Mechanism of polymer regulated high internal phase CO2-in-water foam viscoelasticity for enhanced oil recovery

Polymer-enhanced foam can reduce viscous fingering by controlling CO2 mobility, thus improving the sweep efficiency and CO2 sequestration. High internal phase CO2 foam with a foam quality of 0.9 can further improve viscosity and flow ratio due to its tightly packed structure. In this study, cocamidopropyl betaine (CAPB) and four polymers were used to produce high internal phase CO2 foams. The rheological behavior of the foam was measured via a steady-state flow experiment using a straight tube. Polymer-enhanced foams exhibited high viscosities, but they all exhibited shear-thinning non-Newtonian behavior and conformed to the power-law model. The changes in the rheological properties were mainly due to the different adsorption behaviors of the polymers. Core flooding experiments showed that high-viscosity foam significantly improved oil recovery compared to water. Among them, polyvinyl alcohol (PVA)- and poly (2-acrylamide-2-methyl-1-propanesulfonic acid) (PAMPS)-enhanced foams exhibited a significant increase in ultimate oil recovery, reaching 85.21% and 80.69%, respectively. By combining the displacement pressure difference and two-phase flow simulation in porous media, the synergistic effects of the viscosity coefficient and power-law index on enhanced oil recovery (EOR) were verified. The viscosity of the foam determines its ability to plug high-permeability zones, which is the premise of the EOR. With an increase in the shear resistance of the foam, the foam fluid can further spread in the low-permeability zones, enhancing the sweep efficiency and residual oil recovery.