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Bureau of Mines investigations show the Hartshorne coal beds of the Arkoma basin are among the most gassy in the United States. The Hartshorne coal beds in Haskell and
LeFlore Counties, Oklahoma, contain 1.1 to 1.5 Tcf of methane; these coal beds are expected to contain a similarly high methane content in deep parts of the basin farther 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 coal beds with an apparent thickness of up to 8 ft (2.4 m), flanking a linear body of Hartshorne Sandstone in Pittsburg and Coal Counties. The natural gas produced from wells along this and other linear trends of thick Hartshorne Sandstone probably originated in the associated coal beds.
The depth of the coal (up to 4,000 ft or 1,219 m) and its proximity to several gas fields producing from the Hartshorne Sandstone suggest a high methane content (200 to 600 cu ft/ton) for the Hartshorne coal beds in the western parts of the Arkoma basin. However, methane content is not as high as in coal beds farther east at similar depths because of the lower rank (less thermal maturation and therefore lower gas generation) of coal beds 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 coal beds.
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