抄録
Relating to the assessment of the cap rock integrity on CO2 geological sequestration, we measured threshold pressure for supercritical CO2 under pressure and temperature conditions of 1,000 m depth (i.e., 10 MPa and 40°C). The present study aims to quantify various factors which affect the variability of rock's threshold pressure and to model the threshold pressure range of a cap rock. We prepared sintered compacts composed of uniformly-sized silica glass beads (0.2-10 μm), and examined a correlation between threshold pressure and permeability for each diameter. The result revealed that threshold pressure of sintered compacts increased drastically with a decrease of component particle size. Moreover, there existed a good linearity between the logarithm of threshold pressure and the logarithm of permeability. The fitted line is an important basis specifically from a viewpoint of safety assessment because it corresponds to the standard value of threshold pressure of homogeneous rocks. For threshold pressures of samples composed of smaller size particles, measured values were much lower than theoretical values. Although it is required to verify the discrepancy from an ideal particulate alignment of our samples and the validity of used contact angle value, the present result suggests that supercritical CO2 may have a potential to permeate a cap rock easily more than expected.
