(206b) Investigation of Mass Transfer and Sorption in CO2/Brine/Rock Systems via in-situ FT-IR

CO₂ geological sequestration in deep saline aquifer is considered a promising method to mitigate manmade CO₂ emissions and, thereby, minimize changes to the earth’s atmosphere. A fundamental understanding of CO₂ mass transfer and sorption phenomena in brine saturated reservoir formation is necessary to understand the long-term fate of injected CO₂ through different trapping mechanisms: Physical trapping, dissolution trapping and mineral trapping. In this work, we investigate CO₂ sorption in brine saturated and dry Mt. Simon sandstone samples via in-situ Fourier Transform infrared spectroscopy (FT-IR). The CO₂ sorption was characterized at elevated pressure from 50 psig to 1200 psig at a temperature of 50⁰C. A single symmetrical absorption band, centered at 2342 cm^−1, was observed for CO₂ sorption in a brine saturated sample, which is also detected when CO₂ dissolves in the bulk water/brine. However, 2 asymmetric peaks, located near 2330 cm^−1 and 2360 cm^−1, were observed for CO₂ adsorption onto the dry sample. The different position of the detected CO₂ peaks in these 2 cases implies that when CO₂ sorption occur in a brine saturated sample, almost all the CO₂ molecules are dissolved in the brine and that no CO₂ adsorption on the surface is detectable via the FT-IR technique. The amount of CO₂ sorption in the brine saturated sample was quantified by a correlation of the integrated peak area to the CO₂ solubility in the same bulk brine, as measured separately via a PVT-cell approach. Finally, the CO₂ mass transfer in the brine saturated sample, as detected by the FT-IR, was subsequently delineated by a simple mathematical model formulated based on Fick's law for diffusive mass transfer. The presented observations and analysis suggest that the adsorbed CO₂ on the surface of Mt. Simon rocks samples is reduced substantially by the presence of brine in the pore spaces, and that the CO₂ mass transfer in this system is consistent with the molecular diffusion in the brine inside the pore spaces.