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Coalbed natural gas production and desorption characteristics of Pennsylvanian coals in eastern Kansas
David Newell1, Timothy R. Carr2
1Kansas University, 2Dept. of Geology and Geography, University of West Virginia, Morgantown, WV
Middle Pennsylvanian coal units in eastern Kansas commercially produce coalbed natural gas (CBNG). Annual CBNG production in 2008 was approximately 48.3 bcf (12.8% of state output); cumulative production since 2000 is 165 bcf. Individual coal seams are commonly <2 ft in thickness and are mostly produced by vertical wells in 80- to-160 acre spacing. Wells usually produce from several seams. Most production is from a four-county area (Labette, Montgomery, Neosho, and Wilson Counties) near the Oklahoma state line. Most wells are not prolific, for the maximum production rate of 90% of these wells is <65 mcf/day. Decline rates are low, however, and the best CBNG wells have cumulatively produced over 400 mmcf over a 15-year lifetime. Northwest-southeast trending production fairways are evident by mapping maximum production rates. These fairways generally correlate to where coal seams are individually and compositely thick.
The median as-received gas content for coal samples in southeastern Kansas is 140 scf/ton, with maximum gas content of ~400 scf/ton recorded. Gas content in east-central Kansas coal seams generally runs half that of southeastern Kansas, indicating economics of CBNG production are harsher northward. Coal seams increase in depth westward at a rate of ~20 ft per mile. Their gas content commensurately increases by 10 to 20 scf/ton for each 100 ft of burial. Thin (<4 ft) black shale beds interbedded with the coal may also have commercial potential, for their as-received gas content can be great as 65 scf/ton, but 20 scf/ton is the median of all samples assayed.AAPG Search and Discover Article #90097 © 2009 Tulsa Geological Society, Tulsa, Oklahoma
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