Basic Well Log Analysis for Geologists (AAPG Methods in Exploration 3)

232 Pages·1983·13.24 MB·English

by  George B. Asquith

LOG ABBREVIATIONS USKD IN TEXT
a - tortuosity factor
BHT - bottom hole temperature
BVW - bulk volume water
C - conductivity
CNL - compensated neutron log
c - compaction factor for sonic porosity
p
Arj - radius of invaded zone
At - interval transit time of formation
At, - interval transit time of fluid in borehole
At - interval transit time of formation matrix
ma
d - diameter of borehole
h
d - diameter of invaded zone (flushed zone)
- diameter of invaded zone
di
F - formation factor
FDC - formation density compensated log
GR|g - gamma ray reading from formation
0
GRmax - gamma ray reading from shale
GRmin - gamma ray reading from clean sand
"mc - thickness of mudcake
K - absolute permeability
a
K - effective permeability
e
K - relative permeability to gas
rg
K - relative permeability to oil
r0
K - relative permeability to water
rw
111 - cementation exponent
ML - Microlog
MLL - Microlaterolog
MOS - moveable oil saturation (S - S )
x0 w
PL - Proximity Log
<P - porosity
PSP - pseudostatic spontaneous potential
Pb - bulk density of the formation
Pi - density of fluid in the borehole
Ph - hydrocarbon density
Pma - density of the formation matrix
- resistivity of shallow focused log
RFL
K - resistivity of invaded zone
- resistivity induction log medium
R|LM
- resistivity induction log deep
RlLD
- resistivity of Laterolog* deep
R|_Ld
- resistivity of Laterolog* shallow
RLLS
Rm - resistivity of drilling mud
r*mc - resistivity of mudcake
- resistivity of mud filtrate
Rmf
- resistivity of Microspherically Focused Log*
RMSF
Ro* - resistivity of the formation 100% water saturated
(i.e. wet resistivity)
ROS - residual oil saturation (1.0 - S )
xo
R - resistivity of adjacent shale
s
RsFL - resistivity of Spherically Focused Log
Rt - resistivity of uninvaded zone
R - resistivity of formation water
w
- apparent formation water resistivity
- resistivity of flushed zone
Rxo
s - hydrocarbon saturation (1.0 - S )
h w
S.N. - short normal log
SNP - sidevvall neutron porosity
SP - spontaneous potential
SPI - secondary porosity index
SSP - static spontaneous potential SSP = -K log (R /R )
mf w
- irreducible water saturation
k'wirr
- water saturation of uninvaded zone (Archie method)
\a
- water saturation of uninvaded zone (Ratio Method)
\r
- moveable hydrocarbon index
- water saturation of flushed zone
- formation temperature
- volume of shale
LOG NAMES USED IN TEXT
bulk density log microcaliper
caliper log Microlaterolog* (MLL)*
Compensated Density Log Microlog* (ML)*
Combination Gamma Ray Neutron-Density Log Microspherically Focused Log* or (MSFL)*
Combination Neutron-Density Log neutron log
Compensated Neutron Log normal logs
density log nuclear logs
Dual Induction Log porosity log
Dual Induction Focused Log Proximity Log* or (PL)*
Dual Laterolog* resistivity logs
electrode logs Resistivity Spherically Focused Log* or (RSFL)*
gamma ray log short normal log
Induction Electric Log Sidewall Neutron Log
induction log sonic log
Lateral Log Spectralog**
Laterolog* Spherically Focused Log* (SFL)*
Laterolog-8* spontaneous potential log (SP)
Basic
Well Log Analysis
For Geologists
~y:
George Asquith
With:
Charles Gibson
The American Association
of Petroleum Geologists

Basic Well Log Analysis for Geologists
By
George B. Asquith
Pioneer Production Corporation
with
Charles R. Gibson
Alpar Resources Inc.
Methods in Exploration Series
Published by
The American Association of Petroleum Geologists
Tulsa, Oklahoma USA
Published try
The American Association of Petroleum Geologists
Tulsa, Oklahoma 74\0L USA '--'
Copyright • 1982 by
The American Association of Petroleum Geologists
All Rights Reserved
Published October 1982
Second Printing: (revised), August 1983
Library of Congress Catalog Card No. 82-73052
lSBN: 0-89181-652-6
For AAPG:
Editor: M. K. Horn
Science Director: E. A. Beaumont
Project Editors: A. L. Asquith, R. L. Hart
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Table of Contents:
1. Basic Relationships of Well Log Interpretation ........... .. ..................................... .
Introduction .... ..... .. .. ... ....... ... ... ... ..... .. .. .. .... .. ... ...... ..... .. ... . .. ...... .
Borehole Environment .. ............ ..... ... .... ... . .. ...... ..... .. . ... ... . 2
Invasion and Resistivity Profiles .... ....... .. . 4
Fonnation Temperature ........... ...... ... . 5
2. The Spontaneous Potential Log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Fonnation Water Resistivity (Rw) Determined . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Volume of Shale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3. Resistivity Logs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
[nduction Electric Log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Dual Induction Focused Log 42
Laterolog* . . . . . . . . . . . . . . .... ... . 43
Dual Laterolog-Microspherically Focused Log* 43
Micrulog* . . . . . . . . . . . . . . . . ....... ... .. .. ... . ... ....... .... ... .. . .. . · · · · · · · · · · · · · · · · · 43
Microlaterolog* and Proximity Log* .... .. . 44
Resistivity Derived Porosity ...... ..... .. ..... . 44
4. Porosity Logs 66
Sonic Log 66
Density Log 66
Neutron Log .... .. ... ....... .. ... ...... .. . ...... ... ... .. . 67
Combination Neutron-Density Log .. .... ... . 68
5. Gamma Ray Log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
\blume of Shale Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
6. Log Interpretation 96
Archie Equation 96
Ratio Method 96
Bulk Volume Water .. ..... ... .... ... ..... .. ... .... . . . ...... ..... .. .. . ...... ... . 98
Quick Look Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... .... . ... ... . 98
Pickett Crossplot Method .. ...... ... ....... .. .. . 100
Hingle Crossplot ........ . .. ... ... ... . . 101
Permeability from Logs ........ .... .. .... .... ... ... . . ... .. ... ... .. .. ........ ..... . 102
Shaly Sand Analysis ..... .......... ...... . . 103
7. Lithology Logging and Mapping Techniques ........................................... ......... . 118
Combination Gamma Ray Neutron Density Log . . . ...... .......... .. . ... .. . 118
M-N* Lithology Plot .. .. .. .... ... .. .. ... ... ...... ..... ... ....... .. ... .. . 118
MID* Lithology Plot . . . . . . . . . . . . . . . . ... ... ...... ... ...... ... . 118
Alpha Mapping from SP Log . . . . . . . . . . . . . . . . . . . . ........ .. . ll9
Clean Sand or Carbonate Maps from Gamma Ray Log . . . . . . . . . . . . . . . . . . . ....... .. . 120
Rock Typing and Facies Mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....... ... . 120
8. Log Interpretation Case Studies ............... .... ............................................ 140
Pennsylvanian Atoka Sandstone. Permian Basin
Mississippian Mission Canyon Formation, Williston Basin
Eocene Wilcox Sandstone. Gulf Coast
Pennsylvanian Upper Morrow Sandstone. Anadarko Basin
Cretaceous Pictured Cliffs Sandstone. San Juan Basin
Devonian Hunton Formation, Anadarko Basin
Appendices of Charts Used in Plotting ... ........ ........... ... ........... ........ ................ 209
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
Index ...... ............................................ ........ .. ... ......................... 215
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Acknowledgements:
The construct of this book would have been entirely different had it not been for the creative contributions of Edward A.
Beaumont and Ronald L. Hart. As Science Director of the American Association of Petroleum Geologists, Mr. Beaumont early-on
recognized the need for a logging course designed especially for geologists. His efforts and encouragement led to the development
of the AAPG school on basic logging from which the text was derived. The considerable editorial talents of Ronald L. Hart,
Manager of the AAPG Projects Department and his assistance with formating and writing figure captions, helped ensure the book
would meet its goal of introducing the reader to fundamental concepts of well logging.
Perhaps the most significant contribution of all, however, was by Ann L. Asquith. She helped her husband with both the writing
and editing of the manuscript. Her unflagging efforts to improve readability, her assistance with writing, and her suggestions
concerning content were an incalculable asset. She was assisted in her editing tasks by Robert V. Brown, who critically read the
manuscript and offered many useful suggestions; the text's introduction owes much to his insight. Robert J. Mitchell also lent his
technical expertise to a review of the manuscript, as did Edith C. Campbell and Leon Williams. Their assistance is recognized and
gratefully acknowledged.
Many charts and figures used in the text were provided by Dresser Industries and by Schlumberger Well Services. Their
cooperation in allowing reproduction of these items, and their unwavering courtesy eased the task of authorship.
By assisting her husband with some of the drafting and graphic layout work, Pearl Gibson helped ensure that the text's complex
figures would be legible and easily understood. The quality of the graphics work was also enhanced by Rick Blackburn's efforts on
behalf of the photographic reproduction of various charts and figures. Bette Haimes typed the finished manuscript copy; her
commitment to accuracy, with a difficult and often tedious task, does not pass unnoticed.
IV
Preface:
This book is a basic introduction to open hole logging.
Study of the properties of rocks by petrophysical techniques using electric, nuclear, and acoustical sources is as important to a
geologist as the study of rock properties by more conventional means using optical, x-ray, and chemical methods. Nevertheless,
despite the importance of petrophysics, it is frequently underutilized by many geologists who are either intimidated by logging
terminology and mathematics, or who accept the premise that an in-depth knowledge of logging is only marginally useful to their
science because, they feel, it more properly belongs in the province of the log analyst or engineer.
The enormous importance of logging dictates that as geologists, we put aside old notions and apply ourselves diligently to
learning log interpretation. The rewards are obvious; in fact, no less than achieving an understanding of the ancient record hangs in
the balance. And, it is likely that the success or failure of an exploration program may hinge on a geologist's logging expertise.
In the interest of conciseness, and so that logs used most often in petroleum exploration are thoroughly discussed, the text is
restricted to open hole logs. I hope that the reader initiates his or her own study of other log types which are beyond the scope of this
book.
Unfortunately, learning about open hole logging requires more of the reader than a light skimming of the text's material. The plain
truth is that a great deal of hard work, including memorizing log terminology, awaits the serious student; and even then, a facility
with logs develops only after plenty of real-life experience. The intent here is simply to provide a foundation of knowledge which
can be built upon later. Consequently, many exceptions to rules are left to more advanced books.
It is quite possible that some colleagues will raise objections about the lack of time devoted to tool theory; they may also comment
on the paucity of qualifying statements in the text. These objections are understood and indeed there may be disagreements about
what constitutes over-simplification. In defense of brevity, it should be pointed out that the surfeit of information available on
petrophysics often discourages all but the most ardent beginner. Certainly, many of the difficult decisions which had to be faced in
preparing the manuscript dealt with selecting information judged indispensable at an elementary level.
Many in the audience will note frequent references to a book by Douglas Hilchie, Golden, Colorado entitled Applied Open Hole
Log Interpretation (1978). For those who are interested in expanding their knowledged of logs, his book will be a great help.
Another helpful book is The Glossary of Terms and Expressions Used in Well Logging, The Society of Professional Well Log
Analysts (1975), which explains the meaning of logging terms by extended definitions.
Finally, a last word - a substantial effort was expended to ensure that a minimum number of errors would appear in the text.
However, given the nature of the subject and the almost infinite possibility for mistakes, there may be slip-ups, regardless; hopefully
they will not be too serious.
George B. Asquith
Pioneer Production Corporation
Amarillo, Texas
October, 1982
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