Preparation Of Polyethylenimine Based Polymer And Their Research On The Emulsifying Properties Of Extra-Heavy Oil

With the gradually growth of the global economy and population,people's demand for energy is increasing,and conventional oil resources are decreasing.Heavy crude oil is the unconventional oil and gas resources that has increasingly attracted the researchers'attention,due to large reserves and wide distribution.However,heavy oils have high viscosity,high density and poor fluidity,which make them difficult to be effectively recovered and transported.At present,the emulsifying is considered to be one of the most promising ways,because of its simple operation and remarkable effect,and is usually used in oil layer mining,wellbore viscosity reduction and pipeline transportation,regularly.In this dissertation,a series of PEI-based polymer emulsifiers were prepared by grafting different lipophilic groups on the PEI molecules with polyethylenimine?PEI?as the molecular skeleton through Hofmann alkylation to control the hydrophilic/lipophilic properties of the products,and they were characterized by FT-IR,¹H NMR,XRD and elemental analysis.Then,the effects of benzyl grafting,n-alkyl grafting and PEI molecular weights on the performance of emulsifier were investigated with the Shengli Oilfield extra-heavy crude oil as the research object.Finally,the cause of the difference in emulsifier performance was analyzed by means of optical microscope,dynamic light scattering,surface tension and interfacial tension in detail,and the mechanism of emulsifying viscosity reduction was proposed.The main research contents and results of this dissertation are as follows:1.Preparation of benzyl grafted amphiphilic polymers and their emulsifying properties for extra-heavy oilsA series of amphiphilic polymers were prepared by reacting PEI with benzyl bromide.The hydrophilicity/lipophilicity of the polymer can be regulated by changing the number of benzyl group grafted onto the polymer molecule,and it is used as emulsifiers which apply to Shengli extra-heavy oil emulsified viscosity reduction.Then,we investigated several factors that affect the emulsification properties of polymers,such as,hydrophilic/lipophilicity,oil-water mass ratio,the dosage of emulsifier,formation mineral water and temperature.The results showed that BP-1-5,BP-1-10 and BP-1-20 with high HLB value could emulsify Shengli extra-heavy oil when the oil-water ratio was 60:40 and the dosage was 1.8 wt%,and form stable O/W emulsions,meanwhile,the viscosities of emulsions were less than 100 mP·s at 50°C.These three polymers not only have excellent salt resistance,but also have better emulsifying properties than commercial surfactants AEO₉,Tween40 and potassium oleate.In addition,the BP-1-5 can also form stable O/W emulsions with four other heavy oils that have different viscosities,showing a certain universality.Tracing it to its cause,adding an appropriate amount of emulsifier can reduce the oil-water interfacial tension to form O/W droplets,thus reducing the viscosity of the heavy oil.2.Preparation of n-alkyl grafted amphiphilic polymers and their emulsifiying properties for extra-heavy oilsThe PEI-based amphiphilic polymers with different branch lengths were prepared by grafting linear n-alkyl branches with carbon number 3,7,12,16 on the PEI molecular chain,and used as emulsifiers for heavy oil viscosity reduction.Afterwards,the effects of branch length,emulsifier concentration,temperature and viscosity of different viscosity heavy oil on its emulsifying properties were investigated.The results show that the emulsifier performance trend is weak first,then strong,and then weakened,as the length of the grafted alkyl branch increases.It shows that the cability of the polymers to emulsify heavy oil is HP-1-5,DP-1-5,CP-1-5,PP-1-5,successively.For short-branched polymer?PP-1-5?,its weak emulsifying capability is due to its poor surface activity,but for the long-branch grafted polymers?DP-1-5 and CP-1-5?,it may due to long-branches chains interwining with each other.Moreover,if the branch is too short or too long,the lipophilic group of emulsifier will not match the heavy oil structure,so that the oil droplets are aggregated to form large particles,finally,the emulsifier emulsifying properties are weakened.In addition,for the suitable-branch grafted polymer?HP-1-5?,when the oil-water ratio and dosage is 60:40 and 0.9 wt%,respectively,it can completely emulsify the Shengli extra-heavy crude oil to form a stable O/W emulsion,and the viscosity reduction rate can reach over 99%.Besides,it can also emulsify other four heavy oils with different viscosity,indicating that it has certain universality.3.Preparation of amphiphilic polymers with different PEI molecular-weights and their emulsifying properties for extra-heavy oilIn addition to the PEI with a molecular weight of 10000,which was mainly studied in this dissertation,we selected PEI with molecular weights of 1800 and 600 as the emulsifier molecular backbone in this chapter,respectively,and the effect of backbone length or PEI molecular-weights,graft group?benzyl and n-heptyl?on the emulsifier performance was investigated.The results show that the polymers'emulsifying performance gradually deteriorated as the molecular weight of PEI shrinked,and the molecular weight of PEI affects benzyl grafted PEI based polymers more than n-heptyl grafted polymers.This may be due to the fact that a quite small amount emulsifier is needed to form a stable O/W droplet when its molecule weight is higher.However,it is necessary to add more emulsifier to completely coat the oil droplets when the molecular weight of the emulsifier is low.Because the critical micelle concentration?CMC?of short chain polymer is extremely small,it quickly reaches saturation in the water,making it difficult to effectively reduce the oil-water interfacial tension.Besides,the interfacial film strength of O/W droplets formed by emulsifier and heavy oil is further weakened,resulting in the deterioration of emulsification ability of the polymer.