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RESERVOIR ENGINEERING H A N D B O O K Third Edition This฀Page฀Is฀Intentionally฀Left฀Blank RESERVOIR ENGINEERING H A N D B O O K Third Edition Tarek Ahmed . . . . . . . . AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO . . Gulf Professional Pub...

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RESERVOIR ENGINEERING

H A N D B O O K Third Edition

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RESERVOIR ENGINEERING H A N D B O O K Third Edition

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Tarek Ahmed

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AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Gulf Professional Publishing is an imprint of Elsevier

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Gulf Professional Publishing is an imprint of Elsevier 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA Linacre House, Jordan Hill, Oxford OX2 8DP, UK Copyright © 2006, Elsevier Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone: (+44) 1865 843830, fax: (+44) 1865 853333, E-mail: [email protected]. You may also complete your request on-line via the Elsevier homepage (http://elsevier.com), by selecting “Support & Contact” then “Copyright and Permission” and then “Obtaining Permissions.”

⬁ Recognizing the importance of preserving what has been written, Elsevier prints its books on acid-free paper whenever possible.

Library of Congress Cataloging-in-Publication Data Application submitted

British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. ISBN 13: 978-0-7506-7972-5 ISBN 10: 0-7506-7972-7 For information on all Gulf Professional Publishing publications visit our Web site at www.books.elsevier.com 06 07 08 09 10 11

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Printed in the United States of America

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This book is dedicated to my children, Justin, Brittany, Carsen, and Jennifer Ahmed. I do hope that at least one of them will grow up to be a petroleum engineer in the future.

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CONTENTS

Acknowledgments, xi Preface to the Third Edition, xiii Preface to the Second Edition, xiv Preface to the First Edition, xv

1 Fundamentals of Reservoir Fluid Behavior . . . . . . . . . . .

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Classification of Reservoirs and Reservoir Fluids, 1; Problems, 27; References, 27

2 Reservoir-Fluid Properties . . . . . . . . . . . . . . . . . . . . . . . . . 29 Properties of Natural Gases, 29; Behavior of Ideal Gases, 30; Behavior of Real Gases, 36; Effect of Nonhydrocarbon Components on the Z-Factor, 44; Correction for High-Molecular Weight Gases, 49; Direct Calculation of Compressibility Factors, 54; Compressibility of Natural Gases, 59; Gas Formation Volume Factor, 65; Gas Viscosity, 67; Methods of Calculating the Viscosity of Natural Gases, 68; Properties of Crude Oil Systems, 75; Methods of Calculating Viscosity of the Dead Oil, 115; Methods of Calculating the Saturated Oil Viscosity, 117; Methods of Calculating the Viscosity of the Undersaturated Oil, 119; Properties of Reservoir Water, 124; Problems, 126; References, 133

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3 Laboratory Analysis of Reservoir Fluids . . . . . . . . . . . . . 136 Composition of the Reservoir Fluid, 137; Constant-Composition Expansion Tests, 137; Differential Liberation (Vaporization) Test, 149; Separator Tests, 152; Extrapolation of Reservoir Fluid Data, 164; Laboratory Analysis of Gas Condensate Systems, 171; Problems, 184; References, 188

4 Fundamentals of Rock Properties . . . . . . . . . . . . . . . . . . . 189 Porosity, 190; Saturation, 195; Wettability, 199; Surface and Interfacial Tension, 200; Capillary Pressure, 203; Permeability, 227; Rock Compressibility, 254; Net Pay Thickness, 260; Reservoir Heterogeneity, 261; Areal Heterogeneity, 274; Problems, 281; References, 286

5 Relative Permeability Concepts . . . . . . . . . . . . . . . . . . . . . 288 Two-Phase Relative Permeability, 289; Relative Permeability Ratio, 308; Dynamic Pseudo-Relative Permeabilities, 311; Normalization and Averaging Relative Permeability Data, 313; Three-Phase Relative Permeability, 320; Problems, 329; References, 330

6 Fundamentals of Reservoir Fluid Flow . . . . . . . . . . . . . . . 331 Types of Fluids, 332; Flow Regimes, 334; Reservoir Geometry, 336; Number of Flowing Fluids in the Reservoir, 339; Fluid Flow Equations, 340; Steady-State Flow, 342; Unsteady-State Flow, 373; Constant-Terminal-Pressure Solution, 384; Constant-Terminal-Rate Solution, 384; Pseudosteady-State Flow, 413; Principle of Superposition, 442; Transient Well Testing, 453; Problems, 476; References, 482

7 Oil Well Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484 Vertical Oil Well Performance, 484; Horizontal Oil Well Performance, 528; Problems, 542; References, 544

8 Gas Well Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546 Vertical Gas Well Performance, 546; Horizontal Gas Well Performance, 577; Problems, 580; References, 581

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9 Gas and Water Coning . . . . . . . . . . . . . . . . . . . . . . . . . . . 583 Coning, 584; Coning in Vertical Wells, 587; Breakthrough Time in Vertical Wells, 620; After Breakthrough Performance, 624; Coning in Horizontal Wells, 629; Horizontal Well Breakthrough Time, 638; Problems, 646; References, 648

10 Water Influx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650 Classification of Aquifers, 651; Recognition of Natural Water Influx, 654; Water Influx Models, 655; Problems, 728; References, 731

11 Oil Recovery Mechanisms and the Material Balance Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733 Primary Recovery Mechanisms, 734; The Material Balance Equation, 752; Problems, 806; References, 809

12 Predicting Oil Reservoir Performance . . . . . . . . . . . . . . 810 Phase 1. Reservoir Performance Prediction Methods, 811; Phase 2. Relating Reservoir Performance to Time, 850; Problems, 853; References, 854

13 Gas Reservoirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855 The Volumetric Method, 856; The Material Balance Method, 859; Material Balance Equation as a Straight Line, 874; Abnormally Pressured Gas Reservoirs, 880; Problems, 906; References, 908

14 Principles of Waterflooding. . . . . . . . . . . . . . . . . . . . . . . . 909 Factors to Consider in Waterflooding, 910; Optimum Time to Waterflood, 915; Effect of Trapped Gas on Waterflood Recovery, 917; Selection of Flooding Patterns, 927; Overall Recovery Efficiency, 932; I. Displacement Efficiency, 934; II. Areal Sweep Efficiency, 985; III. Vertical Sweep Efficiency, 1041; Methods of Predicting Recovery Performance for Layered Reservoirs, 1058; Waterflood Surveillance, 1069; Problems, 1085; References, 1094

15 Vapor-Liquid Phase Equilibria . . . . . . . . . . . . . . . . . . . . 1096 Vapor Pressure, 1096; Equilibrium Ratios, 1099; Flash Calculations, 1103; Equilibrium Ratios for Real Solutions, 1107; Equilibrium Ratios for the Plus Fraction, 1120; Applications of the Equilibrium

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Ratio in Reservoir Engineering, 1122; Equations of State, 1154; Applications of the Equation of State in Petroleum Engineering, 1194; Splitting and Lumping Schemes of the Plus-Fraction, 1207; Problems, 1225; References, 1229

16 Analysis of Decline and Type Curves . . . . . . . . . . . . . . . 1235 Decline-Curve Analysis, 1235; Type-Curve Analysis, 1264; Problems, 1333; References, 1335

Appendix, 1338 Index, 1351 About the Author, 1360

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ACKNOWLEDGMENTS

Much of the material on which this book is based was drawn from the publications of the Society of Petroleum Engineers (SPE). Tribute is due to the SPE and the petroleum engineers, scientists, and authors who have made numerous and significant contributions to the field of reservoir engineering. This book reflects my style of teaching during my tenure at Montana Tech of the University of Montana and my understanding of the subject of reservoir engineering. I would like to thank all my former students at Montana Tech for putting up with me and my Egyptian temper; it was fun. I am sure they will remember that I did my best to teach them reservoir engineering and my sincere desire to help them with their careers. I hope that my friends and colleagues in academia will enjoy this edition of the book. I know most of them were so surprised to see me crossing the line and joining the “dark side” after years of teaching at Montana Tech, but surprisingly, I am enjoying the dark side very much, so you guys take it easy on me next time. Thanks to Dr. Bob Chase, Dr. Tom Blasingame, Dr. J. Tiab, and Dr. F. Civan for their constructive (I think) criticism and discussions. I would also like to express my deep thanks to Anadarko Petroleum Corporation for granting me permission to publish this book and, in particular, Bob Daniels, Senior VP for International Exploration and Production, and Mark Pease, Senior VP for North America Exploration and Production. xi

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For the past 31⁄2 years, I have had the pleasure of knowing and working with Anadarko’s Chief Technical Engineer, Scott Albertson. I always enjoy our “painful” early-morning technical discussions, as well as exchanging ideas and bouncing mathematical derivations off him, even when his mind is floating somewhere in la-la land. Scott is capable of exhibiting many different facial expressions that he has mastered over the years, and they are, indeed, more powerful than words. Usually, many of his facial expressions can give me the clue, the light, and perhaps the answer to my question (seldom, but remotely possible, in the neighborhood of P-1). I would like also to thank my friend, Senior Staff Reservoir Engineer, Brian Roux, for sharing his considerable knowledge and experience with me and for reading the first few pages of the manuscript (I think he has read the first 7 pages) at Landry’s. The truth is that Scott and Brian are two of the brightest engineers that I have ever worked with. I would like to thank Aydin Centilmen for helping me learn VIP software; I owe him a big lunch at Taco Bell for that. I also would like to thank the following engineers for their support and technical advice: chief engineer, Steve Martin; Julie Struble (only 5 feet tall, but a pure powerhouse); Tom Bergstresser (Tom is not an engineer; he has a PhD in Geology, but nobody is perfect, of course); manager of CBM group, Brad Miller; senior reservoir engineer, Walt Dobbs; acquisitions manager, Craig Walter; manager of EOR group, Dane Cantwell; and senior engineering advisor, Frank Lim. I would like to thank the editorial staff—in particular, Christine Brandt of SPI Publisher Services—for their work and professionalism. Lastly, this edition of the book could not have been completed without my special friend, Wendy. I would like to thank Wendy for her superb typing, hard work, and encouragement.

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PREFACE TO THE THIRD EDITION

To make the third edition of this textbook as complete as possible, I have included the following: a new chapter on decline curve and type curve analysis, a section on tight and shallow gas reservoirs, and waterflood surveillance techniques. Many of my colleagues have provided me with valuable recommendations and suggestions that I have included through the textbook to make it more comprehensive in treating the subject of reservoir engineering.

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PREFACE TO THE SECOND EDITION

I have attempted to construct the chapters following a sequence that I have used for several years in teaching three undergraduate courses in reservoir engineering. Two new chapters have been included in this second edition; Chapter 14 and 15. Chapter 14 reviews principles of waterflooding with emphasis on the design of a waterflooding project. Chapter 15 is intended to introduce and document the practical applications of equations of state in the area of vapor-liquid phase equilibria. A comprehensive review of different equations of state is presented with an emphasis on the Peng-Robinson equation of state.

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PREFACE TO THE FIRST EDITION

This book explains the fundamentals of reservoir engineering and their practical application in conducting a comprehensive field study. Chapter 1 reviews fundamentals of reservoir fluid behavior with an emphasis on the classification of reservoir and reservoir fluids. Chapter 2 documents reservoir-fluid properties, while Chapter 3 presents a comprehensive treatment and description of the routine and specialized PVT laboratory tests. The fundamentals of rock properties are discussed in Chapter 4 and numerous methodologies for generating those properties are reviewed. Chapter 5 focuses on presenting the concept of relative permeability and its applications in fluid flow calculations. The fundamental mathematical expressions that are used to describe the reservoir fluid flow behavior in porous media are discussed in Chapter 6, while Chapters 7 and 8 describe the principle of oil and gas well performance calculations, respectively. Chapter 9 provides the theoretical analysis of coning and outlines many of the practical solutions for calculating water and gas coning behavior. Various water influx calculation models are shown in Chapter 10, along with detailed descriptions of the computational steps involved in applying these models. The objective of Chapter 11 is to introduce the basic principle of oil recovery mechanisms and to present the generalized form of the material balance equation. Chapters 12 and 13 focus on illustrating the practical applications of the material balance equation in oil and gas reservoirs.

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FUNDAMENTALS OF RESERVOIR FLUID BEHAVIOR

Naturally occurring hydrocarbon systems found in petroleum reservoirs are mixtures of organic compounds that exhibit multiphase behavior over wide ranges of pressures and temperatures. These hydrocarbon accumulations may occur in the gaseous state, the liquid state, the solid state, or in various combinations of gas, liquid, and solid. These differences in phase behavior, coupled with the physical properties of reservoir rock that determine the relative ease with which gas and liquid are transmitted or retained, result in many diverse types of hydrocarbon reservoirs with complex behaviors. Frequently, petroleum engineers have the task to study the behavior and characteristics of a petroleum reservoir and to determine the course of future development and production that would maximize the profit. The objective of this chapter is to review the basic principles of reservoir fluid phase behavior and illustrate the use of phase diagrams in classifying types of reservoirs and the native hydrocarbon systems.

CLASSIFICATION OF RESERVOIRS AND RESERVOIR FLUIDS Petroleum reservoirs are broadly classified as oil or gas reservoirs. These broad classifications are further subdivided depending on:

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Reservoir Engineering Handbook

• The composition of the reservoir hydrocarbon mixture • Initial reservoir pressure and temperature • Pressure and temperature of the surface production The conditions under which these phases exist are a matter of considerable practical importance. The experimental or the mathematical determinations of these conditions are conveniently expressed in different types of diagrams commonly called phase diagrams. One such diagram is called the pressure-temperature diagram. Pressure-Temperature Diagram Figure 1-1 shows a typical pressure-temperature diagram of a multicomponent system with a specific overall composition. Although a different hydrocarbon system would have a different phase diagram, the general configuration is similar. These multicomponent pressure-temperature diagrams are essentially used to: • Classify reservoirs • Classify the naturally occurring hydrocarbon systems • Describe the phase behavior of the reservoir fluid 2700 id by Liqu

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Fundamentals of Reservoir Fluid Behavior

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To fully understand the significance of the pressure-temperature diagrams, it is necessary to identify and define the following key points on these diagrams: • Cricondentherm (Tct)—The Cricondentherm is defined as the maximum temperature above which liquid cannot be formed regardless of pressure (point E). The corresponding pressure is termed the Cricondentherm pressure pct. • Cricondenbar (pcb)—The Cricondenbar is the maximum pressure above which no gas can be formed regardless of temperature (point D). The corresponding temperature is called the Cricondenbar temperature Tcb. • Critical point—The critical point for a multicomponent mixture is referred to as the state of pressure and temperature at which all intensive properties of the gas and liquid phases are equal (point C). At the critical point, the corresponding pressure and temperature are called the critical pressure pc and critical temperature Tc of the mixture. • Phase envelope (two-phase region)—The region enclosed by the bubble-point curve and the dew-point curve (line BCA), wherein gas and liquid coexist in equilibrium, is identified as the phase envelope of the hydrocarbon system. • Quality lines—The dashed lines within the phase diagram are called quality lines. They describe the pressure and temperature conditions for equal volumes of liquids. Note that the quality lines converge at the critical point (point C). • Bubble-point curve—The bubble-point curve (line BC) is defined as t...