We developed an experimental system of constant pressure permeability test to measure relative permeability and specific storage of reservoir rocks under the injection of supercritical CO2. The experimental system was designed to reproduce deep reservoir condition within high pressure and high temperature. Rock specimen of Ainoura sandstone and Berea sandstone were employed. Supercritical CO2 was injected into the rock specimen with constant differential pressure imposed, and the flow into and out from the rock specimen were measured continously. In order to interpret the experimental results, the analytical method of constant pressure permeability test was developed by incorporating two-phase flow drainage displacement. The relative permeability to CO2 in the Ainoura sandstone was found to be about 0.5 of the relative permeability to water at 100% water saturation. In comparison, the relative permeability to CO2 in the Berea sandstone is 0.95. Specific storage of the Ainoura sandstone for CO2 is 1.63×10–4 1/Pa, whereas that of the Berea sandstone is only 1.12×10–7 1/Pa. The CO2-water displacement efficiency in the Ainoura sandstone appears to be lower than the Berea sandstone. Constant pressure permeability test with developed experimental system is suggested to be an efficient alternative method to investigate CO2-water multiphase flow system in reservoir rocks.

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