Pore Scale Simulation of Surfactant Flooding by Lattice Boltzmann Method

Abstract

Surfactants play an important role in the widely used enhanced heavy oil recovery methods such as surfactant-polymer flooding and alkali-surfactant flooding. In this study, we focus on the effects of surfactant during surfactant flooding and provide a pore scale simulator of surfactant flooding based on the Lattice Boltzmann (LB) method. We introduce a dipole to present the amphiphilic structure of surfactants in the Lattice Boltzmann model, and characterizes microscopic fluid interactions at the kinetic level. There are three velocity distribution functions to present the oil, water, and surfactant species, and every distribution follows the discrete Boltzmann-BGK equation. There is also an additional dipole vector representing the orientation of amphiphile, so that the interactions related with surfactants depend not only on particle relative distances but also on their dipolar orientations. The simulation results show that surfactants can reduce the oil-water interfacial tension and recover more oil trapped by capillary force. Moreover, surfactants are able to emulsify the flooding system, forming O/W emulsions or bi-continuous micro-emulsions. Higher surfactant concentration leads to smaller oil droplets in emulsions. In addition, the phase distribution morphologies in porous media are much different in different wetting conditions. By associating the fluid-solid interfacial tension with the surfactants adsorption concentration on walls, we characterize the wettability alteration mechanism in LB model accurately. The oil recovery can be improved by changing the wettability from oil-wet to water wet, increasing the surfactant concentration, and enhancing the adhesion parameters. However, the adsorption onto walls leads to unnecessary waste and could decrease the surfactant concentration in bulk phase. The study provides an effective pore scale tool to simulate the surfactant involved interfacial flows in porous media. In addition, we can use it to study the flow mechanisms and remaining oil distributions during surfactant flooding.