Newell, K. David1, Troy A. Johnson1, W. Matthew Brown1, Jonathan P.
Lange1, Timothy R. Carr1
(1) Kansas Geological Survey, University of Kansas, Lawrence, KS
ABSTRACT: Geological and Geochemical Factors Influencing the Emerging Coalbed Gas Play in the Cherokee and Forest City Basins in Eastern Kansas
Coals and organic shale in the Middle Pennsylvanian (Desmoinesian) Cherokee and Marmaton Groups are becoming increasingly important commercial sources for unconventional gas in eastern Kansas, with over 200 wells being drilled in the last two years. Most of the development is in a five-county area in southeastern Kansas (Chautauqua, Labette, Montgomery, Neosho, and Wilson counties), but exploration and production is expanding northward and westward, particularly along pipelines. Initial data indicate that numerous coals can be perforated and produced in an individual well. Pennsylvanian paleotopography and depositional processes have a strong influence on the distribution, thickness and quality of individual coals. Gas content of individual coals generally decreases north-northeast along regional strike, and eastward where strata onlap onto the Ozark dome. Gas content of the coals generally increases with depth and confining pressure to a maximum of 250 to 300 standard cubic feet/ton (scf/ton). However, some shallow coals at less than 700 feet in depth have unexpectedly large gas contents (>100 scf/ton) exceeding that of deeper coals. Compositional (hydrocarbon gas wetness) and isotopic analyses (C13, D for methane) for coalbed gases suggest that a microbial influence may account for local enrichment. Analyses of conventionally-produced gases from Pennsylvanian and Mississippian reservoirs in eastern Kansas indicate that coalbed gases can have a microbial component, with a thermogenic influence increasing with increasing depth into the Cherokee and Forest City Basins.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.