Petroleum geology exploration 3rd ed pennwell corp 2012 3

Norman J. Hyne, Ph.D.

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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
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Library of Congress Cataloging-in-Publication Data

Hyne, Norman J.
Nontechnical guide to petroleum geology, exploration, drilling, and production
/ Norman J. Hyne. -- 3rd ed.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-59370-269-4
1. Petroleum--Geology. 2. Petroleum engineering. 3. Petroleum--Prospecting.
I. Title.
TN870.5.H9624 2011
665.5--dc23
2011038698
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
1 2 3 4 5  16 15 14 13 12

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Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
1 The Nature of Gas and Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Petroleum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
The Chemistry of Oil and Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Crude Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Natural Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Reservoir Hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2 The Earth’s Crust—Where We Find It . . . . . . . . . . . . . . . . . . . . . . . . 13
Rocks and Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Types of Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Structure of the Earth’s Crust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3 Identification of Common Rocks and Minerals . . . . . . . . . . . . . . . 25
Identification of Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Identification of Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4 Geological Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Absolute Age Dating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Relative Age Dating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
The Geologic Time Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Earth History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5 Deformation of Sedimentary Rocks . . . . . . . . . . . . . . . . . . . . . . . . . 47
Weathering, Erosion, and Unconformities . . . . . . . . . . . . . . . . . . . . . . . . 47
Anticlines and Synclines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Domes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Homoclines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Fractures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
6 Ocean Environment and Plate Tectonics . . . . . . . . . . . . . . . . . . . . . 67
Continental Margins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Deep Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Ocean Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Earth’s Interior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Continental Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Seafloor Spreading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Plate Tectonics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Failed Arm Basins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Middle East Oil Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

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7 Sedimentary Rock Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Basin Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Sedimentary Rock Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Subsurface Rock Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
8 Mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Topographic Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Geologic Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Base Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Subsurface Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
9 Source Rocks, Generation, Migration, and Accumulation
of Petroleum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Source Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Accumulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

Age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Reservoir Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
10 Reservoir Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Sandstone Reservoir Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Dune Sandstones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
Shoreline Sandstones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
River Sandstones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Delta Sandstones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Granite Wash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Carbonate Reservoir Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
Reefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
Limestone Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
Karst Limestone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Chalk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Dolomite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Fractured Reservoirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
11 Petroleum Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Structural Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Stratigraphic Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
Combination Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
12 Petroleum Exploration—Geological and Geochemical . . . . . . . . 193
Seeps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
Geological Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
Geochemical Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
Plays and Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

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 Contents

13 Petroleum Exploration—Geophysical . . . . . . . . . . . . . . . . . . . . . . . 211
Gravity and Magnetic Exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
Seismic Exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
14 Drilling Preliminaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Land and Leasing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Foreign Contracts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
Authority for Expenditure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
Economic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
Drilling Contracts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
Joint Operating Agreements and Support Agreements . . . . . . . . . . . 241
Site Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
Types of Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Government Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
Cable Tool Rigs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
15 Drilling a Well—The Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
Hoisting System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
Rotating System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
Circulating System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
Drilling Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
Modern Rotary Drilling Rigs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
16 Drilling Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
Subsurface Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279

Problems While Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
Dry Holes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
17 Drilling Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
Vertical Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
Directional Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
Well Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
Air and Foam Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
18 Testing a Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
Sample or Lithologic Log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
Drilling-Time Log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
Mud Log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
Wireline Well Logs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
Measurements-While-Drilling and Logging-While-Drilling . . . . . . . 338
Drillstem Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
Repeat Formation Tester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
19 Completing a Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
Casing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
Bottom-Hole Completions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353

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Expandable Casing and Liner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356

Tubing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356
Wellhead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
Chokes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
Surface Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
Sucker-rod Pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
Gas Lift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
Electric Submersible Pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
Hydraulic Pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
Multiple Completions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
Intelligent Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372
20 Surface Treatment and Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
Flowlines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
Gas Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379
Storage and Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
Modern Lease Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
21 Offshore Drilling and Completion . . . . . . . . . . . . . . . . . . . . . . . . . 389
Mineral Rights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389
Offshore Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390
Exploratory Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
Spudding an Offshore Exploratory Well . . . . . . . . . . . . . . . . . . . . . . . . 395
Developmental Drilling and Production . . . . . . . . . . . . . . . . . . . . . . . . 397
Subsea Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
Subsea Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
Unstable Sea Bed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406
22 Workover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
Well Intervention on Offshore Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
Preparing the Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415
Well Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415

23 Reservoir Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
Reservoir Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
Maximum Efficient Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430
24 Petroleum Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431
Well and Reservoir Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431
Well Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432
Cased-Hole Logs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434
Production Logs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
Decline Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
Bypassing and Coning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437

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 Contents

Cycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439
Well Stimulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439
Disposal of Oilfield Brine and Solution Gas . . . . . . . . . . . . . . . . . . . . . 443
Surface Subsidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445
Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
Production Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
Stranded Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448
25 Reserves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
Recovery Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451

Shrinkage Factor and Formation Volume Factor . . . . . . . . . . . . . . . . . 452
Reserve Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454
Types of Reserves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458
26 Improved Oil Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
Waterflood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
Enhanced Oil Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468
Unitization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468
Plug and Abandon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468
27 Unconventional Oil and Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471
Tight Formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471
Coal Bed or Coal Seam Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478
Oil Shales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
Tar Sands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
Gas Hydrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485
Figure References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655
Unit Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 661
Oil and Gas Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667

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Preface
This book contains an enormous amount of useful information on
the upstream petroleum industry. It is designed for easy reading, and the
information is readily accessible. The introductory chapter should be read
first. It is an excellent overview that shows how everything in petroleum
geology, exploration, drilling, and production is interrelated.
Each subject has its own chapter that is well illustrated with figures and
plates. The rocks, minerals, and seismic examples are in color. Industry
terms are defined in the text and shown in italics. All measurements are
in both English and metric units. A useful index and extensive glossary
are located at the back of the book, as well as an interesting list of
petroleum records.

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Introduction
Both crude oil and natural gas occur naturally in subsurface deposits.
Crude oil is a black liquid that is sold to refineries to be refined into

products such as gasoline and lubricating oil. Natural gas is a colorless,
odorless gas that is sold to gas pipelines to be transported and burned for
its heat content. There are many different types of crude oils and natural
gases, some more valuable than others. Heavy crude oils are very thick and
viscous and are difficult or impossible to produce. Light crude oils are very
fluid, relatively easy to produce, rich in gasoline, and more valuable. Some
natural gases burn with more heat than others and are more valuable. Some
natural gases also contain almost pure liquid gasoline called condensate
that separates from the gas when it is produced. Condensate is almost
as valuable as crude oil. Sulfur is a bad impurity in both natural gas and
crude oil. Sour crude oils contain sulfur, and sour natural gases contain
hydrogen sulfide and are less valuable. Crude oil is measured by volume in
barrels (bbl). Natural gas is measured by volume in thousands of cubic feet
(Mcf) and by heat content in British thermal units (Btu).
In order for there to be a commercial deposit of natural gas or crude
oil, three important geological conditions must be met. First, there must
be a source rock in the subsurface of that area that generated the gas or
oil at some time in the geological past. Second, there must be a separate,
subsurface reservoir rock that holds the gas or oil. When we drill a well into
that reservoir rock, the gas and oil are able to flow through the reservoir
rock and into our well. Third, there must be a trap on the reservoir rock to
concentrate the gas or oil into commercial quantities.
The crust of the earth in oil- and gas-producing areas is composed of
sedimentary rock layers. Sedimentary rocks can be source and reservoir
rocks for gas and oil. These rocks are called sedimentary rocks because
they are composed of sediments that were formerly loose particles such
as sand grains, mud, and seashells or salts that precipitated out of water.
Sedimentary rocks are millions of years old and were deposited when the
sea level rose and covered the land many times in the past. These sediments
are relatively simple materials such as sands deposited along beaches, mud

deposited on the sea bottom, and beds of seashells. Ancient sediments,
piled layer upon layer, form the sedimentary rocks that are now sandstones
composed of sand grains, shales composed of mud particles, and limestones
composed of seashells. These are drilled to find and produce oil and gas.
The source of gas and oil is the organic matter—dead plant and animal
material—that is buried and preserved in some ancient sedimentary rocks.
The most common, organic-rich sedimentary rock and the source rock
for most gas and oil is black shale. It was deposited as organic-rich mud

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on ancient ocean bottoms. In the subsurface, temperature and time turn
organic matter into crude oil. As the source rock is covered with more
sediments and buried deeper in the earth, it becomes hotter and hotter.
Crude oil starts to form at about 150°F (65°C) at a depth of about 7,000 ft
(2,130 m) below the surface of the land (fig. I–1). It is generated from there
down to a depth of about 18,000 ft (5,500 m) at about 300°F (150°C). The
reactions that change organic matter into oil are complex and take a long
time. If the source rock is buried deeper where the temperatures are above
300°F (150°C), the remaining organic matter can generate natural gas.

Fig. I–1. Generation and migration of gas and oil
Gas and oil are relatively light in density compared to the water that
also occurs in subsurface sedimentary rocks. After oil and gas form, they
rise due to buoyancy through fractures in the subsurface rocks. The rising

gas and oil can intersect reservoir rock, which is a sedimentary rock layer
that contains billions of tiny spaces called pores. A common reservoir rock
is sandstone, composed of sand grains like those on a beach. Sand grains
are like spheres—there is no way the grains will fit together perfectly. There
are pore spaces between the sand grains on a beach and in a sandstone rock.
Limestone, another common reservoir rock, is often deposited as shell
beds or reefs, and there are pores between the shells and corals. Because
limestone is soluble, there can also be solution pits in the limestone.
Porosity is the percent of reservoir rock that is pore space, and it is
commonly 10 to 30%. The gas and oil flow into the pores of the reservoir
rock layer. Because the reservoir rock also contains water, the gas and oil
will continue to rise by flowing from pore to pore to pore up the angle of the

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 Introduction

reservoir rock layer toward the surface. The movement of gas and oil up the
angle of the reservoir rock toward the surface is called migration. The ease
with which the gas and oil can flow through the rock is called permeability.
Because of migration, the gas and oil can end up a considerable distance,
both vertically and horizontally, from where they were originally formed
(fig. I–1).
As the gas and oil migrates up along the reservoir rock, it can encounter

a trap. A trap is a high point in the reservoir rock where the gas or oil is
stopped and concentrated. One type of trap is a natural arch in the reservoir
rock (fig. I–2) called a dome or anticline. In the trap, the fluids separate
according to their density. The gas is the lightest and goes to the top of
the trap to fill the pores of the reservoir rock and form the free gas cap.
The oil goes to the middle to fill the pores and form the oil reservoir. The
saltwater, the heaviest, goes to the bottom. To complete the trap, a caprock
must overlie the reservoir rock. The caprock is a seal that does not allow
fluids to flow through it. Without a caprock, the oil and gas would leak up
to the surface. Two common sedimentary rocks that can be caprocks are
shale and salt.

Fig. I–2. Cross section of a subsurface petroleum trap
Most gas and oil deposits are located in basins where sedimentary
rocks are relatively thick. Subsurface deposits of gas and oil are found by
locating traps. In some areas, the rock layers that crop out on the surface
can be projected into the subsurface to discover traps (fig. I–3). Today,
these surface rocks can be mapped using photographs from airplanes and
satellites. In the subsurface, the rocks in different wells that have already

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been drilled are matched by correlation to make cross sections, and maps
of the depths to the top of subsurface reservoir rocks and their thickness
are drawn.
Seismic exploration is commonly used today to locate subsurface traps.
The seismic method uses a source and detectors (fig. I–4). The source, such
as dynamite, is located on or near the surface and gives off an impulse
of sound energy into the subsurface. The sound energy bounces off
sedimentary rock layers and returns to the surface to be recorded by the
detectors. Sound echoes are used to image the shape of subsurface rock
layers and find traps.

Fig. I–3. Rock outcrops on surface above a dome

Fig. I–4. The seismic method showing sound impulse bouncing off
subsurface rock layer

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The only way to know for sure if a trap contains commercial amounts
of gas and oil is to drill an exploratory or wildcat well. Many wildcat wells
are dry holes with no commercial amounts of gas or oil. The well is drilled
using a rotary drilling rig (fig. I–5). There can be thousands of feet of steel

drillpipe with a bit on the end, called the drillstring, suspended in the well.
By rotating the drillstring from the surface, the bit on the bottom is turned
and cuts the hole. As the well is drilled deeper, every 30 ft (9.1 m) drilling
is stopped and another section of drillpipe is screwed on the drillstring to
make it longer. The power to the rig is supplied by diesel engines. A steel
tower above the well—the derrick or mast—along with a hoisting line and
pulley system, is used to raise and lower equipment in the well.

Fig. I–5. Parts of a rotary drilling rig
An important system on the rig is the circulating mud system. Drilling
mud, usually made of clay and water, is pumped down the inside of the
drillpipe where it jets out of nozzles on the bit and returns up the outside

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of the drillpipe to the surface (fig. I–6). The drilling mud removes the rock
chips made by the bit, called well cuttings, from the bottom of the hole and
prevents them from clogging up the bottom of the well. The well is always
kept filled to the top with the heavy drilling mud as it is being drilled. The
pressure of the drilling mud prevents any fluids such as water, gas, and oil
from flowing out of the subsurface rocks and into the well. If gas and oil
flowed up onto the floor of the drilling rig, they could catch fire, causing

a blowout. Even if only water flowed out of the surrounding rock into the
well, the sides of the well could cave in, and the well could be lost. As the
well is being drilled, it can be drilled straight down, out at an angle as a
deviated well, or out horizontally as a horizontal well through the oil and
gas reservoir (fig. I–7). Horizontal wells typically produce oil and gas at a
greater rate than vertical wells.

Fig. I–6. Well cutting removal by circulating
drilling mud on bottom of well

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A

B

C

Fig. I–7. Types of wells: (a) straight hole, (b) deviated well, and (c) horizontal well
Offshore wells are drilled into sedimentary rocks on the ocean bottom
the same way as on land. For offshore exploratory wells, the rig is mounted
on a barge, floating platform, or ship that can be moved. Once an offshore

field is located by drilling, a production platform is installed to drill the
rest of the wells and produce the gas and oil. The production platform can
be fixed with legs that sit on the ocean bottom or floating with anchors and
cables to hold it in position.
Because drilling mud keeps gas and oil in the rocks, a subsurface
deposit of gas or oil can be drilled without any indication of the gas or oil.
To evaluate the well after it has been drilled, it must be logged, and well
logs must be created. A well log is a record of the rocks and their fluids in
the well. A mud logger is a service company that makes a mud log as the
well is being drilled. The mud logger carefully analyzes both the drilling
mud and well cuttings for traces of crude oil and natural gas. Another
service company drives a logging truck out to the well after the well is
drilled to make a wireline well log. A long cylinder containing instruments
called a logging tool is unloaded from the truck and run down the well
on a wireline (fig. I–8). As the logging tool is brought back up the well, the
instruments remotely sense the electrical, sonic, and radioactive properties
of the surrounding rocks and their fluids. These measurements are
recorded on a long strip of paper called a wireline well log (fig. I–9) in the
logging truck and are also digitized, encoded, and sent by radio telemetry

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to a data center. Well logs are used to determine the composition of each
rock layer, whether the rock layer has pores and how much is pore space,
and what fluid (water, gas, or oil) is in the pores. Depending on the test
results, the well can be plugged and abandoned as a dry hole or completed
as a producer.


Fig. I–8. Well logging with a logging tool run down
a well on a wireline

Fig. I–9. A wireline well log

To complete the well, many sections of large-diameter steel pipe called
casing are screwed together to form a long length of pipe called a casing
string that is lowered down the hole. Wet cement is then pumped between
the casing and well walls and allowed to set (fig. I–10) during a cement job.
This stabilizes the hole. The casing is done in stages called a casing program,
during which the well is drilled, cased, drilled deeper, cased again, drilled
deeper, and cased again (fig. 1–11). In order for the gas or oil to flow into the
well, the well is either completed open-hole or with perforated casing. In an
open-hole completion (fig. I-11a), the casing string is cemented down to
the top of the reservoir rock and the bottom left open. In perforated casing
completion (fig. I-11b), the casing is cemented through the reservoir rock

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 Introduction

and the casing is shot with explosives to form holes called perforations.
A long length of narrow-diameter steel pipe called a tubing string is then
suspended down the center of the well. The produced fluids (water, gas,
and oil) are brought up the tubing string to the surface to prevent them
from touching and corroding the casing string that is harder to repair.
An expandable rubber device called a tubing packer on the bottom of the
tubing string keeps the tubing string central in the well and prevents the
fluids from flowing up the outside of the tubing (fig. 1–11). The tubing
string is relatively easy to repair during a workover.

Casing

Cement

Fig. I–10. Casing cemented into a well

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A

Tubing

B

Tubing
packer

Perforation

Casing

Fig. I–11. Wells with casing programs of smaller and smaller diameter casing strings.
The two bottom-hole completions are (a) open-hole and (b) perforated casing.
A tubing string and tubing packer are shown.
In all gas wells, gas flows to the surface by itself. There are some oil
wells, usually only early in the development of the oil field, in which the
oil has enough pressure to flow up to the surface. Gas wells and flowing
oil wells are completed on the surface with a vertical structure of pipes,
fittings, gauges, and valves called a Christmas tree, which is used to control
the flow (fig. I–12a).
Most oil wells, however, do not have enough pressure for the oil to
flow to the surface and the oil will fill the bottom of the well only up to
a certain level. A sucker-rod pump or beam-pumping unit (fig. I–12b) is
commonly used to lift the oil and water up the tubing string to the surface.
A downhole pump on the bottom of the tubing string is driven by the
surface beam-pumping unit. A motor causes a beam on a pivot, called the
walking beam, to pivot up and down. The walking beam is connected to a
downhole pump by a long, narrow, sucker-rod string that runs down the

center of the tubing string (fig. 1–12b). The pump lifts the oil and water up
the tubing string to the surface.

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Fig. I–12. Surface completions (a) gas well and flowing oil well, (b) oil well with
beam-pumping unit
On the surface, gas is prepared for delivery to a gas pipeline by
gas-conditioning equipment that removes impurities such as water vapor
and corrosive gases. Valuable natural gas liquids, such as condensate, are
removed from the gas in a natural gas processing plant and sold separately.
The gas can then be sold to a gas pipeline. For oil, a long vertical or
horizontal steel tank called a separator is used to separate natural gas that
bubbles out of the oil and the saltwater that settles to the bottom (plate
I–1). The oil is then stored in steel stock tanks until it is sold to a refinery.
The production rate from wells can be increased by acid and frac jobs.
Acid is pumped down a well to dissolve some of the reservoir rock adjacent
to the wellbore during an acid job. During a frac job, the reservoir rock is
hydraulically fractured with a liquid pumped under high pressure down
the well. Propping agents such as sand grains are pumped down the well
with the frac fluid to hold the fractures open and allow the oil and gas to
readily flow into the well. Periodically, production from the well must be

interrupted for repairs or to clean out the well during a workover. A service
company drives out to the well with a production unit to do the workover.
As fluids are produced from the subsurface reservoir, pressure on the
remaining fluids drops. The production rate of oil and gas wells and the
whole field decreases with time on a decline curve. Ultimate recovery of
gas from a gas reservoir is often about 80% of the gas in the reservoir. Oil
reservoirs, however, are far more variable and less efficient. They range

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from 5 to 80% recovery but average only 35% of the oil in the reservoir. This
leaves 65% of the oil remaining in the pressure-depleted reservoir. After
the reservoir pressure has been depleted in an oil field, waterflood and
enhanced oil recovery can be attempted to produce some of the remaining
oil. During a waterflood, water is pumped under pressure down injection
wells into the depleted reservoir to force some of the remaining oil through
the reservoir rock toward producing wells (fig. I–13). Enhanced oil recovery
involves pumping fluids such as carbon dioxide, nitrogen, or steam down
injection wells to obtain more production.

Plate I–1. Oil well with separator and stock tanks

Fig. I–13. A waterflood

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Recently, an enormous amount of natural gas has been produced from
shales with a special technique. A shale is a very fine-grained rock. Even
though many shales contain gas, shale has no permeability and the gas
cannot flow through the shale into a well. Horizontal wells drilled into
these shales, however, are used for a special frac job called a slickwater frac,
which allows the gas to flow through the shale and into the well.
After the well has been depleted, it is required by law to be properly
plugged and abandoned to prevent pollution. Cement must be poured
down the well to seal the depleted reservoir and to protect any subsurface
freshwater reservoirs. A steel plate is then welded to the top of the well and
the well is covered with soil.

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