Pore-scale simulation frameworks for flow and transport in complex porous media

Abstract

Fundamental understanding of flow and transport in porous media is central to the development of better oil and gas recovery processes. Pore-scale simulations, with the advent of advanced algorithms and parallel computing, have become indispensable tools to average the microscopic mechanisms and uncover the macroscopic behaviors. In order to perform direct numerical simulations of microscopic flow and transport, pore-scale simulation frameworks including stochastic geometry models, simulators for single-phase flow, multiphase flow, and transport, were developed. Stochastic geometry models were generated based on Voronoi tessellations for three basic types of porous media - granular, tubular and fibrous. The models can be used to create controlled complex microstructural features and heterogeneities so that one can study the effect of complex geometry on flow and transport. Lattice Boltzmann methods were implemented to model single-phase and two-phase flows through porous media. Validation tests were conducted on permeability, surface tension and contact angle against analytical equations and experimental data; it is shown that the simulators are able to quantitatively capture the dynamics of single- and two-phase flows. The random walk particle tracking method was implemented to model the advection-diffusion of solute in porous media. Validation tests were conducted against previous results and the Taylor-Aris analytical solution for dispersion; they show that the numerical errors gradually diminish with increasing resolution of the velocity field. All the flow and transport simulators in this study have been massively parallelized using Message Passing Interface (MPI). Performance tests were conducted on up to 262,144 cores on the world's largest supercomputers; the performance of our parallelized simulators closely matches or exceeds the state-of-art as found in the literature. Applications and case studies were performed using the flow and transport simulators and stochastic geometry models. We studied the porosity-permeability / porosity-tortuosity relations for homogeneous and heterogeneous granular, tubular, and fibrous geometries. Particularly, the effect of heterogeneity such as fractures and vugs on the porosity-permeability / porosity-tortuosity relations has been explored. We conducted case studies of two-phase flows, with different wettability conditions, in a single cylindrical pore, in serially arranged cylindrical pore bodies and pore throats, and in a complex fractured granular stochastic geometry.