Effect of sodium-montmorillonite particles on the stability of oil droplets in produced water from alkali/surfactant/polymer flooding

Abstract

The concentration of suspended Na-montmorillonite particles (Na-Mt particles) in the treated produced water beyond the criteria of injection water in many oilfields has raised great concerns in recent years. Especially when solid particles are present because they increase the emulsion stability of produced water. Simulation experiments were conducted to investigate the effects of Na-Mt particles and alkali/surfactant/polymer (ASP) on the stability of oil droplets in the produced water. Experimental results showed that the Na-Mt particles, surfactant and polymer have the synergetic effects on the emulsion stability when the concentration of Na-Mt particles was less than 100 mg/L. Oil concentration in the water phase increased with the increase of polymer and surfactant concentrations when the concentration of alkali was increased to 400 mg/L, but then decreased with the further increase of alkali concentration. As the concentrations of Na-Mt particles and alkali were less than 100 mg/L and 400 mg/L, surfactant and polymer were found to increase the density of the negative electric charges of oil droplets greatly, causing the electrostatic repulsive interaction to increase between the droplets and particles. The electrostatic repulsive interaction and steric effect may be the main stabilizing mechanism. The zeta potential remained stable, the interfacial tension increased and the interfacial elastic modulus decreased when the concentrations of Na-Mt and alkali were more than 150 mg/L and 800 mg/L, respectively, resulting in the oil–water separation. Therefore, the concentration of Na-Mt particles was the key factor affecting the emulsion stability.