Characteristics of Wax Gel Formation in the Presence of Asphaltenes

Abstract

When pipelines are shutdown, waxy crude oils tend to form gels, which tend to plug the lines and stop flow. Restart requires sufficient pressure to overcome the yield stress of gelled oils. This study examines the yield strength of well-characterized waxy model oils at temperatures below the pour point. First, the yield stresses of model oils were determined by the vane method at different temperatures. Yield stress values were strongly dependent upon wax amounts and compositions, as expected. The extent of increase in yield stress values with temperature was greater for model oils that had a higher percentage of wax. The x-intercept values obtained from yield stress versus temperature were interpreted as no-flow points, which could be used as alternative measures of pour points. Second, the role of asphaltenes was examined in the evolution of the yield stress as the oil is cooled below the pour point. Asphaltene additions resulted in pour-point reductions, of up to 4 °C for additions of asphaltenes up to...