The Study On Mass Transfer And Partial Miscibility Of Reservoir Fluids In CO₂ Flooding

Reservoir heterogeneity can cause “non-uniform” mass transfer of fluids in the process of CO₂ flooding,and make CO₂ and oil only partially miscible in small scale,so the CO₂ and oil cannot reach the reservoir-scale miscibility even under minimum miscible pressure.In order to take account of the effect of mass transfer and partial miscibility on CO₂ flooding in heterogeneous reservoirs,theoretical research,physical test,and numerical simulation are conducted.On the base of analysis for reservoir heterogeneity,this paper study the vaporizing and condensing miscible in the process of partial miscibility and mass transfer;Provide the mathematical model of one-dimensional and two-dimensional dispersion between CO₂ and oil,the dispersion coefficients determined by experiments range from 10.9×10-9m2/s to 20.4×10-9m2/s;The physical simulation of CO₂ flooding for heterogeneous cores indicate that: the heterogeneity of cores can influence the recovery and production significantly;In order to take account of the dispersion between CO₂ and oil,numerical simulations of CO₂ flooding in heterogeneous reservoirs are conducted.The results shows that: the plane heterogeneity can cause non-uniform mixing between CO₂ and oil,and in the transition zone between condensation band and vaporization band when the interfacial tension reduces to a certain degree,CO₂ and oil can only form partial miscibility in small scale;And partial miscibility can reduce the effective concentration of CO₂ in the front and prolong the miscible front,resulting in the trap of remaining oil.