Synergism Of Polymer/surfactant Mixed System On The Formation And Stability Of The Oil-in-water Emulsion

Surfactants and amphiphilic polymers can adsorp at the oil-water interface,which reduce the interfacial tension and make the interface more elastic.In this case,the oil-water interface is more stable.In recent days,many oil fields in China have been into the tertiary oil recovery stage,which large amounts of fluids containing surfactants and polymers are injected for enhancing oil recovery.However,the amphiphilic materials injected into strata cause tough problems to environment.Formation of a extreme stable O/W emulsion results from mutual interactions between surfactants and polymers at the oil-water interface.The O/W emulsion,called oilfield wastewater,has much oil and can't be discharged directly.Therefore,separation of oil from the water is an important operation for emission of oilfield wastewater.Moreover,injection of fluids may cause expansion of clays because of hydration and sediment resulting from interactions between injected fluids and materials in the stratum,which block the oil channels and reduce the oil production.In the first chapter,the research background and significance of the study are discussed.Reducing injected fluid into oil channels can prevent from damaging the reservoir.At the same time,study of interactions between polymer/surfactant mixtures at the interface can provide theoretical guidance for oilfield wastewater treatment.Research of interface behavior of amphiphilic materials at oil-water and air-water interface published in recent years are summarized.In addition,methods of preparing nano-emulsion and effects on preparation of nano-emulsion are introduced.In the second chapter,interfacial properties of the polymer/surfactant mixtures at the heptane-water interface are studied.Interfacial tension(IFT)and interfacial dilational modulus(E)are two key parameters for enhancing oil recovery.The present study investigated the dynamic interfacial properties of similarly charged and oppositely charged polymer/surfactant mixtures at the oil-water interface.Partially hydrolyzed polyacrylamide(HPAM),sodium dodecylbenzenesulfonate(SDBS),and dodecyltrimethylammonium bromide(DTAB)were used to prepare polymer/surfactant mixtures.The effects of the molecular weight and concentration of the polymer,surface charge and concentration of the surfactant,pH,and ionic strength on the interfacial behavior of polymer/surfactant mixtures at the interface have been investigated.HPAM-1 exhibited a higher interfacial activity than HPAM-2.Strong binding interactions were observed between anionic HPAM and cationic DTAB.The binding was driven by electrostatic attraction,hydrogen bonding,hydrophobic interactions,and van der Waal forces.HPAM had a strong tendency to form more hydrophobic and interfacial activity complexes with DTAB.These complexes could remarkably affect the interfacial properties of polymer/surfactant mixtures at the interface.It was observed that the adsorption kinetics of polymer/surfactant mixtures were controlled not only by the diffusion occurring between the bulk phase and the interface,but also by the energetic and steric barriers generated by the electrostatic interactions and already formed adsorption layers.In addition,the dilational viscoelasticity of polymer/surfactant mixtures was significantly affected by the pH and ionic strength.The HPAM/DTAB mixtures with the addition of salts have higher E values than those of salt-free systems and HPAM/SDBS mixtures.The addition of salts might enhance the association of HPAM with DTAB and improve the adsorption efficiency of HPAM/DTAB mixtures at the interface due to the"salting out" effect.In the third chapter,the preparation of nano-emulsion is studied.Phase inversion composition(PIC)method is a appropriate approach of preparing nano-emulsion,which costs a little and is applied to mass production.O/W nano-emulsion is produced in the system water/Span80-Tween80/white oil-solid paraffin.The effects of oil properties,temperature,ratio of Span80 and Tween80 and surfactant concentration on resulting nano-emulsion are investigated.A obvious increase happens to droplet size when solid paraffin is added to the oil phase.Preparation of nano-emulsion at high temperature makes the droplet size of resulting nano-emulsion small,which may be attributed to the low viscosity and interfacial tension.The high temperature changes the amphiphility of surfactants and adsorp effectively at the interface.At the same time,the ratio of Span80 and Tween80 is other factors of changes the surfactants layer.It has been proven that the optimized value of HLB was 9.5,which surfactants prefer to be at the interface and stabilize the largest active interfacial area.Moreover,at certain volume fraction of oil,the droplet size of nano-emulsion decrease with increasing concentration of surfactants.sufficient agitation plays an important role in the preparation of nano-emulsion with small droplet size and a narrow droplet size distribution.At last,The water shutoff rate is more than 90%when nano-emulsion is used as temporary plugging agent.And nano-emulsion in the oil channel could be reversed during the oil production,which doesn't bring damages to the reservoir.