Study On The Mechanism Of Hydrate Formation And Growth In Bubble Flow Of Deepwater Drilling Wellbore

Hydrate formation in low temperature and high pressure environment will not only affect the rheology of drilling fluid,increase the friction pressure drop,but also deposit on the pipe wall,even enter the interspaces in the connector,plug the blowout preventer and throttling line,which poses a serious threat to the well control and drilling operations,and this requires an intensive study on the mechanism of hydrate formation and growth.This thesis is targeted at deepwater drilling operations and focused on bubble flow.In this parper,the prediction model of hydrate formation rate in the wellbore is constructed by experiments and theoretical analysis.This parper has designed two sets of experimental apparatus for experimental study on hydrate formation,the spherical hydrate reaction container is used to research on the hydrate lateral and vertical growth process,cylindrical tube is used for the simulation of deepwater drilling wellbore and investigating hydrate growth in bubble flow.In accordance with the theory of heat and mass transfer,a new model of hydrate lateral and vertical growth rate is established by combining experimental observation and growth law.On the basis of these two models,the influence of hydrate formation on bubble dynamics and size distribution is studied,hydrate formation rate model in bubble flow is established.Simultaneously,this model is verified by combining with experimental data.Simulation results show that hydrate film lateral growth rate model considering natural convection heat transfer agrees well with experimental data in level gas-liquid interface and bubble surface,the prediction error of hydrate film initial thickness is not more than 20%;hydrate film growth rate on bubble surface is related with the different position of bubble surface and bubble size,which is characterized by heat transfer efficiency of hydrate film frontier.According to the experimental observations on vertical growth of hydrate shell,this process has undergone three complicated stages: rapid growth zone,continuous collapse zone and growth stagnation zone.Hydrate formation can affect the rising velocity and morphology of the bubble surface,and also influences the fluidity of aqueous solution.Hydrate formation rate in bubble flow is not only related to hydrate formation rate of single bubble,but also controlled by bubble size distribution.This model is used to predict hydrate formation rate in a wellbore,and the results show that the peak of hydrate formation rate in hydrate formation region will arrive in advance relative to the peak of the system subcooling.Based on the prediction of hydrate formation rate,a new method of hydrate prevention is proposed,which can provide a theoretical basis for overcoming the overuse of hydrate inhibitors in deepwater drilling.