Application of Rheo-optic In Situ Measurement Technology to Study Waxy Crude Oil Rheology

Abstract

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.