Influence of CO ₂ Saturation on the Mechanical Behavior of Quartz and Clay-Rich Sandstone and Their Thermal Responses under Inert and Oxic Conditions

The geological sequestration of carbon dioxide (CO2) poses mechanical risks after its injection into hydrocarbon reservoirs. The mechanical and thermal stabilities of reservoir rocks are crucial for the integrity of long-term storage and the safety of injection in carbon sequestration operations. This research investigated the mechanical and thermal characteristics of Dholpur sandstone (DS) and Gondwana sandstone (GS) under different saturation and environmental conditions. The mechanical studies indicate that water and brine saturation considerably decrease rock strength due to the wetting–softening phenomenon. CO2 saturation leads to a minor decrease in strength, suggesting greater mechanical stability in CO2-saturated conditions. GS specimens revealed a significant reduction in strength relative to DS specimens related to their greater clay mineral concentration and weakening mechanisms. Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) results indicate that DS specimens possess greater thermal stability than GS specimens. The DTA trend indicated that α-quartz converted to β-quartz at around 573 °C, marked by an endothermic drop during the quartz phase transition. However, a significant decrease in sample weight occurred between 470 and 540 °C because of kaolinite dehydrogenation. The results highlight the contrasting responses of quartz-rich and clay-bearing sandstones. Therefore, the experimental findings are expected to provide valuable insights and improve our understanding of the mechanical and thermal performance of reservoir rocks during carbon sequestration and enhanced oil recovery (EOR).