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Abstract

Laboratory coreflood experiments were conducted on Athabasca oil sands using hot water and caustic or carbon dioxide. Production temperatures were maintained at 150.degree. C. or lower and at an injection pressure of 3.55 MPa (500 psi). The objective of the experiments was to determine the conditions under which oil-in-water (O/W) emulsion could be produced in-situ. In addition, the study was to investigate the potential benefit of adding carbon dioxide to hot water to improve bitumen recovery. The results prove that when the pH of injected fluids is between 10.5 and 11.5, the O/W emulsion predominates. The emulsion is stable and has a viscosity much lower than that of the oil itself, due to the continuous water phase, and should beneficial in the recovery of heavy oil and bitumen. When the injected fluids have a pH less than 10.5, the water-in-oil (W/O) emulsion predominates. The laboratory data indicate that even this type of emulsion behaves as an O/W in the core but it is unstable and when produced the droplets quickly coalesce and immediately form the observed W/O emulsion. The addition of carbon dioxide to hot water at low temperatures proved to be effective in improving bitumen recovery over that from hot water alone. This is believed to be due to the effect of carbon dioxide absorption in reducing bitumen viscosity which resulted in improved bitumen mobilization. Another beneficial effect is the increase in pressure gradient due to the presence of free carbon dioxide, beyond the solubility limit, in the injected stream. The hot water-CO.sub.2 runs produces mostly W/O emulsion. The best recovery was achieved when the produced fluids temperatures was around 130.degree. C.

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