This paper presents interim data for an ongoing project funded by the Gas Research Institute (GRI). The project objective is to obtain quantitative estimates of reservoir properties for a subbituminous Powder River Basin coal gas reservoir. The study is important since coal gas reservoir data are scarce in the Powder River Basin and for subbituminous coal in general.
The subbituminous Powder River Basin (PRB) coal possesses characteristics that are dramatically different from the commercially developed areas in the San Juan, Warrior, and other basins. In particular, water content is very high, gas content is low, ash content is low, and absolute permeability is much greater, ranging from tens of millidarcies to more than a Darcy. Early in this decade, conventional wisdom concluded that large-scale commercial production of natural gas from Powder River coal seams was not possible. The coals were recognized as high permeability aquifers that could not be sufficiently “dewatered” to produce sorbed natural gas. Conventional wisdom was wrong, as has so often been the case when dealing with coal seams. Gas can be released from the coal matrix in commercial quantities even when gas content is low and permeability is high. This fact has been proven by numerous PRB operators over the past six years who have concentrated development along the basin's margins in thick coals typically 250 to 1,000 feet deep.
Redstone Resources, Inc. allowed GRI access to the Triton Federal #21C-2623 well located in Section 26, Township 52 North, Range 73 West, Campbell Co., WY. This well was cored and logged and is currently being tested. Redstone has also graciously allowed us to present data from the Twenty Mile #21C-3523 well located roughly 1 mile south of the Triton well in Section 21. Both wells are located on the eastern margin of the basin as illustrated in Figure 1, just west of large strip mines located near the outcrop. The specific coal target was the Canyon coal seam that belongs to the Tongue River Member (late Paleocene) of the Fort Union Formation. The depth of the Canyon coal seam is shallow in both these wells, 557 to 621 feet at the Triton location and 530 to 594 feet at the Twenty Mile location.