Measurements of threshold capillary pressure with extreme low permeability rock

Abstract

In CO 2 Capture and Storage CCS project, the caprock formations overlying the injection unit play an important role in avoiding CO 2 leakage. Measurement of threshold capillary pressure is one of the most effective methods to know the sealing ability of caprocks. We measured threshold capillary pressure with three mudrock core plugs. The purposes of our study are to examine the impact of the injected uid properties on threshold capillary pressure using N 2 and CO 2 and to estimate relative permeability and capillary pressure of extreme low permeability rock such as a mud or shale from the results of dynamic approach. We compared threshold capillar y pressures between N 2 and CO 2 under 10 MPa back pressure and found the threshold capillary pressure for CO 2 was smaller than that for N 2. This result shows the injected uid properties affect the measured threshold capillary pressure. And with one sample, we counted the displacement volume of brine swept by injected gases, CO 2 and N 2. In N 2 experiment, the displacement volume was 2.7 5.3 of pore volume and in CO 2 experiment, it was 6.9 12.1 of pore volume, which was much larger than that in N 2 experiment. The injected gas properties also affect the displacement volume. In addition, we successfully estimated relative permeability and capillary pressure curves by simulating gas ooding with dynamic approach.