The micromechanism of waxy crude oil gelling is the interaction between wax crystals to form a certain intensity flocculation structure, which significantly increases the cost of production and transmission. In this paper, rheo-optic in situ measurement technology is applied to the rheological study of waxy crude oil for the first time and also to the rheological response of typical waxy crude oil to thermal history, the micromechanism of shear-thinning, and the dynamic behavior of wax crystal. Through the new experimental technique and analysis method, it is found that two types of wax crystals can be formed under certain thermal historical conditions, which have opposite performances in microscopic morphology, mechanic properties, and flocculation tendency, and the change of its proportion in crude oil is the root cause of the initial cooling temperature affecting the fluency of waxed crude oil. It was found that the microscopic behavior of waxy crude oil with the increase of shear rate went through the following whole process: the waxy crude oil system changes from static to dynamic, the wax crystal flocculation network undergoes deformation, cracks, and ruptures, and wax crystal aggregates break, small aggregates orient along the flow field, and small aggregates continues to deform and break. When the shear rate is below 5 s –1 , the crack of the flocculation structure plays a leading role. It is only after the shear rate exceeds 5 s –1 that the deformation of the wax crystal and its flocs begins to function. Furthermore, according to the microscopic images of the wax crystals motion sequence, the micromorphology of different types of flocs and the dynamic behaviors under shearing are systematically analyzed by dynamic micro-object capture technology.
Numerical simulation of coherent structure in two-dimensional compressible mixing layers Science in China Series A-Mathematics 39, 1183 (1996); Nucleus-free two-dimensional electron gas structure enhanced Raman scattering
3D atomic-scale growth characteristics of {10-12} twin in magnesium
The motion behaviors, rheological properties, and mechanical properties of a wax crystal mesoscale force chain network of waxy crude oil during gelation were experimentally studied and simulated by rheo-optic in situ measurement and computational fluid dynamics–discrete element method (CFD–DEM) numerical simulation, respectively. The motion behavior characteristics of wax crystals and the changes in the average coordination number of wax crystal networks were obtained at different temperatures. The study investigates the rule of crude oil rheological deterioration, the increase of wax crystals, and the changes in wax crystal motion behaviors with decreasing temperature. The relationship between the structure of the mesoscale force chain of the wax crystal network and the motion behaviors of the wax crystal and its rheological properties was analyzed. The results show that the average motion velocity of wax crystals or aggregates decreases from 28.48 to 22.56 μm/s when the temperature decreases from wax appearance temperature (48 °C) to 25 °C. The rotation and rolling trend of wax crystals gradually flatten, and the average coordination number increases 4.39 times. The viscosity of waxy crude oil increases from 6.27 to 8369.7 mPa·s, and the average coordination number of wax crystals obtained by CFD–DEM also increases significantly, which confirms the experimental results. We also found that when the system tended to gelation, a complex and stable force chain network was formed between the wax crystals, with a force chain coverage of 87.93% and a significant increase in the pressure drop in the flow field, which is consistent with the variation pattern of the system viscosity. The micro–meso-dynamic behavior analysis of waxy crude oil combined with CFD–DEM coupling provides a new way to explore the rheological properties of waxy crude oil and the microscopic mechanism of its modification.
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