Pennsylvanian Black Shales and Underground Coal Gasification (UCG) Considerations in Indiana

N. R. Shaffer and M. Mastalerz
Indiana Geological Survey, Bloomington, IN 47405 [email protected]

Thin but widespread black, organic-rich shales overlie several commercial coal beds in Indiana. Such shales should be considered an additional resource when investigating underground coal gasification (UCG) prospects. Several sites in the Springfield Coal Member of the Petersburg Formation and Seelyville Coal Member of the Linton Formation have been identified for UCG in Indiana and many other black-shale rich prospects occur throughout the Illinois Basin. Black Pennsylvanian shales (associated with coals) are known to produce oil, gas, and other fluids during Fischer Assay analyses. Oil yields range from traces to more than 20 gallons/ton; shales above the Springfield Coal Member yield as much as 17.9 gallons/ton. Water (up to 24 gallons/ton), ammonia, and other gases are produced upon retorting. These reactions would also likely occur underground because coal gasification will subject overlying shales to conditions yielding heat, gases, hydrocarbons, and water, which may affect the coal gasification process in many ways. Also, the availability of water is an important factor in gasification processes. Water that is generated through shale reactions could provide in-situ water and so improve prospects for UCG as would added heat input. Shale behavior after heating will also affect gas flow, roof stability, and other geomechanical details. For chemical, energy, and geotechnical reasons, black shales that overlie prospective UCG coal beds should be investigated along with the targeted coals.

AAPG Search and Discovery Article #90095©2009 AAPG Eastern Section Meeting, Evansville, Indiana, September 20-22, 2009