Analysis of the CO2 Storage and Migration Characteristics of a Low-Permeable Sandstone using the μ-Focus X-Ray CT Method

Abstract

Carbon dioxide capture and storage (CCS) is expected to be a promising method for reducing the amount of CO 2 emitted into the air. In the CCS method, CO 2 is pushed into the porous aquifer deep underground. Large-scale CCS sites have been operating in European countries, Canada, etc. Large and uniform aquifers are needed to achieve a large-scale CCS. However, it is difficult to determine the type of aquifer near the Japanese islands. Instead, porous rock layers, such as sandstones, which are suitable for reservoirs, are scattered in various places.The purpose of this study was to analyze the storage and migration characteristics of CO 2 in porous rocks. Here, Ainoura sandstone, which has a relatively high porosity and low permeability, was used as the rock sample. Gas and liquid and CO 2 were injected into the rock samples saturated with a solution of potassium iodide, and the flow process and storage states were analyzed using a μ-focus X-ray CT scanner. The histogram difference method and image subtraction method were also employed to evaluate the replacement ratio obtained in the gas and liquid CO 2 injection tests. Of note, these techniques can be used to extract density changes due to gas and CO 2 injection into the pores. The replacement process was found to depend on the rock samples, even though the outlook of the rock samples was very similar. The replacement processes and the amount of replacement differed between gas and liquid and CO 2 . However, the mean value of the replacement ratio was not significantly different among the samples. Approximately 20%-40% of the pore volume was replaced by the gas and CO 2 .