Abstract

We describe a two-phase pore network simulator of drainage and imbibition, which integrates a realistic representation of pore connectivity and morphology, a quasi-static description of fluid displacement mechanisms, and a sound representation of wetting properties of a sedimentary rock and their alteration. The simulator works with 3D disordered networks of ducts with triangular, square and circular cross-sections obtained directly from the analysis of micro-CT images of rock samples. All pore-level displacement mechanisms: piston-type, snap-off, and cooperative pore body filling are considered with arbitrary receding and advancing contact angles. Bond invasion percolation description is used in primary drainage, while bond-site invasion percolation with ordinary percolation on a dual network and compact cluster growth are used in secondary imbibition. In the paper, we resolve how to calculate the relative permeability of NAPL in the quasi-static approximation of imbibition, and provide complete spatial distribution of the clusters of trapped NAPL using our generalization to disordered networks of the Hoshen-Kopelman cluster-labelling algorithm. To understand the impact of wettability alteration on the capillary pressure and relative permeability functions, we perform a series of drainage and imbibition simulations by changing the range of advancing contact angles. Our study indicates that in imbibition transport properties of the permeable solid are quite sensitive to the hysteresis between the receding and advancing contact angle. This sensitivity reflects competition among the different displacement mechanisms which shapes the relative permeabilities, capillary pressures, and the distribution of the trapped NAPL.