Study On The Reversible Emulsion System Controlled By Salt Concentration

Emulsion is widely applied in the oilfield development due to its great physicochemical property.And it is common condition of oil-water in the petrochemical industry.Due to the significantly different nature of water-in-oil emulsion and oil-in-water emulsion,it is of vital importance to study the mechanism and technology of emulsion phase reversible inversion during the transportation and the exploitation of crude oil.The phase state of the emulsion is currently controlled by changing the external conditions.Common triggering mechanisms for environment-responsive reversible emulsions include temperature,light,pH,salinity,etc.Oilfield operating environment is mainly strata or pipes,so temperature and light are hard to be controlled.Changing the pH of the environment easily leads to formation pollution and pipeline corrosion.Therefore,it is worthwhile to study the reversible emulsification technology controlled by salinity.A salinity controlled reversible emulsion system was prepared.And we studied the effects of emulsification procedure,the type and concentration of inorganic salts,the type and concentration of co-emulsifier,and the type of oil phase on the phase and stability of the emulsion system by observing the water/oil separation rate,conductivity,emulsion-breaking voltage,and microstructures.Firstly,the effects of emulsifier concentration,oil-water ratio,stirring time and speed,and temperature on the stability of the emulsion were studied.Results showed that the stability of emulsion increased significantly at first and then decreased slightly with the increase of emulsifier concentration or emulsifying time.The stability of emulsion reached optimal when the ratio of oil to water was 1:1.The negative correlation between emulsion and temperature can be detected,in other words,higher temperature led reduced stability.Stirring speed was the most significant factor affecting the emulsion stability,the faster the stirring speed,the more stable the emulsion will be.Secondly,a reversible emulsion system controlled by salinity was prepared.Two salinity-responsive surfactants,sodium dodecyl benzene sulfonate and sodium petroleum sulfonate were selected.These two surfactants and their compounds could emulsify 5^#white oil and deionized water to form oil-in-water emulsion,which could inverse from oil-in-water to water-in-oil by adding CrCl₃,the phase of inverted emulsion achieved the reversion from water-in-oil to oil-in-water again under the action of Na₂SiO₃.The emulsion stabilized by compounded surfactant composed of 20wt%SPS and 80wt%SDBS was the most stable.Finally,the factors influencing the phase and stability of the reversible emulsion were studied.The emulsion formed by diesel,kerosene or 5^#white could occur reversible phase inversion,of which 5^#white oil was optimal.Low molecular alcohols could enhance the stability of the reversible emulsion,of which n-butanol had the best effect.Isomeric alcohols and macromolecular alcohols were not conducive to the stability of the reversible emulsion.With the concentration of n-butanol and salts increasing,the stability of the emulsion initially enhanced and then declined.The reversible emulsion system could undergo 4 cycles of phase inversion.The stability of the emulsion was gradually weakened with the phase inversion.