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John R. SanFilipo1, Charles E. Barker2, Ron W. Stanton1, Peter D. Warwick1, Loyd E. Morris3
(1) U.S. Geological Survey, Reston, VA
(2) U.S. Geological Survey, MS 939, Box 25046, Denver, CO
(3) Texas A&M University, College Station, TX

Abstract: A shallow coal-bed methane show in the Gulf Coast of Texas, indication of down-dip commercial potential?

A shallow USGS coal-bed methane (CBM) test hole drilled about 25 km southeast of Carthage, in southeastern Panola County, TX, yielded a sub-commercial show of gas. Sixteen sequential samples of the 5.5-m-thick Naborton-2, a regionally extensive lower Wilcox (Paleocene) coal bed in the Sabine uplift area, penetrated at 108 m depth, all yielded gas. Compositional analyses indicate that the gases desorbed from the coal were diluted to about 16% methane by the introduction of air during sampling. Hydrocarbon analyses indicate that the coal-bed gas is very dry with a C1/C2+C3 ratio of 103. Isotopic analyses of the methane indicate a ^dgr13C of -55.82‰ and a ^dgrD of -194.6‰. The isotopic composition of CO2 is ^dgr13C of -11.22‰. These isotopic signatures suggest that the gas was generated in place during the transition between biogenic and thermogenic realms, consistent with the presumably subbituminous rank of the coal (analyses in progress). The dryness of the gas, however, suggests little thermogenic contribution. Total coal-gas content on a whole-coal basis ranged from 3 to 7 scf/ton. A second hole located near the LA state line, about 20 km up dip to the northeast, yielded no gas from the same bed at similar depths. At both localities this bed is dominantly composed of fusain-rich, attrital coal facies, with a minor amount of vitrain-rich (woody) facies. Although the gas yield is very low, our data suggest that deeper or less inertinitic Gulf Coast coals may warrant testing for commercial CBM.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana