Yield Stress of Wax Gel using Vane Method

摘要

Wax gel formation occurs in pipelines under quiescent conditions during a scheduled or emergency shutdown of flow. Paraffinic wax precipitates from the bulk oil when oil temperature decreases below the characteristic wax precipitation temperature, while the gelling begins as the temperature decreases below the pour point. Further temperature reductions below the pour point result in the development of a stronger gel. In this study, the gel strength was measured by determining the yield stress using the vane method. The method consisted of identifying the maximum torque exerted on the sample at various temperatures. Model oils were prepared by mixing low vacuum gas oil wax, mineral oil, and kerosene. Linear increase in gel strength with decreasing temperature was observed in the measured temperature range. As the wax content increased, so did the yield strength of the gel below the solution pour point. The slope of the yield-stress versus temperature line was also steeper for the model oil containing higher amount of wax. Recovery of gel strength was also examined by aging at the same temperature and by decreasing temperatures after breaking the gel at certain temperature.