Measurement of the threshold capillary pressure is one of the most effective methods to know the sealing ability of caprocks especially in the project of carbon dioxide (CO2) Capture and Storage (CCS).

In this work we measured the threshold capillary pressure and have studied the effects of different injection gases on the threshold capillary pressure. One mud rock core plug was used throughout this work. The porosity was estimated at 30.4% by High Pressure Mercury Injection (HPMI) and the water (NaCl brine) permeability was 1.8 microDarcy.

Firstly, the N2 threshold capillary pressure was directly measured using the step-by-step approach under two conditions, atmospheric and in situ conditions. These measured threshold capillary pressures were slightly different, higher in atmospheric condition. This result can be explained by the difference of the contact angle and the interfacial tension (IFT) described in Lucas Washburn equation.

Secondly, with the same core plug, the CO2 threshold capillary pressure using the step-by-step approach was measured under in situ condition.

Thirdly, the nitrogen (N2) and CO2 threshold capillary pressures using the dynamic approach were measured under in situ condition. The measured threshold capillary pressures with these two approaches; the step-by-step and the dynamic approach, were very similar. On the other hand, the measured values using different injection gases, N2 and CO2, were different. The threshold capillary pressure for CO2 was smaller by two-thirds than that for N2. This result shows that the injection fluid property affects on the threshold capillary pressure. However, the difference of the threshold capillary pressure between N2 and CO2 is too small to be explained by Lucas Washburn equation.

In addition, the displacement volume in the CO2 experiment was measured 6.9~12.1 % of the pore volume which was larger than in the N2 experiment (2.7~5.3 % of the pore volume). We considered that the difference of displacement volume between two different gases was also attributed to the difference properties of the injection gases.

This content is only available via PDF.
You can access this article if you purchase or spend a download.