Pore-Scale Modeling of Two-Phase Flows with Soluble Surfactants in Porous Media

In this paper, a lattice Boltzmann method is developed to simulate two-phase flows with soluble surfactants in complex porous media. This method not only can recover the Langmuir adsorption isotherm when the bulk surfactant concentration is relatively low but also allows the surfactant concentration to exceed the critical micelle concentration. Thanks to its versatility, this method is used to study the influence of surfactants on steady-state fluid distributions, specific interfacial lengths (SILs), and relative permeabilities under different wetting fluid (WF) saturations (S-w) and viscosity ratios (M) of WF to non-WF (NWF). Regardless of the values of S-w and M, the SIL between two fluids and the SIL between a grain surface and WF are always higher in a surfactant-laden system than in a clean system, while the SIL between a grain surface and NWF is always lower in a surfactant-laden system. For M = 1, we find that the addition of surfactants dramatically increases the relative permeability (RP) of NWF but slightly decreases the RP of WF. By adjusting M at S-w = 0.5, the RP of NWF is always higher in a surfactant-laden system than in a clean system, while the relative magnitude of the WF relative permeabilities in both systems depends on M: for M < 1, the RP of WF in a surfactant-laden system is higher, whereas for M >= 1, the RP of WF in a clean system is higher.