Impact of Pore Pressure on Wormhole Generation due to CO₂-Saturated Brine Injection

Deep saline aquifers are promising locations for carbon sequestration, but the impact of the CO2 injection on rock properties requires careful investigation. This study will examine the effects of CO2-saturated brine injection on limestone, specifically analyzing how pore pressure influences wormhole formation and subsequent changes in the petrophysical and geomechanical properties. Four Indiana limestone samples, each with dimensions of 1.5 in. in diameter and 3 in. in length, were utilized. These samples exhibited an average porosity of 15.7% and an average permeability of 2.6 mD. During the experiments, the samples were subjected to one of selected pore pressure values (4000, 3000, 2000, and 1500 psi) and a temperature of 60 °C, with a brine concentration of 120,000 ppm mixed with CO2 at a ratio of 70:30. Notice that the pressure was kept in the accumulator at 1200 psi initially before compressing it to the desired pressure to maintain the same mass of CO2 in all experiments. An injection rate of 1 cm3/min was employed for the coreflooding experiments. Before and after coreflooding, Young’s modulus (YM) and Poisson’s ratio of the samples were measured at various confining pressures. Additionally, the porosity, permeability, and surface hardness of the treated samples were assessed. A micro-CT scan was employed to visualize the generated wormholes and quantify their volumes. Our study demonstrated that among the four tested injection pressures, 2000 psi yielded the lowest pore volume to breakthrough (PVBT). No clear trend was observed between PVBT and pore pressure. However, a strong correlation emerged between the mechanical properties of the treated samples and pore pressure values. The investigation established that increasing injection pressure results in greater damage to the core, as evidenced by reductions in both surface hardness and dynamic YM.