Stratigraphic Architecture of Lower to Middle Pennsylvanian Coalbeds in the Forest City Basin of Northeastern Kansas

W. Matthew Brown¹, Timothy R. Carr², and K. David Newell^2
1 Kansas Geological Survey - University of Kansas, Lawrence, KS
² Kansas Geological Survey, Lawrence, KS

The Forest City Basin of northeastern Kansas contains between 5 and 20 thin coalbeds (typically less than 1 m, but as thick as 1.2 m) of variable depositional environments. These coals are interstratified within mixed siliclastic-carbonate cyclothem deposits of the Cherokee and Marmaton groups (Lower - Middle Pennsylvanian). These coals comprise a significant resource within the subsurface of Kansas and vary in rank from high volatile A to C bituminous. While not optimal for coalbed methane production due to thinness and high volatile ranks, lateral persistence across a ten-county area in northeastern Kansas, coupled with sufficient overburden and competent seals make the Forest City basin an intriguing play for coalbed methane exploration.

Continuous cores were described and linked to geophysical well-logs to construct structure and isopach maps and regional cross sections for a better understanding of depositional environments of major coals. Desorption tests of cores and cuttings of numerous coals show gas contents typically ranging from 10 to 60 scf/ton, although there have been measurements up to 160 scf/ton. Methane and proximal coal analyses were performed to determine any variations in geochemical factors. A high-resolution sequence-stratigraphic framework was developed for the Cherokee and Marmaton groups to create depositional models and deduce potential relationships between depositional environment, coal quality, and gas content. A better understanding of spatial, geological and geochemical factors that influence the Cherokee and Marmaton coals is important to understanding coalbed methane potential in northeastern Kansas.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005