Mechanical Properties Degradation in Depleted Clastic Reservoirs for CO₂ Storage

Understanding the effects of CO² exposure to the mechanical properties of a reservoir formation is critical in qualifying any CO² storage candidate field. Two depleted clastic fields, D-Field and L-Field have been selected for evaluation for their CO² storage potential. In this study, core samples from key reservoirs have been selected and their mechanical properties analyzed. Multi-stage triaxial tests were conducted on pristine samples classified as Pre- and Post-CO² samples which have undergone 14 days of CO² ageing with supercritical CO² under reservoir conditions. The comparison of the results between the Pre- and Post-CO² samples provides an understanding of the mechanical properties degradation observed on the samples which have been exposed to CO². The results showed that both D-Field and L-Fields samples exhibited a general weakening trend observed between the Pre- and Post-CO² samples comparison. However, D-Field exhibited higher magnitude of degradation compared to L-Field, as indicated from the reduction of Young’s Modulus (8 – 11% against 5%), unconfined compressive strength (20 – 34% against 0.3 – 4.5%) and cohesion (30 – 34% against 5.8 – 8%) between the Pre- and Post-CO² samples. The lower magnitude of degradation observed in L-Field samples may indicates it as a more potentially viable storage candidate when compared to D-Field. However, the overall comparison of storage viability should also consider various other critical elements such as injectivity, storage capacity, seal capacity, leakage risks, etc., which are not deliberated in this laboratory study.