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GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions Vol. 58 (2008), Pages 607-621

Hydrocarbon Potential of the Deep Travis Peak Formation and Underlying Strata, Western Margin of the East Texas Basin

Yamin Li1 and Walter B. Ayers2

1Schlumberger Data Consulting Services, 1700 Research Pkwy., Ste. 100, College Station, Texas 77845

2Harold Vance Department of Petroleum Engineering, Texas A&M University, 3116 TAMU, College Station, Texas 77843

ABSTRACT

As U.S. conventional natural gas resources are depleted, resources in low-permeability (tight) sandstone are increasingly important to domestic gas supply, and their importance will increase worldwide in future decades. Tight sandstones in the Travis Peak Formation (TP) have produced gas since the 1940s. From 1961 through 2005, TP cumulative gas production along the western margin of the East Texas Basin was 1.43 trillion cubic ft (TCF) from fluvial-deltaic sandstones. The objective of this study was to assess the potential for basinward (southeastward) extension of TP production from the western margin of the basin.

We evaluated structural and stratigraphic settings of the TP in an 11-county area, using five regional 2D seismic lines and 580 well logs. Along the west margin of the East Texas Basin, TP gas is produced from southeast-trending sandstones that were deposited by the Ancestral Red River fluvial-deltaic system. In the downdip study area, TP sandstones were deposited in fluvial-deltaic, shelf, slope, and deepwater environments.

Drilling mud densities suggest that strata deeper than 12,500 ft (3800 m) may be overpressured, and the geothermal gradient (1.6°F / 100 ft; 2.9°C / 100 m) indicates that this overpressure may be relict, resulting from hydrocarbon generation by source rocks of the Smackover and Bossier formations (Li, 2007). Faults associated with the Louann Salt deformation extend from the Smackover and Bossier formations to the TP, providing possible gas-migration pathways to reservoir sandstones.

Along the western margin of the East Texas Basin, TP gas is produced from structural, stratigraphic, and combination traps. Because there are few downdip well logs and seismic lines, our ability to identify specific structural or stratigraphic traps in this region was limited. However, several potential downdip hydrocarbon plays observed in the TP and/or underlying strata include (1) updip pinch-outs of fluvial, deltaic, slope, and submarine fan sandstones, (2) pinch-outs of deltaic sandstones below a TP unconformity, (3) sandstone pinch-outs at margins of salt-withdrawal basins, and (4) traps associated with salt structures.

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