Liquid and Gaseous Hydrocarbons from Underground Coal Thermal Treatment

Much attention has been focused on in-situ processing of unconventional fossil reserves such as oil shale for production and liquid and gaseous hydrocarbons; however, there is potential for higher hydrocarbon yields with the thermal processing of deep coal seams, that may not be accessible by conventional mining practices but can be accessed using modern horizontal drilling technology. The University of Utah has been studying the feasibility of Underground Coal Thermal Treatment (UCTT) as a means of producing an alternative source for hydrocarbon liquids and gases. UCTT involves the in-situ pyrolysis of large coal seams in the absence of oxygen to yield a synthetic natural gas and some liquids. By pyrolyzing in-situ, much of the coal-based carbon remains underground as char, which produces hydrocarbon products with a higher H:C ratio than the parent coal. While coal pyrolysis has been extensively studied over several decades, the unique conditions relevant to UCTT of very low heating rates, low pyrolysis temperatures, very extended physical pyrolysis domains (not small particles), and physical confinement of the pyrolyzing coal, have received very little investigation. This paper will present the results of a series of experimental studies that have focused on identifying and quantifying gaseous and liquid hydrocarbons species and their evolution rates under conditions that are unique to UCTT.