Using Computational Fluid Dynamics for Determining the Optimum Pre-flush Fluid Injection Condition During Matrix Acidizing

Optimum oil displacement is the most important goal of pre-flush stage during matrix acidizing. In this study, the visco-capillary behavior of the two-phase flow in the pore-scale is analyzed using computational fluid dynamics. A two-dimensional model, based on Cahn–Hilliard phase-field and Navier–Stokes equations, was established and solved using the finite element method. To recognize the effective forces of two-phase flow displacement, a stability phase diagram based on the Logarithm of capillary number (Nc) versus the Logarithm of viscosity ratio (M) was constructed and then compared with the reported experimental data. After identifying both viscous fingering and capillary fingering regions, the most stable displacement region was found to be located at Log M ≈ 0.5 and Log Nc ≈ -2. Furthermore, the impact of four independent variables that critically affect the efficiency of the pre-flush stage, including pore volume of injection (1<PV<5), capillary number (-60.95) occurred at Log M > 0, -4.5 1, and θ> π/6 conditions. It is worth mentioning that for Log M< 0, the optimum condition occurred at Log M ≈ 0, Log Nc ≈ -3.5, PV ≈ 4 and θ ≈ π/6.