Pore Scale Simulation of Carbonate Acidizing Using Lattice Boltzmann and Local Grid Refinement Method

During the Acidizing process in oil and gas reservoirs, the injected acid reacts with the rock grains, changes the rock pore structure and affects the flow conditions. Due to the presence of a concentration gradient at the vicinity of the rock grains and the continuous changes in rock-fluid interfaces, the continuum assumption of the effective local mass transport coefficient and porosity-permeability relation in the continuum scale modeling of this process has been remained debatable. Therefore, the need for pore scale modelling is evident. The novelty of this study relies in adapting the grid refinement method on reactive flow modeling that implements the Lattice Boltzmann method to compute the effective local mass transport coefficient on the pore scale and in changing porous media. Quadtree grid refinement method is a multiscale mesh refiner that adjusts the grid resolution based on recursive subdivisions, and it is able to reduce the computational load while keeping the desired precision. The simulation results with one- and two-level refinements show that quadtree is two to three times faster relative to uniform fine grid model. Meanwhile, this study uses the constructed model to regenerate the experimental results of wormhole dissolution pattern and discusses the variation in the porosity-permeability relation and the mass transport coefficient due to rock dissolution at different flow conditions that are characterized using the dimensionless numbers of Damkohler, Peclet and Sherwood. The simulation results demonstrate the relation between the dissolution and the Sherwood number and indicate that accurate investigation of the variation in porosity-permeability relation can be performed through analyzing the Kozeny-Carman relation in different flow conditions. Therefore, grid refinement method provides a Pore-Darcy scale bridging tool by achieving larger simulation domains on the pore scale.