--> Abstract: Hydrology and Production of Coalbed Methane in Western United States Intermontane Basins, by W. R. Kaiser and W. A. Ambrose; #91012 (1992).

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ABSTRACT: Hydrology and Production of Coalbed Methane in Western United States Intermontane Basins

KAISER, W. R., and W. A. AMBROSE, Bureau of Economic Geology, The University of Texas at Austin, Austin, TX

Hydrologic control on methane production in Upper Cretaceous and lower Tertiary coal beds in the Greater Green River, Piceance, Powder River, and Raton Basins can be evaluated by analogy to the San Juan Basin, the leading coalbed methane producing basin in the U.S. Preliminary data suggest that the hydrologic setting of coal beds in these basins is similar to the San Juan Basin and may reflect the present-day attitude of aquifers and aquitards, climate, topography, and permeability. In each of these basins, recharge occurs over wet, elevated margins. Ground-water flow is basinward, down regional topographic gradient and structural dip, convergent on the basin's topographically lowest point. These basinal fluid-flow patterns likely reflect regional permeability contrasts.

As in the San Juan Basin, reservoir conditions in other western coalbed methane basins can be inferred from hydraulic gradient, pressure regime, and hydrochemistry. Normally pressured or artesian coal seams in the Greater Green River Basin yield large volumes of low-chloride water upon production, indicating high permeability. High initial water potentials (~500 bbl/d) in wells along the east and south margins of the basin reflect recharge over the Park Uplift and westward ground-water flow. In the Raton Basin, ground-water flow is eastward from the elevated flank of the Sangre de Cristo Mountains toward the eastern outcrop belt. High water production on the western basin margin reflects proximity to the recharge area. Other areas of high water production are in the Purgatoire River v lley and may also reflect convergent, upward flow. Inferred artesian conditions and associated higher reservoir pressures may contribute to higher gas contents in those areas.

The Piceance Basin is dominated by underpressure and hydrocarbon-related overpressure, indicating overall low permeability. Very low permeabilities (microdarcys) are reported from the underpressured part of the basin, whereas the highest permeabilities (~10 md) are from artesian overpressured coal seams along the Divide Creek Anticline. Artesian conditions are suggested by flowing wells, low-chloride formation waters, and an elevated recharge area. In the Powder River Basin, high-permeability, artesian coal seams may limit economic production of coalbed methane; these coal seams are major aquifers that basinward produce excessive volumes of water (IP's >1,500 bbl/d). Understanding regional ground-water flow patterns is essential to predicting coalbed methane productivity and relate need for water disposal.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)