Study On Characteristics Of PVT Of Non Condensate Gas And Heavy Oil System At High Pressures And Elevated Temperatures

For heavy oil,the thermal recovery technologies such as multivariate thermal fluid huff and puff have become the main develpoment technology because of its high viscosity and poor flow properties.In order to improve the exploitation effect, non condensate gas, such as CO2, N2 or flue gas, can be injected into reservoir to enlarge heating area and improve the effect of water drainage and oil recovery.With the constant changes of reservoir’s temperature, pressure and fluid saturation,the PVT characteristics of non condensate gas and heavy oil system inevitably change constantly.While these characteristic parameters are very important for studying the mechanism of non condensate gas improving the heavy oil recovery,for the optimization of the injection parameters of steam and gas composite development,and also important for the PVT fitting in the process of reservoir numerical simulation. Therefore,in this paper,we conducted the PVT experiments at high pressures and elevated temperatures with the heavy oil samples of QinHuangdao 33-1 South oilfield, to determine the PVT parameters of heavy oil and non condensate gas system, and to analyze the influence of temperature, pressure and type of gas on the characteristics of PVT.And we also have studied the micro mechanism of the interaction between heavy oil and non condensate gas, combined with the interfacial tension experimental.Then, by combining the Peng-Robinson equation of state(PR EOS) with the modified α function, we have studied the phase behavior of the CO2-heavy oil sytems at high pressures and elevated temperatures.Finally,we conducted physic displacement simulation experiments in order to verify the validation of the PVT law of non condensate gas and heavy oil system through the analysis of oil displacement efficiency.From the result of PVT experiments we can know that, CO2 has a higher solubility in the heavy of QinHuangdao 33-1 South oilfield,and its viscosity reduction effect is obvious,the viscosity reduction rate up to 86%, while the viscosity reduction of N2 rate is 19.8%, the flue gas is 33.8%;The effect of decreasing the density is obvious for CO2,with the highest reduction of 8.48%,which is over three times more than N2’s 2.31.While the flue gas is 2.97%,close to N2.Overall,the effect of temperature on the density and volume factor is much smaller than that of dissolved gas.For CO2,the increase of volume factor is 9.85%,while the N2 is only 2.62%,and flue gas is 3.84%, also more closed to the N2 on the effect of heavy oil.Viscosity reduction mechanism of non condensate gas for heavy oil systems is mainly the bubble viscosity reduction,the dilution viscosity,colloidal structure damage, and the effect on the interfacial tension.Interfacial tension is hardly affected by temperature, but mainly affected by the dissolved gas. CO2 can reduce the interfacial tension by 6 0%~70% which is significantly higher than that of N2, so CO2 has a high solubility in heavy oil.From the study on the phase behavior of non condensate gas-heayy oil systems we can see that,the characterization scheme of treating heavy oil as six pseudocomponents can not only accurately predict saturation pressure,but also can accurately predict the swelling factor.