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