Influence of Supercritical CO ₂ –Water–Rock Geochemical Interactions on CO ₂ Storage in Carbonate Reservoirs

The capture and storage of CO2 are recognized as a strategy to combat global warming and climate change caused by the increased emission of CO2 into the atmosphere. Among the various geological carbon storage options, carbonate reservoirs have been highly debated and have drawn wide attention due to the effects of geochemical interactions between CO2–water–rock on reservoir properties and, consequently, the safe storage of CO2. This study investigates how geochemical interactions between CO2 and carbonate rocks influence carbonate reservoirs’ properties. The aim is to assess the feasibility of CO2 storage in depleted reservoirs. To achieve this objective, a static test was performed at a temperature of 65 °C and a pressure of 75 bar for 28 days. To elucidate the effects of interactions before and after exposure to supercritical carbon dioxide (scCO2), porosity and permeability were quantified, and the mineralogical composition was examined by X-ray diffraction and X-ray fluorescence. The sample’s morphology was evaluated using a scanning electron microscope. Additionally, alterations in the solution chemistry were analyzed via inductively coupled plasma–mass spectrometry, and ultimately, the pH of the solution was assessed. The findings of this study show that the injection of scCO2 and its solubility in water lead to the formation of carbonic acid, which results in the dissolution of carbonate and sulfate minerals and an increase in the solution’s pH. The dissolution process increased pore connectivity and created a rough texture on the surface-examined samples. Furthermore, for samples A and B, permeability increased by 36.3 and 1.6%, respectively, while porosity increased by 14.5 and 10.5%. These findings offer a theoretical basis for assessing carbonate reservoirs for CO2 storage.