Desenvolvimento de metodologias para simulação de escoamentos multifásicos com formação de hidratos

Abstract

Hydrates are responsible for several operational issues during off-shore oil production. These solid compounds are formed by water and nonpolar molecules under high pressure and low temperature conditions. This work aims on the development of a computational code for the simulation of hydrate formation in oildominated multiphase flows using the open-source computational fluid dynamics software OpenFOAM®. The Eulerian multi-fluid model was applied to a system composed of a continuous oil phase with dispersed gas bubbles and a polydispersed population of water droplets that are converted into hydrate particles. Then, a trivariate population balance model is developed to describe the droplet/particle population, based on the particle volume, hydrate mass and energy as internal variables. It was observed the effect of the water and gas phase fractions in the increase of the pressure drop due to hydrate formation, that varied between 1.8% e 170%. Besides that, several enhancements in the numerical methods used for the solution of the model equations were performed. We proposed enhancements to the DQST (Direct Quadrature Spanning Tree), a method for the solution of the population balance equation, including new initialization, numerical integration and smoothing methodologies, which reduced the second order moment errors by several orders of magnitude when compared to the original DQST formulation. We also developed a simultaneous and implicitly coupled method for the solution of the pressure and velocity fields in the Eulerian multi-fluid model, which is capable to solve problems where the inter-phase momentum coupling is strong, with a reduction in the computational cost of up to 30% when compared to the segregated solution.