Laboratory Investigation of the Water-Driven Carbon Dioxide Process for Oil Recovery

Abstract

Abstract Water-propelled banks of carbon dioxide recovered both high- and low-viscosity crude oil substantially in excess of that recovered by water flood in linear flow model experiments. The increase in oil recovery is explained by oil swelling and viscosity reduction. Additional oil was recovered by solution gas drive at the end of the carbon dioxide floods when the model systems were depressured. Introduction This study was an investigation of the use of a water-driven carbon dioxide bank to recover crude oil. Techniques involving the injection of carbon dioxide have aroused considerable interest in recent years among methods considered for increasing oil recoveries. A number of investigators have studied the process in the laboratory and in the field. Laboratory studies referenced indicate that carbon dioxide in conjunction with water flooding recovers more oil than does water flooding alone. These reports diverge widely, however, in stating magnitude of improvement. We believed that a water-driven carbon dioxide bank would increase recovery of crude oils by two mechanisms: viscosity reduction and oil swelling. Due to reduction in the oil viscosity caused by solution of carbon dioxide, displacement efficiency should be improved. In addition, the residual oil should be highly swollen by the carbon dioxide held in solution. Thus, the final residual oil saturation, in terms of stock-tank oil, would be lower than in the absence of carbon dioxide. To test this hypothesis, experiments were carried out to recover both high- and low-viscosity crude oils from linear laboratory models. Tests reported here were carried out in small-diameter models at low rates of fluid advance, where diffusion is a powerful factor in preventing fingering or channeling. The volumetric sweep efficiency of the injected fluids should, under these conditions, be close to 100 per cent. In a field operation it would be necessary to evaluate stratification effects and to consider areal sweep efficiency.