Computational Study On Miscibility Characteristics Of CO₂/H₂O/Oil Two-Phase System

Based on the broad prospect of CO₂in enhanced oil recovery(CO₂-EOR)and geological sequestration of greenhouse gases,a thermodynamic calculation study of the miscibility characteristics of CO₂/H₂O/Oil system under formation conditions was carried out in this paper.The paper firstly verifies the PR-EOS of the modified?function and binary interaction parameters(BIPs)of the relevant sub-systems,namely CO₂/Oil system,CO₂/H₂O system,H₂O/Oil system and CO₂/Na Cl brine system.The influence of the presence of water phase on the miscibility characteristics of CO₂/Oil phase system was deeply analyzed.Three oil phases were used in the simulation of the CO₂/Oil system,the minimum miscible pressure(MMP)and experimental AAD of the simulated CO₂/C₁₀H₂₂system are 4.262%,the MMP and experimental AAD of the simulated CO₂/C₁₂H₂₆system are 4.69%,and the simulated CO₂/C₁₆H₃₄The MMP of the system and the experimental AAD were 5.93%.The mutual solubility of the CO₂/H₂O system and the H₂O/Oil system is consistent with the literature.In the CO₂/Na Cl brine system,a new formula for the BIP is innovatively proposed.Based on the S(?)reide-Whitson equation of state(SW EOS),it is considered that the calculation accuracy can be improved by adding a linear term of salinity and a logarithmic function term,expanding the calculation interval,and comparing with213 experimental data points,its AAD is 3.8%.It is proved that the simulation results of the two-element system are in good agreement with the experimental results,which shows that the two-element system model used in this simulation is correct.The CO₂/H₂O/Oil was calculated using the Peng-Robinson equation of state(PR-EOS)with the modified?function and binary interaction parameters through the concept of ternary and two-phase(water was introduced into the binary system as a dissolved component in CO₂).The MMP of the CO₂/H₂O/Oil system was investigated by simulation and comparison with experiments.In CO₂/H₂O/Oil system,miscible phase calculation and analysis were carried out using C₁₂H₂₆and C₁₆H₃₄as oil components,respectively.It is found that the AD of the simulated and experimental MMP of the CO₂/H₂O/C₁₆H₃₄system is less than 10%,and the AAD is less than 8%.Indicating that the model proposed in this paper can be well applied to the calculation of the miscible characteristics of the CO₂/H₂O/Oil system.The parametric study found that the presence of water component can consistently reduce the MMP of the CO₂/Oil system,and the degree of MMP reduction is related to the molar ratio of CO₂.When the molar ratio of the two components is the same,that is,the same working condition.The higher the pressure and the closer the CO₂molar ratio is to 1,the larger the minimum miscible pressure increases for every 0.1molar ratio increase.Observing the gas-liquid fraction diagram,it can be seen that the higher the temperature,the slower the gas-liquid fraction changes under the condition of changing the same pressure.This phenomenon has nothing to do with the value of the molar ratio of CO₂.The molar ratio of CO₂in the CO₂/H₂O/C₁₂H₂₆system is slightly different,and the molar ratio of CO₂in the CO₂/H₂O/C₁₆H₃₄system is similar.