Direct numerical simulation of pore scale particle-water-oil transport in porous media

In this work, a direct numerical simulation method, for pore scale particle-water-oil transport in porous media is proposed in hybrid Eulerian-Lagrangian framework. In this method, Navier-Stokes equation in Eulerian framework is coupled with discrete element method (DEM) in Lagrangian framework through direct numerical evaluation of fluid-particle interaction using fictitious domain method (FDM). In Eulerian framework, volume of fluid (VOF) method is employed to capture immiscible two-phase interface; Ghost fluid method and balanced-force scheme are used to treat the surface tension to lower interface spurious currents. In Lagrangian framework, RIGID algorithm is employed to detect the contact states between spherical particles with arbitrarily topological pore walls, making the method adapt to arbitrary pore space; Injection of particles with arbitrary size distribution at a specific mass flow rate makes the method adapt to open system. After validating the new method using two benchmark test cases, a numerical simulation of particle flooding process in a real rock is performed. Numerical results show that in the particle flooding process, three different stages, i.e. drainage period, analogy water flooding period and effective period of particle flooding, are involved. Distinct macroscopic flow characteristics are observed in different periods. Particle size is an important factor influencing the pore scale behaviors (such as, particle space translation and diffusion, remaining oil distribution, degree of fluid diversion) and macroscopic flow phenomena (such as, average oil fraction, average water or oil migration velocity in mainstream direction and transverse direction, sweeping efficiency).