Permeability and storativity of low permeable rock under the supercritical co₂ injection using flow pump method

Instead of carbon capture and geological storage (CCS) that does not rely on structural aquifers, injecting carbon dioxide into sedimentary rock deep underground has been considered. For advection velocity of the fluid is slow, the permeability of sedimentary rock deep underground is low. In order to perform the CCS on the low permeable sedimentary rock, it is necessary to clarify the behavior of long term storage properties of carbon dioxide (CO₂). In this study, the permeability and storativity of CO₂ injected into low permeable rock has been evaluated. The injection of supercritical CO₂ has been conducted on the specimen of Ainoura sandstone (unit weight: 2.39 g/cm³, porosity: 11.9 %) saturated with water by using flow pump method. The experiment has been set up to reproduce te similar condition of deep underground reservoir under 20 MPa confining pressure, 10 MPa pore pressure, 35°C temperature and 3 μl/min CO₂ injection rate. In order to prevent an increase in pore pressure, the boundary condition on the outlet side of specimen has been 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. Furthermore, the relative permeability and specific storage of rock under supercritical CO₂ injection has been examined by the theoretical analysis of flow pump permeability test incorporating Darcy's law for two-phase flow. It is observed that CO₂ has been transmitted gradually while CO₂ stored in the rock. It is also clarified that residual water has existed in specimen after showing the constant differential pressure in the end of the experiment. Using the results of the experiment, 3D core-scale flow-simulation by using TOUGH2 has been conducted due to confirm the flow of fluid and CO₂ distribution in the specimen. From the experimental results and analytical solution to them, permeability and storativity are identified, and simulation results support the validity of the experimental results.