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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.
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.