Study On Formation And Dissociation Characteristics Of The Natural Gas Hydrate

Natural gas hydrate, as the new generation of clean energy, is experiencing a researching breakthrough key point of its exploration and development technology.In hydrate seepage, the formation and dissociation properties of natural gas hydrate plays a decisive role in its safe and effective exploitation. This paper takes the key issues of safe and effective exploitation of hydrate sediments as study background. The growth law and occurrence structure of hydrates in porus media, as well as the styctural changes and flow characteristics in the process of dissociation are systematically researched in this paper.In order to realize the real-time visualization of hydrate flow properties and hydrate formation and dissociation, this research designs and develops an in situ experimental system of hydrate formation, dissociation and flow properties in pours media. MRI sequence is also improved to realize the real-time visualization of hydrate occurrence structure and flow characteristics in the process of dissociation.The formation of different hydrates in different porus medias is studied. The occurrence structure law of different hydrates is ascertained.It is found that liquid hydrates represented by THF belong to sementing modal. The formation process visualization of THF, methane, and carbon dioxide hydrate reveals the occurrence law of different hydrates. Liquid hydrates represented by THF belong to sementing modal. The hydrate structure begins to transfer from sementing modal to floating modal when the solution concentration reduces; gas hydrate occurrence structure belongs to floating modal. Based on dynamical model, the nucleation and growth process of hydrates are microanalyzed, and that the occurrence structure of hydrates can switch between floating and sementing is proved.Methane and carbon dioxide hydrate dissociation in porus media is in situ measured. The change law of hydrate bearing porus media structure during dissociation is drawn. No obvious change of porus media structure and displacement of porus media particles are found. There is no displacement of porus media particles, and hydrates don't flow with heat flow. Second generation phenomenon can be witnessed in the dissociation process when insufficient heat flow is injected. As a result, dissociation will be impeded.The absolute and relative permeability curve is obtained through the research of absolute and relative permeability change law in the process of hydrate bearing porus media formation. The permeability of hydrate bearing porus media increases as the hydrate dissociates. The permeability increases dramatically in the early phase, and the process slows down when the dissociation is halfway finished.The relationship between non-uniformity of fluid distribution and porus media structure is illuminated by means of studying the two-dimentional velocity profile of single-phase fluid with different thermal velocity in the dissociation process of hydrate bearing porus media. The velocity is proportional to the pore size. The average speed in the cross section decreases as the hydrate dissociates.To sum up, this paper studies on the occurrence structure and dissociation properties and flow law of hydrates in porus media. The structure change of hydrate bearing porus media and the permeability change and floating law in dissociation process are also researched on. It plays a significant role in hydrate reservoir model, the assessment of its energy effect and environmental impact, and the resource utilization of natural gas hydrate.