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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 64 (1980)

Issue: 9. (September)

First Page: 1556

Last Page: 1556

Title: Environment of Deposition of Upper Wilcox Sandstones, Katy Gas Field, Waller County, Texas: ABSTRACT

Author(s): Gilbert J. Depaul

Article Type: Meeting abstract


At Katy gas field, sandstones of the upper Wilcox Group produce gas at depths of 10,021 to 11,000 ft (3,054 to 3,353 m) in reservoirs controlled by stratigraphic and structural characteristics. Producing zones are from 6 to 42 ft (1.8 to 12.8 m) in the upper Wilcox "First Lower Massive" sandstones, and "D," "C," "B," "A," and "Second Wilcox" interbedded sandstones and shales. The reservoir sandstones are dip-trending with production being localized on the top of the anticline.

The upper Wilcox sequence has been interpreted as delta-front grading upward to bay-marsh transitional deposits and, alternately, as deep-water turbidite deposits. The field is located downdip from the Wilcox fault zone, downdip from known delta-destructional deposits in the upper Wilcox, and is as much as 45 mi (75 km) downdip from the postulated late Sabinian shoreline. Full-diameter cores from the upper Wilcox sequence show the sandstones are submarine, constructional-channel turbidites, giving way vertically to thinner turbidite sandstones in a predominantly shale section. The sandstones are representative of submarine fan deposits, having bedset associations characteristic of channel deposits (A, AB, and ABD) becoming middle fan associations (AE, BE, ABCE, and BCE) and then outer fan associations (ABE, BDE, CDE, and DE) upward in the section. The thicker channel sandstones show limited lateral extent along strike, grading to thin, overbank sandstones.

Sandstones are sparsely bioturbated, and shales are bioturbated only when they overlie sandstones. The burrows are characteristic of a wide range of water depths from middle neritic to bathyal. Benthonic forams found in the cores are abraded by transport and represent a range of water depths from middle to outer neritic. Therefore, water depths during Wilcox deposition were probably bathyal, as indicated by deeper water trace fossils.

The deposition of the upper Wilcox Group is associated with transgression during late Sabinian and incipient uplift of a deep-seated, diapiric mass under the field. Electric-log correlations and sandstone isopach maps suggest that the sands were deposited as parts of a submarine fan that shifted northeastward through time.

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