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

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

Hydrologic controls on methane production from Upper Cretaceous and lower Tertiary coal beds in the Greater Green River, Piceance, Powder River, and Raton basins were evaluated by analogy with the San Juan basin. Hydrology of these basins reflects the present-day attitude of aquifers and aquitards, climate, topography, and permeability. In each basin, recharge occurs over its wet, elevated margins. Groundwater flows basinward, down regional topographic gradient and structural dip, convergent on the basin's topographically lowest point. Reservoir conditions were inferred from hydraulic gradient, pressure regime, and hydrochemistry. Gas and water production are predictable in the context of the regional flow system.

In the Greater Green River basin, large volumes of low-chloride water (>500 bbl/day) are produced from coalbed wells along the east and south margins of the basin, reflecting recharge over the nearby Park uplift and Williams Fork Mountains, high permeability, and ground-water flow to the west and north. In the Raton basin, flow is eastward from the elevated flank of the Sangre de Cristo Mountains toward the eastern outcrop belt and Purgatoire River. Water and gas production is high on the west due to proximity of the recharge area, local artesian conditions, and high permeability. Regional underpressure reflects insulation from recharge and an eastward decrease in permeability. The Piceance basin is dominated by underpressure and hydrocarbon-related overpressure, indicating overall low permeability. Very low permeabilities (md) 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, where flowing wells produce low-chloride waters. In the Powder River basin, coal beds are major aquifers that basinward yield large volumes of water (~1500 bbl/day) and small volumes of gas (<100 MCFGD). Produced water will create disposal problems and add to production costs.

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)