Differential Scanning Calorimetry contribution to a better understanding of the aging of gelled waxy crude oils

Abstract

Below Wax Appearance Temperature (WAT), waxy crystals appear within the crude oil and make it viscous with yield stress and shear thinning properties. Particular attention has been paid during the past works on different parameters such as temperature, pressure, shear history, etc. Another important parameter is the holding time of the sample once it has gelled and left at rest under isothermal conditions. Actually, the network of waxy crystals is known to change with time. This phenomenon has been particularly observed in the case of deposit that is expected to harden. The set of rheological tests and calorimetric analysis that were performed on a real waxy crude oil confirm that a gel formed with waxy crystals may evolve with time and that the extent of this phenomenon depends on the thermo-mechanical past of the sample. Actually, a strengthening of the gel during holding time is observed in the case of fast cooling because the sample gets supersaturated. Aging takes place through isothermal crystallization that lasts a few minutes. The results have also shown that slowly cooled samples do not lead to any aging.