Novel approaches to waxy crude restart: Part 1: Thermal shrinkage of waxy crude oil and the impact for pipeline restart

This paper identifies cooling-induced phenomena that can follow pipeline shut-in. Resultant shrinkage flow can affect the viscosity of gelled semi-solids that develop in pipelines containing waxy fluids. Pressure gradients develop in accordance with flow rate and direction. These same processes may also induce gel fracture and fragmentation. The relationship between these thermally driven events and easily measured parameters is used in numerical calculation for predicting gel viscosity and the distribution of void space and intact gel. The resultant map of the gel state within the line thus delineates the conditions prior to restart. Simulation allows parametric testing to provide a powerful design tool. Laboratory tests are described that support such predictions. The insights provided by this novel approach can indicate cost effective solutions to pipeline design and operation, and possible sources of laboratory testing inaccuracy. The findings reported in this paper represent part of an ongoing investigation into aspects of waxy crude restart that may lead to predictive errors.

Research Highlights
► Demonstrated gradients of reducing pressure during cooling of waxy crude oil.
► Numerical simulation of shrinkage flow corresponding to these gradients.
► This shearing flow can modify the apparent viscosity of the gel.
► Voids form at sites of flow-induced cohesive failure, changing gel compressibility.
► Numerical mapping indicates large variation in restart resistance.