Relative permeability curves of water and supercritical CO2 (scCO2) were obtained for two porous sandstones under steady-state flow conditions. The present measurements provide accurate relative permeability values for water and scCO2, which is important to better understand the behavior of CO2 injected into the deep saline aquifer when carrying out carbon dioxide capture and storage (CCS).
We have developed a new method for measuring the volume of scCO2 and water under the same pressure and temperature conditions as in the porous rock employing a high-pressure water-CO2 separator. Water saturation in the sandstone was determined with a mass balance analysis measuring changes of the surface boundary between water and scCO2. We measured Berea sandstone and Tako sandstone, which were cored and shaped into a cylinder form. The mixed fluid of water and scCO2 was injected into a rock sample that was previously saturated with CO2-saturated water. The flow volumes of the water and scCO2 were measured for different saturation conditions by changing the mixing ratio of the fluids at the sample inlet. All measurements were made at 40°C and 10 MPa, including those for the water-CO2 separator. The injection flow rate was 0.5 ml/min. By plotting the ratios of water and scCO2 of the inflow and outflow with respect to elapsed time, we can determine whether the flow is steady or unsteady.
The relative permeability curve is obtained by plotting the relative permeability values with respect to the degree of water saturation. The results for Berea sandstone suggest that the relationship between relative permeability and the relative saturation of water and scCO2 correspond well to those of the previous study. However, the results for Tako sandstone deviate from the predicted curve of the previous study. This is likely to be due to the heterogeneity of Tako sandstone.
