Capillary Pressure and Pore Size Distribution from Water Injection: a Feasibility Study

MICP (Mercury Injection Capillary Pressure) is a standard procedure for core analysis. However, the use of mercury is forbidden in some environments and so far there are no alternative methods. NMR provides information on pore distribution but is not directly related to the capillary pressure. This paper presents a feasibility study for replacing mercury by water or brine (BICP: Brine Injection Capillary Pressure). The principle is to change the wettability of the rock in order to have a surface not wetted by water in the presence of air. We present experimental results realized with a siliconate treatment that has the advantage to be safe and water soluble (no solvent). The samples are 100% saturated with a siliconate solution and then dried. This treatment phase is also used to determine the porosity of the sample from the difference of mass before and after drying (assuming a known grain density). The experiment is conducted similar to mercury injection in a penetrometer with brine instead of mercury. Initially, the sample is not evacuated under vacuum and air compressibility is taken into account in the interpretation. So far, the pressure is limited to 30 bars, but there is no technical limitation. Cycles of injection/withdrawal are also performed like for mercury. The first important result is that the spontaneous imbibition when the treated sample is put into brine is limited to around 10% of the pore volume. The second point is that we are able to build capillary pressure curves, with volume stabilization at each step, in both injection and withdrawal. Results on samples with a wide range of permeabilities show a qualitative agreement with results obtained with mercury injection. In conclusion, we do not claim the same accuracy as with mercury but the method can be useful for safe and quick rock-typing measurements. INTRODUCTION MICP (Mercury Injection Capillary Pressure) is a standard procedure for core analysis. The advantage of mercury is that it is a non-wetting fluid for any type of surface and that the contact angle does not depend on the nature of the surface. However, the use of mercury is forbidden in some environments and so far no alternative methods are available. NMR provides information on pore distribution but is not directly related to the capillary pressure.