Partitioning behavior of organic contaminants in carbon storage environments: A critical review

Carbon capture and storage is a promising strategy for mitigating the CO₂ contribution to global climate change. The large scale implementation of the technology mandates better understanding of the risks associated with CO₂ injection into geologic formations and the subsequent interactions with groundwater resources. The injected supercritical CO₂ (sc-CO₂) is a nonpolar solvent that can potentially mobilize organic compounds that exist at residual saturation in the formation. Here, we review the partitioning behavior of selected organic compounds typically found in depleted oil reservoirs in the residual oil-brine-sc-CO ₂ system under carbon storage conditions. The solubility of pure phase organic compounds in sc-CO₂ and partitioning of organic compounds between water and sc-CO₂ follow trends predicted based on thermodynamics. Compounds with high volatility and low aqueous solubility have the highest potential to partition to sc-CO₂. The partitioning of low volatility compounds to sc-CO₂ can be enhanced by cosolvency due to the presence of higher volatility compounds in the sc-CO₂. The effect of temperature, pressure, salinity, pH, and dissolution of water molecules into sc-CO₂ on the partitioning behavior of organic compounds in the residual oil-brine-sc-CO₂ system is discussed. Data gaps and research needs for models to predict the partitioning of organic compounds in brines and from complex mixtures of oils are presented. Models need to be able to better incorporate the effect of salinity and cosolvency, which will require more experimental data from key classes of organic compounds.