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Waxy crude oil rheology measurements are essential to the accurate simulation of pipeline shut-in and restart processes. Flow start-up simulators have recently emerged with powerful capabilities to exploit pressure wave propagation and ensure flow commencement, while minimizing usage of environmentally adverse chemicals. In comparison to conventional force balance methodologies, the currently presented analytical and simulation technique constitutes a step change improvement in flow assurance capabilities by integrating accurate deformation-dependent gel degradation rheology with an Eulerian numerical scheme, affording predictive assessment of restart delay times. The new methodology is applied to the case of a real 1.84 km field pipeline transporting high waxy crude oil.

Gelation and breakage of model wax–oil systems is investigated using microscopy, densitometry, rheometry, and XRD. Various model waxy oils are prepared, including 1 to 20 wt % (w/w) macrocrystalline wax in dodecane, 1 to 20 wt % microcrystalline wax in dodecane, and 5 wt % macrocrystalline wax in Primol 352. The influence of shear history, thermal history, and fluid composition is ascertained. A novel gel breakage model is introduced which spans the entire mechanical response of wax gels from initial Hookean behavior at low strains to equilibrium slurry flow at the infinite strain limit. The local rheology model will benefit shut-in and restart processes of waxy crude pipelines via application of standard fluid mechanics relationships.

Incipient wax−oil gel deposits form in crude oil transport pipelines when long-chain n-paraffins precipitate at the cold interior surface of the pipe wall. The kinetics of paraffin gel formation was studied using model fluids consisting of monodisperse and polydisperse n-paraffin components dissolved in petroleum mineral oil. Classical homogeneous nucleation theory was applied to investigate the supersaturation conditions necessary for crystal formation. Differential scanning calorimetry was used to monitor paraffin crystallization rates and to provide solid-phase fraction measurements. Gelation occurs when growing n-paraffin crystals interlock and form a volume-spanning crystal network which entrains the remaining liquid oil among the crystals. Paraffin wax−oil gels exhibit a mechanical response to an imposed oscillatory stress, which is characterized by the elastic storage modulus G‘ being greater in magnitude than the viscous loss modulus, G‘ ‘. Low-temperature rheological gels can form from model flui...