Oil displacement mechanisms of viscoelastic polymers in enhanced oil recovery (EOR): a review

Polymer flooding has proved economically and technically successful in numerous enhanced oil recovery (EOR) projects, which can often increase oil recovery from 12 to 15 % of the original oil in place. When a reservoir is flooded with viscous polymer solution, the mobility ratio between the displacing fluid (i.e., water) and the displaced fluid (i.e., oil) becomes more favorable if compared to conventional water flooding. Therefore, the volumetric sweep efficiency and correspondingly the overall oil recovery are effectively improved. Currently, there is a widespread idea that polymer flooding is inefficient in improving the microscopic oil displacement (at pore scale). However, recent research based on laboratory studies and pilot field testing has proved otherwise. It seems that the viscoelastic properties of polymeric systems indeed improve the microscopic displacement efficiency of residual oil. This paper reviews and emphasizes the recovery mechanisms that have been proposed to explain oil displacement by polymer flooding within oil reservoirs. The aim of this review is to provide a synopsis of polymer flooding which is rapidly emerging as a popular and advantageous EOR process.