Study On Microscopic Characteristic Of Waxy Crude Oil

The content, shape and structure of the precipitated wax crystals were the major factors to effect crude oil rheology. And the heat and shear conditions effect the macroscopic rheological of crude oil, just by effecting the shape and the structure of wax crystals.Therefore, in this paper, multi-crude oils'microscopic characteristics were studied comprehensively through microscope image collection system, and combined with rheometer, the relationship between microscopic characteristics and macroscopic rheological of crude oil was researched farther.Using polarizing microscope, four kinds of crude oils'wax crystal's precipitation process following temperature dropping were observed, and the wax crystals'parameters changes were systematically analyzed comparatively. Combined with viscosity-temperature curve, the relationship between viscosity and the wax crystals'parameters was qualitatively analyzed. There were many parameters such as wax area content, particle count and particle size, but those parameters were insensitive to wax crystal dispersion quality. So, a new concept, i.e. characteristic free-space length, was put forward, and we made experimental verification. The result showed that this new concept could distinguish accurately two images with the same wax area content but different wax crystal dispersion, which was a new method to describe wax crystal image quantitatively. Then, orthogonal testing programs were designed, aimed to study the importance-degree of temperature, cooling velocity, heat treatment temperature and standing time for various wax crystal parameters and appropriate factors'level. The results showed that temperature of oil was the most important factor, and the other factors were relatively weaker. Then we researched how those factors including cooling velocity, heat treatment temperature, standing time and added pour point depressant effect the characteristics of wax crystallization. Finally, as there were many influence factors and complex relationship for wax crystal's precipitation, so the support vector regression method was applied to predict the wax area content under different testing conditions. The result showed that this method was effective to predict test points and neighbouring points. Meanwhile, a nonlinear multivariate analysis was made between oil viscosity and three wax crystals'parameters including wax area content, wax crystal number and characteristic free-space length, which established quantitative relation between microscopic characteristics and macroscopic rheological of crude oil. We hope that these researches can play a guiding role to the low-temperature fluidity research about waxy crude oil.