Partitioning of Organic Compounds between Crude Oil and Water under Supercritical CO2 Condition

Abstract:

In recent years depleted oil reservoirs have received special interest as carbon storage reservoirs because of their potential to offset costs through collaboration with enhanced oil recovery projects. Leakage of the injected CO₂ may occur either as supercritical CO₂ or CO₂-saturated (brine) water. The injected supercritical CO₂ is a nonpolar solvent that can potentially mobilize the residual oil compounds into supercritical CO₂ and brine water through phase partitioning. For detailed risk assessment of CO₂ leakage, various models can be used to quantify the mass of organic contaminants transported from carbon storage sites to potential receptors such as potable aquifers, in which the partition coefficients of crude oil hydrocarbons between CO₂/crude oil/brines for subsurface CO₂ sequestration scenarios are the key parameters controlling the fate and transport of organic contaminants along the CO₂ leakage pathways. However, the solubilities of many of the oil organic compounds in brines under supercritical CO₂ condition have not been yet fully determined. In this study, we developed a novel method to accurately measure the partitioning of crude oil organic compounds (BTEX, PAHs, etc.) between supercritical CO₂ and brines and to study the effects of temperature, pressure, salinity, and compound’s cosolvency (solubility enhancement) on the partitioning behavior of oil organic compounds along the various CO₂ leakage paths in the subsurface.