ASSESSING THE CARBON SEQUESTRATION POTENTIAL OF “UNMINEABLE” COAL BEDS IN THE APPALACHIAN BASIN

There are increasing global initiatives to limit anthropogenic atmospheric carbon. In order to address the potential need for limiting carbon emissions, the U.S. Department of Energy has initiated a network of federal, state, and private sector partnerships to determine suitable technologies, regulations, and infrastructure for future carbon capture, storage, and sequestration in different parts of the country. Unmineable coal beds are one potential type of geologic sequestration reservoir. Coal beds are attractive sequestration reservoirs because they adsorb CO2 and because the sequestered CO2 will displace in-place methane, which can be recovered as a fuel. For sequestration purposes, coal beds need to be below drainage and below the level of surface fractures. Deep coal exploration tests and density logs from oil and gas wells that do not case off coal-bearing strata can be used to estimate cumulative thickness and depth of coals more than 1 foot thick and more than 500 feet below drainage. However, defining “umineable” coals from this cumulative deep resource is problematic. In concept, the idea of using unmineable coals offers a vast reservoir area for sequestration because the Appalachian Basin (and other basins) has significantly more deep, thin, unmined coals than shallow, thick, mineable coals. Also, many coal beds have broad spatial distribution in the basin, so may be near carbon dioxide point sources. The criteria for unmineable resources, however, varies because of geologic, economic, environmental, and political considerations. Some of the criteria addressed in a recent assessment of carbon sequestration potential in the northern and central Appalachian Basin by the Midwest Regional Carbon Sequestration Partnership include thickness and depth restrictions based on current mining practices, stratigraphic limits based on coal beds that are not currently mined, and area restrictions that exclude regions of current mining. These criteria are not universal across the coal fields of the basin, thus different procedures are required in different areas of the basin for accurate CO2 sequestration assessments.