A Mechanism Study Of Hydrophobic Modified Polymer For Enhancing Heavy Oil Recovery

Heavy oil made up a great proportion of crude oil resources（about 70%）.The high viscosity and poor fluidity of heavy oil brought great difficult to exploit it.Emulsification was the mian mechanism for chemical flooding to enhance heavy oil recovery.Hydrophobic modified polymer（HMP）had emulsifying ability for crude oil due to its amphiphilic property.In this thesis,the application of HMP on enhancing heavy oil recovery and the mechanism behind it were studied.Combined with the advantages of silica nanoparticle on enhancing oil recovery,a new method named alkali-silica nanoparticle-polymer（ANP）flooding was firstly designed to enhance heavy oil recovery.Some conclusions had obtained as follow:（1）Polymer with n-Hexadecyl acrylamide(P-C₁₆AM)showed better salt and temperature resistance than the polymers with allyl alcohol polyoxyethylene ether（P-APEG）and fatty alcohol polyoxyethylene（P-AEO）.Based on the the analysis of interfacial dilational viscoelasticity between different polymer solutions and oil phase,it was found that P-C₁₆AM could absorb at the oil-water interface to improve the interfacial film strength significantly.（2）According to the changes of backscattering light intensity of different heavy oil emulisons,we could conclude that flocculation and coalescence between oil droplets were the main causes for the instability of heavy oil emulsion prepared by HMP.Low salinity water would affect the distribution of polar organic components existing in the heavy oil at the oil-water interface due to the“salt in effect”.The combined system of low salinity water(<3000 mg·L^-1)and P-C₁₆AM can improve the stability of the heavy oil emulsion at a certain range of salinity.（3）There were three main emulsification modes during the P-C₁₆AM flooding.（a）The bulk oil was emulsified into oil droplets through the thin pore throat by shear force.（b）The oil existing in the dead end was emulsified by the viscoelasticity of the aqueous HMP solution.（c）The cluster oil was emulsified in the tiny channel.When the average diameter of pore is greater than 40μm,it is conducive to forming pore throat emulsion.（4）Silica nanoparticle could improve the salt and temperature resistance of P-C₁₆AM solution.As the P-C₁₆AM concentration above critical association concentration(1000mg L^-1),the viscosity of composite solution increased by 67.8%.Composite system of Si O₂+P-C₁₆AM could improve heavy oil recovery by 5.98～21.09%compared with single P-C₁₆AM solution.（5）Emulsifying ability of the four flood systems for heavy oil followed the order:P<NP<AP<ANP.Based on the analysis of droplet size distribution of emulsion and changes of IFT value between flood systems and oil phase,the best formula of ANP system to emulsify heavy oil was 0.3%[w/v]Na₂CO₃+0.1%[w/v]silica nanoparticle+1000 mg·L^-1 polymer.Electrostatic repulsion between silica nanoparticles and oil droplets played a dominated role on stabling ANP emulsion.ANP flood system could change the wettability of rock surface to a more water-wet state（contact angle 35.6°）and enhance heavy oil recovery by 21.19%based on the first water flooding in a sandstone core.The results obtainted by microscopic displace test showed that emulsification is the main mechanism for ANP flooding to enhance heavy oil recovery.