MERCURY PENETRATION AND SNAP-OFF IN LENTICULAR PORES

During mercury porosimetry experiments two of the most basic mechanism s responsible for mercury intrusion (drainage) into and retraction (im bibition) from porous media are meniscus intrusion into constrictions and thread snap-off in narrow pores, respectively. The present work co nsists of an experimental and theoretical study of these phenomena in model lenticular capillaries, that is, capillaries with lens-shaped cr oss section. The reason for this apparently strange choice is that sev eral porous media of interest, such as sandstone reservoir rocks (and also model pore networks etched in glass plates and used in numerous e xperimental studies of multiphase flow in porous media) have pores of such type. The critical pressures for mercury intrusion and snap off i n lenticular pores are measured experimentally and expressed in dimens ionless form as functions of the pore aspect ratio (ratio of pore widt h to pore depth) and the contact angle. Analytical mathematical relati onships are also developed for the calculation of these critical press ures. In the case of mercury penetration, very good agreement between experiment and theory is observed over the whole region of pore width to pore depth aspect ratio. In the case of mercury snap-off, very good agreement is observed for small and medium values of pore aspect rati o. A sizable discrepancy in the case of snap-off is observed in pores of large aspect ratio, and this is caused by the considerable deviatio n (in this case) of the pore shape of the experimental models from the lenticular one used in the theoretical calculations, as well as by th e strong effect of the pressure of residual air on the values of measu red pressures. (C) 1997 Academic Press.