A lattice Boltzmann framework for simulating reactive fluid flow with variable viscosity in porous media

Abstract

This study investigates the influence of pH on the dissolution process during acidizing simulations, comparing Newtonian reactive fluids with variable viscosity to those with constant viscosity. To achieve this, a specialized algorithm was developed within the Lattice Boltzmann Method (LBM) framework to model pH-dependent viscosity and evaluate its accuracy. Simulations were conducted in both simple and complex porous media across a range of Damkohler (Da) and Peclet (Pe) numbers. The results demonstrated that the LBM exhibited high accuracy at low (average normalized error: 0.42 %) and medium (average normalized error: 0.19 %) angular frequencies, though accuracy declined at high angular frequencies (average normalized error: 2.02 %). Adjustments to lattice spacing and relaxation times improved convergence rates, achieving an order greater than one. Boundary conditions also significantly influenced LBM performance: Dirichlet conditions ensured reliable accuracy, while sinusoidal conditions introduced errors at higher frequencies. Comparisons between Newtonian reactive fluids with constant viscosity and those with variable viscosity revealed distinct behaviors depending on the medium. In porous media, higher Da numbers (e.g., 100 in this study) resulted in significant permeability enhancement. Conversely, in simple fracture domains, higher Da numbers caused a decline in the permeability-porosity relationship. Furthermore, in porous media, higher Pe numbers (e.g., 7 in this study) led to pronounced permeability increases for both fluids, whereas more complex behavior was observed in simple fracture domains. Fluids with constant viscosity exhibited greater permeability increases during dissolution, attributed to their unique rheological properties. These findings advance the application of the LBM for modeling Newtonian fluids with variable viscosity and provide valuable insights into pH-dependent behavior in acidizing processes.