Multilateral Wells Other SPE Books (Coming Soon) Formation, Removal, and Inhibition of Scale in the Oilfield Environment Analysis of Production Decline Curves Hydraulic Fracturing Book Editor William R. Landrum, ConocoPhillips Company Books Committee (2008) Lee Dillenbeck (Chair), Chevron Energy Technology Company Rosalind A. Archer, University of Auckland James N. Collins, ConocoPhillips Company Tarek Ghazi, Aramco Services Company Eirik Kaarstad, University of Stavanger Robert F. Mitchell, Halliburton Graham Openshaw, PanGeo Subsea Jorge E. Pinedo, Santos Limited Ronald L. Sparks, The Hanover Company Multilateral Wells A.D. Hill Texas A&M University Ding Zhu Texas A&M University Michael J. Economides University of Houston Society of Petroleum Engineers © Copyright 2008 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 passages excerpted for review and critical purposes. ISBN 978-1-55563-138-3 ISBN 978-1-61399-223-4 (Digital) Society of Petroleum Engineers 222 Palisades Creek Drive Richardson, TX 75080-2040 USA http://store.spe.org/ [email protected] 1.972.952.9393 Preface There are few technologies in modern oil- and gas-production practices that exemplify the complexities faced by, and the resulting innovations of, this industry more than multilateral wells. From the 3D seismic needed to plan such wells, to the unique drilling and completion practices used to create them, to the coupled reservoir/ wellbore flow models required to predict their performance, these complex well structures are expanding the boundaries of petroleum engineering technology. The extensive contact with widely distributed reservoir bod- ies connected by a well network requires a coupling of reservoir and wellbore flow aspects much more so than for conventional wells. There is a rapidly growing literature documenting all aspects of multilateral well tech- nology, but it is dispersed throughout the many subdisciplines of petroleum engineering. This book is intended to illuminate the most important aspects of multilateral wells in a concise way. We hope that it will be a valuable resource for engineers and geoscientists desiring an introduction to complex well archi- tectures. We have tried to be comprehensive enough to give readers practical tools they can apply in the design and analysis of multilateral wells, while also pointing to the appropriate literature for more advanced studies. We would be remiss if we did not acknowledge the efforts of the many scientists and engineers whose work on multilateral-well technology is documented here. We also thank our many students who helped us comb the literature, worked through example calculations, and in some cases, developed some of the methods described in this book. Dedication To Woody and Andy Contents Preface 1 . Introduction—Purp o ses and Applications of Multilateral Wells . . . . . . . . . . . . . . . . . 1 1.1 The Utility of Multilateral Wells .......................................... 1 1.2 History of Multilateral Wells ............................................ 2 1.3 Synergistic Technologies .............................................. 6 1.4 Organization of This Book ............................................. 6 2 . Application of Complex Well Architecture to Common Geological Settings . . . . . . . 7 2.1 Introduction ........................................................ 7 2.2 Geometry of the Well Drainage Volume ................................... 7 2.3 Using Seismic Techniques for Reservoir Description and Complex Well Planning ... 13 3 . Drilling Multilaterals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.1 Initiating a Lateral From the Main Wellbore—Sidetracking .................... 17 3.2 Drilling the Lateral ................................................... 23 3.3 Well Control for Multilateral Wells ....................................... 28 3.4 Multilateral Drilling Case Histories ....................................... 28 4 . Multilateral Well Completions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 4.1 Introduction ........................................................ 35 4.2 Considerations in Designing a Multilateral Completion ....................... 35 4.3 Junction Classifications ............................................... 36 4.4 Lateral Completions .................................................. 47 5 . Multilateral Well Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 5.1 Introduction ........................................................ 65 5.2 Horizontal Well Reservoir Inflow Performance .............................. 65 5.3 Wellbore Flow Behavior ............................................... 82 5.4 Multilateral Well Deliverability ........................................... 91 5.5 Wellbore Crossflow in Multilateral Wells .................................. 100 Appendix 5A ....................................................... 103 Appendix 5B—Derivation of Dimensionless Transform of Diffusivity Equation ..... 103 Appendix 5C—Point/Plane Source Method ................................ 105 6 . Multilateral Well Performance Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 6.1 Introduction ........................................................ 111 6.2 Low-Cost Reserves Access With Multilaterals .............................. 111 6.3 Heavy-Oil Development With Multilaterals ................................. 115 6.4 Multilaterals for Improved Sweep Efficiency ............................... 115 6.5 Low-Cost Reserves Access With Multilaterals .............................. 119 7 . Enhanced Multilateral Well Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 7.1 Introduction ........................................................ 123 7.2 Multilateral-Well Performance Diagnosis .................................. 123 7.3 Well Stimulation in Multilateral Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 8 . Intelligent and Smart Well Completions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 8.1 Introduction ........................................................ 143 8.2 Intelligent-Completion Equipment ....................................... 143 8.3 Intelligent Completion Models .......................................... 146 8.4 Examples of Field Applications of Intelligent Completions ..................... 153 9 . Multilateral Well Economics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 9.1 Introduction ........................................................ 157 9.2 Costs of Different Classifications of Multilateral Wells ........................ 157 9.3 Basic Economic Considerations ........................................ 158 9.4 Multilateral Wells Driven by Capital Expenditure Reductions ................... 162 9.5 Multilateral Value Driven by Reserves Additions ............................ 163 9.6 Real Options Valuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 Author Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Chapter 1 Introduction—Purposes and Applications of Multilateral Wells 1.1 The Utility of Multilateral Wells Oil and gas wells are no longer just for accessing hydrocarbon formations, a task that they have accomplished for more than a century and which they still do in a far improved and targeted way. Over the past 20 years, with the rapid evolution of, fi rst, horizontal wells and, eventually, multilateral wells, reservoir-to-well expo- sure has increased dramatically to orders of magnitude larger than ever before. Multilateral wells accomplish both of these tasks, the accessing and the exposure, effectively. There are some obvious examples that fall under the category of accessing. Multilateral wells can be drilled to drain discontinuous geological fl ow units, especially those which could not by themselves rationalize dedicated individual wells. Such structures include lenticular sands or braided channels, where the reservoirs are distributed areally, and layered reservoirs having vertically discontinuous bodies. Exposure is also clear. Reservoirs with low mobility—that is, having low permeability or containing high- viscosity fl uids—can readily benefi t from large well-to-reservoir exposure. Such reservoirs include tight oil and gas formations or heavy-crude reservoirs. Needless to say, all applications are subject to rigorous economics, and as usual, while production econom- ics are almost universal, the costs of well construction are eminently local and vary widely. Thus, well architecture that may be attractive in one petroleum province of the world may not be attractive elsewhere. We address all these issues in detail in Chapters 2 and 9. There are, of course, other even more sophisticated and subtle uses of multilateral wells. Consider the following list of simple examples, which is by no means complete, on the uses of multilateral wells to augment reservoir exploitation strategies above and beyond single horizontal wells: · Horizontal wells are relatively more attractive compared to vertical wells in thin reservoirs, irrespective of vertical-to-horizontal permeability anisotropy. They become less attractive as the reservoirs become thicker and with poorer vertical communication. However, stacked multilaterals, drilled on top of each other and spaced in a thick reservoir, may create impromptu vertical no-fl ow boundaries, producing very large production rates and rendering the thick formation eminently attractive. · It is also well known that production rates from horizontal wells, while logically they should be greater from longer wells, even in the best cases, do not come close to monotonically increasing with length. Reasons include the fact that fl ow disproportionately comes from the edges of the well; the adverse effects of pressure drop in the well itself, which is a function of the length; and the greater likelihood of lateral heterogeneities. Thus, for example, two opposing laterals, each of a certain moderate length, would produce in many cases at least 50% larger production rate than a single horizontal well as long as or longer than the sum of the lengths of the two opposing laterals. · Horizontal well orientation is quite important in areally anisotropic reservoirs. Drilling a well in natu- rally fractured formations is generally not a problem. But permeability anisotropy always occurs, and