Relating to the assessment of the cap rock integrity on CO2 geological sequestration, we measured threshold pressure for upercritical 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 lower limit of threshold pressure of homogeneous rocks.
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