Maria Mastalerz¹, Erik P. Kvale¹
(1) Indiana Geological Survey, Bloomington, IN

Abstract: Coalbed gas potential in Illinois Basin based on recent data from Indiana

The occurrence of coal-bed gas shows an uneven distribution in Pennsylvanian coalbeds in the Illinois Basin. Along the eastern margin of the Illinois Basin in Indiana, such a variable distribution is evident both laterally and vertically within the Pennsylvanian section. In the Atokan Brazil Formation of Daviess County, volumes of gas can be generally related to the depth of burial. However, some coal seams, for example the Lower Block Coal Member, are more gas prone than others. Rapidly deposited mud-rich tidal rhythmites directly overlying the Lower Block coal formed a suitable cap rock, resulting in the preservation of significant volumes of gas even at depths as low as 200'(61m) to 300'(91m). In the Springfield Coal Member of Gibson County, there is also general correlation between volumes of gas and the depth of burial within the 240' (73m) to 370' (113m) depth interval, although gas is depleted in the sections overlain by thick sandstone bodies. In Posey County (the deepest part of the basin in Indiana), gas contents of all major Pennsylvanian seams were evaluated from two boreholes, the deeper of which reached 1276' (389m). The gas volumes show erratic changes with depth, partly related to the lithological composition of the sediments overlying the coals, and the proximity to the seams of sandstone-dominated sequences in particular.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana