Wilcox group coal-bed methane in north-central Louisiana

Significant coal-bed gas resources may exist in subsurface Wilcox Group (Paleocene-Eocene) coal beds that are found across much of north-central Louisiana. About a dozen wells recently completed in Wilcox Group coal zones in this area have an initial production that ranges from 7 to 229 thousand cubic feet (Mcf) of gas per day. Production of saline water from these wells ranges from 0 to 550 barrels (bbls) per day. Depth to the targeted Wilcox coal beds, which have a maximum thickness of about 20 ft, ranges from 1,500 to 5,000 ft. The thickest coal beds tend to be in the lower Wilcox coal zone. Cumulative Wilcox coal thickness can exceed 100 ft. Measured gas content of the coal beds ranges from less than 40 standard cubic ft per ton (scf/t, raw basis; or 65 scf/t dry, ash free basis, daf) at depths less than 1,600 ft, to greater than 158 scf/t (213 scf/t daf) in deeper (>2,700 ft) parts of the basin. Although geochemical and petrographic data from Wilcox Group coals from across the region show that the coal beds are lignite in rank at depths less than about 350 ft, they reach a rank of subbituminous B, or greater, at depths of approximately 2,500 ft. Preliminary gas isotope data indicate that Wilcox coal gas originated from the microbial reduction of CO₂ and that, in some places, these gases may be mixed with migrated thermal gases.