Study on the mechanism of W/O emulsion flooding to enhance oil recovery for heavy oil reservoir

Abstract

W/O emulsion is able to effectively improve the sweep volume and oil recovery factor during the waterflooding due to its strong mobility control ability, it has a great EOR appliance for heavy oil reservoirs. In this study, emulsion stability, droplet size distribution (DSD) and rheological behavior at different water content and salinity were investigated. Then core flooding experiments was conducted to study the oil displacement efficiency of W/O emulsion formed at different water content, and a visual micromodel was designed to observe the mechanisms of W/O emulsion flooding at the pore-throat scale. Results showed that W/O emulsion had the characteristics of the pseudoplastic fluid, exhibiting shear thinning behavior. Emulsion stability and DSD uniformity became worse with the increment of water content. Emulsion viscosity increased with water content varying from 20% to 40%, and then decreased as water content rose from 40% to 90%. Whereas Emulsion stability decreased slightly with the salinity increasing due to its high content of polar components inherent in heavy crude oil. The piston-like displacement could be formed due to its high mobility control ability caused by high viscosity. Meanwhile, the adverse effects caused by formation heterogeneity and viscosity fingering could be inhibited. After subsequent water breakthrough, emulsion droplets produced viscoelastic deformation during waterflooding. The emulsification carrying-on, block, and drag effect were the main mechanism of W/O emulsion flooding at the pore level. The findings of this study are significant for the enhanced oil recovery in heterogeneous heavy oil reservoirs.