POTENTIAL OF ILLINOIS BASIN COALS FOR UNDERGROUND COAL GASIFICATION

Underground coal gasification (UCG) is a technology that can complement traditional methods of coal mining and surface gasification and expand the coal resource base by utilizing deep and poorer quality coals that cannot be mined. This technology converts coal into a combustible gas (syngas) that can be used for industrial heating, power generation, and the manufacture of hydrogen, synthetic natural gas, or diesel fuel. In the UCG process, the cavity formed in the coal seam becomes the reactor, so the gasification of coal takes place underground. Selecting appropriate sites for UCG plants and determining the most suitable UCG technologies and practices are complex processes, and a variety of technical and geological factors must be taken into consideration.

To evaluate UCG potential in the Illinois Basin, we considered operational experiences of various UCG projects around the world along with geological characteristics of Illinois Basin coals. Thickness and depth were chosen as the primary screening criteria, followed by quality of the coal and characteristics of associated clastic sediments. Based on the basin geology and the specifics of the UCG process, we conclude that the most suitable coals for the UCG process in the basin are those thicker than 2 m (6.5 ft) and occurring deeper than 200 m (656 ft) from the surface, whereas those thinner than 1 m (3.2 ft) and shallower than 60 m (197 ft) are unacceptable. The Springfield and the Seelyville Coal Members were identified as the main targets for UCG in the basin. Our evaluation suggests that geological conditions in the Illinois Basin are generally suitable for UCG technology, and environmental impacts such as contaminant transport beyond the reactor zone or subsidence could be successfully addressed by using proper preventive strategies and remediation plans. However, the coal blocks that are large enough to support a long-term commercial UCG project are not common in the basin. In addition, at this point in time, an Illinois Basin UCG plant would likely not be economically competitive with other fossil-fuel-based plants without an economic incentive from federal and state agencies.