Hydrate Deposition And Blockage Mechanism In Annular-mist Flow In Deepwater Well Control

It is proved that the well control process is the most likely occurrence of hydrate deposition and blockage by the international cases of hydrates accident.In the process of deepwater well control,due to the full contact between gas and liquid and the fast rate of mass and heat transfer under annular-mist flow,hydrate formation rate is fast,so the risk of hydrate deposition and blockage in the choke line is large.Therefore,it is necessary to carry out an in-depth study of hydrate deposition and blockage for the annular-mist flow in deepwater well control.Firstly,considering the work done by the volume variation during gas flow,hydrate formation and deposition,as well as different gas composition,a method is established to quantitatively predict the hydrate formation region for the annular-mist flow in deepwater well control.Secondly,throuth the study of the variation in the contents of free water and hydrates in the gas phase due to hydrate formation and deposition,the gas–liquid–solid(hydrate)flow,gas–solid(hydrate)flow and water-saturated gas flow are found to be coexist at different locations of the pipeline.In the gas–liquid–solid(hydrate)flow,the hydrate layer on the pipe wall deposited from the hydrates formed from the liquid droplets and liquid film.Considering the influence of liquid film atomization on the depositon of hydrate particles in gas phase,an effective deposition ratio(EDR)is firstly proposed to calculate the deposition of hydrate particles from the gas phase.In the gas–solid(hydrate)flow,the growth of the hydrate layer on the pipe wall is largely due to the deposition of the hydrate particles in the gas phase.In the water-saturated gas flow,the growth of the hydrate layer on the pipe wall is mainly from the deposition of the hydrates formed from the condensed water.Lastly,based on the research of different hadrate formation and deposition mechanisms under different flow patterns,the hydrate deposition and blockage prediction model is established,which is verified by the literature experimental data and the field measured data.On the basis of the established hydrate deposition and blockage prediction mode,considering the fluid properties,boundary conditions and environmental impacts,the hydrate deposition law under annular-mist flow in deepwater well control is calculated using the method of numerical analysis.The effects of gas flow rate,liquid flow rate,water depth,and pipe diameter on hydrate deposition and blockage,as well as the hydrate deposition on the variation of wellhead backpressure are also anlysised.This work can provide theoretical basis and helpful reference for the prediction and prevention of hydrate deposition and blockage in deepwater well control.