Thermally assisted restart of gelled pipelines: A weakly compressible numerical study

In the present study, the applicability of wall heating for facilitating the restart process of gelled pipelines by the injection of a secondary fresh fluid is evaluated using computational fluid dynamics (CFD). The secondary fluid is assumed to be injected with a constant pressure into the pipeline and at the same time the pipe wall is considered to be electrically heated by a uniform heat flux. To simulate this non-isothermal and non-Newtonian fluid displacement flow prompted by pressure wave propagation along the pipeline, the volume of fluid (VOF) method is employed and the set of governing equations are descritized using finite volume method. It is shown that the restart flow of gelled pipelines in the presence of wall heating consists of two stages: the relatively fast removal of the gelled fluid located in the vicinity of the pipe axis (breakthrough) and a gradual removal of wax-oil gel from the pipe wall (drainage). The effect of wall heating is most evident in the initial breakthrough stage where up to 20% reduction in the breakthrough time is achieved in this study with a moderate heat flux. Generally, uniform heating of pipe wall reduces the apparent viscosity of gelled fluid during restart and subsequently wall heating increases the intensity of restart flow.