Evaluation of permeability and specific storage of a low permeable rock injected by supercritical CO₂ using flow pump method

A low permeable rock mass is focused as an alternative option of carbon capture and geological storage (CCS) suitable for geological structure of Japan with lack of oil and gas reservoirs. However, the properties of the permeability and the storability in low permeable rock mass are not clear, in spite of a lot of researches on the behavior of carbon dioxide (CO₂) in rock. The object of this study is clarified the properties of the permeability, the storability and the storage mechanism of CO₂ in a low permeable rock for the safety and economical CCS. In order to clarify the properties of permeability and storability of the low permeable rock injected with supercritical CO₂, flow pump permeability test is conducted under the in-site condition of CO₂ reservoir. In the experiment, Ainoura sandstone is used. The boundary condition on the outlet side of specimen is kept a constant pressure. As a result, it has been possible to observe step by step the change of the differential pressure between both ends of specimen. The first step has shown the difference pressure changes similar to the permeability test, then once it has shown a constant, but has increased further. Thereafter the differential pressure decreases. Finally, the differential pressure has become the ultimate state. Additionally, the theoretical analysis of flow pump permeability test incorporating Darcy's law for two phases flow has been developed to examine the relative permeability and specific storage of rock under supercritical CO₂ injection. It has been observed supercritical CO₂ flowed into specimen penetrate into microscopic pore and has flowed through captured by sandstone's pores. Furthermore residual water has existed in specimen after showing the constant differential pressure in the end of the test.