COMPUTATION OF THE TWO-PHASE FLOW PROPERTIES OF INTERMEDIATE-WET POROUS MEDIA: A PORE NETWORK APPROACH

A pore-and-throat network including fractal-like roughness features along its surface is employed to simulate primary drainage and secondary imbibition by accounting for the quasistatic motion of menisci in pores and throats and varying the contact angle from 0 degrees (strongly water-wet conditions) to 180 degrees (strongly oil-wet conditions). The angle of sharpness of roughness features defines a range of contact angles within which the cross-section of the throat or pore is occupied completely by the one fluid and conditions of intermediate wettability are established. In contrast, outside this range, both fluids may coexist in a pore or throat. Such differences on the fluid distribution at the pore level affect strongly the capillary, electrical and hydraulic properties of the porous medium and are reflected in the capillary pressure, resistivity index and relative permeability curves. The simulator is used to calculate the aforementioned two-phase flow coefficients as the pore system transits from strongly water-wet or strongly oil-wet to intermediate-wet. The capillary pressure curves are always sensitive to the wetting state and the particular value of the contact angle. The relative permeability and resistivity index curves for secondary imbibition are grouped in families of curves which are sensitive mainly to the wetting state (water-wet, intermediate-wet/water-wet pores, intermediate-wet/oil-wet pores, oil-wet) rather than to the particular value of the contact angle.