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

Phillips, David A.; Forsdyke, Ivor N.; McCracken, Ian R.; Ravenscroft, P.

doi:10.1016/j.petrol.2011.04.003

Cited by 31 publications

(28 citation statements)

References 37 publications

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“…In the current section, gelation was determined by using oscillatory tests as proposed by others (Webber 2001;Venkatesan et al 2003;Coutinho 2004, 2007;Kané et al 2004;Visintin et al 2005;Magda et al 2009;Tinsley et al 2009;Phillips et al 2011). Low-amplitude and low-frequency oscillating shear strain was applied to the oil specimen within the linear viscoelastic region.…”

Section: Gelation Temperaturementioning

confidence: 99%

Influence of the initial cooling temperature on the gelation and yield stress of waxy crude oils

et al. 2014

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One of the major problems in waxy crude oil production and transportation is oil gelation that takes place within pipelines as a result of wax crystallization at low temperatures. In such cases, the pressure needed to restart the oil flow in subsea pipelines can be much larger than the usual steady-state pressure, as the temperature in such environment can be as low as 4°C. The literature has shown that not only the temperature itself but also the fluid shear and thermal histories have significant influence on the yield stress of waxy crude oils. This paper investigates the effect of the initial cooling temperature on the waxy crude oil viscosity, gelation temperature, and yield stress. In order to accomplish that, rheological tests were carried out under static and dynamic cooling conditions. The results show that there is a critical range for the initial cooling temperature that provides maximum values for viscosity, gelation temperature, and yield stress. In other words, the highest values of those properties are observed when the cooling started within this temperature range. The effect of a thermal pretreatment usually used to remove light ends was also investigated. In spite of not changing the initial temperature critical range, the yield stress was slightly affected by the thermal treatment. It is worth noting that the yield stress varies from approximately zero to hundreds after dynamic cooling or to thousands after static cooling within the tested range of the initial cooling temperatures.

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Section: Gelation Temperaturementioning

confidence: 99%

Influence of the initial cooling temperature on the gelation and yield stress of waxy crude oils

et al. 2014

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“…Crystals start forming and the rheological behavior of the crude oil turns from a simple Newtonian to a much more complex behavior and can now exhibit a high yield stress and time-dependent characteristics. Thus, the transport of waxy crude oils through long pipelines in cold environments involves handling some huge flow assurance issues, such as the management of wax deposition at the pipe walls or high pressure gradients needed for flow restart after stoppage, with the possibility of additional issues, e.g., appearance of void fractions during cool down at rest [H enaut et al (1999); Philips et al (2011a)] and pressure propagation effects [Philips et al (2011b); El-gendy (2012)].…”

Section: Introductionmentioning

confidence: 99%

Modeling the rheological behavior of waxy crude oils as a function of flow and temperature history

Mendes¹,

Vinay²,

Ovarlez³

et al. 2015

Journal of Rheology

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International audienceSynopsis The solidification of waxy components during the cool down of waxy crude oils in pipelines may provide complex yield stress fluid behavior with time-dependent characteristics, which has a critical impact for predicting flow restart after pipeline shut-in. Here, from a previous set of data at a local scale with the help of Magnetic Resonance Imaging and a new full set of data for various flow and temperature histories, we give a general picture of the rheological behavior of waxy crude oils. The tests include start flow tests at different velocities or creep tests at different stress levels, abrupt changes of velocity level, steady flow, after cooling under static or flowing conditions. We show that when the fluid has been cooled at rest it forms a structure that irreversibly collapses during the startup flow. Under these conditions, the evolution of the apparent viscosity mainly depends on the deformation undergone by the fluid for low or moderate deformation and starts to significantly depend on the shear rate for larger values. Even the (apparent) flow curve of statically cooled waxy crude oils was observed to be dependent on the flow history, more specifically on the maximum shear rate experienced by the material. After being sufficiently sheared, i.e., achieving an equilibrium state, the rheological behavior is that of a simple liquid for shear rates lower than the maximum historical one. A model is proposed to represent those trends experimentally observed. In contrast with most previous works in that field, the model is built without any a priori assumption based on classical behavior of a class of fluids. Finally, it is shown that this mode

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“…During the pipeline restart process, the formed gel needs to be broken. [5][6][7] Therefore, an accurate rheological model is necessary to simulate pipeline shut-in and restart processes. [8] Various rheological models exist for fluid behavior prediction, several which are based on Herschel-Bulkley [9] or cross formulations.…”

Section: Strain-dependent Rheological Model and Pressure Wave Predictmentioning

confidence: 99%

Strain-Dependent Rheological Model and Pressure Wave Prediction for Shut in and Restart of Waxy Oil Pipelines

Zhao

Paso

Sariman

et al. 2014

Journal of Dispersion Science and Technology

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Waxy oil gelation and rheology is investigated and modeled using strain-dependent viscosity correlations. Rotational rheometry shows a sharp viscosity increase upon gel formation. High creeping flow viscosities are observed at small deformation conditions prior to yielding. A new strain-dependent rheological model, following analogous formulation to the Carreau-Yasuda shear rate-dependent model, captures viscosity reduction associated with yielding. In addition, shear viscosity and extensional viscosity are investigated using a capillary rheometry method. Distinct shear-thinning behavior is observed in the shear mode of deformation, while distinct tension-thinning behavior is observed in the extensional mode of deformation for the model fluid systems. High Trouton ratios are obtained for the gelled model fluid systems, confirming strongly non-Newtonian fluid rheology. Finally, axial pressure wave profiles are computed at real pipeline dimensions for idealized moderate yield stress fluids using a computationally efficient 1D pipeline simulator. The Rønningsen time-dependent gel degradation model is used to emulate the fluid rheology in the simulator. Axial stress localization phenomena are shown to depend on the overall magnitude of gel degradation as established by the reduction in yield value. A high degree of gel degradation serves to afford flow commencement in a timely manner.

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

Cited by 31 publications

References 37 publications

Influence of the initial cooling temperature on the gelation and yield stress of waxy crude oils

Influence of the initial cooling temperature on the gelation and yield stress of waxy crude oils

Modeling the rheological behavior of waxy crude oils as a function of flow and temperature history

Strain-Dependent Rheological Model and Pressure Wave Prediction for Shut in and Restart of Waxy Oil Pipelines

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