Study On Depressurization And Demulsification Characteristics Of Dissolved Crude Oil Emulsion In Changqing Oilfield

In the actual oilfield exploitation process,due to the application of steam injection and flooding oil recovery method,water-in-oil（W/O）crude oil emulsion will inevitably be in a pressurized state and dissolve the corresponding gas-driven gas,because the research on the depressurization characteristics of pressurized dissolved gas crude oil emulsion is relatively lacking.In this paper,the properties of experimental crude oil and oilfield water are first tested,and then the optimal stability conditions for crude oil emulsion are determined by changing different conditions.The emulsion with pressure is emulsified under different dissolved gases（CO₂,N₂）and different pressures（1Mpa,2Mpa,3Mpa）using the pressure dissolved gas emulsification device.And the solubility R_s,volume coefficient Bo,water separation rate/oil separation rate ft,interfacial tensionγ,interfacial film expansion modulusε,interfacial film elastic modulusεd,dissolved gas crude oil viscosityμ,and apparent viscosityμap of dissolved crude oil emulsion were measured by dissolved gas characteristic testing device,high-pressure rheometer,interfacial tensiometer,etc.The effects of the formation of crude oil emulsion on the solubility of gas in emulsion,dissolved gas type and dissolved gas pressure on the stability and oil/water interface characteristics of dissolved crude oil emulsion were studied.The results of the dissolved gas characteristics of crude oil emulsion show that the solubility of the gas used in the experiment in the liquid phase conforms to the following laws as follows:Rs（CO₂）>Rs（N₂）,and the solubility of the gas increases with the increase of the dissolved gas pressure.Moreover,the existence of oil/water interface film will inhibit the migration of gas from the outer phase to the inner phase to a certain extent,so that the solubility of the gas in the crude oil emulsion is less than the sum of the solubilities of the internal and external phases.The viscosity increase of dissolved CO₂crude oil is the largest after emulsification,while the emulsification and viscosity of dissolved N₂crude oil is the smallest.Due to the different solubility of different gases in the oil/water phase,it will inevitably affect their interface characteristics.The results of dissolved oil/water interface characteristics show that in the environment of dissolved CO₂,because of its minimum oil/water interface tension,its emulsification effect is the best,and because of the largest elastic modulus of oil/water interface,the oil/water interface film formed has the strongest rigidity and is the least easy to separate free water.In the environment of dissolved N₂,the oil/water interface tension is large,the crude oil emulsion system formed is uneven,the emulsification effect is the worst,and its interfacial elastic modulus is the smallest,which is easy to separate free water.Due to the dissolution of gas in the oil-water two-phase weakens the interaction between asphaltenes and other interfacial active substances on the oil/water interface film,the rigidity of the oil/water interface film is weakened in the dissolved gas state,and the elastic modulus of the oil/water interface film tends to decrease with the increase of dissolved gas pressure.The dissolution of gas in crude oil emulsion will change the viscosity of the oil phase and the interface characteristics of the oil/water interface film,which in turn will affect the stability of the crude oil emulsion in terms of oil separation rate and water separation rate.The stability results of dissolved crude oil emulsion showed that with the increase of dissolved gas pressure,the oil separation rate of dissolved CO₂crude oil emulsion increased,and the oil separation rate of dissolved N₂crude oil emulsion decreased.With the increase of dissolved gas pressure,the water separation rate of the same dissolved emulsion increases.Under the same pressure,the relationship between the water division rate of different dissolved gas emulsions is:ft（N₂）>ft（CO₂）.When the pressure relief rate is increased,the oil separation rate of dissolved N₂crude oil emulsion increases with the increase of the depressurization rate,while the dissolved CO₂is the opposite.This is mainly because N₂mainly compresses the entire system in the emulsion,when the pressure decreases,there is no external force exerted by the outside world,the friction of the entire system is reduced,and the internal phase droplets will accelerate the separation,so there will be the same time to dissolve N₂crude oil emulsion oil separation rate with the increase of pressure relief rate and increase.CO₂is sufficiently soluble in water and can also be dissolved in oil because it is a polar molecule,because the solubility is different between oil and water.CO₂gas cannot be directly dissolved in the outer phase after escaping from the dispersed phase,and the quality of the inner phase cannot change and cannot sink,resulting in the oil separation rate of dissolved CO₂crude oil emulsion decreasing with the increase of pressure relief rate at the same time.