Turbidite sandstones form gas reservoirs in the deeper Tertiary section of the Gulf Coast province of Texas. Turbidite reservoirs are of three types: (1) thin-bedded sandstones of middle-shelf origin, (2) constructional-channel-fill sandstones, and (3) stacked-channel turbidites. Production in all these reservoirs is associated with structures, but it appears that stratigraphic control exerts a fundamental influence on the accumulation of gas.

Oligocene Frio sandstones at Nine Mile Point field are turbidites which formed in water depths of about 300 ft (100 m). The thin-bedded sandstones are interbedded with bioturbated shales. Sandstones are largely channel turbidites of the "AE" and "ABE" types, but more complete sequences are also present. Bed associations resemble those of submarine fans, but Frio turbidites are concentrated on the downthrown sides of major normal faults, and adjacent anticlinal crests are nearly barren of porous sand. The sandstones are clayey, and maximum permeabilities are in the range of 10 to 50 md.

Eocene lower Wilcox sandstones at Northeast Thompsonville field are massive turbidites of channel

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origin. Bed sets are of the "AE" and "ABE" types. The channel-fill sandstones appear to have been deposited in constructional channels, narrowly bordered by more thinly bedded levee deposits. Multiple-channel sandstones cross anticlinal structure at Northeast Thompsonville field, but in others areas the occurrence of oil and gas is not related to structural closure. The sandstones are highly quartzose, and maximum permeabilities are in the range of 100 to 200 md.

Oligocene Vicksburg sandstones at McAllen Ranch field form a thick series of channel turbidites of the "AE" and "ABE" types with interbedded, more complete, turbidite sequences. These stacked-channel sandstones probably represent inner-fan deposits. Associated anticlinal structures are probably the result of differential compaction over thick concentrations of channel turbidites. The sandstones are clayey, and maximum permeabilities are in the range of 10 to 50 md.

The relatively abundant turbidites in these deep sections indicate that sand transport in a dip direction was a common mechanism that operated through much of the Tertiary. Although many of these sandstones have low permeabilities, they have the potential to form important, stratigraphic accumulations of natural gas through most of the deep, basinal section.

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