Essentials of Modern Open-Hole Log Interpretation

374 Pages·1983·28.611 MB·English

by  John T. Dewan

ESSENTIALS OF
MODERN
OPEN-HOLE LOG
INTERPRETATION
JOHN T. DEWAN
Disclaimer
The recommendations, advice, descriptions, and the methods in this book are
presented solely for educational purposes. The author and publisher assume no
liability whatsoever for any loss or damage that results from the use of any of the
material in this book. Use of the material in this book is solely at the risk of the user.
Copyright © 1983 by
PennWell Corporation
1421 South Sheridan Road
Tulsa, Oklahoma 74112-6600 USA
800.752.9764
+1.918.831.9421
[email protected]
www.pennwellbooks.com
www.pennwell.com
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National Account Executive: Barbara McGee
Library of Congress Cataloging-in-Publication Data Available on Request
Dewan, John T.
Essentials of Modern Open-Hole Log Interpretation
ISBN 978-0-87814-233-0
All rights reserved. No part of this book may be reproduced, stored in a retrieval
system, or transcribed in any form or by any means, electronic or mechanical, including
photocopying and recording, without the prior written permission of the publisher.
Printed in the United States of America
6 7 8 9 10 11 10 09 08 07
DEDICATION
This book Is dedicated to my former colleagues at Schlumberger, who
did much to advance the science of well logging, and to my present
associates and my family, who patiently endured Its preparation.

CONTENTS
DEDICATION v
INTRODUCTION xi
1 The Logging Environment 1
The borehole 1
logging procedure 2
The undisturbed reservoir 4
Disturbance caused by drilling 8
Summary 13
References 15
2 Evaluation of Hydrocarbons 17
Fundamental Interpretation relations 17
The basic Interpretation procedure 22
Impact of Invasion on resistivity measurements 26
Summary 31
References 33
3 Permeable Zone Logs 35
Spontaneous Potential (SP) log 35
Source of spontaneous potential 36
SP behavior over a long log 39
Shape of the SP curve 40
Computation of Rw from the SP 43
SP log In shaly sands 49
SP anomalies due to vertical migration of filtrate 49
SP anomalies due to noise 50
The Gamma Ray (GR) log 50
Basic GR logs 50
Spectral GR logs 53
Statistical fluctuations 57
Summary 60
References 61
vII
viii CONTENTS
4 Resistivity logs 63
Classification and Application 63
Electrical survey (ES) tools 65
Fresh mud tools 66
Salt mud tools 68
Ranges of application of Induction logs and laterologs 69
Dual Induction-Spherically Focused logs 70
The spherically focused log (SFl) 76
log presentation 77
Duallaterolog-Rxo logs 82
The Dll-MSFl tool 83
Depth of investigation 86
Characteristics of the MlcroSFl (MSFL) 88
Log presentation 88
Quick-look hydrocarbon indication 89
Summary 93
References 94
5 Porosity Logs 95
The current trend in porosity logging 95
Recent developments 96
Compensated Density and litho-DenSity logs 97
The compensated density tool 98
Porosity derivation from the density log 105
The litho-Density log 108
lithology interpretation with Pb-Pe curves 114
Compensated Neutron and Dual Porosity Neutron logs 115
Neutron tool evolution 117
The Compensated Neutron 117
Combined Density-Neutron Interpretation 128
The Dual Porosity Compensated Neutron log 136
Compensated Sonic and long-Spaced Sonic logs 139
The borehole compensated log 141
Porosity determination from Sonic logs 146
The long-Spacing Sonic log 158
CONTENTS Ix
Electromagnetic Propagatlon-Microlog Combination 170
The EPT-ML sensor array 172
The Mlcrolog 173
in
The Electromagnetic Propagation Log
Summary 191
References 194
6 Clean Formation Interpretation 199
Resistivity-Porosity Crossplots 199
The Hingle plot 200
The Pickett plot 207
Range of uncertainty In calculated water saturations 209
Multlmlneralldentlflcation 211
The M-N plot 211
The MID plot 214
The Litho-Denslty-Neutron method 217
Trends In multlmlneral Identification 223
References 225
7 Shaly Formation Interpretation 227
The nature of shale 230
Shale or clay distribution In shaly sands 231
Shaly sand Interpretation models 236
Cation exchange capacity 237
Shale porosity and conductivity 243
Application of the dual-water method to shaly sands 247
Summary of dual water Interpretation 257
Summary of earlier shaly sand Interpretation methods 261
References 265
8 Prediction of Producibility 267
Flow relations 267
Absolute. relative. and effective permeabllitles 269
Irreducible water saturation 271
Estimation of permeability from logs 279
x CONTENTS
The Multiple Formation Tester 284
Permeability from pretest drawdown 290
Permeability from pressure buildup 292
Sampling and sample analysis 301
Applications of pressure measurements 307
Summary 313
References 314
9 Wellsite Computed Logs 317
TheRwa log 318
Porosity overlays 319
Resistivity overlays 322
The SP overlay 324
The Cyberlook log 327
The Prolog analysis 331
Office-computed logs 333
Summary 334
References 335
10 Recommended Logging Suites 337
Fresh mud, medium-fe-soft rock logging suites 340
Hard-rock, salt-mud logging suites 343
Special situations 346
References 349
Index 351
INTRODUCTION
The aim of this book is to present modem log interpretation as simply
and concisely as possible. The book is written for the geologist,
petrophysicist, reservoir engineer, or production engineer who is familiar
with rock properties but has little experience with logs. It will help him
specify good logging programs with up-to-date tools and hand-interpret
zones of interest with the latest techniques. The book will also familiarize
him with computer-processed logs generated by the service companies at the
wellsite.
Accordingly, obsolete logging tools are mentioned only in perspective.
Very brief descriptions of the instruments in common use indicate how they
apply to different logging conditions. Salient features of new tools,
including Spectral Gamma Ray, Litho-Density, Dual Porosity Neutron,
and Long-Spacing Sonic, emphasize how these tools fit into the everyday
logging picture. The interpreter need not be overly concerned how a tool
operates. What is important is the instrument's response to the various
formation and borehole variables.
In a similar vein, interpretation equations and charts are kept to the
minimum needed for routine evaluation of logs. Fundamental principles
are stressed, rather than mechanical application of formulae. This is
particularly true in the chapter on shaly formation interpretation where an
effort has been made to draw together the latest concepts in this ever
changing field.
This book addresses the normal well situation where a standard set of
logs is run in a liquid-filled open hole to locate hydrocarbons in place and
where promising zones are then tested to evaluate their producibility.
Abnormal situations such as empty hole, water well, and geothermal and
mineral logging are not included.
To provide a little perspective, well logging is in its third major
development stage. The first 20 years, from 1925-1945, saw the
introduction and gradual worldwide acceptance of the so-called ES
(Electrical Survey) logs. These logs were run with simple downhole tools
and, while quite repeatable, were often difficult to interpret.
The second phase, from 1945-1970, was a major tool development era,
made possible by the advent of electronics suitable for downhole use.
Focused electrical devices were introduced, having good bed resolution and
various depths of penetration. A variety of acoustic and nuclear tools were
developed to provide porosity and lithology information. There was a
progression through second- and even third-generation tools of increasing
capability and accuracy. Simultaneously, much laboratory and theoretical
work was done to place log interpretation on a sound, though largely
empirical, basis.
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