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SOCIETY OF PETROLEUM ENGINEERS FUNDAMENTALS OF DRILLING ENGINEERING Robert F. Mitchell Stefan Z. Miska SPE TEXTBOOK SERIES VOL. 12 Fundamentals of Drilling Engineering Fundamentals of Drilling Engineering Editors: Robert F. Mitchell Halliburton Stefan Z. Miska University of Tulsa Contributors: Bernt S. Aadnoy, University of Stavanger Neal Adams, Neal Adams Services John W. Barker, ExxonMobil J.C. Cunha, Petrobras America Alfred W. Eustes III, Colorado School of Mines Ross L. Kastor, Antelope Engineering Vassilios C. Kelessidis, Technical University of Crete Roberto Maglione, Eni SpA Stefan Z. Miska, University of Tulsa Robert F. Mitchell, Halliburton Evren Ozbayoglu, University of Tulsa Jim Powers, ExxonMobil Ronald Sweatman, Halliburton Society of Petroleum Engineers © Copyright 2011 Society of Petroleum Engineers All rights reserved. No portion of this book may be reproduced in any form or by any means, including electronic storage and retrieval systems, except by explicit, prior written permission of the publisher except for brief pas- sages excerpted for review and critical purposes. Manufactured in the United States of America. ISBN 978-1-55563-207-6 ISBN 978-1-55563-338-7 (Digital) Society of Petroleum Engineers 222 Palisades Creek Drive Richardson, TX 75080-2040 USA http://www.spe.org/store [email protected] 1.972.952.9393 Preface Drilling engineering is a multidisciplinary subject, including a broad spectrum of topics in engineering, geology, chemistry, and physics. A general textbook must cover all these topics at greater than superficial depth and with reasonable balance in an abbreviated form. This is not an easy task. For instance, a well-known book on drilling fluids fills more than 600 pages, while Fundamentals of Drilling Engineering must cover similar topics in only 60 pages. Similar problems of topic selection, condensation, and presentation must be solved for each of the other disciplines covered in the textbook. Because the book must be useful for introductory studies, intermedi- ate studies, and post-graduate studies, each topic not only must cover elementary concepts but also include more advanced topics. The specific chapter topics covered in this book include the following: • Rotary Drilling. This chapter describes the basics of rotary drilling; there are a number of elementary problems posed, suitable for an introductory course on drilling. • Introduction to Geomechanics in Drilling. The objective of this chapter is to introduce the basic concepts of geomechanics related to drilling, including wellbore stability and the selection of suitable mud weights. • Drilling Fluids. This chapter describes the types, functions, formulation, and testing of drilling fluids. • Cementing. This chapter describes the primary objectives of cementing, the formulation and testing of cement, and methods for cement placement. • Drilling Hydraulics. This chapter describes how wellbore pressures are calculated in a variety of sce- narios, such as circulation and surge pressures. • Rotary Drilling Bits. This chapter discusses bit types and selection criteria, factors affecting bit wear and drilling rate, and optimization of bit performance. • Casing Design. This chapter addresses the types and functions of casing strings and the methods used for the selection, sizing, and design of well completions. • Directional Drilling. This chapter presents directional well trajectory design, the control of the well path while drilling, and methods for modeling the torque and drag forces on a drillstring. • Fundamentals of Drillstring Design. This chapter presents descriptions of the components of a drillstring, determination of the forces and moments in the drillstring, the effect of wellbore pressures on drillstring forces, and overall drillstring design. • Drilling Problems. This chapter presents specific drilling problems and their solutions, including lost circulation, well control, recovery of broken drillstring components, and stuck drillpipe. Most important among the first drilling engineering textbooks was Applied Drilling Engineering, written by Adam T. Bourgoyne, Keith Millheim, Martin Chenevert, and F.S. Young, which was published in 1986. A second edition was published in 1991 and remains available today, and almost every drilling engineer has a copy of the “red book” on his or her bookshelf. This landmark publication summarized the state of the art of scientific drilling that was developed in the 1945–1980 time period. A survey of the academic community tells us that this text is considered the most comprehensive of available textbooks, that it represents a good mix of theory and practice, that it is clear and easily understood, and that the example problems are effective teaching aids. Fundamentals of Drilling Engineering is intended to be the successor to Applied Drilling Engineering. Why do we need a new book, and why change the title? No matter how you calculate the age of the latter work, it is at least 20 years old. Not many technical books can remain state of the art for 20 years or more, and this book is no exception; drilling technology has changed (significantly, in some areas) over the last 20 years. Further, the authors of Applied Drilling Engineering had a vision of the drilling engineering practices of the future; in many ways, the industry has taken different, unanticipated directions. The basic approach to drilling engineering has also moved from “rules of thumb” and correlations to a more fundamental, physics-based science, and there are many examples of this older style in that textbook. Some topics, such as torque-drag drillstring analysis, extended-reach wells, and underbalanced drilling, have taken on an importance not anticipated by the authors. v Drilling fluids and cementing technologies have evolved to solve new problems, notably environmental and dis- posal concerns. Geological topics cover wellbore pressures but miss other important problems, such as wellbore stability. Cuttings transport analysis has progressed far since the first book’s publication. Other topics of modern importance, such as environmental, health, and safety issues, are completely absent from that textbook. Neverthe- less, it will remain available, both as a useful source of information and as a historical document describing the state of the art of drilling engineering during a period of rapid technological development. While the past 20 years have produced explosive growth in new technologies in the drilling industry, the greatest change has been the greatly increased use of computer analysis in exploration, well design, planning, and reporting. In the mid-1980s, when Applied Drilling Engineering was first published, computer applications were largely confined to “mainframe” or “minicomputers” not generally available to drilling engineers on a daily basis. The personal computer was still too primitive to be useful for engineering calculations, and drilling engineering calculations were still in the “hand calculation” stage. Any calculation that could not be summarized on the back of a file card was considered too complex to be useful. The first IBM PC was introduced in 1981, and with the introduction of the Intel 80386 chip in 1986, personal computers became capable of intense engineering calculations. In 2011, most routine engineering calculations are done with commercial software packages on personal computers. The effective and correct use of these programs is a new teaching problem for the petroleum industry, especially considering the large turnover in manpower expected over the next decade. How do you replace a classic textbook, and why change the name? First, you don’t replace it. Applied Drill- ing Engineering still has value. Because Applied Drilling Engineering will remain available for the foreseeable future, the new textbook would necessarily need a new name. One problem with the original name is that it is somewhat misleading in that it suggests a collection of drilling applications, rather than the fundamentals of drilling engineering it actually contains. To correct this potential misunderstanding, the word “Fundamentals” is prominent in the name of the new textbook. Second, to produce a worthy successor to Applied Drilling Engineer- ing, we have taken the same approach used by the industry to drill a well—that is, we assembled a drilling team. Drilling engineering covers a widely diverse set of disciplines, and no single person can be an expert in all areas. Thus, the drilling team has experts in drilling fluids, cementing, geology, drillbits, and other areas. The editors sought out experts in industry and academia to contribute to this new textbook. The following pages give brief biographical information on each of these authors. This book could not have been produced without their efforts. Robert F. Mitchell Houston vi Notes from the Editors A Note on Prerequisites This book is intended primarily for junior and senior petroleum engineering students in a four-year university- level type of program. Some parts also can be useful for graduate students as well as practicing engineers. We have assumed that the readers have successfully completed courses in calculus and differential equations, fluid mechanics and thermodynamics, engineering static, dynamics, and mechanics of materials. In general, a good understanding of conventional Newtonian mechanics (both fluid and solid) is sufficient for solving most drilling engineering problems, but some parts (e.g., those discussed in Chapters 3 and 4) also require a good background in chemistry that may be found in many textbooks at the bachelor’s level. Most developments are furnished with derivations followed by numerical examples. Careful review of example problems is highly recommended before working on the solve at home types of problems provided at the end of each chapter. We certainly hope that this book will also inspire the readers to study more advanced topics, as addressed in the recently published SPE book Advanced Drilling and Well Technology. A Note About Units An engineer or student new to drilling engineering will encounter the most peculiar collection of units to be found in any discipline. One reason for these odd units is that drilling engineering first developed as a craft. Wells have been drilled for millennia, and for much of that time, drilling has been a craft, not a science. The young driller learned his craft as a roughneck on a drilling rig and, as he acquired experience and seniority, eventually was put in charge of a drilling rig. Wells were successfully drilled because of the driller’s intuition in anticipating and experience in solving problems. Drilling engineering did not really exist as an engineering science before approximately 1945. Measurements were made with tools convenient to the driller. Mud weight would be measured in pounds of mud per gallon because the driller likely had a gallon bucket in which to weigh the mud. The origins of the 42- gal oil barrel are obscure, but some historical documents indicate that around 1866, early oil producers in Pennsylvania, USA decided they needed a standard unit of measure to convince buyers that they were getting a fair volume for their money. They agreed to base this measure on the more-or-less standard 40-gal whiskey barrel, but added an additional 2 gal to ensure that any measurement errors would always be in the buyer’s favor. Drilling companies outside of the United States adopted metric units as well, measuring well depth in meters, volumes in liters, and diameters in centimeters. We have to contend with this odd assortment of units because for almost any engineering calculation, unit conversion will be necessary. For instance, the exact formula for calculating hydrostatic pressure for a constant density fluid is: "p=!g"Z , (1) where p is pressure, ! is density, g is the acceleration of gravity, and Z is true vertical depth. Field units are psi for pressure, lbm/gal for density, and feet for depth. To reconcile these units, the equation has to be rewritten: "p=0.05195!"Z (2) This mysterious coefficient 0.05195 equals 12/231, where 231 is the number of cubic inches in a gallon and 12 is the number of inches in a foot. The acceleration of gravity g is given in the unfamiliar unit of 1 lbf/lbm. A more challenging calculation is dynamic pressure: p=!v2, (3) where p is pressure, ! is density, and v is velocity. Field units are psi for pressure, lbm/gal for density, and ft/sec for velocity. To reconcile these units, the equation has to be rewritten: p=0.001615!v2 . (4) This coefficient 0.001615 equals 12/(231*32.17), where 231 is the number of cubic inches in a gallon, 12 is the number of inches in a foot, and 32.17 is the acceleration of gravity in ft/sec2. Notice that it is necessary to vii convert the field unit density to a consistent unit of density in this equation, but this time the conversion is the acceleration of gravity in ft/sec2, not 1 lbf/lbm. The potential pitfall is the confusion of weight with mass. We have tried, in this text, to keep equations in the form of Eq. 1 or Eq. 3 and to avoid the use of equations like Eq. 2 and Eq. 4. The drawback to Eqs. 1 and 3 is that we must convert units. It would be preferable to have measurements in a system of units such that we wouldn’t have to convert each property to a different unit to make a correct calculation. There are systems of units, called consistent units, which have the properties we desire. The system most commonly used is the SI system of units, based on the metric system. There exist consistent English units systems as well, but they are even more obscure than drilling engineering units and are not commonly used. The SI units and conversion factors can be found in The SI Metric System of Units and SPE Metric Standards, published by SPE. It is highly unlikely that drillers will adopt this system, but the scientific world uses it as a matter of course. When making engineering calculations, the safest approach is to convert all properties to SI units, perform the calculation, and then convert the result back to field units. With practice, some calculations (such as Eq. 1) become so familiar that one would simply use the coefficient 0.052. With computer programs and spreadsheets, use of SI units is particularly easy, and we recommend their use. For instance, Eq. 3 in SI units can be calculated with no concern about gravity constants whatsoever. For a proposed list of standard symbols for drilling engineering, please refer to the Appendix that begins on page 677. viii Acknowledgments While working on this book, particularly on Chapters 8 and 9, I received help from many students, staff, and faculty collaborating with me under the auspices of the University of Tulsa Drilling Research Projects (TUDRP). I would also like to express my appreciation to the students in my Advanced Drilling course for their constructive feedback. Comments and suggestions from Texas A&M University students related to Chapter 9 are also greatly appreciated. I also wish to thank those students who helped to develop figures and verify calculations. I am very grateful to all member companies of TUDRP for their financial assistance and the guidance and technical support of their representatives. Their contributions to my research help make it possible to formulate new and useful concepts and to educate young, talented engineers. Ms. Paula Udwin deserves special thanks for her support and help with the typing of Chapters 8 and 9. I am deeply thankful to my wife Anna for her many years of continual support, understanding, and patience. Stefan Miska Tulsa First, I would like to acknowledge the influence of John Thorogood on the inception and development of this text and the companion text, Advanced Drilling and Well Technology. Second, I would like to thank the authors for their efforts in making this text technically sound and state of the art. They have performed an important service to the industry. Stefan and I both appreciate the help and support of SPE and the SPE staff, especially Jennifer Wegman. Robert F. Mitchell Houston ix About the Authors Robert F. Mitchell is a Halliburton Technology Fellow in the Drilling and Evaluation Division of Halliburton. He has published more than 80 papers on wellbore and well completion problems, including wellbore thermal/ flow simulation, drillstring mechanics, tubing buckling analysis, arctic well completions, tubular stress analysis, and geomechanics. Principal technical accomplishments include the first deep permafrost thaw subsidence casing design, the comprehensive analysis of the post-buckling equilibrium of tubulars, and the accurate prediction of dynamic surge pressures. Mitchell wrote the Casing and Tubing Design chapter for the textbook Petroleum Well Construction, was the Drilling Engineering volume editor for SPE’s Petroleum Engineering Handbook, and was an editor of and contributor to the SPE book Advanced Drilling and Well Technology. He has served as a technical editor for Applied Mechanics Reviews, the Journal of Energy Resources Technology, SPE Computer Applications, and SPE Journal and as Executive Editor for SPE Drilling & Completion. Mitchell was vice president of Enertech Engineering and Research Company from 1980 to 1996 and worked at Exxon Production Research Co from 1973 to 1980. He holds BA, MME, and PhD degrees from Rice University and is a registered professional engineer in Texas. Mitchell received the 2005 SPE Drilling Engineering Award and is an SPE Distinguished Member. Stefan Z. Miska is currently the Jonathan Detwiler Endowed Chair Professor of the McDougall School of Petro- leum Engineering and Director of the Tulsa University Drilling Research Projects (TUDRP) at the University of Tulsa. He holds MS and PhD degrees from the University of Mining and Metallurgy in Cracow, Poland; recently, he was awarded the title of Professor of Technical Sciences by the president of Poland. Over the years, Miska has taught at his alma mater, the Norwegian Institute of Technology, and New Mexico Tech. In 1992, he joined the University of Tulsa as chair of its Petroleum Engineering Department. Miska has published more than 170 technical papers and contributed to several books. He was involved in the successful design and development of a downhole, turbine-type motor for air drilling and has been instrumental in the development of research facilities for wellbore hydraulics at simulated downhole conditions. He also has made contributions to the development of new buckling concepts and the axial force transfer in extended-reach drilling. Miska’s current research interests are focused on wellbore hydraulics, mechanics of tubulars, and directional drilling. He is involved with SPE in many capacities, including serving as a Technical Editor for SPE Drilling & Completion and as a member of the Drilling and Completions Advisory Committee. He was the recipient of the 2000 SPE Distinguished Petroleum Engineer- ing Faculty Award and the 2004 SPE Drilling Engineering Award. He is also an SPE Distinguished Member. Bernt S. Aadnoy is Chairman and Professor of Petroleum Engineering at the University of Stavanger; he previ- ously worked for Phillips Petroleum, Rogaland Research, Statoil, and Saga Petroleum. Aadnoy has published more than 130 papers, mostly on rock mechanics and well technology. He is the author of several books, including Mechanics of Drilling, Modern Well Design, and Petroleum Rock Mechanics, and he served as editor of the SPE book Advanced Drilling and Well Technology. He also has served as a Technical Editor for SPE Drilling & Com- pletion, SPE Journal, and the Journal of Petroleum Science and Engineering. Aadnoy holds a mechanical engineering degree from Stavanger Tech., a BS degree in mechanical engineering from the University of Wyoming, an MS degree in control engineering from the University of Texas, and a PhD degree in petroleum rock mechanics from the Norwegian Institute of Technology. He was the recipient of the 1999 SPE Drilling Engineering Award. Neal Adams has more than 39 years of oil industry experience. Having started his career as a roughneck and floorhand on drilling and workover rigs, he has developed a worldwide reputation as a leading specialist in safety, well control, drilling and production, training, and problem solving. He is the author of numerous books and technical papers and has been an active member of SPE for 30 years; his contributions include serving as a Distinguished Lecturer (1982–1983), on the Board of Directors of the Gulf Coast Section, Program Committee for the SPE Annual Technical Conference and Exhibition, and chapter author for SPE’s Petroleum Engineering Handbook, Volume II: Drilling Engineering. Adams holds an MS degree in petroleum engineering from the Uni- versity of Houston. He is a registered engineer in Texas and Oklahoma. x