Study And Treatment Of The Stability Of The Produced Fluid From Polysurface Flooding

In recent years,polymeric surfactant flooding has emerged as a new type of highly efficient oil recovery technology.In recent years,polymeric surfactant flooding has emerged as a new type of highly efficient oil recovery technology.As a new tertiary oil recovery technology,polymeric surfactant flooding,which can enhance oil recovery efficiently,has a promising development prospect.However,residual polymeric surfactants usually cause changes of the rheology property and stability of the produced liquid,thereby affecting the transport and treatment of the produced liquid.Therefore,the investigation of the effect of polymeric surfactants on the rheology property,stability,and treatment of crude oil emulsions is significant for popularizing the effective application of in oil field.In this paper,we studied the effect of polymeric surfactant's molecular weight,degree of hydrolysis and concentration on stability of W/O and O/W emulsion.Furthermore,the effect of polymeric surfactant on properties of demulsifier and flocculant has been studied.In the first part of this paper,the physical properties of crude oil in a certain oilfield of Bohai Sea are analyzed.The structure of polymeric surfactant is simply discussed by IR,CNMR and HNMR.At the same time,polymeric surfactants with different molecular weight and degree of hydrolysis are prepared by degradation experiment.Secondly,the simulated W/O emulsion was taken as the studying object.The effects of oil-water ratio(7:3,6:4,5:5,4:6,3:7),molecular weight(6.89 million-13.53 million),degree of hydrolysis(30%-41%)and concentration(50 mg/L-300 mg/L)on the properties of emulsion,such as shear rheology,demulsification voltage,thermal stability,water droplet size distribution and median particle size were investigated.As result showed,(1)the higher the water content,the greater the apparent viscosity,viscoelasticity,emulsion-breaking voltage and the smaller the particle size distribution and median diameter.With increase of polymeric surfactant's concentration,the viscosity,viscoelasticity and emulsion-breaking voltage increased and the particle size distribution and median diameter decreased.It means that polymeric surfactant can improve the emulsion stability.(2)The smaller the molecular weight of the polymeric surfactant,the lower the viscosity,viscoelasticity and emulsion-breaking voltage,and the wider range of particle size distribution and median diameter of emulsion.It means that stability of W/O emulsion decreased with decreasing molecular weight.(3)While when degree of hydrolysis increase,the viscosity,viscoelasticity and emulsion-breaking voltage increase,and the range of particle size distribution and median diameter of emulsion decrease.It can be seen that the increase of degree of hydrolysis can improve stability of emulsion.And also we found that polymeric surfactant had an impact on dehydration ratio of demulsifiers.The lower stability of emulsion,the better treatment effect of demulsifier is.Finally,the simulated O/W emulsion(oilfield produced water)was taken as the research object.We investigated the effect of polymeric surfactant's molecular weight,degree of hydrolysis on emulsion stability with the aid of ultraviolet spectrophotometry and optical tweezers.Subsequently,Zeta potentiometer,distribution coefficient experiment and dual polarized polarization interferometry analyzer were used to study the effect of polymeric surfactants on electrostatic interaction and steric hindrance effect of emulsion droplets.Especially,interface parameter analyzer was used to investigate the influence of polymeric surfactants on the interfacial tension and interfacial film strength,thus acquiring a deep insight into the factors influencing the stability of the wastwater.The experimental results indicated that(1)emulsion stability decreased with the addition of polymeric surfactant,but the stability increased with the increase of concentration.Emulsion stability increased with the decrease of molecular weight.The influence of degree of hydrolysis on the stability of emulsion was greatly affected by the concentration of polymeric surfactant.When concentration of polymeric surfactant is lower than 200 mg/L,emulsion stability increase with degree of hydrolysis increase.While with increasing the concentration of polymeric surfactant further,the emulsion stability decreased.(2)The presence of polymeric surfactants in wastewater caused the decrease of electrostatic interactions between oil droplets and dilational modulus of oil/water interfacial film,as a result,the stability of the produced emulsion decreased.The decrease of the molecular weight of polymeric surfactants resulted in an increase in the emulsion stability by enhancing electrostatic interactions.The emulsion stability changed with the increase of the hydrolysis degree of polymeric surfactants under the synergistic functions of electrostatic interactions and steric effects.In addition,increasing the concentration of polymeric surfactants resulted in the enhancement of emulsion stability,mainly because the electrostatic interactions were enhanced and the interfacial tension was decreased.