Effects of Supercritical CO2-Water-Rock Interactions on the Geochemical Properties of Tight Sandstone Reservoirs in the Ordos Basin

Abstract

Against the background of the “dual-carbon” targets, CO2-EOR and geological CO2 storage are regarded as important technological pathways for achieving the coordinated development of cleaner and more efficient fossil energy utilization and carbon emissions reduction. Supercritical CO2-water-rock interaction experiments were conducted under high-temperature and high-pressure conditions on tight sandstone reservoirs of the Yanchang Formation in the Ordos Basin. These experiments systematically investigated the effects of temperature- and pressure-dependent water-rock reactions on reservoir geochemical characteristics and pore structure evolution. The results show that under supercritical CO2 injection conditions, formation water pH decreases markedly, while minerals such as calcite, dolomite, and feldspars undergo varying degrees of dissolution. This process leads to significant increases in the concentrations of Ca2+, Mg2+, and K+ in solution and the development of abundant secondary dissolution pores. Increasing reaction pressure enhances CO2 solubility in the aqueous phase and intensifies the acidic environment, thereby significantly promoting mineral dissolution and increasing reservoir porosity. In contrast, increasing reaction temperature reduces CO2 solubility and exerts an overall inhibitory effect on water-rock reactions, particularly suppressing calcite dissolution. These results indicate that supercritical CO2-water-rock interactions substantially alter the physical and geochemical properties of tight sandstone reservoirs, with important geological implications for improving reservoir flow conditions during CO2-EOR and for evaluating the long-term stability of subsequent geological CO2 storage.