A Model of Multiphase Flow Dynamics Considering the Hydrated Bubble Behaviors and Its Application to Deepwater Kick Simulation

Abstract

The interaction between hydrated bubble growth and multiphase flow dynamics is important in deepwater wellbore/pipeline flow. In this study, we derived a hydrate shell growth model considering the intrinsic kinetics, mass and heat transfer, and hydrodynamics mechanisms in which a partly coverage assumption is introduced for elucidating the synergy of bubble hydrodynamics and hydrate morphology. Moreover, a hydro-thermo-hydrate model is developed considering the intercoupling effects including interphase mass and heat transfer, and the slippage of hydrate-coated bubble. Through comparison with experimental data, the performance of proposed model is validated and evaluated. The model is applied to analyze the wellbore dynamics process of kick evolution during deepwater drilling. The simulation results show that the hydrate formation region is mainly near the seafloor affected by the fluid temperature and pressure distributions along the wellbore. The volume change and the mass transfer rate of a hydrated bubble vary complicatedly, because of hydrate formation, hydrate decomposition, and bubble dissolution (both gas and hydrate). Moreover, hydrate phase transition can significantly alter the void fraction and migration velocity of free gas in two aspects: (1) when gas enters the hydrate stability field (HSF), a solid hydrate shell will form on the gas bubble surface, and thereby, the velocity and void fraction of free gas can be considerably decreased; (2) the free gas will separate from solid hydrate and expand rapidly near the sea surface (outside the HSF), which can lead to an abrupt hydrostatic pressure loss and explosive development of the gas kick.