EXPERIMENTAL DETERMINATION OF THE CO2-BRINE PARTITION BEHAVIOR OF ORGANIC CONTAMINANTS AND TRACER COMPOUNDS WITHIN A GEOLOGIC CARBON STORAGE P-T ENVELOPE

After subsurface injection, a migrating buoyant plume of carbon dioxide experiences a range of pressure and temperature conditions that affect the relative partitioning of nonionic chemical species between the fluid CO₂ phase and the aqueous phase. These effects are most dramatic near the critical point of CO₂. While most groundwater is relatively low in organic contaminants, groundwater associated with hydrocarbon migration pathways, enhanced oil recovery, and hydrocarbon storage or extraction can contain high values of known contaminants. Therefore, CO₂ injection in these systems is therefore more likely to result in partitioning of organic contaminants into the CO₂ phase that could, upon migration, represent an important risk to groundwater resources. When considering the need to accurately model and predict behavior of organic contaminants in the subsurface the existing data related to organic contaminant and tracer partition coefficients between brine and carbon dioxide are insufficient. This work describes the experimental apparatus and determination of partition coefficients between brine and CO₂ for a suite of compounds including benzene, toluene, ethylbenzene, xylene (BTEX), and polynuclear aromatic hydrocarbons (PAHs). These experiments are undertaken in cylindrical flexible gold foil cells with pre-treated Ti tops encased by a high-pressure autoclave. In addition, CO₂-brine partition coefficients are determined for the important gas phase tracer compounds: SF₆, krypton, and xenon covering a P-T envelope consistent with CO₂ injection and CO₂-rich fluid migration pathways.