Heavy-Oil-Recovery Enhancement With Choline Chloride/Ethylene Glycol-Based Deep Eutectic Solvent

Abstract

Summary Because of increasing energy demand, unconventional resources such as heavy oil are being explored and recovered. Enhanced-oil-recovery (EOR) methods such as surfactants and polymer flooding must be optimized and new chemicals must be designed to produce more oil. This paper introduces a new deep eutectic solvent (DES) that is based on choline chloride/ethylene glycol for EOR. As preliminary investigations revealed, different concentrations of DES solutions in brine (0 to 100 vol%) were characterized by measuring density, viscosity, conductivity, surface tension, and refractive index at different temperatures (25 to 55°C). Then, the effects of the DES/brine solutions on emulsification with oil phase, wettability alteration, oil/solvent interfacial tension (IFT), formation damage, and tertiary heavy-oil recovery were studied. Potential of the DES solution on enhancing heavy-oil recovery was explored by use of coreflood experiments. This was performed at reservoir condition (pressure = 1,200 psi, temperature = 45 to 80°C) with Berea sandstone core samples and fluids from the field of interest (formation brine and crude oil). An increase in IFT rather than a decrease was observed between the DES/brine solution and the oil. The spontaneous-water-imbibition tests suggested that a decrease in oil-wetness led to an increase in oil production. Approximately 52% of residual oil after waterflooding was recovered with the DES from the coreflooding. The results show an increase in oil recovery with reservoir temperature (6, 13, and 16% on the basis of initial oil in place at 45, 60 and 80°C, respectively). The interaction of the DES with the core materials did not lead to formation damage, as demonstrated by the permeability measurements of the DES/brine solution before and after injection. Viscous forces and wettability alteration were found to be the dominant mechanisms for the tertiary oil-recovery enhancement.