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Abstract

AAPG Bulletin, V. 88, No. 2 (February 2004), P. 213-239.

Copyright copy2004. The American Association of Petroleum Geologists. All rights reserved.

Petroleum geology and geochemistry of the Council Run gas field, north central Pennsylvania

Christopher D. Laughrey,1 Dan A. Billman,2 Michael R. Canich3

1Pennsylvania Department of Conservation and Natural Resources, Topographic and Geologic Survey, Subsurface Geology Section, 400 Waterfront Drive, Pittsburgh, Pennsylvania 15222-4740; [email protected]
2Billman Geologic Consultants, P. O. Box 567, 402 Lincoln Avenue, Mars, Pennsylvania 16046
3Equitable Production, Allegheny Center Building, South Commons, Suite 414, Pittsburgh, Pennsylvania 15212

AUTHORS

Christopher D. Laughrey is a senior geologic scientist with the Pennsylvania Geological Survey where he has worked since 1980. He also teaches a graduate course in sandstone petrology for the Department of Geology and Planetary Sciences at the University of Pittsburgh. Laughrey worked as a geophysical analyst for the Western Geophysical Company in Houston, Texas, before taking his present position in Pittsburgh, Pennsylvania. His special interests include isotope and organic geochemistry, sedimentary petrology, borehole geophysics, and geographic information system applications in the earth sciences.

Dan A. Billman received his B.S. degree from the University of Toledo in 1986 and his M.S. degree from West Virginia University in 1989. Dan worked for Mark Resources Corporation and Eastern States Exploration Company prior to forming Billman Geologic Consultants, Inc., where he is president and principal geologist. Dan's current interests include geologic and economic evaluation of development and exploratory projects, especially in the Appalachian basin.

Michael R. Canich has worked 26 years in the oil and gas industry, beginning with two years developing exploration prospects in the Gulf of Mexico. The last 24 years have been spent in the Appalachian basin exploring and developing natural gas in Silurian and Devonian aged tight gas sand reservoirs. He is currently the director of Reserve Development for Equitable Production Company in Pittsburgh, Pennsylvania.

ACKNOWLEDGMENTS

We thank Equitable Resources and Statoil Energy, Inc., for permission to use freely their geological and geophysical data in the preparation of this report. We especially thank Bruce Jankura, Statoil's former senior vice president of Production and Operations at Council Run, for his help with collecting data and arranging gas sampling. We thank Dennis Coleman, Isotech, for his assistance in obtaining stable isotope data for the gases produced at Council Run and adjacent fields. Donald Hoskins, Samuel Berkheiser, John Harper, Kathy Flaherty, and Thomas Flaherty all read earlier drafts of this report, and we appreciate their reviews and constructive comments. We also appreciate the beneficial reviews by R. C. Milici, M. H. Feeley, and T. L Dunn, which helped us improve the manuscript. Released by permission of the director, Pennsylvania Bureau of Topographic and Geologic Survey.

ABSTRACT

The Council Run field of north central Pennsylvania is one of the most productive natural gas fields in the central Appalachian basin. The field is enigmatic because of its position near the eastern edge of the Appalachian Plateau, where strata with reservoir potential elsewhere have low porosities and permeabilities or are poorly sealed. Council Run has four principal reservoir sandstones. The lower three occur in a distinct fourth-order type 1 stratigraphic sequence. The stacking pattern of sandstones in this sequence defines lowstand, transgressive, and highstand systems tracts.

Core, well-log, and map interpretations reveal that the lowest interval consists of multiple coarsening-upward parasequences deposited in deltaic and nearshore environments of the lowstand systems tract during a forced regression. Most of these sandstones are lithic, and some are highly feldspathic. Productive sandstones display hybrid void textures that consist of reduced primary intergranular pores preserved, in part, by relatively early petroleum emplacement and secondary oversized fabric-selective pores.

The generative potential of the organic matter in the potential source rocks is exhausted, but geochemical and petrographic evidences indicate that these black shales originally contained oil-prone kerogens and generated liquid hydrocarbons. Stable isotope geochemistry suggests that gases were generated by primary cracking of kerogens and/or by secondary cracking of oil between 320 and 290 Ma. Dispersive migration paths were both lateral and vertical because of compression associated with Alleghanian orogenesis. Most of the oil in the Devonian section was cracked to gas during deeper burial between 270 and 240 Ma.

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