Using Stable Carbon Isotopes to Monitor for Potential Leakage of CO2 at an Enhanced Coal Bed Methane Recovery Site in Marshall County, WV.

摘要

Enhanced coal bed methane recovery, also known as ECBM, is a carbon capture and storage method in which carbon dioxide is injected into depleted gas formations (specifically unmineable coal beds) to aid in coal bed methane recovery for industrial uses. Produced natural gas, shallow groundwater, and soil vadose gas samples were collected at the CONSOL Energy Inc. CO2 Sequestration Pilot Test Site located in Marshall County, WV to test the feasibility using carbon isotope signatures to detect potential leakage of CO2 into overlying formations. CO2 was injected into the Upper Freeport coal seam at a depth of 396 m below valley bottom surface intermittently from September 2009 to December 2013. Water and gas samples were collected for isotopic analysis over a 12-month period (August 2013-August 2014). One set of water and gas samples collected in August 2013 was during an extended period of injection. The rest of the samples were collected during times the system was down or during the post-injection monitoring period that began in January 2014. The distinct carbon isotope signatures of the injected CO2, soil CO2, and coal bed CO2 allows us to use delta 13C as a natural tracer to detect any potential leakage from the injection coal bed into the overlying coal bed, aquifers and shallow soil zone. The range of the carbon isotope values observed in each of the overlying systems (i.e. overlying Pittsburgh coal seam, groundwater aquifer and shallow soil) indicate carbon originated from natural sources and processes within individual systems. There appears to be no influence of the injected CO2 on the delta13C values of the overlying systems. The initial results indicate that there was no significant leakage of CO2 from the Upper Freeport coal seam to the overlying formations at the time of sampling.