Experimental Study On Supercritical-CO₂ Emulsion Stability And Fluid Flow Mechanism In Porous Media

Reducing greenhouse gas CO₂ emissions by capture has become the growing focus,after the capture of CO₂ can significantly improve EOR.At the reservoir condition,the low viscosity and high diffusivity of supercritical CO₂ will cause channeling in the process of oil displacement,then affect the swept volume and oil displacement efficiency.CO₂ emulsion flooding can effectively control the CO₂ flow and improve CO₂ flooding gas channeling and viscous fingering in inhomogeneous reservoir.In the process of supercritical CO₂ emulsion flooding,reservoir temperature,pressure,salinity,and other factors such as surfactant type will influence the stability of the emulsion CO₂.The experimental study optimized the surfactants of CO₂ emulsion by the literature research,then used the Waring Blender method for further optimization of surfactant type and concentration.The study finally choosed AOT OS and C₁₂E₉P₃ as CO₂ emulsion surfactant.Used TECLES Interfacial Rheometer to study the interface characteristics of CO₂ and water,oil,surfactant system,then the study determined the influence of temperature,pressure,water salinity,surfactant types to CO₂ system.The results show that with the increase of pressure,the interface tension of CO₂-aqueous surfactant solution rapidly decreases,gradually trends to be stable,meanwhile the expansion modulus increases first,then gradually trends to be stable.With the increase of temperature,the interfacial tension increases while the expansion modulus decreases;the interfacial tension decreases first and then increases with the increase of salinity,while the expansion modulus increases first and then decreases.The CO₂ emulsion stability in the reservoir condition was researched by high temperature and pressure reaction kettle,which was related with temperature,pressure,water salinity and surfactant types.With regard to anionic surfactants such as AOT and OS,with the increase of pressure,the emulsion stability increases,interface properties and the emulsion stability have corresponding relationship.To nonionic surfactant such as C₁₂E₉P₃,with the increase of pressure,the emulsion stability reduces.By comparing the AOT,OS and C₁₂E₉P₃,AOT emulsion stability performance is the best,C₁₂E₉P₃ emulsion stability is the worst,and it is more sensitive to pressure.CO₂ emulsion seepage characteristics were studied by micro-etching model in porous media.The study analyzed theinfluence of different temperature and pressure to CO₂emulsion stability in existence state,migration rule in porous media and the influence of the displacement characteristics.The results show that there are three kinds of CO₂ emulsion flow in the micro medium.With the increase of pressure,CO₂ emulsion microscopic stability increases,and the stability is better than low pressure one.With the increase of temperature,CO₂ emulsion microscopic stability decreases,and the diffusion to the crude oil is faster than low temperature one.The swept volume and the sweep efficiency of CO₂ emulsion have increased substantially compared to CO₂ gas flooding.The plugging and oil displacement performance of CO₂ emulsion were studied through sandpack displacement experiment system.The study compared CO₂ emulsion flooding effect with N₂ foam flooding effect,and analyzed the changes of four components of output oil and the viscosity changes.The results show that,although the CO₂ emulsion plugging ability is a bit poorer than N₂ foam,but its oil displacement effect is better than that of N₂ foam.CO₂emulsion can greatly reduce the interfacial tension and crude oil viscosity.The results of the study for CO₂ emulsion can provide certain theoretical guidance in oil and gas field development.