Novel approaches to waxy crude restart: Part 2: An investigation of flow events following shut down

This paper describes cooling-induced flow events following the shut-in of waxy fluids in a transparent model pipeline. Flow, indicated by entrained marker spheres, and gel fracture and fragmentation, are recorded by digital photography. Pressure changes during cooling were also recorded. The observed flow events and pressure changes are consistent with numerical simulations of shrinkage flow. The test results show comparability with previously reported observations obtained with steel model pipelines. Numerical simulations of shrinkage in pipes are presented as comparative examples. The paper also reports predicted and experimental results for shrinkage of a wax-free high viscosity Newtonian standard fluid in a steel model pipeline, which indicate that gradients of reducing pressure are a general phenomenon associated with high flow resistance during cooling in pipes. The findings reported in this paper represent part of an ongoing investigation into aspects of waxy crude restart that may lead to predictive inaccuracy.

Research highlights► Visual demonstration of cooling-induced flow of waxy hydrocarbon fluids. ► Visual demonstration of void formation and gel fracture. ► Demonstration of relationship between shrinkage flow and pressure gradients. ► Possible effects of shrinkage flow on wax structural development. ► Significance of void formation and compressibility.