Assessing the geological storage capacity of CO2 in Khorat Sandstone: Geochemistry and fluid flow examinations

Abstract

To achieve a gigaton-scale CO₂ geological storage, several sedimentary formations are widely assessed for their potential for dedicated storage projects. As one of the large formations in Southeast Asia, the Khorat Plateau in Thailand is of significant interest. While previous studies have reported discrepancies in the capacity estimate, effective capacity considering experimental examination is needed to properly elucidate project development in the area. In the current study, geochemistry and CO₂-brine flow were experimentally examined using samples of Khorat sandstone. Owing to CO₂ geochemical reactions coupling with flow-induced fines migration, dissolution-precipitation of the sample minerals at sub-core scales were intricate and led to changes in core-scale properties as a result. After the samples were exposed to CO₂-saturated brine, quartz likely dissolved while calcite precipitated. At the core scale, permeability declined due to residual clay blockage. On the contrary, after supercritical CO₂ exposure, the minerals were severely dissolved, which led to the expansion of pore networks and increases in porosity and permeability. Relative permeabilities of CO₂ and brine were characterized, and the residually trapped amount of CO₂ was obtained (26% of pore volume). The storage capacity was calculated to be 9.66 kg/m³, which was found to be relatively less influenced by the geochemistry-induced physical alterations.