Experimental Research On Dynamic And Static Loading Response And Deformation Characteristics Of Hydrate-bearing Sediment

Natural gas hydrate is an ice-like solid substance formed by water and methane gas at low temperature and high pressure.It has also become the most potential new type of plot energy in the 21 st century.At the same time,scholars and governments around the world have carried out corresponding research on hydrate and issued corresponding mining plans.In 2017 and 2020,my country conducted the first and second sea hydrate test mining in the Shenhu waters of the South China Sea respectively,which broke many world records.A major leap from exploratory test mining of hydrate to experimental test mining has been achieved.The hydrate distribution in nature is mainly distributed in the deep ocean and permafrost areas.However,hydrate reservoirs have the characteristics of shallow burial depth,unconsolidated or weak consolidation,etc.When the hydrate is exploited,the hydrate in the reservoir will decompose,resulting in a significant weakening of the cementation force and mechanical properties inside the reservoir.In severe cases,it may lead to the instability of the gold well wall,ocean slope and reservoir subsidence,and a series of marine geological disasters,etc.Therefore,the study of the mechanical properties of hydrate-bearing sediments is the premise and foundation to ensure the safe exploitation of hydrate.At present,the research on the dynamic,static and deformation characteristics of hydrate-bearing sediments is still relatively scarce.Therefore,in this thesis,an experimental study is carried out on the dynamic load mechanical response before and after the hydrate-bearing sediments,the static load mechanical response during hydrate disociation,and the deformation mechanical response under the multi-field coupling during hydrate disociation under different influencing factors.The evolution law of dynamic and static properties and deformation characteristics of hydrate-bearing sediments under actual engineering conditions is analyzed,and the strength theory and deformation model during hydrate disociation are established by theoretical derivation,which provides guidance for practical engineering.The full text is divided into six chapters,which are as follows:(1)The first chapter introduces the purpose and significance of studying the mechanical and deformation characteristics of hydrate-bearing sediments are introduced,and the research progress of hydrate at home and abroad is also introduced.At the same time,the deficiencies and problems of the current research status are also analyzed.Finally,based on the shortcomings of the above problems,the main research content,research objectives and technical route of this thesis are introduced.(2)The second chapter mainly uses the hydrate resonance column system to test the dynamic load mechanical response of the sample,and analyzes the dynamic shear modulus of hydrate-bearing sediments under different particle sizes,effective confining pressure,shear strain,and hydrate status before and after hydrate dissociation.(3)The third chapter mainly uses the hydrate triaxial instrument to test the static load mechanical response of the sample during hydrate dissociation process,and the effects of different hydrate dissociation degrees,hydrate saturation,effective confining pressure and framework materials on the characteristic typical curve,secant modulus,peak strength,cohesion and internal friction angle of hydrate-bearing sediments were analyzed.(4)Chapter 4 adopts the multi-functional hydrate test system independently developed by our research group,simulates the actual depressurization production process,and tests the deformation response of the sample under multi-field coupling.The effects of different hydrate saturation,pressure drop,axial pressure,pressure drop rate and clay content on the wave velocity,permeability,fluidsolid production and deformation of hydrate-bearing sediments were analyzed.(5)In chapter 5,combined with the test data and Mohr-Coulomb and Durcker-Prager strength criteria,the strength and deformation prediction models applicable to hydrate-bearing sediments during dissociation are established respectively.(6)Chapter 6 summarizes the main understandings of this research,puts forward the innovations and shortcomings of this research,and looks forward to the next work.