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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
2004. The American Association of Petroleum Geologists. All rights reserved.
Factors controlling prolific 
gas
production from low-permeability sandstone reservoirs: Implications for resource assessment, prospect development, and risk analysis
gas production from low-permeability sandstone reservoirs: Implications for resource assessment, prospect development, and risk analysisKeith W. Shanley,1 Robert M. Cluff,2 John W. Robinson3
17 Lantana, Littleton, Colorado 80127; [email protected]
2The Discovery Group, Inc., 1560 Broadway, Suite 1470, Denver, Colorado 80202; [email protected]
322 North Ranch Road, Littleton, Colorado 80127; [email protected]
AUTHORS
Keith W. Shanley is a consulting geologist with more than 22 years experience in exploration, development, and research. He has published numerous papers dealing with sequence stratigraphy and reservoir architecture and has served as editor of several publications. He received his B.A. degree in geology from Rice University and his M.Sc. degree and his Ph.D. in geology from the Colorado School of Mines. His current research interests include sequence stratigraphy and reservoir architecture, the integration of petrophysics, and risk analysis.
Bob Cluff is a geologist with 28 years petroleum exploration and development experience. Bob's research interests include the integration of geology with petrophysics and the evaluation of nonconventional reservoirs. Bob received his B.S. in geology from the University of California-Riverside, his M.S. from the University of Wisconsin-Madison, with additional studies at the University of Illinois-Urbana-Champaign, University of Colorado-Denver, and Metropolitan State College Denver in geology, math and physics. Bob founded The Discovery Group in 1987.
John W. Robinson is a consulting geologist in Denver and has 30 years of experience in exploration and development. In 1999, he and coauthor Peter McCabe received the AAPG Wallace Pratt Award for the best paper in the 1997 AAPG Bulletin. He received B.S. and M.S. degrees in geology from San Diego State University and a Ph.D. in geology from the Colorado School of Mines. His research interests are in fluvial sedimentology and multidisciplinary reservoir studies.
ACKNOWLEDGMENTS
The ideas expressed in this paper have emerged over many years of trying to better understand tight-gas reservoirs and a near-constant interchange of ideas among the authors. K.W. Shanley acknowledges the contribution of Lee T. Shannon (Anadarko Production Co.) to many of the ideas expressed in this paper. Conversations with Lee regarding the nature of tight gas date back to 1981 when both the senior author and Lee Shannon were graduate students at the Colorado School of Mines. Those conversations have continued to the present. In addition, K.W. Shanley benefited from several people at BP, where exposure to tight-gas data sets had a profound impact. Peter Jordan, Mike Short, Kate Hadley, and Hunter Rowe provided management support of joint projects between business units and the Technology Group. Alan Skorpen, Todd Stephenson, and Mike Bowman provided guidance and support within the Technology Group. Insights into low-permeability reservoirs were gained through discussions with many, including Jack Thomas, Robert Lengerich (now deceased), Dennis Cox, Bill Hanson, and Kirk Hird. In terms of understanding the risks associated with tight-gas decisions, conversations with Peter Carragher were instrumental. Since leaving BP, conversations with Alan Byrnes (Kansas Geological Survey), Sue Cluff (The Discovery Group), Bob Coskey (Platte River Associates), John Dacy (Core Laboratories, Houston, Texas), Tom Feldkamp (Kerr McGee, Denver, Colorado), Jack Thomas (Consultant and AAPG, Tulsa, Oklahoma), and Mihai Vasilache (SCAL Inc., Midland, Texas) have been instrumental. Alan Byrnes provided data on relative permeability, and Dan Soeder (U.S. Geological Survey, Baltimore, Maryland) and Shirley Dutton (Texas Bureau Economic Geology, Austin, Texas) provided photographs of various pore types. Discussions with Peter McCabe and Don Gautier (U.S. Geological Survey, Denver, Colorado) and AAPG reviewers Lee Billingsley, Lee Krystinik, Kent Bowker, and John Lorenz helped to further focus this paper.
ABSTRACT
Low-permeability reservoirs from the Greater Green River basin of southwest Wyoming are not part of a continuous-type gas accumulation or a basin-center gas system in which productivity is dependent on the development of enigmatic sweet spots. Instead, gas fields in this basin occur in low-permeability, poor-quality reservoir rocks in conventional traps. We examined all significant gas fields in the Greater Green River basin and conclude that they all occur in conventional structural, stratigraphic, or combination traps. We illustrate this by examining several large gas fields in the Greater Green River basin and suggest that observations derived from the Greater Green River basin provide insight to low-permeability, gas-charged sandstones in other basins. We present evidence that the basin is neither regionally gas saturated, nor is it near irreducible water saturation; water production is both common and widespread. Low-permeability reservoirs have unique petrophysical properties, and failure to fully understand these attributes has led to a misunderstanding of fluid distributions in the subsurface. An understanding of multiphase, effective permeability to gas as a function of both varying water saturation and overburden stress is required to fully appreciate the controls on gas-field distribution as well as the controls on individual well and reservoir performance. Low-permeability gas systems such as those found in the Greater Green River basin do not require a paradigm shift in terms of hydrocarbon systems as some have advocated. We conclude that low-permeability gas systems similar to those found in the Greater Green River basin should be evaluated in a manner similar to and consistent with conventional hydrocarbon systems.
To date, resource assessments in the Greater Green River basin have assumed a widespread, continuous-type resource distribution. Failure to recognize some of the fundamental elements of low-permeability reservoirs has led to an underappreciation of the risks associated with exploration and development
investment decisions in these settings and likely a significant overestimation of available resource levels.
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