Linkage Between Lower Pennsylvanian Sandstone Diagenesis and Carbon Sequestration Reservoir Quality in Russell County, Virginia
Carbaugh, Joyce E.
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An enhanced coal-bed methane facility in Russell County, Virginia is targeting lower Pennsylvanian coals for CO2 storage, but the shallow sandstone units intercalated with the coals may also prove to be potential CO2 reservoirs, since the injection apparatus is already in place. Using samples from a continuous core in southwestern Virginia, this detailed review of the petrography and local volume of the Breathitt Formation sandstone units examines their diagenetic alterations in order to assess the unitsâ reservoir quality. The high-frequency sequences of immature sandstones, heterolithics, shales and coals in Russell County represent deposits from the transverse fluvial facies association of a broad braided-fluvial drainage system in the central Appalachian Basin. The sandstone units within these sequences are laterally extensive, maintaining similar thickness and gamma ray signature across the study area. Lower Pennsylvanian sandstone units are consistently sublitharenite with a diagenetic mineral assemblage including siderite, chlorite, kaolinite, albite, illite, silica and calcite. Primary porosity is not preserved, but secondary porosity (5 Â± 3.1 %) has developed at the expense of feldspars and unstable lithic fragments. Permeability assessments collected in Grimm (2010) measured impervious values (0.005-0.008mD) for the medium-coarse grained sublitharenites. At the temperatures and pressures present within these units, CO2 is unlikely to react with either the primary or diagenetic mineralogy in a way that negatively impacts continued injection on human time scales. Low pore volume and permeability due to the timing of certain authigenic mineral emplacement are the main hindrance to reservoir quality. Lower Pennsylvanian sandstones are not viable potential reservoirs for carbon sequestration.
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