Experimental Test And Computational Study On Phase Equilibrium Characteristics Of CO₂/oil Two Phase System

The CO₂ miscible flooding technology has broad application prospects in enhancing oil recovery and geology of greenhouse gasses.Therefore,the research on the miscibility of CO₂/oil/water systems has become an important research topic.In this paper,the phase equilibrium disappearance method?VIT?was used to test the phase equilibrium characteristics of CO₂/oil phase system,and to obtain the miscibility pressure of CO₂/oil phase system under different oil components and different temperatures.At the same time,the thermodynamic calculation method was used to calculate the phase equilibrium characteristics of CO₂/oil phase system.Based on the good agreement between the calculated results and the experimental results,the phase equilibrium characteristics of the CO₂/water system were further calculated and the results were in good agreement with the literature results.Finally,the calculation of the phase equilibrium characteristics of the CO₂-water/saline-oil three-phase system is calculated using the calculation method to guide the industrial practice.The main conclusions of this project are as follows:?1?In the experimental study of CO₂/oil system,the phase equilibrium characteristics of system were studied using two methods of surface tension measurement and phase equilibrium state observation.In the surface tension test experiment,when the oil phase was C₁₀H₂₂,experimental studies were conducted respectively at temperatures of 26.2°C,47.7°C,and 58.1°C,and the miscibility pressure of the mixed system were about in the6-7 MPa,8-9 MPa,and 10-11 MPa.Therefore,with the increase of temperature,the miscibility pressure of the mixed system gradually increases with the same oil phase.In addition,when the temperature is 47.7°C and the oil phase is liquid paraffin,the mixed phase pressure of the system is about 7-8 MPa.Compared with the CO₂-C₁₀H₂₂ system,it was found that at the same temperature,as the number of carbon atoms in the oil phase of the system increases,the miscibility pressure of the mixed system gradually increases.In the phase equilibrium observation experiment,the‘bubble point'appearance process was clearly observed,and the mixed phase pressure of the CO₂/liquid paraffin system and the surface tension test results were basically the same.?2?In the simulation study of the miscibility of CO₂/oil system,compared with the experiment,when the oil phase is C₁₀H₂₂ and the temperature is 26.2°C,47.7°C,and58.1°C respectively,the miscibility pressure is 6.5 MPa,8.8 MPa,and 10.3 MPa,which is consistent with the experiment results.Compared with the literature,when the oil phase is C₁₀H₂₂ and the temperature is 20°C,30°C,and 37.8°C respectively,the miscibility pressure is 5.33 MPa,6.53 MPa,and 7.61 MPa,which is consi stent with the literature results,and the error is less than 4%.Comprehensive experimental and literature comparison results we can see that the simulation calculation model in this paper is available and acculturate.?3?In the simulation of CO₂/water system,the simulation results show that the solubility of CO₂ continued to increase with the pressure increased at the same temperature.Under the same pressure,as the temperature increased,the percentage of CO₂ in the liquid phase gradually decreased,while the percentage of CO₂ in the gas phase gradually increased.However,when the temperature of the systems is higher than the critical temperature,the system would appear to‘cross-over-Area'under a large pressure.In addition,the gas phase viscosity of the salt-containing system was almost constant,and the viscosity of the liquid phase was equal first approximately and then increased.In addition,the simulation results are consistent with the trend of the literature research,that is,the simulation results are accurate.?4?In the CO₂-water/saline-oil system,compared with the pure water system,the salt-containing system had a large vapor fraction,a higher mixed pressure and a lower solubility of CO₂ in the liquid phase.In other words,the salt-containing system favored the gasification of the mixed system,but not conducive to the dissolution of CO₂ in the liquid phase.In addition,the gas phase viscosity of the salt-containing system was almost constant,and the viscosity of the liquid phase wa s equal first approximately and then increased...