Measurement of Electrical Impedance and P-wave Velocity of a Low Permeable Sandstone Core during the Displacement of Saturated Brine by CO₂ Injection

Evaluating and monitoring the CO₂ behavior in the reservoir, understanding the mechanism of CO₂ flow and distribution in the water-CO₂ mixture state is essential. In this study, measurement of the complex electrical impedance (Z) and P-wave velocity (V_p) is conducted during the CO₂ injection into the rock core under the reservoir condition. Specimen is low permeable sandstone and injection rate is ultra-low (in the low capillarity number (C_n) area) to high. In addition to measuring Z and V_p, differential pressure on the both sides of the specimen and CO₂ saturation (S_CO2) of the entire specimen are measured. The change of Z and V_p are observed according to the change of differential pressure and S_CO2. After the injection test, S_CO2 in cross-section of the specimen is estimated using Archie's law and Gassmann's equation (Patchy saturation model) to the experimental results.