m e t h a n e , a s well a s t h o s e which a r e developed in an a t o m o s p h e r e of v a p o r i z e d hyd r o c a r b o n s , control a n a l y s e s m u s t be conducted to d e t e r m i n e whether m e t h a n e is being f o r m e d a s a r e s u l t of the activity of m e t h a n e - p r o d u c i n g b a c t e r i a which d e c o m p o s e fatty a c i d s under a n a e r o b i c conditions. C o n t r o l a n a l y s e s a r e a l s o r e q u i r e d s i n c e b a c t e r i a which develop in an a t m o s p h e r e of v a p o r i z e d h y d r o c a r b o n s m a y grow in polluted w a t e r s owing to the e a s i l y a s s i m i l a t e d o r g a n i c s u b s t a n c e s , while m e t h a n e - o x i d i z i n g b a c t e r i a m a y grow owing to the m e t h a n e f o r m e d a s a r e s u l t of b i o c h e m i c a l d e c o m p o s i tion of t h e s e s u b s t a n c e s . A n a l y s e s f o r m e t h a n e - g e n e r a t i n g b a c t e r i a a r e used in conjunction with h y d r o c h e m i c a l a n a l y s e s of w a t e r s f o r a m m o n i a , n i t r i t e s , and n i t r a t e s . C o m p a r i s o n of b a c t e r i o l o g i c a l a n a l y s e s of w a t e r with h y d r o c h e m i c a l c h a r a c t e r i s t i c s has shown that such f a c t o r s a s high salinity of the w a t e r (up t o 7 ° B£), the p r e s e n c e of s a l t s of b r o m i n e and iodine in quantities a s high a s 12 m g . / l . f o r iodine and 170 m g . / l . f o r b r o m i n e , pH f r o m 6.0 t o 10.0, and w a t e r t e m p e r a t u r e up to 40° C do not limit the development of oil- and g a s - i n d i c a t i n g b a c t e r i a . The p r e s e n c e of H2S in p e t r o l e u m w a t e r s i s the only c i r c u m s t a n c e which inhibits the growth of h y d r o c a r b o n m i c r o f l o r a . The m o s t f a v o r a b l e locations f o r g a s o m i c r o b i o l o g i c a l s u r v e y s in w a t e r s a r e w h e r e underground w a t e r s d i s c h a r g e a s wells and s p r i n g s o r w h e r e t h e r e a r e a g r e a t n u m b e r of s u m p s or w a t e r w e l l s . In a m i c r o b i o l o g i c a l s u r v e y of w a t e r s , s m a l l s t r e a m s flowing f r o m alluvial deposits should not be t e s t e d e s p e c i a l l y in the a b s e n c e of any kind of c a p r o c k . Sumps and wells with s i g n s of pollution should not be t e s t e d e i t h e r . C o l o r i m e t r i c d e t e r m i n a t i o n s of n i t r a t e s , n i t r i t e s , and a m m o n i a conducted on the spot may s e r v e a s an index of pollution Depending on the p r e s e n c e and a r r a n g e m e n t of the underground o r capping s t r u c t u r e s , one of the following m e t h o d s of s a m p l i n g of w e l l s , s p r i n g s , and s u m p s is used.

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a . F o r overflowing wells or t h o s e used f o r w a t e r , and a l s o f r o m capped s p r i n g s , w a t e r s a m p l e s a r e taken by pouring s a m p l e s into s t e r i l e bottles placed d i r e c t l y under the d r a i n p i p e , f a u c e t , o r spout. b. F o r s u m p s and r e c e n t l y d r i l l e d , a s yet ùnused w e l l s , w a t e r s a m p l e s a r e taken with the aid of a s p e c i a l b a c t e r i o l o g i c a l b a t h o m e t e r (Fig. 141, a and b). The b a t h o m e t e r is l o w e r e d into the well o r s u m p on a r o p e and brought into action with the aid of a t r a v e l i n g weight. The a p p a r a t u s con-

s i s t s of a g l a s s bulb enclosed in a m e t a l l i c h o u s ing. The lower end of the bulb i s h e r m e t i c a l l y s e a l e d by a g l a s s s t o p p e r , while the upper end is sealed by s p e c i a l g l a s s c a p s u l e (1). With the aid of the coil s p r i n g (2), the bulb is s e c u r e d to the m e t a l l i c housing (3), to the top of which is s c r e w e d the cap (4) with s i d e - i n l e t s f o r the a d m i s s i o n of w a t e r . At the upper end of the cap, s e c u r e d by a s p r i n g , is a block (5), which b r e a k s the capsule in the cap (6) a s a r e s u l t of the action of the t r a v e l i n g weight (7). W a t e r then p a s s e s into the bulb through the opening created. c. In taking water s a m p l e s f r o m uncapped s p r i n g s , the w a t e r is e i t h e r

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poured d i r e c t l y into a bottle at the outlet of the s p r i n g o r d r a w n t h r o u g h a r u b b e r h o s e , p r e v i o u s l y boiled in w a t e r . The f i r s t portion of w a t e r d r a w n t h r o u g h the h o s e is d i s c a r d e d . In c a s e s w h e r e the s p r i n g flows into a pool of w a t e r , the s a m p l e is taken by i m m e r s i n g a s t o p p e r e d bottle. The s t o p p e r is r e m o v e d under w a t e r at the outlet of the s p r i n g . In a m i c r o b i o l o g i c a l s u r v e y the t i m e of s t o r a g e of s a m p l e s i s v e r y i m portant, b e c a u s e the r e l a t i o n between the d i s s o l v e d g a s e s and h y d r o c a r b o n m i c r o f l o r a contained in the w a t e r b e a r s a dynamic c h a r a c t e r . In the p r e s ence of significant quantities of dissolved h y d r o c a r b o n s (methane or heavy h y d r o c a r b o n s ) the b a c t e r i a originally contained in the w a t e r will develop until they have exhausted the e n t i r e supply of h y d r o c a r b o n s and oxygen. F o r t h i s r e a s o n two s a m p l e s a r e taken f r o m e v e r y w a t e r point f o r the m i c r o b i o l o g i c a l a n a l y s i s of w a t e r . One of t h e s e is analyzed at once in the field l a b o r a t o r y , while the other is analyzed within 30 - 40 days in the c e n t r a l l a b o r a t o r y . With duplicate a n a l y s e s it is p o s s i b l e to obtain m u c h m o r e c o n s i s t e n t b a c t e r i a l i n d i c e s c o r r e s p o n d i n g t o a r e a s of m a x i m u m gas evolution. The r e s u l t s of joint gas and m i c r o b i o l o g i c a l s u r v e y s of w a t e r s show the definite r e l a t i o n s h i p between gas and b a c t e r i a l i n d i c e s . In the m a j o r i t y of a q u i f e r s at shallow depths, the d i s s o l v e d h y d r o c a r b o n g a s e s , a s a r u l e , a r e p r e s e n t in m i c r o q u a n t i t i e s . If conditions in a l a y e r a r e u n f a v o r a b l e f o r the m e t a b o l i s m of b a c t e r i a , the concentration of h y d r o c a r b o n g a s e s i s m a r k e d l y i n c r e a s e d . A r e l a t i v e deficit of d i s s o l v e d oxygen i s o b s e r v e d in a r e a s in which an abundant h y d r o c a r b o n m i c r o f l o r a i s found. The r u l e s e n u m e r a t e d above indicate the n e c e s s i t y of combining g a s and m i c r o b i o l o g i c a l m e t h o d s of investigating u n d e r g r o u n d w a t e r s in oil and gas p r o s p e c t i n g work. F i e l d work in w a t e r s u r v e y i n g r e q u i r e s r e l a tively low e x p e n d i t u r e s , s i n c e it does not involve the d r i l l i n g of wells or other work in the ground. The w a t e r s u r v e y is completely dependent on the p r e s e n c e in a r e g i o n of s p r i n g s , w a t e r - w e l l s , and s u m p s . If t h e s e a r e absent l a r g e p o r t i o n s of a locality r e m a i n u n s u r v e y e d . If such gaps due to the a b s e n c e of s a m p l e points need to be filled s p e c i a l l y drilled wells d i s t r i b u t e d within a r a d i u s of 50 - 100 m . around the designated point m a y be s a m p l e d . Biologging M i c r o b i o l o g i c a l investigations of r o c k s m a y be conducted in d e e p - l y i n g d e p o s i t s by m e a n s of c o r e - d r i l l e d w e l l s . In t h i s c a s e , well c o r e s a r e e x amined f o r the p r e s e n c e of b a c t e r i a l i n d i c a t o r s . Depending on the p u r p o s e of the given c o r e - d r i l l i n g o p e r a t i o n , biologging m a y involve e i t h e r a r e c o n n a i s s a n c e or a detailed investigation. An e x a m p l e of a r e c o n n a i s s a n c e application of biologging i s the e x amination of c o r e s f r o m a well located on a s p e c i f i c geological p r o f i l e . In this c a s e the biologging data a r e used f o r the c o m p a r a t i v e evaluation of the extent of m i c r o s c o p i c h y d r o c a r b o n m a n i f e s t a t i o n s in wells and s p e c i f i c p a r t s of the d r i l l e d s e c t i o n . The r e s u l t s of biologging m a y be e x p r e s s e d by c u r v e s of the v a r i a t i o n of b a c t e r i a l i n d i c e s along the s e c t i o n of a well o r by i s o l i n e s of a v e r a g e v a l u e s of d e g r e e of growth of i n d i c a t o r m i c r o o r g a n i s m s , s u m m e d up with r e g a r d to s p e c i f i c s t r a t i g r a p h i c i n t e r v a l s or to the well a s a whole (Fig. 142). The technique of taking s a m p l e s of r o c k c o r e s is n e a r l y the s a m e a s

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Fig. 142. C o m p a r i s o n of biologging r e s u l t s with a gas log in a r o t a r y well. 1 — content of hydrocarbon g a s e s in drilling mud; 2 — p r e s e n c e of h y d r o c a r bon m i c r o f l o r a in c o r e s in a r b i t r a r y units of intensity of growth.

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that e s t a b l i s h e d f o r the e x t r a c t i o n of r o c k s f r o m shallow w e l l s . The m a i n p r o b l e m in t h i s work is the s e p a r a t i o n of the e x t e r n a l , contaminated p a r t of the c o r e f r o m its i n t e r n a l p a r t (center), which a f t e r t r i m m i n g is t r a n s f e r r e d to a s t e r i l e package. The s t e r i l e t r e a t m e n t of c o r e s is r e l a t i v e l y e a s i l y a c c o m p l i s h e d when s a n d s t o n e - c l a y r o c k s p r e d o m i n a t e in the s e c t i o n . S t e r i l e t r e a t m e n t of c a r b o n a t e and halide r o c k s is m o r e difficult. T h i s r e q u i r e s the u s e of s p e c i a l d e v i c e s f o r cleaving and c r u s h i n g the s a m p l e . The c o r e s a r e examined f o r the following t y p e s of b a c t e r i a : (1) m e t h a n e oxidizing b a c t e r i a , (2) b a c t e r i a growing in an a t o m o s p h e r e of pentane, (3) propane oxidizing b a c t e r i a , and (4) hydrogen oxidizing b a c t e r i a . The f i r s t two types of i n d i c a t o r o r g a n i s m s a r e the m o s t w i d e s p r e a d at g r e a t d e p t h s . The chief value of biologging work is that it i s p o s s i b l e to d e t e r m i n e the p r e s e n c e in c o r e s of m i c r o q u a n t i t i e s of m e t h a n e , heavy h y d r o c a r b o n s , and hydroben by using b a c t e r i a l i n d i c a t o r s . T h i s r e q u i r e s p r e l i m i n a r y d e s o r p t i o n of gas f r o m the c o r e s and the u s e of complex m i c r o a n a l y t i c a l apparatus. The B a c t e r i a l Gas-Output Survey and O t h e r Analytical Methods All the v a r i a t i o n s of the m i c r o b i o l o g i c a l method given above, w a t e r s u r v e y , soil s u r v e y , and biologging, a r e based on a study of the indigenous b a c t e r i a l population. The d i f f e r e n c e s among t h e m a r e mainly d e t e r m i n e d by t h e n a t u r e of the m e d i u m in which t h e s e s u r v e y s a r e conducted. The b a c t e r i a l g a s - o u t p u t s u r v e y is b a s e d on a d i f f e r e n t p r i n c i p l e . T h i s method of m i c r o b i o l o g i c a l investigation involves the u s e of v a r i o u s b a c t e r i a l c u l t u r e s f o r d e t e r m i n i n g the output of d i f f u s i n g g a s e s . The t e c h n i q u e of b a c t e r i a l g a s - o u t p u t m e a s u r e m e n t s c o n s i s t s in lowering an a s s e m b l y of b a c t e r i a l c u l t u r e s of definite t i t e r into shallow t e s t wells and allowing it to r e m a i n 12 - 14 d a y s . B a c t e r i a which oxidize m e t h a n e , ethane, p r o p a n e , liquid h y d r o c a r b o n s , and hydrogen a r e u s e d a s i n d i c a t o r s . If t h e r e is an influx of h y d r o c a r b o n g a s e s , development of the c o r r e sponding c u l t u r e s o c c u r s . At the end of the e x p o s u r e period, the c u l t u r e s a r e withdrawn f r o m the w e l l s , fixed, and visually evaluated. An exact e s t i m a t e of the growth of b a c t e r i a l cells is m a d e in the l a b o r a t o r y m i c r o s c o p i c a l l y or with a p h o t o m e t e r . Equipment f o r b a c t e r i a l g a s - o u t p u t m e a s u r e m e n t s c o n s i s t s of a d u r a l u min tube and c a s e f o r lowering t e s t tubes with c u l t u r e s of b a c t e r i a . In the d i a g r a m (Fig. 143) the m a i n o p e r a t i o n s in a b a c t e r i a l g a s - o u t p u t s u r v e y a r e indicated. B a c t e r i a l g a s - o u t p u t m e a s u r e m e n t s m a y be used in u n d e r w a t e r s u r v e y s . The b a c t e r i a l c u l t u r e s a r e lowered to the bottom of r e s e r v o i r s in s p e c i a l b e l l s f o r this p u r p o s e . The b a c t e r i a l g a s - o u t p u t s u r v e y h a s not a s yet been used in p r a c t i c e owing to the g r e a t amount of l a b o r involved in l a b o r a t o r y and field w o r k . H o w e v e r , the technique of b a c t e r i a l g a s - o u t p u t o p e r a t i o n s m a y be applied when it is n e c e s s a r y to investigate s h a f t a i r and g a s e s evolved f r o m w e l l s . S e v e r a l other m e t h o d s of distinguishing h y d r o c a r b o n - o x i d i z i n g b a c t e r i a and the m i c r o b i o l o g i c a l d e t e r m i n a t i o n of h y d r o c a r b o n g a s e s d e s e r v e mention. One of t h e s e methods c o n s i s t s in the detection of h y d r o c a r b o n m i c r o f l o r a with the aid of l u m i n e s c e n c e m i c r o s c o p y . This is b a s e d on the f a c t that d i f f e r e n t types of h y d r o c a r b o n m i c r o f l o r a give d i f f e r e n t l u m i n e s c e n t e f f e c t s . B a c t e r i a which oxidize v a p o r i z e d h y d r o c a r b o n s have a n a t u r a l

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F i g . 1 4 3 . D i a g r a m of the conduct of a b a c t e r i a l g a s - o u t p u t s u r v e y . I — p r e p a t o r y o p e r a t i o n s : a — p a c k i n g a m p u l e s with c u l t u r e s of b a c t e r i a which o x i d i z e m e t h a n e o r propane and liquid h y d r o c a r b o n s ; b — o p e n i n g a m p u l e with c u l t u r e ; c — t a k i n g c u l t u r e f r o m a m p u l e ; d — t r a n s f e r r i n g c o n t e n t s of a m p u l e s t o f l a s k s containing s t e r i l e m i n e r a l o i l ; e — i n t r o d u c t i o n of p o r t i o n of c u l t u r e s t o s t e r i l e t e s t t u b e s ; f — p a c k i n g t e s t tubes with c u l t u r e s in c a s e . I I — f i e l d w o r k and t r e a t m e n t of m a t e r i a l s : a — s e c t i o n of b a c t e r i a l g a s - o u t p u t w e l l ( p e r i o d of e x p o s u r e of c u l t u r e s , up to 15 d a y s ) ; b — b a c t e r i a l c u l t u r e s f i x e d on w i t h d r a w a l f r o m w e l l s ; c — c o u n t i n g b a c t e r i a under the m i c r o s c o p e ; d — f i e l d of v i e w of m i c r o s c o p e with o c u l a r g r i d f o r counting b a c t e r i a .

luminescence in ultra-violet rays and wood rays. Bacteria which oxidize gaseous hydrocarbons luminesce on application of special dyes. Investigations carried out in this field by G. P. Slavnina and M. I. Meisel (40) showed the possibility of using luminescence microscopy to determine hydrocarbon-oxidizing bacteria in various stages of their development under laboratory conditions and also in the field with the aid of a few fixing a c cessories. An evaluation of the biological oxygen demand of the organisms is used to detect the hydrocarbon microflora in underground waters and also to determine the degree of microbiological decomposition of organic matter in the waters. This method is especially ittiportant in making analyses under field conditions. MICROBIOLOGICAL RESULTS AND THEIR INTERPRETATION Regardless of variations in the method and technique of geobiochemical prospecting for oil and gas, its ultimate purpose is to find zones (within the survey area or in a well section) with anomalous values of hydrocarbon indices and to determine whether or not these anomalies are associated

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with oil o r g a s pools of i n d u s t r i a l s i g n i f i c a n c e . T h i s l a t t e r p u r p o s e is a c c o m p l i s h e d in the f i n a l s t a g e of the work, the geological i n t e r p r e t a t i o n of the obtained data. However, a p r e l i m i n a r y t r e a t m e n t of the f a c t u a l d a t a is r e q u i r e d f o r a complete i n t e r p r e t a t i o n and c o n s i s t s of s e v e r a l s t a g e s . T r e a t m e n t of F a c t u a l Data F i r s t of all, the n u m b e r of o b s e r v a t i o n s on the m i c r o o r g a n i s m s is computed and the a v e r a g e development of i n d i c a t o r m i c r o o r g a n i s m s is calculated f o r the r e g i o n a s a whole, a p a r t i c u l a r s u r v e y a r e a , or f o r individual wells in biologging. A v e r a g e data on s p e c i f i c types of m i c r o f l o r a a r e e s s e n t i a l in e s t i m a t i n g the n a t u r e of the s o u r c e of d i f f u s i o n . T h e s e data a r e a l s o used in quantitative c o m p a r i s o n s of a r e a s w h e r e the geological s t r u c t u r e s a r e s u f f i c i e n t l y s i m i l a r . In t r e a t i n g biologging data the r e g u l a r i t y in v a r i a t i o n of m i c r o b i o l o g i c a l i n d i c a t o r s with depth and t h e i r a s s o c i a t i o n with s p e c i f i c s t r a t i g r a p h i c l e v e l s i s studied. The next s t a g e in the t r e a t m e n t of the a n a l y t i c a l data c o n s i s t s in c o m piling t a b l e s of the r e l a t i o n s h i p between the i n d i c e s of m i c r o b i o l o g i c a l s u r v e y s and v a r i o u s f a c t o r s which affect the r e s u l t s ( t e m p e r a t u r e and m o i s t u r e content of the r o c k s , t h e i r lithological c o m p o s i t i o n , how long s a m p l e s a r e kept, etc.). In a h y d r o m i c r o b i o l o g i c a l s u r v e y it is e s p e c i a l l y i m p o r t a n t to d e t e r m i n e f o r e a c h w a t e r - p o i n t being sampled the p o s s i b l e e f f e c t of p r o c e s s e s of c o n t e m p o r a r y f o r m a t i o n of m e t h a n e and v a r i o u s i m p u r i t i e s in the u n d e r ground w a t e r s on the growth of indicator m i c r o o r g a n i s m s . F o r t h i s p u r pose the data of c h e m i c a l a n a l y s e s of w a t e r s f o r n i t r a t e s , n i t r i t e s , and a m m o n i a a r e c o m p a r e d with the r e s u l t s of m i c r o b i o l o g i c a l d e t e r m i n a t i o n s of m e t h a n e - p r o d u c i n g b a c t e r i a in the w a t e r s or with the index of biological oxygen d e m a n d . F o r the s o i l s u r v e y , data on the o c c u r r e n c e of m e t h a n e - o x i d i z i n g b a c t e r i a a r e c o m p a r e d with c o r r e s p o n d i n g data f o r c e l l u l o s e - d e c o m p o s i n g b a c t e r i a in the s a m p l e s . S a m p l e s in which s i m u l t a n e o u s growth of t h e s e two m i c r o o r g a n i s m s is o b s e r v e d a r e c o n s i d e r e d doubtful and a r e not cons i d e r e d to indicate anomalous z o n e s . This r e s t r i c t i o n is not usually a p plied to c a s e s in which p r o p a n e - o x i d i z i n g b a c t e r i a a r e found, s i n c e heavy h y d r o c a r b o n s a r e not f o r m e d in the d e c o m p o s i t i o n of c e l l u l o s e . The r e s u l t s of m i c r o b i o l o g i c a l a n a l y s e s a r e plotted in t e r m s of population density on a m a p . The density is e x p r e s s e d a s the p e r c e n t a g e of positive c u l t u r e s out of the total n u m b e r of c u l t u r e s . The intensity of d e velopment of indicator m i c r o o r g a n i s m s , e x p r e s s e d in a r b i t r a r y u n i t s , i s m o r e widely used, e s p e c i a l l y in w a t e r s u r v e y s . Anomalous g r a d a t i o n s a r e s e l e c t e d a f t e r calculation of a v e r a g e data on o b s e r v a t i o n s of i n d i c a t o r b a c t e r i a f o r the m a i n p a r t s of the s u r v e y . F o r biologging the r e s u l t s of a n a l y s e s a r e e x p r e s s e d by i s o l i n e s of a v e r a g e v a l u e s of intensity of development of i n d i c a t o r o r g a n i s m s within the l i m i t s of the d r i l l e d a r e a . Gas and m i c r o b i o l o g i c a l s t u d i e s conducted at the s a m e place g r e a t l y f a c i l i t a t e the p r o b l e m s of i n t e r p r e t a t i o n . With the d a t a obtained in t h e s e c a s e s , it i s p o s s i b l e to c o r r e l a t e b a c t e r i a l a c cumulations and the zones of d i f f e r e n t c o n c e n t r a t i o n f r o m g a s s u r v e y s .

332

GEOCHEMICAL PROSPECTING FOR P E T R O L E U M Evaluation of B a c t e r i a l A n o m a l i e s

B a c t e r i a l or g a s - b a c t e r i a l a n o m a l i e s detected a s a r e s u l t of preliminaryt r e a t m e n t of f a c t u a l data a r e not a s yet good enough to be t r u s t e d . F u r t h e r evaluation of t h e i r qualitative and quantitative n a t u r e m u s t be m a d e . The following m u s t be c o n s i d e r e d : (1) the c o m p l e t e n e s s of the data on b a c t e r i a l a c c u m u l a t i o n s and the e x i s t e n c e of d i s t o r t i n g e f f e c t s of the r e g i o n a l and soil background; (2) the d e g r e e of localization of b a c t e r i a l e f f e c t s in the s u r v e y a r e a ; (3) the shape of the b a c t e r i a l anomaly and its p o s s i b l e c o r r e spondence with the location of an oil or gas pool in depth; (4) the qualitative c h a r a c t e r of the anomaly with r e g a r d to the n a t u r e of the predominant types of m i c r o f l o r a ; (5) the v a l u e s of the quantitative indices of the s u r v e y . If the r e s u l t s of an investigation a r e negative, the c o m p l e t e n e s s and a c c u r a c y of the o b s e r v a t i o n s m u s t be d e t e r m i n e d b e f o r e h a n d b e c a u s e the negative r e s u l t s m a y be due to v a r i o u s d e f e c t s in the m e t h o d s of field and l a b o r a t o r y work, such a s i n s u f f i c i e n t s a m p l e taken at the location, i n a d e quate r e p r o d u c i b i l i t y of b a c t e r i a l c u l t u r e s , keeping s a m p l e s f o r a long t i m e , e t c . Investigations of u n d e r g r o u n d w a t e r s and deep s u r v e y s m a y a l s o be conducted in o r d e r t o v e r i f y negative data. If the c h a r a c t e r i s t i c s of the examined a r e a a r e positive, the p o s s i b l e effect of r e g i o n a l and soil background m u s t be d e t e r m i n e d . P r o c e s s e s of c o n t e m p o r a r y gas f o r m a t i o n , to which the s o i l background is due, may be discounted with the aid of control a n a l y s e s in the p r e s e n c e of c e l l u l o s e decomposing b a c t e r i a . Regional background, o b s e r v e d in a n u m b e r of g a s - and o i l - b e a r i n g p r o v i n c e s in the r e g i o n s of Maikop, Grozny, and Buguruslan and e l s e w h e r e , is due to the shallow deposition of native r o c k s containing s c a t t e r e d b i t u m e n s and g a s e s . In such c a s e s , g a s - b a c t e r i a l a n o m a l i e s can only be d i s tinguished if a definite p a t t e r n of positive points is p r e s e n t . The l a r g e s t accumulations of indicator b a c t e r i a m u s t be a d j a c e n t to zones of lower b a c t e r i a l concentration or points w h e r e the value is equal to z e r o . If this condition is not fulfilled, the r e s u l t s of the s u r v e y m u s t be c o n s i d e r e d i n conclusive. B a c t e r i a l a n o m a l i e s d e t e c t e d in a s o i l - o r w a t e r - s u r v e y , or f r o m b i o logging data, m a y be c l a s s i f i e d a c c o r d i n g to a n u m b e r of f e a t u r e s . Depending on the d e g r e e of localization of positive points, the following m a y be distinguished: a . the focal anomaly, w h e r e i n d i c a t o r m i c r o o r g a n i s m s a r e found at s e p a r a t e , disconnected points, but at the s a m e t i m e a r e grouped in a d e f i nite r e g i o n f o r which a g e n e r a l boundary m a y be drawn and within which a p a r t i c u l a r indicator o r g a n i s m o c c u r s ; b. the continuous anomaly, w h e r e i n d i c a t o r o r g a n i s m s within the l i m i t s of a definite r e g i o n a r e found at all examined points with c o n s i d e r a b l e i n tensity of development. In r e l a t i o n to the s t r u c t u r a l f a c t o r s of the a r e a being studied, o v e r lying a n o m a l i e s and p e r i p h e r a l ones a r e d i s t i n g u i s h e d . Overlying a n o m a l i e s m a y be p r o j e c t e d over the e n t i r e a r e a of an oil or gas pool or only over s p e c i f i c p a r t s of it. G a s - b a c t e r i a l e f f e c t s m a y s i m u l t a n e o u s l y a r i s e along the s l o p e s of the s t r u c t u r e — outside the productive l i m i t s of an oil reservoir. As a r u l e , p e r i p h e r a l a n o m a l i e s a r e the r e s u l t of f i s s u r e s in the r o c k s , motion of g r o u n d - w a t e r s , and g e o m o r p h o l o g i c a l p e c u l i a r i t i e s in the s t r u c t u r e

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of the e a r t h ' s s u r f a c e . The d e e p e r the oil o r gas pool l i e s , the m o r e r e a son t h e r e is to expect that the geobiochemical anomaly c o r r e s p o n d i n g to it will be p r o j e c t e d to a wider a r e a and a c c o m p a n i e d by p e r i p h e r a l e f f e c t s . Deep oil and gas zones in the e a r t h ' s c r u s t a r e a c c o m p a n i e d in m o s t c a s e s by f o c a l a n o m a l i e s , not continuous o n e s . H o w e v e r , a s g a s o m i c r o biological investigations a p p r o a c h the s o u r c e of diffusion in w a t e r - s u r v e y s and biologging work, the s e p a r a t e focal a n o m a l i e s r e c o m b i n e to f o r m a g e n e r a l a n o m a l o u s zone. As was s t a t e d e a r l i e r , this is explained by the f a c t that underground w a t e r s p r o m o t e m o r e u n i f o r m distribution of m i g r a t i n g h y d r o c a r b o n s over a pool and a l s o by the fact that at g r e a t depth h y d r o c a r b o n s and the b a c t e r i a which oxidize t h e m a r e encountered in h i g h e r c o n c e n t r a t i o n s . T h u s , in o r d e r to solve the p r o b l e m of the p o s s i b l e b o u n d a r i e s and location of oil and gas a c c u m u l a t i o n s , s o i l - s u r v e y s , w a t e r - s u r v e y s , and biologging w o r k m u s t be combined. C l a s s i f i c a t i o n of m i c r o b i o l o g i c a l a n o m a l i e s a c c o r d i n g to the p r e d o m i nating types of i n d i c a t o r m i c r o o r g a n i s m s is e s s e n t i a l to d e t e r m i n e the p o s s i b l e composition of the s o u r c e of diffusion. In a s o i l - s u r v e y , a n o m a l i e s m a y be found which contain m e t h a n e oxidizing b a c t e r i a , propane-oxidizing b a c t e r i a , or both of t h e s e types of m i c r o o r g a n i s m s in v a r i o u s p r o p o r t i o n s . T o a g r e a t extent, a n o m a l i e s containing both types of i n d i c a t o r m i c r o o r g a n i s m s , i . e . , m e t h a n e - o x i d i z i n g and p r o p a n e - o x i d i z i n g b a c t e r i a , c o r r e s p o n d to oil and gas pools of c o m m e r c i a l i n t e r e s t . The growth of p r o p a n e - o x i d i z i n g m i c r o o r g a n i s m s alone in s u b s o i l d e p o s i t s is s o m e t i m e s a s s o c i a t e d with the o c c u r r e n c e of t r a c e s of oxidized oil at slight depth. Methane-oxidizing b a c t e r i a usually p r e d o m i n a t e over g a s f i e l d s . A n o m a l i e s d e t e c t e d in the c o u r s e of a w a t e r - s u r v e y m a y contain: (a) m e t h a n e - o x i d i z i n g b a c t e r i a ; (b) b a c t e r i a which grow in an a t m o s p h e r e of v a p o r i z e d h y d r o c a r b o n s ; (c) p r o p a n e - o x i d i z i n g b a c t e r i a ; (d) the e n u m e r a t e d t y p e s of m i c r o o r g a n i s m s in v a r i o u s p r o p o r t i o n s . The m o s t w i d e s p r e a d types of b a c t e r i a in s o i l - and s t r a t u m - w a t e r s a r e t h o s e which utilize v a p o r i z e d h y d r o c a r b o n s (pentane, hexane, and heptane). They a r e encount e r e d m o r e often in the w a t e r s than m e t h a n e - o x i d i z i n g b a c t e r i a . P r o p a n e - o x i d i z i n g b a c t e r i a a r e found r e l a t i v e l y r a r e l y , e s p e c i a l l y in investigations of d e e p - l y i n g w a t e r s . N e v e r t h e l e s s , a n o m a l i e s in the o c c u r r e n c e of p r o p a n e - o x i d i z i n g b a c t e r i a in s u b t e r r a n e a n w a t e r s a r e of g r e a t p r a c t i c a l i n t e r e s t , since the m e t a b o l i s m of t h e s e o r g a n i s m s is not a s s o c i ated, a s a r u l e , with p r o c e s s e s of c o n t e m p o r a r y d e c o m p o s i t i o n of o r g a n i c m a t t e r . Heptane-oxidizing b a c t e r i a cannot be u s e d a s an index f o r the d e t e r m i n a t i o n of the qualitative composition of a s o u r c e of diffusion, s i n c e d i f f e r e n t f o r m s of h y d r o c a r b o n m i c r o f l o r a m a y develop in an a t m o s p h e r e of v a p o r i z e d h y d r o c a r b o n s under a e r o b i c conditions. E x a m p l e s of the I n t e r p r e t a t i o n of M i c r o b i o l o g i c a l Data Below a r e given s e v e r a l e x a m p l e s of m i c r o b i o l o g i c a l a n o m a l i e s d e t e c t e d by s o i l - and w a t e r - s u r v e y s . The f o r m a t i o n s d i f f e r in depth and in the n a t u r e of the h y d r o c a r b o n s found in t h e m . In the N o r t h e r n C a u c a s u s , m i c r o b i o l o g i c a l (soil- and w a t e r - ) s u r v e y s w e r e conducted in s e v e r a l a r e a s w h e r e i n d u s t r i a l l y significant gas f i e l d s w e r e finally found. In one of the s t r u c t u r e s , in which a s o u r c e of d i f f u s i o n

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at a depth of around 450 m. was indicated by the data of microbiological soil-survey, an intense anomaly was detected, the boundaries of which satisfactorily coincided with the contour of the gas formation ultimately found in the lowest parts of the Maikop deposits (Fig. 144). At the time of

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F i g . 1 4 4 . S c h e m a t i c m a p of the r e s u l t s of a s o i l - s u r v e y c o n d u c t e d in 1 9 4 6 in the a r e a of an a n t i c l i n a l fold ( N o r t h e r n C a u c a s u s ) , c o m p a r e d with the r e s u l t s of s u b s e q u e n t s u r v e y w o r k . 1 — z o n e o f o c c u r r e n c e of h y d r o c a r b o n m i c r o f l o r a ; 2 — a r e a s i n s i d e the b o u n d a r i e s of a h y d r o c a r b o n m i c r o f l o r a - b e a r i n g r e g i o n w h e r e the m i c r o flora i s a b s e n t ; 3 — h y d r o c a r b o n a n o m a l y a c c o r d i n g to g a s - s u r v e y data.

the gasomicrobiological survey, the configuration of the anticlinal structure has not been fully ascertained. Within the bounds of the anomaly being considered lie several areas which are devoid of indicator microflora. They correspond to surface outcroppings of pyritized clays having an acid reaction which is unfavorable for bacterial activity. A gas soil-survey was conducted simultaneously in the same area. The anomaly detected from the data of this survey only r e flected part of the gas-bearing area. The boundaries of the gas anomaly also extended toward the north and south, far beyond the limits of production. It should be noted that the greatest microconcentrations of gases are found in areas where hydrocarbon microflora is absent. In another area, where a gas-bearing stratum is situated at a greater depth (about 850 m.), a microbiological ground-survey detected only part of the gas pool. Here the propane anomaly was found to correspond with that part of the formation having the greatest output, which in turn c o r r e sponded to the sides of the fold (Fig. 145). Closer agreement with the r e sults of subsequent drilling was obtained with biologging data.

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F i g . 145. S c h e m a t i c m a p of a m i c r o b i o l o g i c a l s o i l - s u r v e y conducted in 1948 in an a r e a of b r a c h y a n t i c l i n a l upheaval (Northern C a u c a s u s ) c o m p a r e d with the r e s u l t s of s u b s e q u e n t s u r v e y work and biologging. 1 — z o n e s of o c c u r r e n c e of m e t h a n e - o x i dizing b a c t e r i a ; 2 — z o n e s of development of p r o p a n e - o x i d i z i n g b a c t e r i a ; 3 — i s o l i n e s of p e r c e n t of c a s e s in which p r o p a n e - o x i d i z i n g b a c t e r i a w e r e found in the c o r e s of s u r v e y w e l l s f r o m the data of biologging; 4 — c o r e - d r i l l e d w e l l s .

In the third area, under the same geological conditions, a new gas field was located by using the data of a water-survey which involved microbiological testing of springs (Fig. 146). All wells in which edge water was found were outside the boundaries of anomalies, while wells containing industrial quantities of gas, with the exception of two peripheral ones, were inside the boundaries of anomalies distinguished earlier. Microbiological investigations here preceded all other forms of geological prospecting work and made possible the first prediction of the geological structure of the a r e a . In the Middle Volga region a microbiological (soil- and water-) survey was conducted in several a r e a s . The final surveying haß now been completed and oil formations have been discovered. One of these a r e a s is of interest because of the relationship between the gas and microbiological indicators. In a part of the soil-survey, a focal distribution of methane-oxidizing bacteria was found, and in the western portion of the examined area, a band of propane-oxidizing bacteria was also observed (Fig. 147). The

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F i g . 146. S c h e m a t i c m a p of a h y d r o m i c r o b i o l o g i c a l s u r v e y c o n d u c t e d in 1946 a n d 1948 in a n e w s u r v e y a r e a ( N o r t h e r n C a u c a s u s ) c o m p a r e d w i t h the r e s u l t s of s u b s e q u e n t d r i l l i n g . 1 — w e l l s t e r m i n a t i n g in g a s p o o l s ; 2 — w e l l s e n c o u n t e r i n g g a s a n d w a t e r ; 3 — w e l l s t e r m i n a t i n g in e d g e w a t e r ; 4 — z o n e s of h y d r o c a r b o n m i c r o f l o r a a c c o r d i n g t o d a t a of t h e w a t e r - s u r v e y of 1946; 5 — t h e s a m e a c c o r d i n g to d a t a of t h e w a t e r - s u r v e y of 1948.

F i g . 147. S c h e m a t i c m a p of a m i c r o b i o l o g i c a l s o i l s u r v e y c o n d u c t e d in 1943 in a s u r v e y a r e a in the m i d d l e Volga r e g i o n c o m p a r e d with d a t a of s u b s e quent d r i l l i n g . 1 — z o n e of p r o p a n e - o x i d i z i n g b a c t e r i a ; 2 — z o n e of m e t h a n e - o x i d i z i n g b a c t e r i a ; 3 — geologic s t r u c t u r e contours; 4 — projected wells; 5—oil-producing wells; 6—dry holes.

MICROBIOLOGICAL METHOD

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stability of the anomaly detected was confirmed by repeated biochemical surveys. For this reason a negative prediction was made on the b a s i s of gas survey data alone. The gasomicrobiological survey, taking the established zonality of distribution of bacterial and gas indicators into account, made possible the recommendation of this a r e a for further survey work. In subsequent structure drilling in the northern part of the anomaly, an anticlinal uplift was found. Test wells located over the crest of the anticline revealed a commercial oil pool at a depth of about 1,000 m. in Carboniferous strata. The oil has a negligible gas-oil ratio. A map correlating microbiological and gas indicators for the a r e a

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®7

F i g . 148. Map c o m p a r i n g a v e r a g e v a l u e s f r o m m i c r o b i o l o g i c a l s o i l - s u r v e y s and g a s - s u r v e y s conducted jointly in 1943 in a s u r v e y a r e a in the Middle Volga r e g i o n . 1 — z o n e s of i n c r e a s e d population density of h y d r o c a r b o n m i c r o f l o r a in s u b s o i l d e p o s i t s ; 2 — z o n e s of i n c r e a s e d c o n c e n t r a t i o n of methane a n d h e a v y f r a c t i o n s in s u b s o i l d e p o s i t s f r o m g a s - s u r v e y d a t a ; 3 — f i g u r e s on the l e f t a r e a v e r a g e population density of h y d r o c a r b o n m i c r o f l o r a in g r o u n d - s a m p l e s , f i g u r e s on the right a r e a v e r a g e concentration of m e t h a n e and heavy f r a c t i o n s ; 4 — g e o l o g i c s t r u c t u r e contour; 5 — w e l l s p r o j e c t e d ; 6 — o i l - p r o d u c i n g w e l l s ; 7—dry holes.

338

GEOCHEMICAL PROSPECTING FOR PETROLEUM

being considered was constructed by averaging six points in each square (Fig. 148). On the basis of these averages, isolines of methane and the heavy fraction content are shown for the gas-survey, and isolines of the average population density of methane- and propane-oxidizing bacteria are shown for the microbiological results (Fig. 148). Zones of higher m i c r o concentration of heavy fractions and methane and zones of development of hydrocarbon microflora are shown separate from one another. It should be noted that the zone of development of methane-oxidizing bacteria borders on an oil-bearing area while the band of development of propane bacteria overlaps a considerable part of the formation. A water-survey was conducted by microbiological examination of springs throughout this same area, and an extensive anomaly was detected. Within the boundaries of the water anomaly, further survey work revealed two oil formations located side by side (Fig. 149). One of these (the eastern one) was examined by means of a soil-survey (Fig. 147). The area of the second formation was not fully covered in this work.

®

®

7

F i g . 1 4 9 . S c h e m a t i c m a p of p a r t of a h y d r o m i c r o b i o l o g i c a l s u r v e y conducted in 1947 in the t e r r i t o r y of the Middle Volga c o m p a r e d with r e s u l t s of s u b sequent d r i l l i n g . 1 — s p r i n g s containing h y d r o c a r b o n m i c r o f l o r a ; 2 — s p r i n g s giving n e g a t i v e r e s u l t s ; 3 — zone of h y d r o c a r b o n m i c r o f l o r a with a v e r a g e p o p u l a t i o n d e n s i t y of 2 0 % o r m o r e ; 4 — t h e s a m e with popul a t i o n d e n s i t y of 10%; 5 — w e l l s p r o j e c t e d ; 6 — o i l producing w e l l s ; 7 — d r y h o l e s .

In one of the regions of the Kuibyshev Transvolga, a microbiological soil-survey was conducted in an area where the presence of an anticlinal structure in the Permian layers was assumed. The anomalous development of a complex hydrocarbon microflora which the survey revealed, was

MICROBIOLOGICAL METHOD

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found to be shifted considerably to the southeast in relation to the assumed structure in the Permian layers (Fig. 150). The detected anomaly, which was distinguished by a uniform growth of indicator microflora, was recommended for test drilling. As a result of this work it was ascertained that the indicated anomaly corresponds to the central part of a new oil formation situated in Carboniferous layers. The crude oil is characterized by a significant gas-oil ratio. Thus, with specific formations examined in the Northern Caucasus and the Second Baku serving as examples, several regularities may be noted in the correlation of microbiological and gas indices in soil- and watersurveys. The gas-survey (in cases where the source is at a considerable depth) and biologging give a more complete "reflection" of the pool than the soil-survey does. Hydrocarbon effects in subsoil deposits, due to the influence of an oil pool with a low gas-oil ratio, take the form of discrete foci for the

F i g . 150. Schematic m a p of a m i c r o b i o l o g i c a l s o i l - s u r v e y conducted in 1943 in a survey a r e a of the Kuibyshev T r a n s v o l g a c o m p a r e d with results of s u b sequent drilling. 1—untested s o i l - s u r v e y w e l l s ; 2 — s o i l - s u r v e y w e l l s with negative r e s u l t s ; 3 — t h e same in the p r e s e n c e of hydrocarbon m i c r o f l o r a ; 4 — t h e same in the p r e s e n c e of c e l l u l o s e - d e c o m p o s i n g b a c t e r i a ; 5 — z o n e s of growth of hydrocarbon m i c r o f l o r a with intensity of growth up to 150 a r b i t r a r y units; 6 — t h e same with intensity of growth over 150 a r b i t r a r y units; 7 — structure contours outlining an uplift; 8 — c o n t o u r of oil bearing strata according to data f r o m drilling operations of 1951-1953.

340

GEOCHEMICAL PROSPECTING FOR P E T R O L E U M

accumulation of h y d r o c a r b o n m i c r o f l o r a . When the g a s - o i l r a t i o is high, the development of m i c r o o r g a n i s m s in s u b s o i l d e p o s i t s f o r m s a continuous a n o m a l y (when the oil pool l i e s at a depth not exceeding 750 - 1,000 m . ) . F o r portions of the subsoil, and a l s o f o r underground w a t e r s m o r e densely populated with h y d r o c a r b o n - o x i d i z i n g b a c t e r i a , the m i c r o c o n c e n t r a t i o n s of h y d r o c a r b o n g a s e s a r e l o w e r than f o r p o r t i o n s w h e r e the b a c t e r i a l f i l t e r is l e s s s t r o n g l y developed. When the influx of h y d r o c a r b o n g a s e s is i n t e n s e , complete o r p a r t i a l s u p e r p o s i t i o n of gas m a x i m a on the m i c r o b i o l o g i c a l ones i s o b s e r v e d . With a f e e b l e gas s o u r c e , on the c o n t r a r y , the z o n e s of m i c r o b i o l o g i c a l and gas a n o m a l i e s m a y f a i l to coincide within the b o u n d a r i e s of a given g a s f i e l d . T h e r e f o r e , f o r c o r r e c t i n t e r p r e t a t i o n of g e o c h e m i c a l a n o m a l i e s it is n e c e s s a r y to t a k e into account not only the m i c r o b i o l o g i c a l and gas indices s e p a r a t e l y , but a l s o the s p e c i f i c way they a r e r e l a t e d in s p a c e . Only on the b a s i s of t h e s e data can the a c t u a l output of h y d r o c a r b o n g a s e s at any given depth be d e t e r m i n e d ; t h i s includes not only f r e e l y evolved g a s e s , but a l s o t h o s e a b s o r b e d by the b a c t e r i a l f i l t e r . F u r t h e r m o r e , f o r a c o r r e c t u n d e r s t a n d i n g of the g e o c h e m i c a l situation existing within the b o u n d a r i e s of an a r e a u n d e r investigation, s o i l - s u r v e y s m u s t be a c c o m p a n i e d by a study of a q u i f e r s involving m i c r o b i o l o g i c a l , g a s , and s a l t a n a l y s e s . G a s o m i c r o b i o l o g i c a l w a t e r - s u r v e y s m u s t be used a s the m a i n type of r e c o n n a i s s a n c e investigation, b e c a u s e they p r e c e d e s o i l s u r v e y s and e s t a b l i s h o b j e c t i v e s f o r the l a t t e r method. In p r o s p e c t i n g f o r deep oil and g a s pools, g a s o b i o c h e m i c a l i n v e s t i g a tions m u s t be conducted at g r e a t depth, i . e . , n e a r the s o u r c e of diffusion, in o r d e r to i n c r e a s e the s e n s i t i v i t y of the d e t e r m i n a t i o n s . Under t h e s e conditions the m a i n t y p e s of investigations m u s t be gasobiologging and deep water-surveys. GEOBOTANICAL INDICATORS Geobotanical m e t h o d s a r e , a s yet, only of m i n o r i m p o r t a n c e among the v a r i o u s m e t h o d s of oil p r o s p e c t i n g . T h e s e m e t h o d s a r e based on o b s e r v a t i o n s of the plant c o v e r . In the l i t e r a t u r e t h e r e a r e s e v e r a l r e f e r e n c e s t o the fact that m a n y s u b s t a n c e s of the bitumen g r o u p induce changes in the e x t e r n a l a p p e a r a n c e of vegetation. T h u s , f o r e x a m p l e , when lignite f e r t i l i z e r (containing up to 79% bitumens) was applied, v i g o r o u s growth of a n u m b e r of cultivated plants took place owing mainly to i n c r e a s e s in the s i z e s of individual plants (41, 42). Significant i n c r e a s e in the g r e e n p a r t s of plants growing in s o i l t r e a t ed with bitumen was a l s o o b s e r v e d in e x p e r i m e n t s in the t r e a t m e n t of sand with bitumen e m u l s i o n (43). D. M. Guseinov in A z e r b a i j a n u s e d a s f e r t i l i z e r spent " g u m b r i n " containing a l a r g e amount of b i t u m e n s and obtained a cons i d e r a b l e i n c r e a s e in the s i z e and v i g o r of plants growing in a r e a s f e r t i l i z e d by the " g u m b r i n " (44). In geobotanical investigations conducted at the s a m e t i m e , the a p p e a r ance of s p e c i a l f o r m s of plants was noticed on the bituminous e j e c t a of mud v o l c a n o e s a s a r e s u l t of adaptation of the plants to the p e c u l i a r conditions of volcanic mud. T h u s , M. G. Popov found s p e c i a l f o r m s of wormwood ( A r t e m i s i a l i m o s a H. Koidz), p r i m r o s e ( P r i m u l a s a c h a l i n e n s i s ) , and gentian (Gentiana paludicola) (45), native to t h e s e mud e j e c t a alone. P . D. Y a r o shenko h a s d e s c r i b e d the s a l t w o r t Salsola r i g i d a v a r . f o l i o s a , found in the

MICROBIOLOGICAL METHOD

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mud volcanoes of Kara-Chal, and only known to occur on mud ejecta (46). During the period from 1949 to 1951 this matter was investigated by geobotanists of the All-Union Geological Trust (S. V. Viktorov, E . A. Vostokova, and N. G. Nesvetailova). It was shown by these investigations that in bituminous soils, plants usually have peculiar forms, being distinguished by some gigantism (i.e., sizes significantly greater than the normal average value for the given type) and deformity. The normal proportions of the organs of the given plant are altered and its external appearance is changed. In the same investigations it was also found that plants growing in bituminous soils quite often develop a capacity for repeated blooming. Many forms normally blooming once a year, when situated at the margins of kir^ fields or in other soils rich in bitumens, bloomed again in the autumn; some forms did not bloom, but began to vegetate again (i.e., to form new leaves and stems). This capacity for repetition of the flowering cycle appeared in forms belonging to various families and genera: g r a s s e s , thistles, i r i s e s , r o s e s , etc. One case is also recorded in the literature of mass reblooming of brushwoods near a gas seep (47), although there were no indications of bitumen in the soil in this case. The causes of all these phenomena are not entirely clear, since the physiological action of bitumens on plants has been studied very little as yet. It is known that the presence of a large quantity of bitumens suppresses nitrification (i.e., the conversion of ammoniacal nitrogen to nitrate nitrogen) and thus brings about some nitrogen hunger in the plants (48, where the literature on the question is reviewed). It has also been shown that several substances similar to bitumens upset normal cell division in plant tissues and lead to the appearance of deformed, giant cells. However, the latter facts were all ascertained by laboratory investigations and have not been confirmed by observations in the field. Thus, the action of the bituminous substrate on plants is obscure. Furthermore, all observations of the plant cover of bituminous soils were conducted in the semidesert and desert zone (in West Kazakhstan, southwestern Turkemenia, Fergana, and Transcaucasia). Observations in more northerly zones are lacking, with the exception of the above-mentioned work of M. G. Popov. Despite the fact that the origin of the peculiarities of vegetation in bituminous soils is not quite clear, these peculiarities are so great that with their aid it is very easy (in areas such as Central Aisa and Kazakhstan, in any case) to recognize the presence of bitumens in the soil within the limits of extension of the root systems of plants growing in the area under study. For detection of bituminous soils by means of the plant cover, the following very simple and practicable method of field observations may be r e c o m mended. 1. Take note of areas where plants are distinguished by especially large size, luxuriance, or deformities of any kind, particularly those areas in which such peculiarities are found, not in r a r e isolated instances, but in many c a s e s . 2. In cases where it is necessary to determine how pronounced these peculiarities are, the dimensions of two or three of the most conspicuous

^ " K i r " i s an i n d u r a t e d a s p h a l t i c s u b s t a n c e a s s o c i a t e d with e a r t h y m a t e r i a l s .

Ed.

342

GEOCHEMICAL PROSPECTING FOR P E T R O L E U M

ITTSEGEK (Anabasis

aphyUa)

SHVEDKA (Suae da

sp.)

m U77TUN NON-BITUMINOUS SOILS CHD//V BITUMINOUS SOILS F i g . i 51. Average s i z e s of plants in soils with and without bitumens.

types in the a r e a may be measured (selecting 25 - 50 examples of each type); the height of the plant and the greatest diameter of its crown a r e determined. F o r control, measurements in any a r e a where the plants have normal average s i z e s is recommended. Comparative r e s u l t s of m e a s u r e ments a r e shown in the diagram (see F i g . 151). 3. When the investigator conducts his observations in s u m m e r or autumn, it is recommended that he take note of c a s e s of second (especially in the late autumn) blooming of plants. This phenomenon is often observed in a r e a s where gigantism appears. Second blooming of a plant is revealed by the presence on the plant of flowers together with the (mostly withered) remains of flowers and fruits of this y e a r , left over from the f i r s t flowering cycle. In the desert and s e m i d e s e r t regions of the USSR, special reconnaissance surveys for bituminosity may be conducted by geobotanists in a r e a s of interest to geologists. Such reconnaissance is conducted by s e v e r a l geological organizations and gives positive r e s u l t s . BIBLIOGRAPHY 1. G.A. Mogilevskii. On the possibility of biochemical conversion of hydrocarbon gases in the erosion zone. Sb. rabot po gazovio s ' e m k e . GONTI, 1939. 2. G.A. Mogilevskii. Microbiological investigations in connection with the gas-survey. Razvedka nedr, No. 8 - 9, 1938. 3. G.A. Mogilevskii. Method of surveying oil and gas formations. Avt. svid. No. 55154 (June 30, 1939) (applied for Nov. 10, 1937). 4. L.W. Blau. P r o c e s s e s for determination of the location of valuable underground oil pools. 2, 269, 889 (applied for F e b . 27, 1939).

MICROBIOLOGICAL METHOD

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5. G . L . H a s s l e r . Microbiological method of s u r v e y i n g . 398, 635, Aug. 12, 1941. 6. C . E . Z o B e l l . J o u r n a l of B a c t e r i o l o g y , No. 4, 1949. 7. C . E . Z o B e l l . A s s i m i l a t i o n of h y d r o c a r b o n s by m i c r o o r g a n i s m s . Adv a n c e s in Enzymology, vol. X, 1950. 8. I. C o l l i n s . B a c t e r i a m a k e good oil p r o s p e c t o r s . P e t r o l e u m World, vol. 40, pp. 46, 48, 50, 1943. 9. V.A. Sokolov. D i r e c t g e o c h e m i c a l methods of oil p r o s p e c t i n g . G o s t o p tekhizdat, 1947. 10. N.A. K r a s i l ' n i k o v . On the c l a s s i f i c a t i o n of b a c t e r i a . Mikrobiologiya, v. XVII, No. 2, 1948. 11. B.S. Aleev. Introduction to technical m i c r o b i o l o g y . P i s h c h e p r o m i z d a t , 1944. 12. T . L . G i n z b u r g - K a r a g i c h e v a . Microbiological e s s a y s . ONTI, 1932. 13. T . L . G i n z b u r g - K a r a g i c h e v a . On the o r i g i n of m i c r o f l o r a in oil and g a s b e a r i n g l a y e r s . Sov. geologiya, sb. No. 13, 1947. 14. L.D. S h t u r m . M i c r o s c o p i c investigation of the w a t e r s of o i l - b e a r i n g l a y e r s . Mikrobiologiya, v. XIX, No. 1, 1950. 15. L.D. S h t u r m . M a t e r i a l s on m i c r o s c o p i c investigation of oil f o r m a t i o n s of the Second Baku. T r . Inst, nefti Akad. Nauk. SSSR, v. 1, No. 2, 1951. 16. S.I. Kuznetsov. Study of the possibility of s i m u l t a n e o u s f o r m a t i o n of m e t h a n e in g a s - and o i l - b e a r i n g e n v i r o n m e n t s of the S a r a t o v and B u g u r u s l a n r e g i o n s . Mikrobiologiya, v. XIX, No. 3, 1950. 17. Z . I . Kuznetsova and G.A. Mogilevskii. Development of a method of investigation of the b a c t e r i a l population of underground w a t e r s in the oil r e g i o n s of the USSR f o r o i l - p r o s p e c t i n g p u r p o s e s . Izv. VGF, No. 1. Gosgeolizdat, 1946. 18. B . L . Isachenko. S u l f u r - b a c t e r i a f r o m oil w e l l s . Mikrobiologiya, v. XV, No. 6, 1946. 19. M.A. M e s s i n e v a . B i o c h e m i c a l p r o c e s s e s in mud volcanoes. M i k r o biologiya, v. XVII, No. 1, 1948. 20. V.O. Tauson and V.I. Aleshina. On the r e d u c t i o n of s u l f a t e s by b a c t e r i a in the p r e s e n c e of h y d r o c a r b o n s . Mikrobiologiya, v. I, No. 3, 1932. 21. C . E . Z o B e l l . Action of m i c r o o r g a n i s m s on h y d r o c a r b o n s . B a c t e r i o l . Reviews, vol. 10, No. 1 - 2, 1 - 49, 1946. 22. C . E . ZoBell. The r o l e of b a c t e r i a in the f o r m a t i o n and t r a n s f o r m a t i o n of p e t r o l e u m h y d r o c a r b o n s . Science, vol. 102, No. 2650, 368 369, 1945. 23. G.A. Mogilevskii. B a c t e r i a l method of p r o s p e c t i n g f o r oil and n a t u r a l g a s . Razvedka n e d r , No. 12, 1940. 24. G.A. Mogilevskii. Microbiological method of p r o s p e c t i n g f o r oil and g a s pools. Gostoptekhizdat, 1953. 25. V.O. T a u s o n . H e r e d i t y of m i c r o b e s . Izd. Akad. Nauk. SSSR, 1947. 26. S.I. Kuznetsov. Role of m i c r o o r g a n i s m s in the m a t e r i a l cycle in l a k e s . Izd. Akad. Nauk SSSR, 1952. 27. C . E . ZoBell. M i c r o b i a l T r a n s f o r m a t i o n of M o l e c u l a r Hydrogen in M a r i n e S e d i m e n t s . Bull. Am. A s s n . P e t r o l . Geol., 1947, No. 10, 1709 - 1751. 28. M.I. Belyaeva. Physiology and ecology of hydrogen b a c t e r i a . A u t h o r ' s a b s t r a c t of d i s s e r t a t i o n . Inst, mikrobiologii, Akad. Nauk SSSR, 1951.

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29. V.A. Sullin. Hydrogeology of p e t r o l e u m f o r m a t i o n s . Gostoptekhizdat, 1948. 30. H.A. B a r k e r . Studies upon the m e t h a n e - p r o d u c i n g b a c t e r i a . A r c h . M i c r o b . , Bd. 7, 420 - 438, 1936. 31. V . L . O m e l y a n s k i i . On the m e t h a n e f e r m e n t a t i o n of c e l l u l o s e . A r k h . biol. mauk, v. IX, No. 3, 1902. 32. V.L. O m e l y a n s k i i . On the hydrogen f e r m e n t a t i o n of c e l l u l o s e . Arkh. biol. nauk, v. VII, No. 5, 1899. 33. E . Münz. Z u r Physiologie d e r M e t h a n b a c t e r i e n . I n a u g u r a l - D i s s e r t a tion, H a l l e , 1915. 34. G . P . Slavnina. Detection of m e t h a n e - o x i d i z i n g b a c t e r i a by the f e r m e n tation method. Izv. GUGF, No. 3, G o s g e o l i z d a t , 1947. 35. G . P . Slavnina. The p e r o x i d a s e of m e t h a n e - o x i d i z i n g b a c t e r i a . Doklady Akad. NaukSSSR, v. LVI, No. 2, 205 - 227, 1947. 36. E.N. Bokova. Study of the m a i n p r o p e r t i e s of b a c t e r i a which oxidize liquid and g a s e o u s h y d r o c a r b o n s evolved f r o m deep-lying s t r a t a and underground d e p o s i t s , and elucidation of s e v e r a l conditions l i m i t i n g t h e i r growth. Izv. GUGF, No. 3, G o s g e o l i z d a t , 1947. 37. G.A. Mogilevskii, V.S. Butkevich, E.V. Dianova, A.A. V o r o s h i l o v a , and I.V. Bogdanova. Method of p r o s p e c t i n g f o r oil and gas f o r m a t i o n s (by application of p r o p a n e - b u t a n e b a c t e r i a ) . Avt. avid. No. 57933 (applied f o r M a r c h 25, 1940, published Sept. 30, 1940). 38. E.N. Bokova, V.A. Kuznetsova, and S.I. Kuznetsov. Oxidation of g a s e o u s h y d r o c a r b o n s by b a c t e r i a a s a b a s i s f o r m i c r o b i o l o g i c a l o i l - p r o s p e c t i n g . Doklady Akad. Nauk SSSR, v. LVI, No. 7, 755 757, 1947. 39. S.I. Kuznetsov, V.A. K u z n e t s o v a , and Z.S. S m i r n o v a . Study of p r o c e s s e s of b a c t e r i a l oxidation of h y d r o c a r b o n g a s e s under the conditions of t h e i r diffusion t h r o u g h s e d i m e n t a r y r o c k s . Izv. GUGF, No. 8. Gosgeolizdat, 1947. 40. Byulleten*. G e o m i k r o b i o l o g i c h e s k a y a r a z v e d k a . Novosti neftyanoi tekhiniki. Geologiya. T s I M T n e f t ' , 1947. 41. R. L i e s k e . Untersuchungen ü b e r die V e r w a n d b a r k e i t von Kohlen a l s Düngemittel. B r e n n s t o f f - C h e m i e , Bd. 12, H. 5, 1931. 42. F . F i s c h e r . Biologie und Kohle. Angewandte C h e m i e , No. 9, 1932. 43. A. G a e l ' , N. Z a k h a r o v , and E . Malyugin. C e m e n t a t i o n of s a n d s by bitum e n e m u l s i o n s . Sb. " P r o b l e m a r a s t e n i e v o d c h e s k o g o osvoeniya pustyn* " . No. 3, 1935. 44. D.M. G u s s e i n o v . Application of s p e n t g u m b r i n f o r the p u r p o s e of inc r e a s i n g the yield of a g r . c r o p s . Izv. Akad. Nauk AzSSR, 1950. 45. M.G. Popov. E n d e m i c s p e c i e s of the Maguntan mud volcano. Botan. Z h u r n . , No. 5, 1949. 46. P.D. Y a r o s h e n k o . T o w a r d the g e n e s i s of mud v o l c a n o e s n e a r the K a r a Chal State F a r m in s o u t h e a s t e r n Shirvan. Botan. sb. AzGNII, No. 1, 1932. 47. Khokhlov. Repeated blooming of f r u i t s and other p e c u l i a r i t i e s of b e h a v i o r of plants in the vicinity of gas wells in the e n v i r o n s of S a r a t o v . Sov. botanika, v. 15, No. 1, 1947. 48. N . P . R e m e z o v . Conditions of nitrogen supply in pine f o r e s t s . Sov. botanika. No. 6, 1938.

CHAPTER

FOURTEEN

The Role of Geochemical Methods in Petroleum Prospecting The previous chapters of this book have shown that geochemical methods of prospecting and exploration for oil and gas formations vary considerably. The role of these methods in the search for petroleum is also quite varied. Geochemical methods are used in all stages of prospecting and exploration work under very diverse conditions and may serve entirely different functions. In the first stage of exploratory geological reconnaissance, the main tasks of geochemical methods a r e : (a) general evaluation of the possibilities of a region, (b) distinguishing oil-bearing strata, (c) selecting the most promising regions or sometimes, specific a r e a s . The route survey is used primarily for these purposes. A combination of hydrochemical, water-gas, and hydromicrobiological surveys is most useful in evaluating the oil possibilities of a region and in choosing the most likely regions. Bitumen methods (route bitumen and bitumen luminescence surveys) are used primarily in prospecting for oil-bearing strata. Bituminological determinations and investigations of waters are important, but the results must be coordinated through studies of the dissolved bitumens. The results of geochemical reconnaissance surveys must be in close agreement with geological data. This is particularly true of the hydrochemical surveys which, by their very nature, must agree with geological results. In this first stage aerial-radiometric surveys, geobotanical investigations, etc. may be used. Test drilling may also be used. Bituminological examinations of cores, the study of the gas content and gas composition of cores, the hydrochemical investigation of well sections, and gas and luminescence logging are conducted in supporting wells. In the second stage of detailed geological surveys, the task of geochemical methods is to select areas for detailed exploration and to evaluate prospects selected by other methods. Detailed and semi-detailed area surveys are the chief forms of prospecting and exploration used. The hydrochemical (structural) survey is the most practical method and may also be helpful in geological mapping. Geochemical surveys are conducted in areas selected on the basis of geological and geophysical data. The methods that may be used include the gas, g a s - c o r e , water-gas, bitumen and bitumen-luminescence, hydrochemical, soil-salt, redox-potential, and m i c r o biological surveys. These various methods may be and usually are conducted jointly as a combined chemical survey. The combination of methods used may be varied depending on geological and geographical conditions and the purposes of the work or for technical reasons. Gas surveys, for example, are i m possible in marshy localities. On the other hand, water-gas and hydrochemical surveys cannot be used in the case of very deep ground waters. Hydrochemical and soil-salt surveys (except the carbonate-siallite method) are impossible in humid climates. In a combined geochemical survey the area is traversed using a [345]

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GEOCHEMICAL PROSPECTING FOR

PETROLEUM

network of sampling points. Samples of subsoil a i r and s o i l s a r e taken to determine sorbed g a s e s , bitumens, b a c t e r i a , and s a l t s , while s a m p l e s of ground waters a r e collected to determine dissolved s a l t s , g a s e s , and b a c t e r i a , all f r o m the s a m e b o r e h o l e s . T h e purpose of the g a s , c o r e - g a s , bitumen, w a t e r - g a s , redox-potential, and m i c r o b i o l o g i c a l surveys i s to evaluate the petroleum potential of a given a r e a o r , in other words, to predict the p r e s e n c e or a b s e n c e of oil or gas pools below the a r e a surveyed. Hydrochemical surveys a r e usually conducted for a r a t h e r different purpose to confirm data on the geological structure of the a r e a obtained by other (non-geochemical) methods and to improve t h e s e data if possible. S o i l - s a l t surveys a r e conducted for various purposes.. The s o i l chloride survey fulfills the s a m e function as the s t r u c t u r a l hydrochemical survey, while the soil-iodine and s o i l - c a r b o n a t e - s i a l l i t e surveys s e r v e nearly the s a m e purposes as the gas survey, bitumen survey, e t c . The evaluation of r e s u l t s f r o m each type of geochemical survey must be coordinated with the data of other geochemical methods and a l s o with geological and geophysical data.-'- Some geochemical methods (e.g., the c o r e - g a s survey and biologging) may a l s o be used in combination with test drilling f o r mapping purposes. T A B L E 37.

Role of Geochemical Methods in P r o s p e c t i n g and Exploration

Stages of work

Principal tasks

P r i n c i p a l types of geochemical methods

1. Geological prospecting r e c o n naissance work

G e n e r a l evaluation of the o i l - b e a r i n g p r o s pects of l a r g e r e g i o n s , prospecting for o i l bearing s t r a t a , selecting the m o s t likely regions

Route s u r v e y s : hydrochemical, water-gas, bitumen, and bitumenluminescence. Geochemical study of the sections of supporting wells

2. Detailed g e o logical prospecting and p r e l i m i n a r y exploration

Prospecting for e x ploratory a r e a s and evaluating t h e i r p o s s i bilities

Hydrochemical surveys. Detailed a r e a s u r v e y s : g a s , c o r e - g a s , bitumen and bitumen -lumine s c e n c e , b a c t e r i a l , hydrochemical, soil-salt, r e dox -potential

3. Exploration work (drilling for prospecting and structure purposes)

Discovery of pools that have been penetrated by the drilling well. Obtaining supplementary data for detailed d e termination of the g e o logical structure and other secondary t a s k s

Gas and luminescence logging. Hydrochemical i n v e s t i gations

F o r e x a m p l e s o f c o m p l e x g e o c h e m i c a l a r e a s u r v e y s s e e the c o l l e c t i o n , " G e o k h i m i c h e s k i e m e t h o d y p o i s k o v n e f t i i g a z a " (No. 1, 1 9 5 3 ) , a r t i c l e s by V. A . L o b o v and A. A. G e o d e k y a n .

THE P L A C E O F GEOCHEMICAL METHODS

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In the t h i r d s t a g e of e x p l o r a t o r y work (which includes deep e x p l o r a t o r y drilling), g e o c h e m i c a l methods a r e p a r t i c u l a r l y valuable. The p r i n c i p a l u s e of t h e s e m e t h o d s at t h i s s t a g e of the w o r k is to d i s c o v e r pay s a n d s (pools) during d r i l l i n g in a r e a s w h e r e production exploration is being c a r r i e d out a s well a s in a r e a s w h e r e the oil potential is not yet d e t e r m i n e d . The p r i n c i p a l g e o c h e m i c a l exploration m e t h o d s a r e gas logging and b i t u m e n - l u m i n e s c e n c e logging (using the d r i l l i n g mud and d r i l l cuttings). It i s m o s t expedient t o conduct and i n t e r p r e t t h e s e s u r v e y s jointly. T h e data f r o m g e o c h e m i c a l m e t h o d s of logging m u s t be c o o r d i n a t e d with e l e c t r i c logging data, hydrogeological o b s e r v a t i o n s m a d e during d r i l l i n g , and d r i l l i n g data In e x p l o r a t i o n and p r e - e x p l o r a t o r y work, h y d r o c h e m i c a l m e t h o d s a r e a l s o v e r y i m p o r t a n t . They can be helpful in solving the p r o b l e m of p r e dicting oil at a given h o r i z o n in a d j a c e n t a r e a s , d e t e r m i n i n g the geological s t r u c t u r e of a f o r m a t i o n , c o r r e l a t i n g well s e c t i o n s , a s well a s solving c e r t a i n production p r o b l e m s . H y d r o c h e m i c a l investigations can a l s o give i n f o r m a t i o n of much value in the drilling and development of an oil f o r m a tion. All the m a t e r i a l of t h i s c h a p t e r is p r e s e n t e d s c h e m a t i c a l l y in T a b l e 37.

Appendix Generalized Geologic Column for the Oil Producing Regions of the USSR System Series Era Stage Quaternary Khvalynian Khazarian Baku Upper Tertiary Apsheronian Pliocene Akchaghylian Balakhan Lower Pliocene Pontian Upper Miocene Maotis Sarmatian Middle Miocene Tortonian Konk Karagan Chokrak Tarkhan Lower Miocene Maikop* Oligocene Kharkov Eocene Saratov Paleocene Cretaceous Upper Danian Cretaceous Maestrichian Senonian Turonian Cenomanian Lower Albian Aptian Cretaceous Neocomian Barremian Balanzhan Jurassic Malm Upper Volga Lower Volga Kimmeridgian Oxfordian Callovian Dogger Bathonian Bajocian Aalen Lias Triassic Tatarian Permian Upper Permian Kazanian Ufa Lower Permian Kungurian Artinskian Sakmarian Uralian Carboniferous Upper Carboniferous Gshelian Kasimovian Moscovian Middle Bashkirian Carboniferous Namurian Lower Carboniferous Vis^an Tournaisian Devonian Silurian Ordivician Cambrian SOURCE: Compiled by the editors f r o m the following s o u r c e s : (a) Istoricheskaya geologia s osnovami paleontologa, Ya- M. L e v i t e s , Gosgeoltekhizdat, Moscow, 1956; (b) Istoricheskaya geologia, G . P . Leonov, Moscow Univ. P r e s s , 1956; ( c ) The g e o l o g i c a l map of the USSR, D. V. Nalivkin, e d i t o r , Ministry of Geol., USSR. 1956. • T h e Maikop is a transitional stage between L o w e r Miocene and Upper Oligocene.

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