A DEM Model for Assessing the Mechanical Effects of CO2 Alteration in a Carbonate Rock

Abstract

CO2 injection in the subsurface is considered an option to improve oil and gas production and, more recently, to store CO2. Consequently, there is a need to better understand the interactions between CO2 and rock deposits. Among the primary deposit candidates are carbonate rocks. During CO2 injection in the subsurface, the formation's pore structure and mechanical properties are altered by the interaction with CO2, affecting reservoir behavior and fluid flow. This study aims to improve understanding of the effects of CO2 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 CO2 injection. The laboratory tests consist of CO2‐saturated water injection and multistage triaxial tests in Indiana limestone samples. Triaxial tests were performed before and after CO2 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 CO2 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.