CAPILLARY-PRESSURE BEHAVIOR IN PORES WITH CURVED TRIANGULAR CROSS-SECTION - EFFECT OF WETTABILITY AND PORE-SIZE DISTRIBUTION

The capillary behavior of two immiscible fluids in pores of angular cross-section differs appreciably from that in pores of circular cross-section. We have extended the work of Mason and Morrow [G. Mason and N.R. Morrow, J. Colloid Interface Sci., 141 (1991) 262; N.R. Morrow, Paper presented at 1st Int. Symp. on Evaluation of Reservoir Wettability and Its Effect on Oil Recovery, Socorro, NM. September 18-21, 1990] to pores whose cross-section is a triangle with curved, rather than straight, sides. Capillary pressure vs saturation curves were obtained for single pores, as well as for bundles of parallel pores with log-normal pore size distributions of varying geometric standard deviation. Wettability, as expressed by the contact angle, was varied also. In many ways, the computed behavior is qualitatively similar to that observed for real porous media, such as petroleum reservoir rocks. That is, there is drainage-imbibition hysteresis, a residual non-wetting-phase saturation upon imbibition, and a reversal in the sign of the capillary pressure upon imbibition in systems that approach neutral wettability. However, because of the lack of network effects, there is no mechanism for a true irreducible wetting-phase saturation. It seems likely that, to capture all aspects of multifluid behavior in real porous media (capillary pressure, relative permeabilities, electrical resistivity, etc.), models of such media should not only be based on networks but must also incorporate pore angularity.