Effects of Supercritical CO2 on the Integrity of Cap Rock

Abstract

The integrity of cap rock is essential for underground storage of CO2; the typical cap rock, such as shale or mudstone, usually contains organic matter. Supercritical CO2 fluid is capable of extracting organic matter from rocks and the sealing performance of cap rock would be affected. To estimate the effect of supercritical CO2 on the integrity of cap rock, siltstone samples as cap rock of the Nagaoka injection test site were treated with supercritical CO2. The organic contents in pulverized samples and the porosity of block samples were measured. Although pore radius distributions slightly shifted to a larger size after treatment, organic contents and porosity had not changed remarkably. Using average pore radius distribution and threshold pressure, which is a function of pore radius, was calculated. The effect of supercritical CO2 on sealing performance of cap rocks was examined by the organic contents and porosity measurements after supercritical CO2 treatment on cap rock samples. The threshold pressure of the cap rock sample was lowered after CO2 treatment. Organic contents of cap rock should be researched to determine the injection pressure for each injection site.