Capillary pressure correction in irregularly shaped pore channel under fully wetting condition

Pore network modeling (PNM) has been useful to simulate water retention process of the capillary dominated systems. Randomly structured 3D pore geometry can be simplified as the network of pore channels of cylindrical shape. Radii of cylindrical pore channels are determined by minimum inscribing spheres which lead to the overestimation of capillary pressures of irregularly shaped pore throats. The correct capillary pressure can be obtained by bubble analysis using lattice Boltzmann method (LBM). Pore domain larger than its representative elementary volume, however, contains more than hundreds of pore throats. LB bubble simulations for estimating corrected capillary pressures of every pore throats are computationally demanding. Therefore, this study presents a simple shape analysis technique by Euclidean distance transform (EDT) to identify the effective cross-sectional area which is defined as the expected location of the nonwetting fluid during the invasion into a capillary tube filled with wetting fluid. By extending MS-P theory, we calculate capillary pressures of tubes whose effective cross-sections are taken from 3D X-ray CT image compared with LB bubble simulation. We also investigate the applicability of the shape analysis technique by calibrating the pore network drainage simulation results.