Study On Aggregation Control Of Amphiphilic Polymers And Its Mechanism On Enhancing Emulsification

The dependence on foreign oil demand in China has reached more than50%, the state isfacing significant economic and security issues. EOR is a substantial way to enhance oilrecovery in China, polymer flooding and ASP flooding technology can enhance oil recoveryby10%and20%on the basis of water flooding in enhanced oil recovery, respectively. As anovel polymeric oil-displacing agent, amphiphilic polymer could overcome the traditionalshortcomings of traditional polymer used in EOR, the partially hydrolyzed polyacrylamide(HPAM). Amphiphilic polymers have many advantages such as temperature resistant, saltresistant, anti-shearing capability and emulsification and thus have prosperous applicationprospects. In this dissertation, a series of amphiphilic polymers were synthesized, theinfluence factors which can adjust and control the aggregation in amphiphilic polymersolutions such as the structure of amphiphilic polymer, temperature, salinity, pH value andsurfacatant were studied; the emulisification performance and the stability mechanism as wellas the flooding performance were also studied and thus to discuss the enhancing oil recoverymechanism.A series of5amphiphilic polymers were sythensized using free radical micellpolymerization method, such as N, N-dicyclohexyl acrylamide terpolymer, N-benzyl-N-alkylacrylamide terpolymers and N-alkyl acrylamide terpolymers. The synthesis conditions of thesaid amphiphilic polymers were also optimized. FT-IR and1HNMR were employed tocharacterize the structure of the amphiphilic polymers; intrinsic viscosity method wasemployed to measure the molecular weight of the amphiphilic polymers, the MW of thesynthesized amphiphilic polymers is2.3×106~5.1×106. The molecular weight and the apparentviscosity of the N-mono-substituted acrylamide terpolymer amphiphilic polymers is muchhigher than that of N-disubstituted acrylamide terpolymer amphiphilic polymers due to sterichindrance effect of hydrophobic groups during the polymerization reaction. As to thesynthesis of N, N-asymmetric disubstituted acrylamide terpolymers, the hydrophobicmonomers need two step reactions to synthesize and the yield of hydrophobic monomers islower than60%and thus not suitable for large-scale industrial applications. The viscosity of the amphiphilic polymer depends on the hydrophobic substituentnumber and the hydrophobicity of the hydrophobic groups; the viscoelasticity of amphiphilicpolymer solutions depends on the flexibility of the hydrophobic groups mainly. Take N,N-dicyclohexyl acrylamide terpolymer P(AM-NaA-DCHAM) and N-dodecyl acrylamideterpolymer P(AM-NaA-DDAM) for example, both of the two polymers have a dozensubstitutional carbon atoms in their hydrophobic monomers. At the same concentration, theapparent viscosity of P(AM-NaA-DDAM) soluton is much higher than that ofP(AM-NaA-DCHAM). P(AM-NaA-DCHAM) solutions showed elastic gel properties due tothe rigidity of the hydrophobic groups. As to P(AM-NaA-DDAM), above CAC, theamphiphilic polymer solutions showed elastic gel properties due to the association ofhydrophobic groups and the formation of network structures in amphiphilic polymer solutions;below CAC, the amphiphilic polymer solutions showed viscous fluid characteristics.Compared with P(AM-NaA-DCHAM), P(AM-NaA-DDAM) presents much bettersalt-resistant, temperature-resistant and anti-shearing properties. The apparent viscosity of theamphiphilic polymer solutions increased with the increasing nonpolarity of the hydrophobicmicrodomain and the apparent hydrodynamic radius of the aggregation.Above CAC, surfactants at low concentration can stimulate the intermolecularassociation of hydrophobic groups in amphiphilic polymers; the nonpolarity of thehydrophobic microdomain and the apparent hydrodynamic radius of the aggregation increased;the apparent viscosity of amphiphilic polymer solutions and the viscoelasticity increased.Surfactants at high concentration have the opposite effect. Compared withP(AM-NaA-DCHAM), P(AM-NaA-DDAM) presents much better synergistic effect withsurfactant to enhance the apparent viscosity of the binary system. The binary system of3000mg/L HF-E+1000mg/L NS+1000mg/L P(AM-NaA-DDAM) has high viscosity of259mPa·s which is higher than that of P(AM-NaA-DDAM) in simulated formation water ofJilin Olifield and low oil-water interfacial tension of1.3×10-2mN/m between Jilin crude oiland simulated formation water of Jilin Olifield.The stability of O/W emulsions stabilized by amphiphilic polymers increased withincreasing thickening ability and solubilization ability of amphiphilic polymers. Above CAC，the stability of O/W emulsion stabilized by P(AM-NaA-DDAM) is much higher thanP(AM-NaA-DCHAM); the stability gap between the two emulsions increases with increasingpolymer concentration. The stability of emulsions stabilized by amphiphilic polymers can beadjusted by controlling the molecular structure of the amphiphilic polymers. The stabilitymechanism of amphiphilic polymers on O/W crude oil emusions could be depicted as follows: hydrophobic intra-and/or intermolecular interactions between the hydrophobic groups inducethe formation of hydrophobic microdomains in amphiphilic polymer solutions. Above CAC,intensive intermolecular association can induce large quantities of hydrophobic microdomainsand strong elastic polymer gel network structures. The stability mechanism of O/W crude oilemulsions stabilized by amphiphilic polymers is probably because the elastic polymer gelstructure of amphiphilic polymer in the continuous phase has the ability to hold oil droplets.In low permeability cores, HPAM, P(AM-NaA-DCHAM),P(AM-NaA-DDAM) andP(AM-NaA-ODAM) can enhance oil recovery by14.6%,16.1%,17.5%and19.6%respectively based on water flooding; the enhanced oil recovery can raise1~2%in highpermeability cores. As the hydrophobicity of the hydrophobic monomer increased,thepressure drop during core flooding tests increased and the produced liquid was much moreseriously emulsified, the average particle size of the emulsified oil droplets dereased. Bycontrolling the molecular structure of the amphiphilic polymers, the viscosifying andsolubilization performance of amphiphilic polymers can be adjusted to enhance the sweepefficiency and the displacement efficiency and thus to enhance oil recovery at utmost.