Study On The Hydrate Formation,Dissociation And Seepage Characteristics In A Micro-Packed Bed Reactor

The reserves of natural gas hydrate are large,and the full utilization of natural gas hydrate resources is crucial to the sustainable development of energy in China.Micropacked bed reactor combines the advantages of micro-reactor and packed bed.It not only ensures the high-definition visualization,but also is closer to the porous media structure of hydrate reservoirs.In this study,the formation processes of TBAB hydrates under static and dynamics conditions,the growth process and the dissociation process of methane hydrate under different depressurization methods were investigated in a micro-packed bed reactor.Meanwhile,the seepage characteristics of micro-packed bed reactor filled with quartz sands with different particle sizes were studied.Firstly,the growth processes of TBAB hydrates in static state and dynamic conditions were studied,respectively.It was observed that TBAB hydrates in static conditions had two growth modes of coating growth and pore filling.The growth process of TBAB hydrate in dynamic conditions can be divided into three stages.By analyzing the image information of TBAB hydrate growth and blockage process in the dynamic conditions and the flow velocity distribution of the fluid in the micro-packed bed reactor,it was found that the hydrate tended to form blockage at the local high flow velocity in the reactor.Then,the formation process of methane hydrate in a micro-packed bed reactor was directly observed by microscopic visualization method,and the process of multiphase fluid migration,phase transition and hydrate dissociation in the micro-packed bed reactor under continuous depressurization and step depressurization were studied.For these two depressurization methods,the reformation and redistribution of hydrates were observed.The depressurization led to the breakage of the hydrate shell,and the methane gas that was not completely converted into hydrate escaped from the shell,and then methane hydrate was formed,resulting in the change of pore structure of porous media.Compared with the two depressurization methods,the sudden pressure change of the step depressurization leads to more significant dispersed gas distribution and change in pore structure of porous media.Finally,the seepage characteristics of the micro-packed bed reactor with formed hydrate were studied,and it was found that the permeability of micro-packed bed reactor decreased greatly when hydrate existed.In the same microreactor,the permeability decreased with the increase of hydrate saturation.By comparing and analysis of the experimental values of permeabilities and the permeabilities calculated by parallel capillary bundle model,Kozeny-Carman particle model and Dai and Seol models,the possible growth forms of hydrates in porous media could be revealed.