Study On The New Temperature And Salt-Resistant Surfactants For Enhanced Oil Recovery

In order to slow down the continuous increase of import fraction of crude oil consumed in China,it has become a national strategy to develop and apply the enhanced oil recovery technology in mature oilfields to increase oil recovery.Although the alkali-surfactant-polymer(ASP)flooding technology has been widely applied in most large oilfields in China,it tends to be modified to either ASP flooding using weak alkalis or SP flooding free of alkali due to the side effects recently noticed of the ASP flooding using caustic alkalis,such as scaling and corrosion of pipelines and equipments,and the damage to the formation structure.On the other hand,the surfactant flooding technique for high-temperature and high-salinity reservoirs has been on the agenda.However,since the typical weak alkali such as Na2CO3 is not applicable due to the formation of the precipitates with Ca2+and Mg2+in connate water,the surfactant flooding technique for the harsh reservoir relays on the SP flooding free of alkali,in which the development of the new surfactants is key important and far from achieved.On the basis of the researches and developments of a series of double long alkyl sulfobetaines and double long alkyl sulfonate surfactants,this thesis attempts to embed a polyoxypropylene(PO)-polyoxyethylene(EO)chain into these molecules to construct a new series of nonionic-sulfobetaine and nonionic-sulfonate combined surfactants,so that they can be applied to the SP flooding of the high-temperature and high-salinity reservoirs.Specifically,four new surfactants,diC12GE-(PO)10-(EO)10-HSB(?),diC12GE-(PO)10-(EO)10-HS(?),C16GA-(PO)5-(EO)3-HSB(?)and C16GA-(PO)5-(EO)3-HS(?)were synthesized by using 1,3-didecyl glyceryl ether(diC12GE)and C16 Guerbet alcohol(C16GA)as starting materials,respectively,followed by addition of PO and EO to form nonionic intermediates,and finally connected with either hydroxypropyl sulfobetaine(HSB)or hydroxypropyl sulfonate(HS).Among the synthesized surfactants the contents of the surface-active components,sulfobetaine(?,?)or sulfonate(?,?),are more than 90%and 85%,respectively.The purified products were characterized by IR,1H NMR and ESI-MS,consistent with the molecular structure of the target products.The performance studies show that the introduction of the PO-EO chains into the double alkyl chain surfactant molecules significantly improves their aqueous solubility and salt tolerance.For example,the tolerance of(?)to Na+and Ca2+can be as high as 40,000 mg/L and 4,000 mg/L,respectively.At 60?,the four products can be dissolved in the target reservoir(Minsk)connate water with a total salinity of 19,640 mg/L without precipitation or phase separation.It is shown that the surface activity parameters of the surfactants are mainly affected by the length of the embedded PO-EO chain and the type of terminal hydrophilic groups.Therefore(?)and(?)have smaller cmc and higher ?cmc,while(?)and(?)have higher cmc and lower ?cmc(<35mN/m).On the other hand,the saturated adsorption ?? of hydroxypropyl sulfobetaine is about twice that of hydroxypropyl sulfonate.With respect to the Minsk reservoir conditions(76?86?,total salinity 19,640 mg/L,Ca2+and Mg2+840 mg/L),the four surfactants are slightly more hydrophilic than the optimum.However,multiple binary formulations with excellent performances have been obtained by mixing them with lipophilic surfactants.For example,ultra-low equilibrium interfacial tension(IFT)between the Minsk crude oil and connate water can be achieved by the binary mixtures of(?)and(?)with the slightly lipophilic dialkyl glyceryl ether sulfobetaines,diC8GE-HSB and C10+6GE-HSB,where the molar fraction of(?)and(?)is 0.2,the total concentration ranges between 0.1 mM and 5 mM,and partial equilibrium IFT can be as low as 10-4 to 10-5 mN/m.By mixing(?)and(?)with either diC8GE-HSB or C12+6GE-HSB,where the molar fraction of(?)and(?)is 0.4?0.6,the binary mixtures can reduce the equilibrium IFT to ultra-low at the total concentration range between 0.1 mM and 5 mM.By keeping at 90? for 90 days at an initial total concentration of 5 mM,both the diC8GE-HSB/(?)=0.8/0.2 and the C12+6GE-HSB/(?)=0.4/0.6 binary mixture solutions can still achieve ultra-low IFT of 10-3 mN/m magnitude.The synthetic surfactants also have excellent resistance to sand adsorption.For example,under the experimental conditions of 60?,solid/liquid=0.1/0.9(mass fraction ratio),the binary mixture solution C10+6GE-HSB/(?)=0.8/0.2 and C12+6GE-HSB/(?)=0.4/0.6 at an initial concentration of 5 mM can obtain ultra-low interfacial tension until after 8 and 9 consecutive adsorptions by quartz sands,respectively.These surfactant formulations have no in situ hydrophobization to the negatively charged solid surfaces,and always keep the solid surface water-wet.In addition,the obtained binary mixtures have good emulsifying ability to the Minsk crude oil by forming stable O/W emulsions.Obviously,the new surfactants synthesized which are highly temperature-resistant and salt-tolerant have good performances in SP flooding free of alkali,and are therefore potentially applicable for enhanced oil recovery in high temperature and high salinity reservoirs.