Enhancement of in-situ emulsification performance through the synergistic effects of zwitterionic and nonionic-anionic surfactants.

Highlights

• •The synergy of zwitterionic and nonionic-anionic surfactants can significantly enhance the in-situ emulsification performance.
• •The synergistic system of NPEC/OAPB can rapidly reduce IFT to ultra-low level.
• •The synergetic adsorption of NPEC/OAPB surfactants to create dense interfacial film can greatly improve emulsion stability.
• •The NPEC/OAPB for in-situ emulsification flooding can both improve oil displacement efficiency and sweep efficiency

Abstract

In-situ emulsification flooding has the potential to enhance oil recovery in waterflooded heavy oil reservoirs. The objective of this study was to investigate the synergistic effects of a nonylphenol polyoxyethylene ether carboxylate (NPEC) nonionic-anionic surfactant and an oleic amide propyl betaine (OAPB) zwitterionic surfactant on interfacial tension and emulsifying capacity. The synergistic effects of NPEC/OAPB arise from electrostatic attraction between NPEC and OAPB, which facilitates the formation of a dense adsorption film at the oil–water interface to increase the intensity and strength of the interfacial film. Consequently, the interfacial tensions between the emulsification systems and heavy oil rapidly decrease to ultralow levels, which promotes rapid heavy oil dispersion into stable oil-in-water (O/W) emulsions with minimal disturbance. Sandpack flooding tests showed that the injection of a 0.3 wt% NPEC/OAPB synergistic system resulted in an additional oil recovery of 14.8%. Micromodel flooding tests demonstrated that residual heavy oil could be easily emulsified into stable O/W emulsions by an in-situ emulsification system to increase oil displacement efficiency. The formation of stable emulsion droplets via the Jamin effect effectively blocks pore throats to improve sweep efficiency.