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Jonah Field, Sublette County, Wyoming: Gas Production from Overpressured Upper Cretaceous Lance Sandstones of the Green River Basin

Scott L. Montgomery1 and John W. Robinson2

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ABSTRACT

Jonah field, located in the northwestern Green River basin, Wyoming, produces gas from overpressured fluvial channel sandstones of the Upper Cretaceous Lance Formation. Reservoirs exist in isolated and amalgamated channel facies 10-100 ft (3-30 m) thick and 150-4000 ft (45-1210 m) wide, deposited by meandering and braided streams. Compositional and paleocurrent studies indicate these streams flowed eastward and had their source area in highlands associated with the Wyoming-Idaho thrust belt to the west. Productive sandstones at Jonah have been divided into five pay intervals, only one of which (Jonah interval) displays continuity across most of the field. Porosities in clean, productive sandstones range from 8 to 12%, with core permeabilities of .01-0.9 md (millidarcys) and in-situ permeabilities as low as 3-20 µd (microdarcys), as determined by pressure buildup analyses. Structurally, the field is bounded by faults that have partly controlled the level of overpressuring. This level is 2500 ft (758 m) higher at Jonah 


©Copyright 1997. The American Association of Petroleum Geologists. All rights reserved.

Grateful acknowledgment is made to Snyder Oil Corporation and Ron Finch, Integrated Petroleum Technologies, for figures and data used in this article. Thanks also to Floyd Bardsley for artwork.

1Petroleum Consultant, 1511 18th Avenue East, Seattle, Washington 98112.

2Snyder Oil Corporation, 1625 Broadway, Suite 220, Denver, Colorado 80202.

Send reprint requests to AAPG Publications Manager, P.O. Box 979, Tulsa, Oklahoma 74101-0979.

Tcf = trillion cubic feet; Gcf = billion cubic feet; Mcf = million cubic feet; 
kcf = thousand cubic feet.

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