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According to the PVT high pressure physical parameters of oil and gas, Using the PVTI in reservoir numerical simulation software Eclipse to determine the phase characteristics of the fluid, fitting the basic parameters and building component model, using the GEM modular program of CMG to calculate the oil displacement efficiency under different inject pressure, according to oil displacement efficiency and injection pressure relationship curve presents two lines before and after the inflection point, regressing the equation of two lines, and the intersection of the pressure be determined the minimum miscibility pressure of carbon dioxide-crude oil; in order to confirm the results, at the same time using slim tube experiment method and empirical formula methods to determine the minimum miscibility pressure of carbon dioxide-crude oil, and the slim tube experiment should be treated as the reference standard, Calculating the relative error of CMG method and the empirical formula method which are compared with the measured value of slim tube method. The results show that when the reservoir temperature are 90℃and 108℃, the carbon dioxide-crude oil minimum miscibility pressure of Shu 101 block in Yushulin oilfield is predicted by CMG, comparing with measured value of slim tube method, the relative error are 1.54% and 0.72%, the average relative error is 1.13%, which is less than the commonly used empirical formula of relative error average value, showing that carbon dioxide-oil minimum miscibility pressure is accurate and reliable by CMG.

Due to the special phase behavior of near-critical fluid, the development approaches of near-critical condensate gas and near-critical volatile oil reservoirs differ from conventional oil and gas reservoirs. In the near-critical region, slightly reduced pressure may result in considerable change in gas and liquid composition since a large amount of gas or retrograde condensate liquid is generated. It is of significance to gain insight into the composition variation of near-critical reservoir during the depletion development. In our study, we performed a series ofPVTexperiments on a real near-critical gas condensate reservoir fluid. In addition to the experimental studies, a commercial simulator combined with the PREOS model was utilized to study retrograde condensate characteristics and reevaporation mechanism of condensate oil with CO2injection based on vapor-liquid phase equilibrium thermodynamic theory. The research shows that when reservoir pressure drops below a certain pressure, the variation of retrograde condensate liquid saturation of the residual reservoir fluid exhibits the phase behavior of volatile oil.

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