The Relationship Between Molecular Structure Of Heavy Oil Composition And Viscosity-temperature Property

Currently available utilization of light crude oil in the world is declining,while the proportion of heavy crude oil in the global resources of the trend is increasing year by year.However,the high viscosity and large polymeric structure of heavy oil make it difficult to mine and transport,which directly affects the costs and benefits of heavy oil delivery.Therefore,it is necessary to identify important factors that affect crude oil viscosity.Molecular structure of heavy oil is extremely complicated and molecular structure has a significant impact on heavy physical and chemical properties,such as viscosity,density.To predict the physical and chemical properties and chemical reactions of heavy oil,it is necessary to analysis the molecular structure of heavy oil in detail.However,heavy oil is a mixture of compounds which has a relatively large molecular weight and complicated structure.For such material,it is difficult to accurately use a compound to represent it,but we can consider to use an average molecular formula CnHm to represent it.In this paper,the properties of the six heavy crude oils are analyzed.Each oil sample is separated into six fractions by liquid-solid adsorption chromatography,namely saturate,aromatic,light resin,middle resin,heavy resin and asphaltene,according to the molecular weight of each component,elemental analysis,NMR.We calculate structural parameters of the components of crude oil and get average structure with the modified BL method.Due to each component may have a lot of different average molecular structures,so we use molecular mechanics methods to identify the lowest energy and most stable structure.The heavier component has a more complicated structure.In fact,in our paper,heavy resin is more complicated than single asphalt layer.After the structure is determined,according to molecular dynamics method,we can get the results of density and viscosity of each component.We found that,the heavier composition have bigger value of density and viscosity.After the establishing the molecular structures of different components,according to the real proportion of crude oil,the periodic structure models of different crude oils are established.Comparing the experimental value with calculated,we find that the calculated values are much larger than the experimental values.The reason lies in two aspects,error of system and the method of calculation.But the trend is similar to experimental result.There are a lot factors that affect the viscosity of heavy oil and the extent is different.In paper,the method of gray entropy analysis is used and we can get such a result,that is the degree of impact is as follows: resin(including light,middle and heavy resin)?asphalte-ne>Ni>N?aromatic>S>V>Fe.Therefore,the study of molecular structure of resin and asphalttene has important significance to exploitation,processing and transportation of heavy oil.