Research Of Solubility And Stability Of Dissolved Gas Crude Oil Emulsion

W/O emulsion is a common form of production fluid in oil field.Due to the diversification of the oil recovery mode in the Enhanced oil recovery process,different gas drive methods will cause the produced W/O emulsion to be in a pressure-dissolved state,and at this stage,the crude oil emulsion under different dissolved gas types characteristics studies are still relatively lacking.In this paper,the pressurized emulsification of Changqing crude oil is carried out under different dissolved gas environments(CO₂,CH₄,N₂)by using a pressurized gas-dissolved crude oil emulsifying device.The solubility(R_s)of gas and bulk coefficient(B_o)are measured by a solubility measuring device.The water(oil)separation rate(f_t)are measured by a dissolved gas crude oil emulsion stability analysis device.Surface tension(?),dilatation mode(?),elastic modulus(?_d),and angle(?)are measured by an interfacial tension meter.Dissolved gas crude oil viscosity(?)and dissolved gas crude oil emulsion apparent viscosity(?_ap)are measured by a high pressure rheometer.The effect of the formation of crude oil emulsion on the solubility of gas in emulsion,and the influence of dissolved gas type and dissolved gas pressure on the stability of dissolved crude oil emulsion and oil/water interface characteristics were studied.The results of the dissolved gas characteristics of the emulsion show that the solubility of the three gases in the liquid phase is:R_s(CO₂)>R_s(CH₄)>R_s(N₂),and with the increase of dissolved gas pressure,the solubility of different dissolved gases in crude increases.The presence of the 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 solubility of the gas in the inner and outer phases;The viscous CO₂crude oil has the largest viscosity increase after emulsification,while the dissolved N₂ crude oil has the smallest emulsification viscosity.Since the solubility of different gases in different oil and water phases,which inevitably affects its interface characteristics.The results of the interface characteristics of dissolved gas oil and water indicate that in the environment of CO₂ dissolution,the oil/water interfacial tension is the smallest,so the emulsification effect is the best.The oil-water interface elastic modulus is the largest,the oil/water interface film is the most rigid,the pressurized emulsion system is the most stable;In the environment of dissolved N₂,the oil-water interfacial tension is relatively large,the emulsification effect is the worst,crude oil emulsion system is uneven and the interface elastic modulus is small,which easy to separate free water.Since the dissolution of the gas in the oil-water two-phase weakens the interaction between the surface active substances such as asphaltene on the oil/water interface film,the oil/water interface film rigidity is weakened in the dissolved gas state,the elastic modulus of the oil/water interface film has a tendency to decrease with the dissolved gas pressure increases.The dissolution of the gas in the crude oil emulsion changes the oil phase viscosity and the interface characteristics of the oil/water interface film,and further affects the stability of the crude oil emulsion in terms of oil separation rate and water separation rate.The stability of dissolved crude oil emulsion showed that with the increase of dissolved gas pressure,the oil separation rate of the dissolved CH₄ crude oil emulsion and the dissolved CO₂ crude oil emulsion increased,and the oil separation rate of the dissolved N₂ crude oil emulsion decreased.At the same pressure,the dissolved CH₄ crude oil emulsion has a lower oil separation rate than the dissolved CO₂ crude oil emulsion.As the dissolved gas pressure increases,the water separation rate of the same type of dissolved gas emulsion increases.Under the same pressure,the relationship between the water separation rate of different dissolved crude oil emulsions is:f_t(N₂)>f_t(CH₄)>f_t(CO₂).As the rate of pressure drop increases,the oil separation rate of the dissolved CH₄ crude oil and the dissolved N₂ crude oil emulsion increases,and the oil separation rate of the dissolved CO₂ crude oil emulsion decreases.