Study On Mechanism Of How Asphaltene Causes High Viscosity Of Tahe Heavy Oil

More and more attentions have been paid on heavy oils when we face the fact that the reserve and quality of conventional petroleum is decreasing and the demand for energy is increasing. However, the recovery and transport of heavy oils are challengiable due to their complicated compositions, high viscosities and densities and bad flowabilities, high contents of asphaltene. Among these negative factors, the high contents of asphaltene are decisive, so it is considerably significant for us to make clear that how asphaltene influences heavy oil’s properties in order to improve the recovery and transport of heavy oils.On the basis of the analysis of compositions and characters, this paper investigates the isssue that what impact the asphaltene will bring to heavy oil, simultaneously, the mechanism of thickening viscosity has been researched according to the simulated system of asphaltene in the toluene solution, characterization of asphaltene structure and viscosity-temperature characteristics. Finally, advisable viscosity-reducing method is presented. The conclusions are as follows:(1) Tahe heavy oil has the properties of high viscosity, high density, high content of asphaltene; it is the typical heavy oil.(2) The mass fraction of asphaltene imposes main influence on the viscosity. Viscosity increases with the the mass fraction of asphaltene rising, the increasing of viscosity is mild when the mass fraction is less than8%, after the mass fraction excesses this point, viscosity increases sharply. The relative molecular mass of Tahe heavy oil also presents the similar tendency as viscosity. The relationships between mass fraction of asphaltene and viscosity and relative molecular mass separately accord with the following equations:η2=804.2945+537.2001e0.2006x and M=463.34+2.67e0.2782x.(3) The simulated system is greatly infuenced by Tahe heavy oil asphaltene. The Zeta potential of asphaltene in the toluene increases while particle diameter decreases with the concentration enhancing. In addition, the viscosity of simulated system is also increasing by improving the concentration of asphaltene, equation η3=0.3903+2.8784e0.247C can be concluded from the raltionship between viscosity and the concentration of asphaltene, but the index of η3is simaller than that of η2.(4) The characterization of asphaltene structure indicates that its composition is complicated, its core includes eight aromatic nucleus, naphthetic nucleus and two alkyl chains which connect to aromatic necleus, in addition, sulfur exists in thiophene, oxygen exists in hydroxyl and nitrogen exists in pyrrole. Molecular simulation gives the following structure of Tahe heavy asphaltene:(5) Viscosity-temperature characteristics is closely related to the content of asphaltene and exsting forms. Asphaltene moleculars will interact by weak chemical bonds in low temperature, which ultimately led to the enhancement of viscosity.(6) Developed Chmicals are of good viscosity-reducing performance. Designed experiments show that chemicals lower the visocosity of heavy oil by breaching hydrogen bond and coordinate band between asphaltene moleculars, which based on the polar functional groups of chemicals.(7) Reticular structure of asphaltene aggregation which is formed at a low temperature is the main reason of thickening. Combining those fators, such as how asphaltene influences the properties of heavy oil、the mechanism of thickening and the experienments of viscosity-reducing, this aggregation may exsit in the following structure, which is similar to the outcome of J. H. Pacheco-Sanchez’s simulation:...