Theory and Evaluation of Formation Pressures

The EXLOG Series oj Petroleum Geology and Engineering Handbooks

Theory and Evaluation of Formation Pressures A Pressure Detection Reference Handbook

Written and compiled by EXLOG staff

Edited by Alun Whittaker

~

" D. Reidel Publishing Company A Member of the Kluwer Academic Publishers Group Dordrecht/Boston/Lancaster

International Human Resources Development Corporation • Boston

© 1985 by EXLOG® . * All rights reserved. No part of this book may be used or reproduced in any manner whatsoever without written permission of the publisher ex­cept in the case of brief quotations embodied in critical articles and reviews. For infor­mation address: IHRDC, Publishers, 137 Newbury Street, Boston, MA 02116.

Softcover reprint of the hardcover 1 st edition 1985

Library of Congress Cataloging in Publication Data

Main entry under title:

Theory and evaluation of formation pressures.

(The EXLOG series of petroleum, geology, and engineering handbooks) Bibliography: p. Includes index. 1. Reservoir oil pressure. 2. Petroleum-Geology.

I. Whittaker, Alun. II. EXLOG (Firm) III. Series. TN871. T 44 1985 622 '.1828 H5-2287

ISBN-13: 978-94-010-8862-6 e-ISBN-13: 978-94-009-5355-0 DOl: 10.1007/978-94-009-5355-0

[90-277-1979-9 D. Reidel]

Published by D. Reidel Publishing Company P.O. Box 17, 3:'>00 AA Dordrecht, Holland in copublication vvith IHRDC

Sold and distributed in North America by IHRDC

In all other countries, sold ami distributed by Kluwer Academic Publishers Group, P.O. Box :'>22, :'1500 AH Dordrecht, Holland

• EXLOG is a registered sen'ice mark of Exploration Logging Inc.. a Baker Drilling Equipment Com pam',

CONTENTS List of Illustrations ix

Preface xiii

Acknowledgments for Figures Xl'

1. INTRODUCTION 1 WHAT IS PRESSURE EVALUATION? FROM FORMATION LOGGING TO PRESSURE EVALUATION RESPONSIBILITIES 2 INSTRUMENTATION 2 LOGS AND REPORTS 4 2. GEOLOGY 11 INTRODUCTION 11 COMPACTION DISEQUILIBRIUM 15 AQUATHERMAL PRESSURING 25 MONTMORILLONITE DEHYDRATION 25 OSMOSIS 32

REVERSE OSMOSIS 33 IONIC FILTRATION 33

TECTONISM 34 PIEZOMETRIC CHANGES 36 THE TRANSITION ZONE 38 PORE PRESSURE MAINTENANCE 40 REFERENCES 41 3. ENGINEERING 43 INTRODUCTION 43 SUBSURFACE PRESSURES 43

HYDROSTATIC PRESSURE 43 OVERBURDEN PRESSURE 47

PORE PRESSURES, FORMATION BALANCE GRADIENT, AND EQUIVALENT MUD DENSITY 54

EFFECTIVE OVERBURDEN PRESSURE 59 EFFECTIVE CIRCULATING DENSITY 62 DIRECT PRESSURE MEASUREMENTS 68 LOG-DERIVED FLUID DENSITIES 69 4. PORE PRESSURE EVALUATION TECHNIQUES 73 INTRODUCTION 73 GEOPRESSURE EVALUATION FROM SEISMIC DATA 74 DRILLING PARAMETERS 78

MUD DENSITY/GAS RELATIONSHIP 78 GAS-CUT MUD 80 CUTTINGS CHARACTER 84 HOLE BEHAVIOR 85 DRILLING EXPONENTS 85

D-Exponem 88 Nx and Nxb 99

SHALE DENSITY 100 SHALE FACTOR 101 TEMPERA TL'RE 108

vi

MUD RESISTIVITY/CONDUCTIVITY 118 ELECTRIC LOG PARAMETERS 121

THE SONIC LOG 121 RESISTIVITY 126 DENSITY AND NEUTRON LOGS 127

FACTORS AFFECTING EVALUATION 129 LITHOLOGY 129 CONTROLLED DRILLING 130 HYDRAULICS 131 BIT SELECTION AND BIT WEAR 132 MUDTYFE 132

REFERENCES 134 5. LOST CIRCULATION, HYDRAULIC FRACTURING, AND KICKS 137 INTRODUCTION 137 LOST CIRCULATION 137

CAUSES 137 EFFECTS 138 SOLUTIONS 139

HYDRAULIC FRACTURING 141 PAST AND CURRENT TECHNOLOGY 141 LIMITATIONS AND ADVANTAGES OF ACCEPTED MODELS 150

Hubbert and Willis' Minimum Fracture Gradient 150 Matthews and Kelly's Method 150 Anderson et al. 151

ESTIMATION OF FRACTURE PRESSURES 151 SUBSURFACE STRESS STATES 153

Effective Stresses 153 Theoretical Subsurface Stress States 154

THE ZERO TENSILE STRENGTH CONCEPT 156 THE FRACTURE TEST 157 METHOD 160 SUMMARY 168 EXAMPLES 169 MASSIVE HYDRAULIC FRACTURING (MHF) AND STIMULATION 170

KICKS AND KICK TOLERANCE 171 CAUSES OF KICKS 172 RECOGNITION OF KICKS 174

During Connections 174 While Tripping 174 Sequence of Events 175

KICK CONTROL 179 The Time Factor 179 Surface Pressures 180 Downhole Stresses 180 Procedural Complexity 182 Formulae Used in Kick Control Procedures 182 Kick Control Methods 184

The Driller's Method (Two Circulations) 185 The Engineer's Method (One Circulation) 190

The Concurrent Method 192 KICK TOLERANCE 193 "DIFFERENTIAL" KICK TOLERANCE 197

Appendix A: Fonnulae 201 Appendix B: Rw Detennination from SP 209

Appendix C: Nomograms 215 Glossary 219 References 223 Index 227

vii

ILLUSTRATIONS 1-1 Logging unit systems and information flow 3 1-2 Drilling Data Pressure log 5

1-3 Temperature Data log 6 1-4 Wireline Data Pressure log 7 1-5 Shale Data Pressure log 8 1-6 Pressure Evaluation log 9

1-7 GEMDAS Logging Report form 10

2-1 Pore Pressure-Normal, Abnormal and Subnormal 11

2-2 Idealized diagram of zones of abnormal pore pressures and development of overthrust and thrust sheet on the flank of a geosyncline 12

2-3 Typical en-echelon hydraulic fractures found in stressed or tectonically deformed rocks 14

2-4 Porosity/Depth relationship for a typical compacting clay sequence 16

2-5 Bulk density reversal in an abnormal pore pressure zone, with the thoretical and actual compaction paths 17

2-6 Typical pore pressure-depth plot of compaction disequilibrium geopressures. Overall gradient is parallel to overburden pressure gradient 18

2-7 Pressure-Temperature-Density diagram for fresh water. After Barker (1972) 2-8 Pore pressure increases with aquathermal effect 21

2-9 Changes in ionic substitution in three-layered sheets 26 2-lO Hydrogen-bonded water and exchangeable cations 27

2-11 Dynamic structuring of water 28

2-12 Hypothetical dehydration curves of montmorillonite sediments with depth and temperature 30

2-13 Diagenetic stages in the alteration of montmorillonite to illite 31

2-14 Geopressures caused by tectonic compressional folding 34

2-15 Overlapping potentiometric surfaces with normally pressured and geopressured zones 37

3-1 Hydrostatic pressure (P) is a function of the density and vertical height of the fluid column 44

3-2 Variation of hydrostatiC pressure with formation water salinity 46

3-3 Typical densities of rocks and fluids 48 3-4 Typical overburden pressure gradients 51

3-5 ELOS Overburden Gradient Calculation 53 3-6 Relationship between normal pore pressure gradient, normal formation balance

gradient, formation balance gradient, and equivalent mud density 53 3-7 Normal FBG calculation worksheet 56

3-8 Actual formation fluid density and normal FBG (data from Figure 3-7) 57 3-9 Actual formation fluid density and normal FBG 60 3-10 Effective overburden pressure in normal and geopressured formations 61

3-11 ELOS Swab and Surge Calculation 66

x

3-12 ELOS SP log analysis 72 4-1 Interval transit time variations with compaction and lithology 75

4-2 Interval transit time variation with formation pore pressure 76 4-3 Geopressure evaluation from interval transit time 76 4-4 The effect of differential pressure on gas show magnitude 78 4-5 Cavings produced due to underbalanced drilling 85

4-6 Cavings produced due to stress relief and compressional failure 86 4-7 Typical cavings produced by underbalance and stress relief 86 4-8 How drillability is affected by differential pressure in hard formations 89 4-9 Highly stylized curves showing typical response in transition and

geopressured zones 91 4-10 Schematic Dxc responses 95 4-11 Example of formation pore pressure gradients from the Dxc plot 97

4-12 Ideal clay density responses in geopressured zones caused by different mechanisms 101

4-13 Shale factor can be a good indicator of large changes in clay composition, aiding geological interpretation 106

4-14 Shale factor response in geopressures, caused by compaction disequilibrium or montmorillonite dehydration 107

4-15 Distribution of heatflow and isotherms around an insulating (geopressured) zone 109

4-16 Theoretical change of geothermal gradient through an insulating· (high porosity/geopressured) zone 110

4-17 Expected flowline temperature response on drilling through a geopressured interval 110

4-18 Plots of flowline temperature, smoothed end-to-end plot and trend-to-trend plot 112

4-19 Horner-type plot for graphic solution of true bottomhole temperature 114 4-20 Horner plot of linear X-axis. Note less scatter in points 114

4-21 Location of Temp Plates in deviation survey tool 115 4-22 Relationship between FLT, Temp Plate, and BHT data for Southeast

Asia well 117 4-23 Differential mud conductivity and delta chloride log 118 4-24

4-25 4-26 4-27

Transit times for matrices and fluids 120

Geopressure evaluation using the equivalent depth method and sonic plot Formation resistivity typical area trend lines 127

Estimation of Bit Tooth Wear l33 5-1 Stress regimes in relaxed and tectonic areas 142 5-2 Matrix stress coefficient (ki) with depth for Gulf Coast Sands 145

5-3 ki is obtained from the depth at which (J is normal 145

5-4 Empirical "Poisson's ratio" curves with depth for Gulf Coast sands 147

122

5,-5 Extremely high tensile stress is produced at the tip of a crack when the pressure within the borehold is approximately 5 % greater than the minimum horizontal stress 157

5-6 Typical fracture-test plot, showing the point at which the minimum horizontal stress becomes balanced by the total pressure within the borehole (B). If B = D, then the volume of mud returned on bleed-off should be equal to the initial volume pumped 159

5-7 Suggested Poisson's ratios for different lithologies 161 5-8 Typical overburden curve from an offshore well 163 5-9 Hypothetical changes in 0'1' O't and O'H with depth and constant pore pressure

gradient. Resultant fracture pressure curve is shown 164 5-10 Hypothetical changes in 0'1, O't and O'H with depth and changing pore pressure

gradient. Note that all stresses are affected by the pore pressure. fracture pressure curve is shown 165

5-11 ELOS fracture gradient calculation 166 5-12 Typical Swab/Surge printout for a 15,000-ft well with a mud density of

16.5 lb/gal, a PV of 35 and yP of 20 173 5-13 Trip Monitor Printout 176 5-14 Trip Condition Log 177 5-15 Gas expansion on pressure reduction 181 5-16 Different surface pressures produced during the one- and two-circulation

kill methods 181 5-17 Kick composition from influx gradient 183 5-18 ELOS Kick and Kill Analysis program 186 5-19 ELOS Kick and Kill Monitor program 187 5-20 Drillpipe/pressure plot when kill mud is pumped down the drillpipe 188 5-21 First circulation pressures during the driller's method. Drillpipe pressure is kept

constant by gradually opening the choke. As gas reaches the surface, it may be necessary to slow the pump rate in order to keep the drillpipe pressure constant 189

5-22 Second circulation during driller's method: kill mud is pumped around 189 5-23 Drillpipe/pt:essure curve during engineer's kill method 190 5-24 Annulus prssure curve during engineer's kill method. Note casing pressure

reduction after kill mud has reached the bit 191 5-25 Schematic of example pressures and fluid positions during the engineer's

kill method '191 5-26 Typical irregular drillpipe pressure reductions during concurrent method 192 B-1 SP Correction Charts (for representative cases) 209 B-2 SP Correction Charts (empirical) 210 B-3 Resistivity nomograph for NaCl solutions 211 B-4 Rw versus Rweq and formation temperature 212 B-5 Rweq determination from the SSP (clean formations) 213 C-1 Formation fluid salinity and density 214 C-2 Hydrostatic pressure of fluid columns 215 C-3 Dxc nomogram 216 C-4 Geothermal gradient and Bottomhole temperature 217

xi

PREFACE The objectives of this book are: (1) to educate the prospective Pressure Evaluation Geologist to a basic level of expertise; (2) to provide a reference tool for the experienced geologist; and (3) to foster constructuve thought and continued development of the field geologist.

Despite the incorporation of many new ideas and concepts, elaboration of the more re­cent concepts is limited due to space considerations. It is hoped that the geologist will follow up via the literature referenced at the end of each chapter.

Easy reference is provided by the detailed table of contents and index. A glossary of terms, definitions, and formulae adds to the usefulness of this reference text.

ACKNOWLEDGMENTS FOR FIGURES Figure 2-7 is reprinted by permission of the AAPG from Barker, 1972.

Figure 4-21 is courtesy of Totco

Figure 5-2 is reprinted by permission of the Oil and GasJournal from Matthews and Kelly, 1967.

Figure 5-4 is reprinted by permission of the SPE-AIME from the Journal of Petroleum Technology from Eaton, © 1969.

Figure 5-5 is reprinted by permission of the SPE-AIME from Hubbert and Willis, © 1957.

Figures B-1-B-5 are courtesy of Schlumberger Well Services

Figure C-3 is reprinted by permission of the SPE-AIME from the Journal of Petroleum Technology from Jordan and Shirley, © 1966.