Characterization of the Pore SpaceAccessed by the Nonwetting PhaseDuring Constant Rate Injection at theBreakthrough Capillary Pressure

摘要

The breakthrough capillary pressure is an importantmacroscopic property of porous media that is used to predictpermeability and to correlate capillary pressure curves. Inmercury porosimetry, breakthrough capillary pressure isidentified as the pressure corresponding to about 10-20 %nonwetting phase saturation. In the literature it is identified asthe pressure corresponding at the point of inflection in thedrainage capillary pressure curve. A new method of measuringthe breakthrough capillary pressure has been developed, involving a constant rate injection of the non-wetting phase asopposed to constant injection pressure and was reported at theSCA 2002 meeting. The scope of this paper is to report themethodology used for characterization of pore space accessedby the non-wetting phase as it penetrates into a porous mediumat constant injection rate. The pressure trace recorded near theface of injection using a data acquisition system and knowledgeof the volume of the nonwetting phase injected as a function oftime are utilized for the characterization of pore throat sizesand the associated pore volume and the pore body sizes theycontrol in the pore accessibility process. The injection pressure-versus-time plot reveals pressure fluctuations that areassociated with menisci positions in pore throats and in porebodies. The local maximum in pressure represents penetrationin a pore throat and local minimum value in pressure representconditions of meniscus advancing into pore bodies and porethroats of larger size. The transformation of the pressure versustime data into volume accessed versus pore size data enablesthe determination of pore space accessibility associated withthe backbone of pore space. The pore volume fraction ofwetting phase displaced at the condition of gas breakthrough iscorrelated with the structure of the porous medium. The morehomogeneous the sample is, the greater is the fraction ofwetting phase produced at the breakthrough capillary pressure.