Effects of CO₂-Induced Geochemical Reactions on Sandstone and Limestone Reservoirs in Mae Moh Basin: Insights from Subcore to Core Scale Analyses

CO2 capture and storage (CCS) is emerging as a key technology for climate change mitigation, particularly in emerging economies like Thailand, where fossil-based energy remains dominant, yet environmental concerns necessitate sustainable solutions. The Mae Moh Basin, home to a coal-fired power plant and its adjacent mine, has been considered as a potential CCS site. The current study investigates CO2-induced geochemical reactions in the basin’s sandstone and limestone reservoirs, analyzing mineralogical and physical alterations across subcore to core scales using outcrop samples. Experimental results reveal that both sandstone and limestone undergo mineral dissolution, particularly carbonate dissolution in an acidified CO2-rich environment. Reprecipitation of minerals was also observed, confirmed through microstructural imaging, X-ray diffraction, and morphological analyses. At the subcore scale, sandstone exhibited microcracks and expanded corrosion pits, while needle-like aragonite crystals reprecipitated on the limestone surface. These geochemical alterations led to increased porosity and permeability, though the effect remained limited due to the low-permeability nature of these tight reservoirs. Computerized tomography (CT) scanning further confirmed pore-space expansion, particularly in limestone, where carbonate dissolution was more pronounced. While CO2-induced mineral dissolution suggests enhanced injectivity, uncontrolled permeability increases could pose risks of CO2 migration, potentially affecting long-term containment security. The current findings provide detailed geochemical insights into the Mae Moh Basin’s reservoir properties, although further research─particularly geochemical-geomechanical coupling and field-scale assessments─is necessary to ensure the safe and effective deployment of CO2 storage in the basin.