A DEM Model for Assessing the Mechanical Effects of CO ₂ Alteration in a Carbonate Rock

ABSTRACT CO 2 injection in the subsurface is considered an option to improve oil and gas production and, more recently, to store CO 2 . Consequently, there is a need to better understand the interactions between CO 2 and rock deposits. Among the primary deposit candidates are carbonate rocks. During CO 2 injection in the subsurface, the formation's pore structure and mechanical properties are altered by the interaction with CO 2 , affecting reservoir behavior and fluid flow. This study aims to improve understanding of the effects of CO 2 injection on the mechanical behavior of carbonate rocks. Laboratory tests and numerical discrete element models (DEMs) were used to assess the alterations in carbonate rocks due to CO 2 injection. The laboratory tests consist of CO 2 ‐saturated water injection and multistage triaxial tests in Indiana limestone samples. Triaxial tests were performed before and after CO 2 injection to investigate changes in the rock's mechanical properties. A significant reduction in the unconfined compressive strength and Young's modulus was observed. Numerical discrete element models were developed to assess the alterations in carbonate rocks due to CO 2 injection. A contact law accounts for the mechanical effect of material degradation. The laboratory test results were used to calibrate the numerical model. The numerical methodology presented good results and was validated by matching the experimental results, assessing the mechanical changes due to the dissolution of Indiana limestone samples.