NUMERICAL FLOW ANALYSIS OF HYDRATE FORMATION IN OFFSHORE PIPELINES USING COMPUTATIONAL FLUID DYNAMICS (CFD)

摘要

Hydrate formation is one of the major challenges faced by the Oil and Gas industry in offshore facilities due to its potential to plug wells and reduce production. Several experimental studies have been published so far in order to understand the mechanisms that govern the hydrate formation process under its thermodynamic favorable conditions; however, the results are not very accurate due to the uncertainties related to measurements and metastable behavior observed in some cases involving hydrate formation. Moreover, thermodynamic models have been proposed to overcome the latter constraints but they are formulated assuming thermodynamic equilibrium, which such condition is difficult to be achieved in flow systems due to the turbulence effects. Due to the low solubility of methane in water, the mass transfer effects can possibly control several mechanisms that are still unknown about the hydrate formation process. Also, the reaction kinetics plays a major rule in minimizing hydrate formation rate. The objective of this work is to develop a mechanistic Computational Fluid Dynamics (CFD) model in order to predict the formation of hydrate particles along the pipeline from a hydrate-free gas dominated stream constituted by methane and water only. The transient simulations were performed using a commercial CFD software package considering the multiphase hydrate chemical reaction and mass transfer resistances. The geometry used was a straight pipe with 5 m length and 0.0254 m diameter. The results have shown the appearance of regions in the pipeline at which hydrate formation is controlled either by the mass transfer or reaction kinetics. The rate of hydrate formation profile has shown to be high at the inlet even though the temperature at that regions was high, which can be a possible explanation for metastable region encountered in most of recent phase diagrams.