Start-up of waxy crude oils in pipelines

Autor: Renato do Nascimento Siqueira, Luiz F.R. Dalla, Edson J. Soares
Rok vydání: 2019
Předmět:
Zdroj: Journal of Non-Newtonian Fluid Mechanics. 263:61-68
ISSN: 0377-0257
DOI: 10.1016/j.jnnfm.2018.11.008
Popis: The transport of waxy crude oils in aggressive environments, usually at low temperatures, is very common. Whenever a shutdown occurs and the oil rests at temperatures below the gelation point (GT), wax crystals appear, forming an interlocked structure, with a gel character. The start-up of waxy crude oils after a shutdown is a great problem concerning flow assurance. In fact, a minimal pressure, or equivalent minimal wall shear stress, is required to restart the flow. Usually, the minimal wall shear stress is assumed to be the rheometer yield stress, which is reasonable, but not necessarily true. There are different possible causes for the discrepancies between the rheometer’s data and that measured in a pipeline start-up approach. For a faithful comparison between them, we must consider: 1) the thermal history experienced by the oil, mainly the initial cooling temperature; 2) the radial temperature distribution in the pipeline; 3) the oil shrinkage during the cooling process and 4) the different mechanisms of gel’s rupture (adhesive and cohesive failures). In this work, we use a pneumatic system in which a piston is pressurized step by step to displace the viscoplastic material. By doing so, we record the minimal shear stress necessary to overcome the cohesive forces near the wall. The preliminary tests were carried out with Carbopol solutions before conducting the main tests with a waxy crude oil in a range of initial cooling temperatures. The values of critical stresses in the start-up approach fitted quite well the rheometer yield stress data.
Databáze: OpenAIRE
Externí odkaz: