Rock Mechanics Insights for CO2 Sequestration: Assessing CO2 Degradation Effects on Rock Mechanical Properties

Abstract Laboratory testing plays a critical role in assessing the suitability of storage sites for Carbon Capture and Storage (CCS) projects. In geomechanical analysis, rock mechanics testing is essential for evaluating the elastic and strength properties of overburden and reservoir rocks, which are critical for calibrating 1D geomechanical models to predict caprock and reservoir mechanical integrity and stress regime. Given the potential degradation of rock elastic and strength properties due to CO2 exposure, CO2-rock interaction experiments are necessary to assess rock integrity and to understand long-term mechanical property changes. This study explores the impact of CO2 interaction on the mechanical properties of clastic reservoir rocks, focusing on key geomechanical parameters such as Young’s modulus, Poisson’s ratio, unconfined compressive strength (UCS), cohesion, friction angle, and tensile strength. Rock samples from J-field, offshore Peninsular Malaysia were subjected to CO2 saturated brine injection, followed by a 14-day static reaction period under in-situ conditions. Pre- and post-treatment analysis revealed significant reductions in UCS (23.9%), cohesion (20.5%), friction angle (8.8%), and Young’s modulus (21.5%), along with a 7.5% decrease in Poisson’s ratio and a tensile strength reduction of 26%. Furthermore, Uniaxial Pore Volume Compressibility (UPVC) tests indicated minor matrix deformation without pore collapse, suggesting that the rock matrix retains mechanical integrity in the transient pressure variations. This study underscores the importance of comprehensive laboratory analysis in qualifying CO2 storage reservoirs for CCS projects. The absence of certain field data, such as Global Positioning System (GPS) measurements, can be addressed through alternative indicators like UPVC tests which provide insights into reservoir integrity and compaction behavior. Additionally, findings from post-CO2 degradation analysis are vital for integrating rock property changes into 3D/4D coupled geomechanics-dynamic models, ensuring accurate long-term predictions of CO2 behavior in the subsurface.