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The Methane Potential of the Upper Fort Union Formation Sandstones in the Powder River Basin, Western Campbell County, Wyoming

Michael J. Blackstone
University of North Dakota, Grand Forks, ND

A portion of the Powder River basin (PRB) 96 miles long and 18 miles wide was examined in order to establish the relationships between the major upper Fort Union coal beds and stratigraphically equivalent sand bodies. The area included a south to north divide between thick coal zones as delineated by thickest coal maps of the PRB. Previous authors have written about east to west “deltas” within the coal zone that appeared to coalesce along this south-north thin coal trend. A commercial value exists in studying the sandstones associated with these coals, as stated by Oldham (1997) in his report on the Oedekoven and Chan shallow gas fields. These two fields produced approximately 2 BCF of water-free methane.

Several cross sections were created across the project area. Due to the shallow depth to the sands, mainly gamma ray logs were available to construct the cross sections. Sandstone isopach maps were then created using these cross sections. These maps strongly suggest the presence of a six mile wide, sand-rich paleofluvial system that drained the basin north across the study area, parallel to the strike of the PRB. The “deltas” from the east may be tributary fluvial channels.

Differential compaction and updip meanders in this north-south trending system set up potential traps for gas generated by the coal beds. Discovery will depend upon running resistivity or density-neutron logs along with the common gamma ray logs to detect gas within the sand bodies.