Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/3817161/9781629810232_frontmatter.pdf by guest on 01 October 2021 Application of Resistivity-Tool-Response Modeling for Formation Evaluation
By Hezhu Yin
AAPG Archie Series, No. 2 ExxonMobil Upstream Research Company
Published by The American Association of Petroleum Geologists Tulsa, Oklahoma, U.S.A.
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Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/3817161/9781629810232_frontmatter.pdf by guest on 01 October 2021 About the Author
Hezhu Yin
Dr. Hezhu Yin is a Geophysical Advisor with ExxonMobil. He earned a B.S. in Geophysical Well Log Engineering from China University of Petroleum in 1982, and a Ph.D. in Geophysics from Stanford University in 1992.
From 1982 to 1987, Yin taught and researched at Daqing Petroleum Institute with focus on well logging instrumentation. He designed and developed a Multi-functional Panel of Triple-combo Logging Suite for Daqing Oilfield Well Logging Company. From 1987 to 1992, Yin joined Stanford Rockphysics and Borehole Physics (SRB) Research Project with focus on experimental rockphys- ics, and contributed 17 articles to Standford Rockphysics and Borehole Physics Project Research Volumes. After a year of post-doctorate research at Stanford, Yin acted as a research associate and adjunct professor at Lamont-Doherty Earth Observatory of Columbia University from 1993 to 1995. At Lamont, he taught graduate student courses and his research focused on designing and executing the Ocean Drilling Program (ODP) borehole geophysical operation, and borehole geo- physical research for ODP drilling legs.
In 1995, Yin joined Exxon Production Research Company (now ExxonMobil Upstream Research The AAPG Bookstore Geological Society Publishing House Company, EMURC). His first assignment with Exxon was on Resistivity Tool Response Forward P.O. Box 979 Unit 7, Brassmill Enterprise Centre and Inverse Modeling. From 1995 to 2000, he developed numerous 1-D and 2-D forward and Tulsa, OK 74101-0979 Brassmill Lane, Bath BA13JN practical inverse modeling codes with analytical, finite element, and hybrid methods to simulate U.S.A. U.K. various laterolog, induction, and logging while drilling propagation resistivity tools to meet the Telephone: 1-918-584-2555 or 1-800-364-AAPG (U.S.A. and Canada) Telephone: +44-1225-445046 needs of formation evaluation (FE) for more accurate hydrocarbon saturation estimates. He was Fax: 1-918-560-2652 or 1-800-898-2274 (U.S.A. and Canada) Fax: +44-1225-442836 instrumental in developing EMURC’s Tool Response Modeling workshop and trained many FE E-mail: [email protected] E-mail: [email protected] specialists within ExxonMobil on the applications of the tool response modeling for FE over the www.aapg.org www.geolsoc.org.uk years. He also co-developed AAPG’s workshop on Resistivity Tool Response Modeling for Forma- tion Evaluation with focus on thin-bed analysis. His research interests include electomagnetic and Canadian Society of Petroleum Geologists Affiliated East-West Press Private Ltd. nuclear tool response modeling in complicated borehole environments, acoustic log dispersion 600, 640-8th Avenue S.W. G-1/16 Ansari Road, Darya Ganj analysis and Stoneley permeability inversion, rock physics, and integrated petrophysics-seismic Calgary, Alberta T2P 0M2 New Delhi 110 002 joint inversion. From 2008 to 2010, he was with ExxonMobil Exploration and Development Com- Canada India panies as a Geophysical Advisor, and actively involved in ExxonMobil’s geosteering/well-placement Telephone: 1-403-264-5610 Telephone: +91-11-23279113 work in those world record breaking High Angle and Horizontal wells drilled in Sakhalin, Russia. Fax: 1-403-264-5898 Fax: +91-11-23260538 Yin is a recipient of the SPWLA2010 Technical Achievement Award. E-mail: [email protected] E-mail: [email protected] www.cspg.org
Yin is author and coauthor of 59 publications, and inventor and co-inventor of 9 US and other patents covering his 28 years of academic and industry career. Currently as a Geophysical Advisor at ExxonMobil, Yin is working on world class Extended-Reach-Drilling (ERD) and HAHZ wells’ logging operation, geosteering, and formation evaluation from the active development fields of ExxonMobil in West Africa, North Sea, Middle East, and Far East.
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Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/3817161/9781629810232_frontmatter.pdf by guest on 01 October 2021 Table of Contents
About the Author ...... iii
Table of Contents ...... iv
Acknowledgments ...... v
Preface ...... vi
Chapter 1 Introduction ...... 1
Chapter 2 Basics of Resistivity Tools ...... 11
Chapter 3 Benchmark Responses ...... 39
Chapter 4 Resistivity Modeling as a Formation Evaluation Tool ...... 61
Chapter 5 Case Studies ...... 71
Chapter 6 Sensitivity, Limitations, and Error Inherent in Resistivity-tool-response Modeling ...... 87
Chapter 7 Concluding Remarks ...... 117
References ...... 123
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Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/3817161/9781629810232_frontmatter.pdf by guest on 01 October 2021 Acknowledgments
I wish to express my sincere gratitude to the management of the ExxonMobil Upstream Research Company for the vision of developing resistivity-modeling techniques as a widely used tool for formation evaluation. The encouragement and support from management has not only made this volume possible, but also, most importantly, has ensured that the techniques are directly applied in ExxonMobil’s front-line exploration and development fields.
I wish to thank Quinn Passey and Ken Dahlberg for motivating and encouraging me to develop and apply resistivity-modeling techniques, and to continue working hard on this manuscript despite many distractions over the last few years. I am grateful to my coworkers at ExxonMobil Upstream Research Company. My study in resistivity-tool-response modeling and the preparation of this vol- ume have profited greatly from Bob Brackett, Angel Guzman-Garcia, Keith Sullivan, and Hui Xiao through many thoughtful discussions, support, and continuing friendship as the manuscript was first completed in Exxon Production Research Company in 1998.
I wish to thank Craig Tingey for penetrating discussions on the impact of resistivity modeling in water-saturation and HPV estimations, and Dale Fitz for his insights on tool-response sensitivity in conductive and resistive beds. I wish to thank Fred Haynes, John Campbell, and many others in the ExxonMobil Formation Evaluation group for their stimulating discussion on resistivity-tool- response modeling and uncertainty in thin-bed situations. Also, thanks are due to many I have worked with to apply resistivity-tool-response modeling within ExxonMobil, particularly to David Kennedy, who was instrumental in developing and applying resistivity-tool-response modeling when he was with Mobil and ExxonMobil since the Exxon-Mobil merger.
Special thanks go to Rich Wheeler. His critical technical and managerial reviews have made the documentation possible for today’s publication. Thanks also to Pingjun Guo and Xianyun Wu for their technical reviews, and to Ken Dahlberg and Dale Fitz for their intelligent comments and relentless editing efforts that made the text far more readable for this publication.
Finally, special thanks to Terri Olson, AAPG Publications Committee Chair; Frances Whitehurst, AAPG Editor; and to Beverly Molyneux, AAPG Technical Publications Managing Editor, for their detailed review, insightful and constructive comments, and strong support for AAPG publication.
AIT* (array induction imager tool), DLL* (Dual Laterolog Resistivity), EPT* (electromagnetic propagation tool), FMI* (fullbore formation microimager), HRLA* (high-resolution laterolog array), OBDT* (oil-base dipmeter tool), Phasor* (phasor-induction SFL tool), PeriScope* (bed boundary mapper), Platform Express* (integrated wireline logging tool), SFL* (spherically focused resistivity), are trademarks of Schlumberger. InSite ADRTM (Azimuthal Deep Resistivity) and MSFL™ (Micro Spherically Focused Log) are trademarks of Halliburton. AzitrakTM is a trade- mark of Baker Atlas.
Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/3817161/9781629810232_frontmatter.pdf by guest on 01 October 2021 Preface
The purpose of this volume is to introduce the reader to the fundamental concepts required to understand resistivity-tool response and resistivity-log interpretation for formation evaluation. The subjects covered reflect the author’s research on tool-response forward modeling applied to evaluate service companies’ resistivity tools, and on tool-response inverse modeling for for- mation evaluation.
In this volume, fundamentals of resistivity-logging-tool physics and measurement accuracy are reviewed, and forward- and inverse-modeling resistivity-tool responses are introduced. It is illustrated that resistivity-log response forward and inverse modeling can provide a means to estimate and correct effects of borehole deviation, dipping beds, shoulder beds, thin beds, borehole dimension, mud resistivity, and/or invasion on the apparent resistivity recorded by field resistivity logs, and to enhance the logs’ vertical resolution and resistivity. Consequently, resistivity modeling provides a framework for deriving more accurate estimates of the water saturation in reservoirs. However, limitations in the described inversion process must be understood. The results may involve higher uncertainties when the field deep-reading resistiv- ity log approaches its sensitivity limit and true bed thickness is below the tool’s vertical resolu- tion (i.e., tool physics limits the inversion accuracy in these cases). In general, inverse modeling may result in non-unique solutions. To minimize these, an integrated approach must be taken, dealing with borehole rugosity and incorporating higher-vertical-resolution logs and resistivity logs with different depths of investigation.
Potential readers or users of this volume may include geoscientists and engineers working with and interpreting resistivity logs. Petrophysicists and reservoir engineers integrating resistivity- based and capillary-pressure-based quantitative calculation of formation water saturation, and the formation evaluation specialists running environmental correction on resistivity logs with resistivity-tool-response modeling may especially benefit from case studies and sensitivity- limitation analysis in this publication.
In the case studies presented, well-deviation, shoulder-bed, bed-thickness, borehole, mud- resistivity, and invasion effects on resistivity-log responses are significant. Many seemingly thick beds, based on gamma-ray and deep-induction responses alone, are composed of thinner beds which can be identified by logs of higher vertical resolution, such as formation microelec- tric imager, Micro Spherical Focused Log, bulk density, sonic, etc. Modeling using these thinner beds improves the matching of the reconstructed deep-reading resistivity logs with the field log curves.
The differences between modeled true resistivity (Rt) and apparent resistivity (Ra) from field resistivity logs are often nonlinear. Larger differences are observed as the resistivity contrast between beds increases. The apparent resistivity from field deep-reading resistivity curves is not equal to true formation resistivity in most case studies described in this volume. If reser- voir-saturation estimation will be log-based and integrated with core-based fluid saturation estimation, resistivity modeling may be a necessary procedure for accurate formation evalua- tion. For the case studies cited in this volume, using the modeled resistivity curves in formation evaluation has yielded higher hydrocarbon saturation than using the measured resistivity field logs.
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Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/3817161/9781629810232_frontmatter.pdf by guest on 01 October 2021 Chapter 1 is an overview of resistivity-tool-response modeling and addresses why resistiv- ity-tool-response modeling is needed for formation evaluation and when resistivity modeling should be considered.
Chapter 2 reviews the fundamentals of induction- and laterolog-tool physics, contemporary log processing, and software focusing. This chapter provides some basic tool-response physics and limitations that resistivity-log interpreters need to understand.
Chapter 3 provides a limited number of benchmark tool-response examples under various conditions and geometries that affect resistivity-tool response. These one-, two-, and three- dimensional benchmark responses illustrate the complexity of resistivity-tool response and ambiguity in the interpretation.
Chapter 4 describes resistivity-tool-response modeling as a formation-evaluation tool. A rec- ommended procedure of resistivity modeling for formation evaluation is discussed.
Chapter 5 presents two case studies of resistivity-tool-response modeling applied as a forma- tion-evaluation tool.
Chapter 6 covers sensitivity, limitations, and uncertainty in the resistivity-tool-response mod- eling with a series of benchmark examples. Potential error inherent in the hydrocarbon satura- tion due to the limited accuracy of the tool response is systematically analyzed and illustrated.
Chapter 7 summarizes the learning and the technical conclusions of earlier chapters, and dem- onstrates the cost and benefit of resistivity modeling.
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