Measurement and prediction of PVT properties of heavy and medium oils with carbon dioxide

Immiscible carbon dioxide flooding is one of the most promising non-thermal enhanced oil recovery (EOR) methods. These offer great potential for recovering oils from thin and shaly heavy oil reservoirs found in western Canada and in many other parts of the world. For an accurate assessment of the applicability of this recovery technique, the pressure volume-temperature (PVT) properties and the displacement behaviour of CO{sub 2}-heavy oil systems need to be investigated. This paper presents the PVT behaviour of two different heavy oils and one medium oil collected from different areas in Saskatchewan. These oils were characterized through analysis of stock tank oils with and without CO{sub 2}, of recombined reservoir fluid, and of reservoir fluid with CO{sub 2} at reservoir temperature. The effect of temperature and pressure on the density and viscosity of recombined reservoir fluids was also investigated. Results showed that more CO{sub 2} dissolved in medium oil than in heavy oils at the same saturation pressure. This caused higher swelling of the medium oil than of the heavy oils. However, the reduction in viscosity of heavy oils was considerably larger than that of the medium oil (at the same CO{sub 2} saturation pressure). The effect of saturation pressuremore » on density of the oil-CO{sub 2} mixture was relatively small (less than a 1.3% increase in the concentration range studied) and appeared to be more pronounced in the medium oil. The PVT properties of the reservoir fluid-CO{sub 2} systems behaved similarly to those obtained for the stock tank oil-CO{sub 2} mixtures for all three oils. An increase in temperature from the reservoir temperature to 110{degrees}C caused an approximately fifty-fold reduction in viscosity of the-heavy reservoir fluids, compared with only a slightly over four-fold reduction in the medium oil.« less