極低浸透率岩石を対象としたスレッショルド圧力測定 :

N₂およびCO₂圧入による効果の検証

抄録

In CO₂ Capture and Storage (CCS) project, the caprock formations overlying the injection unit play an important role in avoiding CO₂ 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 fluid properties on threshold capillary pressure using N₂ and CO₂ 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 capillary pressures between N₂ and CO₂ under 10 MPa back pressure and found the threshold capillary pressure for CO₂ was smaller than that for N₂. This result shows the injected fluid properties affect the measured threshold capillary pressure. And with one sample, we counted the displacement volume of brine swept by injected gases, CO₂ and N₂. In N₂ experiment, the displacement volume was 2.7∼5.3 % of pore volume and in CO₂ experiment, it was 6.9∼12.1 % of pore volume, which was much larger than that in N₂ experiment. The injected gas properties also affect the displacement volume.

In addition, we successfully estimated relative permeability and capillary pressure curves by simulating gas flooding with dynamic approach.