Experimental Investigation of the Effect of Polymer Viscoelasticity on Residual Saturation of Low Viscosity Oils

Abstract

Abstract We performed coreflood experiments to determine the effect of polymer viscoelasticity on the residual saturation of low viscosity oils by varying the rock type, wettability, polymer rheology, and flow conditions. Several authors have shown that polymers, if viscoelastic, can recover a significant amount of capillary-trapped oil, beyond inelastic floods, in water-wet sandstones. We demonstrate that the polymer viscoelastic effect works for several different rock types, both water-wet and oil-wet media, and with low viscosity oils which broadens the applicability found in previous works. In polymer field studies, the rheology can be tailored to maximize the effect based on our findings. Eleven corefloods were performed in Bentheimer, Boise, and Berea cores. Two of the cores were made oil-wet using dichlorodiphenylsilane (DCDPS) and chlorotrimethylsilane (CTMS). The cores were initially saturated with brine and then displaced by low viscosity (4-10 cp) crude oil until steady state was reached. Brine was then injected to displace the oil until steady state and residual oil saturation was reached. In most experiments, HPAM polymer was then injected at ∼1 ft/day; the polymer rheology was tailored via the salinity, concentration, molecular weight, and degree of hydrolysis. Once steady state was reached, a second polymer solution (with the same viscosity but higher salinity) was injected until a final oil saturation was reached. A reduction in oil saturation was observed in all corefloods in which the polymer was viscoelastic. On average, the oil saturation was reduced by 5.6% in the first polymer flood and 4.0% in the second, high salinity polymer flood. Higher recoveries were found for some experiments in which the first polymer was more elastic (higher dimensionless Deborah number). Final oil saturations as low as 5% were achieved using only polymer (and no surfactant). Results were not dependent on the rock type (e.g. Bentheimer versus Boise) but the effect was more pronounced in water-wet cores than those changed to oil-wet.