Impact of microscopic NAPL-water interface configurations on subsequent gas injection into water-wet permeable rocks

Predictive field-scale models of the concurrent flow of three fluids require accurate predictions of five macroscopic flow descriptors: three relative permeabilities and two capillary-pressures as functions of the fluid saturations and saturation history. Since direct measurement of these descriptors is very difficult, and empirical correlations are often unreliable, the use of physically-based pore-scale models has become an appealing alternative. In this paper, we describe the features of our quasi-static pore network model for three immiscible fluids. The model integrates a realistic representation of pore connectivity and morphology reconstructed from 3D micro-focused X-ray CT images, a realistic description of fluid displacement mechanisms, and a sound representation of the wetting properties of the rock. All pore-level displacement mechanisms: piston-type, snapoff, cooperative pore-body filling, and double-displacements are considered with arbitrary contact angles and spreading coefficients. The proposed model is used to simulate gas injection into water-wet Bentheimer sandstone that initially contains water and NAPL after two-phase drainage followed by two-phase in hibition. The gas injection is performed using a cluster-based invasion percolation algorithm with trapping.