Thermal and Mechanical Effects of CO2 Injection on Well Integrity in Fractured Reservoirs: Implications of Chemical Reactions with Residual Fluids

Abstract This study investigates the impact of CO2 injection on wellbore integrity in fractured reservoirs by examining the combined thermal, mechanical, and chemical effects. The research aim is to understand how temperature fluctuations, mechanical stress, and chemical interactions with residual fluids (oil or water) influence well stability. By addressing these complex interactions, this study provides critical insights for mitigating well integrity risks and optimizing carbon storage and enhanced oil recovery (EOR) strategies in fractured formations. Finite Element Analysis (FEA) simulation was conducted to evaluate stress distribution and mechanical responses during CO2 injection in fractured reservoirs. The models incorporate key parameters such as fracture geometry, injection rates, wellhead temperatures, and reservoir pressure. Thermal expansion and contraction, mechanical strain, and non-uniform stress distributions caused by fracture networks are analyzed. Additionally, the chemical reactivity of CO2 with residual fluids, including the formation of carbonic acid, is examined. The results indicated significant risks to wellbore integrity arising from thermal, mechanical, and chemical interactions. CO2 injection induces thermal expansion and contraction, leading to cement sheath debonding and potential leakage pathways at casing-cement and cement-rock interfaces. Fracture networks exacerbated these effects by creating localized stress concentrations. CO2 reactions with residual fluids formed localized acid, altering fluid pressure. Fractures concentrated acidic fluids at the cement-casing and cement-formation interfaces, affected stress distribution and identified potential integrity risks. Minimal displacement was observed in the simulation, which indicated that fractures in stiff formations exhibit limited displacement due to stabilized stress-strain behavior following previous loading cycles. Our study illustrated the crucial impact of fracture geometry on stress distribution as well as the compounded failure risks resulting from the interaction of thermal, mechanical, and chemical processes. The findings emphasize the need for optimized injection strategies to improve long-term wellbore integrity and enhance the safety and efficiency of carbon storage and EOR operations.