Abstract

Bureau of Mines investigations show the Hartshorne Coalbeds of the Arkoma Basin are among the most gassy in the country. The Hartshorne Coalbeds in Haskell and LeFlore Counties, Oklahoma contain between 1.1 to 1.5 trillion cubic feet of methane and these coalbeds are expected to have similarly high methane contents in deep portions of the basin further to the west in Pittsburg, Coal, and Hughes Counties.

Various geophysical logs from gas wells were used to analyze thickness, and sedimentary facies of the Hartshorne Formation in the Arkoma Basin. Bulk density and sonic logs indicate the presence of Lower and Upper Hartshorne Coalbeds with an apparent thickness of up to 8 feet flanking a thick, linear body of Hartshorne Sandstone in Pittsburg and Coal Counties. Natural gas production presently occurs along this and other linear trends of thick Hartshorne Sandstone. The gas in the Hartshorne Sandstone reservoir probably originated in and migrated from the associated coalbeds.

The depth of the coal (outcrop to 4,000 feet) and proximity to several gasfields producing from the Hartshorne Sandstone suggest a high methane content (200 to 600 cu ft/ton) for the Hartshorne Coalbeds in the western portions of the Arkoma Basin. However, methane content will not be as high as coalbeds further to the east at similar depths because of the lower rank (less thermal maturation and therefore lower gas generation) of coalbeds in Pittsburg, Coal, and Hughes Counties. Effective placement of gas drainage wells should take into consideration the thickness and depth of coal, possible communication with the natural gas bearing Hartshorne Sandstone, and rank of associated coalbeds.