PRELIMINARY RESULTS FROM A COAL-BED METHANE TEST WELL IN OUACHITA PARISH, LOUISIANA

Little information is publicly available about the coal-bed gas potential of coal deposits underlying the Gulf of Mexico Coastal Plain.  In March 2003, the U.S. Geological Survey, the Geological Survey of Louisiana, and EnerVest Management Partners, LTD., through a Cooperative Research and Development Agreement, drilled and cored a coal-bed methane test well (Lat.: 32^o 39' 24.770" N; Long.: 91^o 57' 23.609" W;  Sec. 4, T19N, R5E) on the flanks of the Monroe Uplift in northeastern Ouachita Parish, Louisiana.  The drill hole reached a total depth of 496 m (1,628 ft).  Coal and carbonaceous shale core samples were recovered from four coaly zones in the Wilcox Group (Paleocene-Eocene) that ranged in depths from 401 to 482 m (1,317 to 1,581 ft).  Maximum individual coal bed thickness is 1.8 m (5.8 ft). 

For the Wilcox coal samples, the equilibrium moisture content ranges from 18.2% to 30.63% by weight and ash yield ranges from 6.24% to 44.54% by weight on an equilibrium moisture basis.   Estimated ranks using the Parr Formula for the coal samples range from subbituminous C to subbituminous B.  Gas content determined by canister desorption ranges from 0.59 to 1.28 cm³/g (18.94 to 41.08 scf/ton) on a raw coal basis, or 1.28 to 2.15 cm³/g (40.98 to 69.01 scf/ton) on a dry, ash-free basis.  The gas content of the coal samples increases with depth.  Methane sorption isotherms performed on both individual and composite samples indicate that the coals are undersaturated with respect to gas content.  The d¹³C_CH4 and dD_CH4 composition of the coal gas ranges in values from -65.57‰ to -63.75‰ (relative to the Pee Dee Belemnite), and from -194.4‰ to -190.8‰ (relative to Standard Mean Ocean Water) respectively.  These values suggest the coal gas originated via bacterial reduction of CO₂.  Several analyses of produced water samples from the test well shows pH ranges from 6.98 to 7.65, and total dissolved solids range from 7,200 to 16,000 mg/l.  A pump test run on the lower 1.2 m (4 ft) coal zone indicates a range of 2 to 18 milidarcies permeability.  Gas production from this well has not proved to be economic to date; however, equivalent, deeper coal beds, occurring down-dip in the basin, are expected to have greater ranks and increased gas contents, and may be more productive than those found in this test well.