Transport of organic contaminants mobilized from coal through sandstone overlying a geological carbon sequestration reservoir

Successful implementation of large scale carbon capture and storage within deep geologic reservoirs will require public acceptance of the associated environmental risks. In order for this to occur, a better understanding of these risks must be developed. An important risk factor associated with deep geologic storage of CO2 is the potential for leakage of fluids from the storage reservoir that could potentially impact valuable groundwater resources that overlie the storage reservoir. The research described here is focused on the transport and fate of toxic organic compounds mobilized by supercritical carbon dioxide (scCO2) from organic rich storage reservoirs such as unmineable coal seams and depleted oil reservoirs. Column experiments were conducted using a water wetted sandstone core installed in a tri-axial core holder to study the potential for toxic organic compounds mobilized from coal by scCO2 under simulated geologic carbon storage (GCS) conditions to impact groundwater. Rock core effluent pressures were set at 0, 500, or 1000 psig and the core temperature was set at 20 or 50 °C to simulate the transport at different subsurface depths. The concentrations of the organic compounds in the column effluent and their distribution within the sandstone core were monitored. Results indicate that the mobility though the core sample was much higher for BTEX compounds than for naphthalene. Retention of organic compounds from the vapor phase to the core appeared to be primarily controlled by partitioning from the vapor phase to the aqueous phase. Adsorption to the surfaces of the wetted sandstone was also significant for naphthalene. Reduced temperature and elevated pressure resulted in greater partitioning of the mobilized organic contaminants into the pore water.