Abstract
Laboratory measurements of threshold pressure, geomechanical property and permeability were conducted on an argillaceous rock when injecting liquid and supercritical CO2. The argillaceous rock was sampled from the Otadai Formation in the Quaternary Kazusa Group, Chiba prefecture, Japan. Strain gages and PZTs were glued on the cylindrical sample (125 mm in length and 50 mm in diameter) to monitor strain and P-wave velocity changes during CO2 injection. Threshold pressures were estimated under simulated in-situ pressure and temperature conditions, when injecting liquid and supercritical CO2, by monitoring the strain and P-wave velocity changes. The threshold pressure for this argillaceous sample was about 3 MPa when injecting liquid CO2 and was about 2 MPa when injecting supercritical CO2. From the triaxial compression tests, we observed that the Young's modulus and Poisson's ratio decreased as the confining pressure increased. Compared to water-saturated condition, after injecting supercritical CO2, the Young's modulus decreased about 21∼24% and the Poisson's ratio decreased about 28∼35%. Permeability to supercritical CO2 measured at ‘Fractured’ condition increased about 30 μD compared to water measured at ‘Intact’ condition. Results of threshold pressure and geomechanical properties for this argillaceous rock are very useful to evaluate caprock integrity in geological CO2 sequestration.
