The Effect of Polyethylene Oxide on Residual Oil Saturation of Low Permeability Carbonates

Abstract

Abstract The objective of this paper is to investigate the transport and incremental oil recovery associated with Polyethylene Oxide (PEO) compared to Hydrolyzed Polyacrylamide (HPAM) through a series of corefloods in low permeability carbonate cores for use in enhanced oil recovery (EOR). Recent studies have brought attention to PEO's improved injectivity in low permeability carbonate reservoirs compared to acrylamide-based polymers offering a promising alternative (Mejia et al., 2022a; Mejia et al., 2022b; Trine et al., 2022). Five two-phase experiments were conducted in Indiana limestone cores (permeability <100 mD) with PEO and HPAM of similar molecular weights (4 MM Dalton) and viscosity; they were designed to measure incremental oil recovery for both polymers. Tracer tests were completed to determine heterogeneity. Brine was displaced by a 50-cP oil, and initial oil saturations averaged 55.8%. The oil was displaced initially with a waterflood for 3-5 pore volumes. The waterflood, on average, recovered 60.7% of original oil in place (OOIP). Oil cut was consistently zero at the conclusion of the waterflood suggesting the cores were at or near residual oil saturation. The polymer flood followed the waterflood for three pore volumes or until oil cut was zero. HPAM was injected in the first two experiments, and PEO was injected in the final three. When HPAM was injected, oil production in terms of OOIP from the polymer flood was minimal (average 2.2%) which was expected since oil saturation was presumed near residual. However, in the experiments when PEO was injected, oil production from the polymer flood averaged 13.5%, suggesting that residual oil saturation was decreased by the polymer. PEO was consistently shown to produce more oil compared to HPAM. This work suggests that PEO may result in higher oil recoveries and reduced residual oil saturation under certain conditions.