Experimental Study on Rock Mechanical Response During CO₂ Injection Into Limestone Reservoir at Different Conditions

CO₂ storage in deep saline aquifers is the green technology to mitigate climate change by greenhouse gas emissions. The carbonate reservoir such as limestone is the popular storage site due to widely existed. However, such reservoirs are sensitive to the acidic CO₂ fluids and how the geomechanical response for different areas in the storage sites are poorly understand. Thus in this paper, we measured the geomechanical response on Savonnières Limestone samples by UCS test on three different reservoir conditions: near the wellbore - scCO₂ flooding, distances with wellbore - CO₂ saturated brine flooding, and far from the wellbore - dead brine saturated. The flooding tests were set as a representative reservoir conditions at approximately 1000m depth with 325 K/50°C, 15 MPa confining pressure and 10 MPa pore pressure. The results show that the CO₂ saturated brine flooding had largest dissolution effect with lowest maxim unconfmed compressive stresses. We thus concluded that the most matrix damaged area by acid fluid dissolution should be some distances around the wellbore but not near the wellbore, and such geomechanical weakening may cause potential geohazard such as layer collapse and fault reactive.