Synthesis Of Salt Thickening Betaine Amphiphilic Polymer And Its Mechanisms Of Action

As the most oil fields in China have entered a period with high water cut,polymer flooding has become an important technology for increasing and stabilizing oil production in major oil fields.At present,most of the amphiphilic polymers widely studied and applied are hydrophobically modified polymer on the basis of partially hydrolyzed polyacrylamide(HPAM).Due to the salt solution properties of polyelectrolytes,it is difficult to apply to high salinity reservoirs within the scope of economic cost control.Betaine-type amphiphilic polymers,as an important branch of the amphiphilic polymer type,are a class of oil displacing agents that are suitable for use in high salinity reservoirs.The research work in this paper will provide theoretical guidance for the synthesis,characterization,mechanism of action of betaine-type amphiphilic polymers and their practical application in high salinity reservoirs.Three kinds of water-soluble associative monomers with different structures,cetyl dimethyl allyl ammonium chloride(C₁₆DMAAC),didodecyl methyl allyl ammonium chloride(Di C₁₂MAAC)and N-methyl-N-allyl lauroyl propane sulfonic acid inner salt(MALPS),were prepared by molecular structure design.Based on the above associative monomers,a series of amphiphilic polymers with betaine functional groups in the molecular structure were prepared by soap-free radical polymerization,and the synthesis conditions were optimized.Those amphiphilic polymers were characterized by infrared spectroscopy(FT-IR),nuclear magnetic resonance(¹HNMR),elemental analysis and laser light scattering.The effects of salt on the apparent viscosity and rheology of the amphiphilic polymer was studied by using rotational viscometer and rheometer,and its salt thickening mechanism was revealed by means of dynamic light scattering,cyclodextrin inclusion and scanning electron microscopy(SEM).The mechanism of the influence of the molecular structure of those amphiphilic polymers on their solution properties was studied.The emulsification law of those amphiphilic polymers in specific reservoir was studied by using stability analyzer,laser particle size analyzer and optical microscope.Finally,the equivalent viscosity method was used to evaluate the oil displacement performance of those amphiphilic polymers in specific reservoir and the microscopic oil displacement mechanism was discussed.The acrylamide betaine-type amphiphilic polymers with salt thickening properties were optimized for synthesis,which were single-tailed amphiphilic terpolymer(PADC),twin-tailed amphiphilic terpolymer(PADD)and three amphiphilic binary copolymers(PAMA-3,PAMA-2.5 and PAMA-2)with different hydrophobic groups contents.The structure-activity relationship between molecular structure and solution properties of amphiphilic polymers was established.Compared with PADC,PADD had a larger aggregate size and greater hydrophobic association strength in the brine because of the introduction of twin-tailed hydrophobic groups,thereby improving its viscosity-increasing,temperature-resistant and shear-resistant properties.The increase of the hydrophobic group content effectively reduced the critical association concentration(CAC)of PAMA,and the strength of the network structure formed by the association between hydrophobic groups increased.In addition,the ability to reduce the surface tension was enhanced,and its salt thickening property and viscoelasticity were more remarkable.The salt thickening properties and mechanism of PADC were revealed.The greater the ionic strength of the salt was,the greater the hydraulic radius of PADC molecule was and the stronger the salt thickening ability of PADC was.In addition,the increase in hydrophobic association strength was due to the formation of a denser spatial network structure.Under high salt conditions,PADC was capable of forming a relatively stable O/W emulsion system.The increase of salt concentration was beneficial to the stability of the emulsion system.Under specific reservoirs and equal viscosity conditions,the enhanced oil recovery rates of PAMA-3,PAMA-2.5,PAMA-2,PADD,PADC and HPAM after water flooding were 20.73%,17.38%,16.46%,16.15%,15.22%and 13.54%,respectively.The microscopic displacement experiments showed that the residual oil at the pore intersection and the“blind end”of the pore after water flooding can be used to some extent,thus improving the micro-washing efficiency.This reflected the important role of emulsification of amphiphilic polymers in enhancing oil recovery by polymer flooding.The betaine amphiphilic polymer has broad application prospects in high-salt reservoirs.