Influence Of Microwave Electric Field On The Hydrogen Bond Within Heavy Oils

At present,the exploitation of heavy oil is increasing gradually,and the content of resin and asphaltene in heavy oil is high,which leads to high viscosity of heavy oil.Therefore how to reduce viscosity efficiently is still an urgent problem to be solved.Molecular dynamics simulation has been used in this paper to study the effect of different compositions and the interactions on heavy oil under different electric fields.Firstly,the change of hydrogen bond in pure asphaltenes in electric field was studied.Secondly,the heavy oil system was simulated to investigate the changes of hydrogen bond in heavy oil with different content of resin and asphaltene under the electric field.Because heavy oil is a very complex mixture,the average molecular structures were used to replace the four components(SARA)of heavy oil in this paper.The structure of asphaltenes and resin were obtained according to literatures,and n-heptane was applied for saturation and naphthalene for aromatics.Finally,since water also has a certain effect on the viscosity of heavy oil,the influence of water content was investigated.The results show that:(1)As the asphaltene molecules are large,contain polar hetero atoms,and have a strong interaction force,the asphaltene has a long relaxation time and low relaxation frequency,which shows that the number of hydrogen bonds is the least when the asphaltene is at a low frequency(0.9GHz).(2)According to the physical model of heavy oil,two kinds of heavy oil systems were established.The mass ratio of resin and asphaltene in system 1 and 2 were 22.1% and 46.5%,respectively.The results made clear that the number of hydrogen bonds in system 1 decreased and that in system 2 increased under the electric field,indicating that microwave has different effects on various heavy oils,and may not have positive effects on viscosity reduction.(3)The effects of water content were studied in the same heavy oil system,and the water contents were 1%,5.5%,10%,respectively.The results showed that for the heavy oil system with the water content of 1%,the water molecules bond more closely and the free water molecules decreased under the electric field,so the number of hydrogen bonds increased.When the water content increased,the total number of hydrogen bonds decreased,the binding between water molecules became loose,and the number of the hydrogen bonds between water-resin,and water-asphaltenes increased.As the water would be evaporated under the electric field,the water molecules can be combined with the decrease of water content,which is benifit to water removal.At the same time,the mean squrare displacement(MSD)of asphaltenes in heavy oil with different water content was investigated.It can be found that the MSDs of asphaltenes increase under electric field,which means the viscosity of the oils decreases.