Evaluation of Travis Peak gas reservoirs, west margin of the East Texas Basin

摘要

Gas production from low-permeability (tight) gas sandstones is increasingly important inthe USA as conventional gas reservoirs are being depleted, and its importance willincrease worldwide in future decades. Travis Peak tight sandstones have produced gassince the 1940s. In this study, well log, 2D seismic, core, and production data were usedto evaluate the geologic setting and reservoir characteristics of the Travis Peakformation. The primary objective was to assess the potential for basinward extension ofTravis Peak gas production along the west margin of the East Texas Basin.Along the west margin of the East Texas Basin, southeast-trending Travis Peaksandstones belts were deposited by the Ancestral Red River fluvial-deltaic system. Thesandstones are fine-grained, moderately well sorted, subangular to subrounded, quartzarenites and subarkoses; reservoir quality decreases with depth, primarily due todiagenetic quartz overgrowths. Evaluation of drilling mud densities suggests that stratadeeper than 12,500 ft may be overpressured. Assessment of the geothermal gradient(1.6 ?F/100 ft) indicates that overpressure may be relict, resulting from hydrocarbongeneration by Smackover and Bossier formation potential source rocks. In the study area, Travis Peak cumulative gas production was 1.43 trillion cubic feetfrom January 1, 1961, through December 31, 2005. Mean daily gas production from 923wells was 925,000 cubic ft/well/day, during the best year of production. The number ofTravis Peak gas wells in ?high-cost? (tight sandstone) fields increased from 18 in thedecade 1966-75 to 333 in the decade 1996-2005, when high-cost fields accounted for33.2% of the Travis Peak gas production. However, 2005 gas production from high costfields accounted for 63.2% of the Travis Peak total production, indicating thatproduction from high-cost gas wells has increased markedly.Along the west margin of the East Texas Basin, hydrocarbon occurs in structural,stratigraphic, and combination traps associated with salt deformation. Downdipextension of Travis Peak production will depend on the (1) burial history and diagenesis,(2) reservoir sedimentary facies, and (3) structural setting. Potential Travis Peakhydrocarbon plays include: updip pinch-outs of sandstones; sandstone pinch-outs atmargins of salt-withdrawal basins; domal traps above salt structures; and deepwatersands.