Dong Hang, Ma RunZe, Zhao Jian, Xi Xiangrui, Wang Zhihua
Northeast Petroleum University, 163000, Daqing, Hei Longjiang, China.
Young and Middle-aged Innovation Team of Northeast Petroleum University, 163000, Daqing, Hei Longjiang, China.
ACS Omega. 2022 May 19;7(21):17948-17962. doi: 10.1021/acsomega.2c01251. eCollection 2022 May 31.
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, the crack of the flocculation structure plays a leading role. It is only after the shear rate exceeds 5 s 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.
含蜡原油胶凝的微观机制是蜡晶之间相互作用形成一定强度的絮凝结构，这显著增加了生产和输送成本。本文首次将流变光学原位测量技术应用于含蜡原油的流变学研究，以及典型含蜡原油对热历史的流变响应、剪切变稀的微观机制和蜡晶的动态行为。通过新的实验技术和分析方法发现，在一定热历史条件下可形成两种类型的蜡晶，它们在微观形态、力学性能和絮凝倾向方面表现相反，其在原油中比例的变化是初始冷却温度影响含蜡原油流动性的根本原因。研究发现，随着剪切速率增加，含蜡原油的微观行为经历以下全过程：含蜡原油体系从静止变为动态，蜡晶絮凝网络发生变形、开裂和破裂，蜡晶聚集体破碎，小聚集体沿流场取向，小聚集体继续变形和破碎。当剪切速率低于5 s⁻¹时，絮凝结构的开裂起主导作用。只有当剪切速率超过5 s⁻¹时，蜡晶及其絮体的变形才开始起作用。此外，根据蜡晶运动序列的微观图像，利用动态微物体捕获技术系统分析了不同类型絮体的微观形态和剪切作用下的动态行为。
