Phase Interaction Of CO₂-oil-water System And Its Impact On Oil Flooding

During the process of CO₂ flooding,CO₂ huff and puff,CO₂ and water alternating flooding,CO₂ dissolved into the oil phase,water phase and the mass transfer process between two phases can change the viscosity and interfacial tension of CO₂-oil-water system.Phase interaction of CO₂-oil-water system is the main factor that influences the effect of CO₂flooding by effectively improving oil-water property and ultimately improving EOR.In this dissertation study,dissolving properties of CO₂ with different oils at the high temperature and high pressure are researched;The diffusion coefficient of CO₂ in crude oil and pure water is measured according to the pressure drop model,U-shaped high temperature and high pressure reaction kettle is designed to measure diffusion coefficient of CO₂migrating from water phase to oil phase and from oil phase to water phase;The interfacial phenomena,interfacial tension（IFT）of the CO₂-oil and the oil-carbonic water systems at high temperature and high pressure are obtained by ADSA method.The CO₂ huff and puff,CO₂flooding and CO₂ gas alternating water flooding physical simulation experiments are studied to analyze the influence on oil displacement of CO₂ dissolved diffusion,and expound the mechanism of CO₂ to improve oil recovery factor.It is shown that compared with CH₄ and N₂,CO₂ can reduce oil viscosity better.Diffusion coefficient is proportional to the temperature and pressure because of the influence of CO₂ concentration and solubility,it’s observed that diffusion coefficient of CO₂ in oil>diffusion coefficient of CO₂ in water>diffusion coefficient of CO₂ from oil phase to water phase>diffusion coefficient of CO₂ from water phase to oil phase.The interaction between CO₂ and oil is divided into two stages,the first stage is that CO₂ dissolved into oil phase and swelled the oil,the second stage is the light-ends extraction and the volume of oil droplet shrinking stage.With the pressure increase,the phase interaction of CO₂ and oil became faster.The initial strong light-ends extraction is dominant and the interface between oil droplet and CO₂ became blurred.In the oil-carbonic water system,the phase interactions are weak,the interface is clearer and the shape of the droplet is more stable,the IFT decreased and achieved equilibrium.With the temperature and pressure increase,the equilibrium time is shorter and the IFT of oil-carbonic water is lower.CO₂ dissolving diffusion process will dynamic influence on flooding recovery:In the process of CO₂ huff and puff,CO₂ retention time is short in the formation,gas channel can form easily,the effects of oil viscosity reduction by CO₂ cannot be fully reflected.