资源环境科技发展态势分析平台

We introduce a simple method to measure the relative permeability of supercritical CO2 in low-permeability rocks. The method is built on the assumption of the stability of formed CO2 percolation pathway under lowered pressure drops. Initially, a continuous CO2 flow pathway is created under a relatively high-pressure drop. Then, several subsequent steps of lowered pressure drops are performed while monitoring the associated flow rates. When the pressure drop is lower than a threshold value, the created flow pathway is assumed to be adequately stable and does not vary significantly during successive flows, with the average saturation and flow rate achieving a quasi steady state. The relative permeability of CO2 is then calculated from the relationship between the pressure drop and flow rate at several lowered pressure drops according to the extended form of Darcy's law. We demonstrate this method using both numerical modeling and an experimental test using X-ray CT imaging. The results indicate the validity of the assumption for the stability of flow pathway under lowered pressure drops. A linear relationship between the lowered pressure drops and the corresponding CO2 flow rate is found. Furthermore, the measurement results suggest that the relative permeability of CO2 can still be high in low-permeability rocks if the CO2 saturation is higher than the threshold value required to build a flow pathway. The proposed method is important for measuring the pathway-flow relative permeability of nonwetting fluids in low-permeability rocks.