Tese: Effects of yield stress and thixotropy in Non-Newtonian isodense displacement
Aluno(a) : Gustavo Vinicius Lourenço MoisésOrientador(a): Mônica Naccache e Ian Alistair Frigaard
Área de Concentração: Petróleo e Energia
Data: 12/04/2016
Link para tese/dissertação: http://doi.org/10.17771/PUCRio.acad.27820
Resumo: One of the main issues in deepwater production in the oil industry is the blockage of production lines, caused by the growth of paraffin crystals that occur when temperature drops below the Wax Appearance Temperature (WAT). The yield stress appearance when gelation occurs constitutes a significant problem in static conditions that occur in the restart flow, needed after a shutdown. In essence, there exist two stages in a flow pipeline restart: apply a large enough pressure drop in order to mobilize the gel in the pipe i.e. a process of fluid start-up or inject either miscible fresh oil or any other low viscosity fluid (preferably Newtonian, e.g. sea water, diesel) at the pipe inlet, to flush the gelled oil out of the pipe, i.e. a process of fluid displacement. We investigate yield stress and thixotropy effects over Non-Newtonian fluid flows in a horizontal pipe. Two flow types are considered: non-Newtonian fluid start-up and isodense displacement of yield stress fluid by a less viscous Newtonian fluid. The yield stress and thixotropic properties of waxy crude oils are rheological simulated by water base fluids: Carbopol solutions and Laponite suspensions. The results of experimental and numerical studies of isodense displacement of a yield stress fluid are presented. A central type displacement flow develops for the configuration given. Three distinct flow types belonging to this central displacement are identified in the experiments namely corrugated, wavy and smooth depending on the level of the residual layer variation along the pipe. The transition between these flow regimes is found to be a function of the Reynolds number defined as the ratio of the inertial stress to the characteristic viscous stress of the viscoplastic fluid. Besides, the influence of NaCl and Laponite concentrations in the rheological parameters of Laponite suspensions is detailed. Start-up experiments of yield stress and thixotropic fluids are also performed and the impact of thixotropy in Laponite suspensions start-up is analyzed.