Geologic carbon sequestration is widely accepted as a key strategy for reducing anthropogenic emissions of CO2. At typical injection depths (&gt;800 m), CO2 will exist as a supercritical fluid that can act as an effective solvent for a broad range of organic compounds. Consequently, at storage locations where organics are present (e.g., depleted oil or gas reservoirs or sites with enhanced oil recovery operations), injected CO2 has the potential to mobilize organic contaminants. Since typical CO2 sequestration reservoirs contain brines, mobilized organics will partition between the CO2 and water phases, which could impact overlying aquifers in leakage scenarios. Therefore, quantitative measurements of the distribution of organics between supercritical CO2 and water are needed for risk assessments and accurate prediction of reservoir behavior. In this work, an in situ UV and near-infrared spectroscopic capability was developed to measure the distribution of organics between CO2 and water at GCS-relevant conditions. Analyses were performed using a custom-designed apparatus consisting of a high-pressure reactor with quartz windows, near-infrared and UV spectroscopic detectors, and switching valves that facilitate quantitative injection of organic reagents into the pressurized reactor. The capabilities of the system were demonstrated by determining the partitioning coefficients of benzene in water and supercritical CO2 over the range 35-65 °C and approximately 25-150 bar. Density changes in the CO2 phase with increasing pressure were shown to have dramatic impacts on benzene's partitioning behavior. In some cases, values were approximately 10 times lower than those previously determined using ex situ techniques that are prone to sampling losses. The in situ methodology reported here could be applied to quantify the distribution behavior of a wide range of organic compounds that may be present in geologic CO2 storage reservoirs.

Measurement of organic partitioning coefficients in water-supercritical CO2 systems by simultaneous in situ UV and near-infrared spectroscopies

249th National Meeting (2015)

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