Synthesis Of Modified Polyethyleneimine Based Emulsifier And Their Study Of The Mechanism Of Emulsification Viscosity Reduction On Heavy Oil

With the increasing exploits of conventional oilfields,the storage of light oil resources is decreasing sharply,resulting in the quick increasing of the price of crude oil.Therefore,unconventional petroleum resources such as heavy oil have attracted much attention due to their abundant reserves.However,the production and transportation of heavy oil are difficult due to their high viscosity,high density and low mobility,and the key to solve these problems is to reduce the viscosity of crude oil.Emulsification is one of the most effective methods to reduce the viscosity of heavy crude oil,and it has been widely used in heavy oil recovery and pipeline transportation.Since the structure of heavy oil component model contains the aromatic ring and the branched chain,in this thesis a series of polyethyleneimine(PEI)-based amphiphilic polymers were synthesized as emulsifiers by grafting the lipophilic groups such as 4-methylbenztl bromide(4-MB)and 1-bromoheptane(HP)on PEI,respectively.Subsequently,the composition and structure of these emulsifiers were characterized by nuclear magnetic resonance spectroscopy(1H NMR),Fourier-transform infrared spectroscopy(FT-IR)and elemental analysis(EA).The influence of grafting radio of 4-MB and both 4-MB and HP on emulsion properties was studied using Shengli heavy crude oil as sample.The emulsifying capability of different synthesized emulsifiers were investigated through optical microscope,emulsion stability test,critical micelle concentration and interfacial tension test.Finally,the mechanism of emulsification was proposed by carrying out experiments in a series of model oils containing four different components(n-heptane,1-methylnaphthalene,resins and asphaltenes).The emulsions forming conditions,the interfacial tension,and the adsorption of heavy components at water/oil interface were studied.The main contents and results are as follows:(1)Preparation of PEI-based emulsifier grafting with 4-MB and its emulsifying and viscosity reducing performances for heavy oil.A new kind of emulsifier 4-MB-PEIs was successfully synthesized by grafting 4-MB on PEI and it was characterized by 1H NMR,FT-IR and EA.The experimental results showed that 4-MB-PEI-10-1 has a very good emulsifying capability for Shengli 2# heavy oil.When the emulsifier dosage is 0.8 wt.%,the viscosity of the heavy oil could reduce from 161800 m Pa?s to 21 m Pa?s(oil to water radio is 60:40)and 44 m Pa?s(oil to water radio is 70:30)at 50oC,respectively.The viscosity reduction efficiencies of both cases are more than 99.9%.In addition,the emulsion has a good stability.The results of the optical microscope showed that the viscosity reduction is due to the formation of small O/W droplets.The lowest critical micelle concentration value and interfacial tension data indicate that 4-MB-PEI-10-1 has the optimum interface activity which result in its best solubility and emulsifying capability.(2)Preparation of PEI-based emulsifier grafting with both 4-MB + HP and its emulsifying and viscosity reducing performances for heavy oil.The emulsifiers of 4-MB-HP-PEIs were successfully synthesized by grafting different molar radios of HP and 4-MB on PEI and used as emulsifiers for viscosity reduction of Shenli 2# oil.The results showed that 4-MB-HP-PEI-7-3-1 has the lowest minimum permissible concentrations(MPC)for forming stable oil/water emulsion and the concentration is only 0.6 wt.%.at the oil to water radio of 60:40.Compared with4-MB-PEI-10-1,the MPC decreased by 0.2 wt.%.The reason of the decrease in MPC concentration might be that the better matching between the aromatic structure and the branched structure of 4-MB-HP-PEI and the structure of the heavy components.As a result,the emulsifiers and heavy components will produce greater van der Waals forces at the interface which will therefore increase the interfacial strength of theO/W emulsion film.(3)Effect of different concentrations heavy components of model oil on O/W emulsion interfacial properties and emulsification capabilityResins and asphaltenes were extracted from Shengli 2# heavy oil and their composition and structure were characterized by FT-IR,1H NMR,EA and synchronous fluorescence spectrometry analysis(SFS).The results showed that polar groups and aromatic structures were both existed in resins and asphaltenes,but they were richer in asphaltenes.The model oil with different heavy components concentrations were prepared by adjusting the concentration of n-heptane,1-methylnaphthalene,resins and asphaltenes.Among them,n-heptane and 1-methylnaphthalene are respectively used as the model compound of saturates and aromatics,and resins and asphaltenes are separated from Shengli 2# heavy oil.The influence of heavy components concentration to form stable emulsions,oil-water interfacial tension,the adsorption of heavy components and the stability of emulsions were studied by mixing 1 wt.% 4-MB-PEI-10-1 aqueous solution with model oil.The experimental results showed that the higher concentration of heavy components,the easier it was to emulsify.And when there is no heavy components,the model oil is very difficult to emulsify.At the same time,with the increasing of heavy components concentration,the oil-water interfacial tension decreases significantly,and the stability of emulsion also increases;the capability to reduce the interfacial activity of asphaltene with 4-MB-PEI-10-1 is far greater than that of resins.The reason of the better emulsification capability for heavy components might be that heavy components,especially asphaltene,contain surface active groups and their structures are similar to emulsifier's.The increase in the concentration of the heavy components can accelerate the adsorption of the substance at the oil-water interface,and the oil-water interface tension is rapidly reduced,and then stable O/W emulsion is formed.