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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 49 (1965)

Issue: 7. (July)

First Page: 1083

Last Page: 1083

Title: Brentwood Field: ABSTRACT

Author(s): Donald F. Collins, Donald C. Conner

Article Type: Meeting abstract

Abstract:

The Brentwood field, discovered in 1962 along the upturned western portion of the Sacramento basin, is the first northern California gas field to yield commercial quantities of oil. Volumetric reserve estimates range from 30 to 40 billion cubic feet of gas and 3 to 5 million barrels of oil. Separate accumulations ranging through about 2,000 stratigraphic feet occur in abruptly truncated, northwest-dipping Paleocene and Upper Cretaceous sandstones. From the thin-bedded, deep-water upper Martinez sandstones, dry gas with minor condensate is produced; black oil is contained only in the 3 shallower marine "Massive" sandstones straddling the Cretaceous-Paleocene boundary.

The updip closure for Brentwood's cuesta-like trap is provided by the Meganos channel, a shale-filled, late Paleocene submarine gorge or channel which originally was swept clean to eroded depths of 2,000-2,500 feet. The channel can be observed in the outcrop belt immediately south of the field where it is predominantly shale-filled; however, coarse sandstones and conglomerates present to the west are indicative of a local submarine fan.

A number of major faults evident in outcrop also transect the Brentwood field where they influence the position of oil and gas pools on the structure. For example, hydrocarbon/water levels in the Second Massive sandstone change from 10 to 175 feet across fault boundaries. Progressive thinning of oil columns from east to west may be a function of fault baffles retarding fluid migration, or of facies change, as in the First Massive sandstone.

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Copyright 1997 American Association of Petroleum Geologists