In-situ Geomechanical Assessment of Carbonate Rocks Undergoing CO2-Saturated Brine Injection: A Preliminary Study

The CO2 storage in saline aquifers or water alternating gas injection (WAG) results in the formation of acidic brine with 3-4 pH. This study highlights the impact of CO2-saturated brine injection on the mechanical properties of limestone rocks undergoing dissolution (i.e., generation of wormholes). Three Indiana limestone samples that are 1 inch in diameter and 2 inches in length were utilized in a coreflooding step. The coreflooding setup contained a linear variable differential transformer (LVDT) to monitor the changes of rock's Young's Modulus (E) and creep at in-situ conditions. The experiments were conducted at 60 oC, 1,500 psi pore pressure, 1,950 psi confining pressure, and 725 psi (5 MPa) deviatoric axial stress. Experiments were conducted at 0.5, 1-, and 2-mL flow rates, respectively, where 700 mL of carbonated brine was injected in each experiment. A continuous wormhole was generated in each experiment as indicated by the pressure drop data (i.e., zero pressure drop) and CT scan images. The rock geomechanics were altered due to dissolution, as indicated by the sharp increase in creep magnitude after CO2-saturated brine injection. Nevertheless, no changes were observed in the axial E as the wormholes created (1-2 vol%) were filled with an incompressible brine.