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

Authors: 
Shi, Z., University of Southern California
Goodman, A., National Energy Technology Laboratory
Tsotsis, T., University of Southern California
Jessen, K., University of Southern California
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.