As far as crude oil is concerned, the existence of paraffins and asphaltenes in oil reservoirs and pipelines can create problems in production, transportation, and the processing industries. Solid precipitation can cause depositions which may lead to plugging of the facilities. The buildup of solid components may also lead to pumping problems.
Crude oils contain a variety of light and heavy hydrocarbons. At temperatures above 60 °C the lighter components keep most of the heavier ones in solution, resulting in flow behavior showing comparatively low viscosity values. However, with decreasing temperature, the solubility of heavy components is reduced, which might cause solid precipitation. This effect is called “wax precipitation”, which can change the crude oil from a Newtonian fluid to a yield stress substance which may in turn increase the danger of plug formation in a pipeline. Wax precipitation in crude oils depends on both the composition of the oil dispersion and the environmental conditions such as temperature and pressure. Tests at high temperature and pressure in a rheometer combined with a pressure cell provide information, for example, about the effectivity of plug inhibitors under transport and production conditions.