Study On The Inhibitory Cehavior Of Comb-polymers Containing Aromatic Side Groups On Asphaltene Aggregation And Its Effect On The Rheological Properties Of Heavy Crude Oil

As the global demand for energy continues to expand,energy consumption is also increasing year by year.Although the development of new energy is rapid,petroleum is still the largest energy demand in many forms of energy.In the past few decades,a large amount of light conventional oil has been extracted,and the proportion of reserves has been decreasing,while the heavy oil that is abundant has a great value in the future.Heavy oil is an important kind of unconventional crude oil.Heavy oil resources in China account for 20%of the total resources,and unconventional crude oil reserves in the world account for 70%of the total oil reserves in the world.Heavy oil has great potential,but it is also difficult to recover.Due to the large amount of asphaltene in heavy oil,the viscosity of heavy oil is much higher than that of conventional crude oil.Asphaltenes are the components with the largest molecular weight and polarity in heavy oil.They are in an unstable equilibrium state in heavy oil.When external factors(temperature and pressure)and the composition of heavy oil change,asphaltenes will accumulate in large quantities.Precipitation and rapid increase in viscosity will cause sedimentation and blockage in the equipment in the process of crude oil extraction and transportation,which will cause great troubles to the petroleum industry.The use of precipitation inhibitors is an ideal method to reduce asphaltene deposition.Among them,polymeric inhibitors are widely used because of their small dosage,high efficiency,and easy modification.When both polar(aromatic)groups and non-polar(long-chain alkyl)groups are present in the polymer,an efficient inhibitory effect can be achieved.The adsorption and binding capacity of aromatic groups and asphaltenes has a significant effect on the overall effect of the inhibitor.Therefore,studying the mechanism and mode of action of different aromatic groups and asphaltenes has important guiding significance for the design of efficient inhibitors.In this study,two asphaltenes from Xinjiang Oilfield were analyzed in-depth and their average structural formulas were derived;a series of maleic anhydride-octadecene polymers with different aromatic side groups were synthesized,the effects of the types of aromatic groups,grafting rate and polymer concentration on the aggregation behavior of asphaltenes were studied;the effects of polymers on the flow properties of heavy oil under different pressures and temperatures were studied.The specific research content is as follows:1.The structure and composition of asphaltenes have an important influence on the aggregation behavior of asphaltenes.Therefore,before studying the inhibitory effect on asphaltene precipitation,it is necessary to deeply understand and analyze the properties of asphaltenes used.Two different asphaltenes were extracted from the asphaltene deposits and extra-heavy oil in different blocks of Xinjiang Oilfield,and they were named Shunbei Asphalt and Tahe Asphalt.The two asphaltenes have certain similarities,but they are different.Elemental analysis,Fourier transform infrared spectroscopy(FT-IR),time-of-flight mass spectrometry(TOFMS)and nuclear magnetic resonance spectrometer were employed to characterize the structure and composition of asphaltenes in detail.The average structure parameters of asphaltenes were calculated by the improved B-L method and NMR carbon spectroscopy,and the possible average molecular structures of the two asphaltenes were deduced.It was shown that both asphalts have a strong tendency to aggregate and are easy to precipitate to form deposits.The molecular weight and molecular weight distribution of Shunbei asphalt and Tahe asphalt are similar,and the aromaticity of Tahe asphaltene is stronger than that of Shunbei asphalt.Both asphalts contain a large amount of nitrogen,oxygen,sulfur and other heteroatoms.The content of oxygen in Tahe asphalt is much greater than that in Shunbei asphalt and other common asphalts,which makes Tahe asphalt more polar.2.The maleic anhydride-octadecene(PMO)intermediate was prepared by free radical polymerization,and different aromatic groups(1-(3-aminopropyl)imidazole and 2-aminopyridine were grafted through amidation reaction.,4-aminopyridine and aniline),different grafting ratios were obtained by changing the feed ratio of aromatic groups and intermediates.Gel permeation chromatography(GPC)and proton nuclear magnetic resonance spectroscopy are employed to characterize the molecular weight of the polymer and the grafting rate of aromatic groups f2.The inhibitory effect of polymer on the precipitation and dispersion of asphaltenes in model oil was evaluated by UV-visble spectroscopy,turbidity meter,dynamic light scattering(DLS),contact angle measuring instrument and SEM.The results show that the polymer grafted with 2-aminopyridine(PMO-2-P)has the best inhibition and dispersion effect in the model oil,and can inhibit the precipitation of asphaltenes to the greatest extent and reduce the amount of asphaltene precipitation and aggregate size.The inhibition and dispersion ability of all aromatic groups follow the following order:2-aminopyridine>aniline>4-aminopyridine>imidazole.The inhibitory ability of the polymer will increase with increasing grafting rate and concentration.The interface contact angle between the polymer grafted with 2-aminopyridine and the asphaltene is the smallest,indicating that PMO-2-P has better dispersibility for asphaltenes.It is found through SEM that PMO-2-P can not only remove large-size The asphaltene aggregates are dispersed into several smaller aggregates,which can also make the morphology more regular.3.In order to verify that the prepared polymer also has good asphaltene dispersibility in heavy oil,a rotary rheometer was used to study the influence of the polymer on the fluidity of heavy oil in heavy oil under different pressures,the polymer concentrations are 0.1 wt%,0.3 wt%,0.5 wt%,and 1 wt%,respectively.The viscosity-temperature curve of heavy oil was measured in the range of 70-50℃,and it was found that when the polymer concentration is 0.1%,0.3%and 0.5%,the viscosity of the heavy oil can be effectively reduced,and the viscosity reduction effect is most obvious when the concentration is 0.5 wt%.Among them,PMO-2-P has the best viscosity reduction effect on heavy oil.The viscoelasticity of heavy oil was analyzed at 70℃,and the best effect was also obtained when the PMO-2-P concentration was 0.5 wt%.When the polymer concentration rises to 1 wt%,the fluidity of the heavy oil becomes worse.This may be due to the interaction between the polymers and other components in the heavy oil.When the pressure is 2MPa and 4MPa,the influence of polymers on the rheological properties of heavy oil is studied.It was shown that as the pressure increases,the viscosity of the heavy oil increases,and the fluidity becomes worse.At this time,the polymers can still reduce the viscosity of the heavy oil,but the viscosity reduction ability of different polymers tends to be consistent with the increase of pressure.