New Approach for the In Situ Microscopic Observation of Wax Crystals in Waxy Crude Oil during Quiescent and Dynamic Cooling.

Abstract

The purpose of this attempt is to present a new investigation approach to achieve the in situ observation of the microscopic structure and morphology of wax crystals under quiescent and shear conditions. The rheo-microscopy simultaneous measurement system of a rheometer is employed to ensure in situ observation. A multi-angle composite light source is created to obtain a high-quality image. It is demonstrated that the new approach can achieve a better identification and distinction of wax crystals, as well as the outstanding wax boundary delineation. Based on this, some new findings related to the microscopic structure and morphology of wax crystals are elaborated. Additionally, the in situ observations of wax crystals under dynamic cooling at different shear rates are performed. It is noticed from the obtained results that wax crystals and their aggregates exhibit significant stereoscopic structural characters, because of growth of wax crystals and their overlap in 3-D space. Shear can change the morphology of single wax crystals, but hardly destroy the structure or growth. The increase of the shear rate can induce the deformation propensity of wax crystals to flow field. The effect of shear on aggregation of wax crystals depends on the chemical composition and inherent structural properties. Normally, a low rate of shear can promote aggregation, and result in a complicated stereo-structure. Upon increasing the shear rate, two opposite effects simultaneously occur including promotion and inhibition of aggregation. As the shear rate further increases, the destructive effect increases and gradually plays a leading role, causing the wax crystal aggregates exhibit a smaller size and a weaker stereo structure.