Study On Micromechanical Properties Of Methane Hydrate Soil Based On Molecular Dynamics

In recent years,as a new type of energy,natural gas hydrate has been put into trial production all over the world.In the process of exploitation,due to the change of external environment,natural gas hydrate decomposes in a disguised form,which leads to the deterioration of mechanical properties of sediments containing natural gas hydrate("methane hydrate soil "),resulting in a series of engineering problems.In this paper,molecular dynamics method will be used to study the methane hydrate soil,to explore the micro mechanism of mechanical behavior of methane hydrate soil and the decomposition and migration of hydrate.The main research contents and achievements are as follows:(1)This paper systematically summarizes and analyzes the research status of methane hydrate soil at home and abroad,and points out the existing problems and the main research contents of this paper.(2)The basic theory of molecular dynamics modeling is systematically expounded,and the molecular dynamics models of natural gas hydrate and methane hydrate soil are established.(3)Based on the molecular dynamics model,the stretching and heating of natural gas hydrate were simulated.During the tensile process,the hydrate is destroyed in the order of the middle first and then the two sides,the failure surface is about 45 ° inclined plane,and the failure form is brittle failure;during the heating process,the hydrate is decomposed in the order of the two sides first and then the middle.(4)The shear simulation of methane hydrate soil was carried out,and the variation of microstructure,hydrogen bond length,stress-strain relationship and radial distribution function of methane hydrate soil were studied.During the shear process,methane molecules mainly escape along the shear direction,while the methane molecules and water molecules which are not escaping are distributed uniformly in the methane hydrate soil,but gather along the shear direction.The increase of confining pressure can slow down the speed of strength reduction and improve the residual strength of methane hydrate soil.(5)The methane hydrate soil is simulated by heating and compression.The variation rules of stress,total energy and interaction between different molecules of methane hydrate soil are analyzed,and the micro mechanism of the influence of the change of hydrate state on the mechanical properties of methane hydrate soil is revealed.It is found that the hydrate in the soil begins to decompose from both sides during the heating process,and the cage structure of the intermediate hydrate is destroyed with the increase of temperature;under the compression condition,the cage structure of hydrate in the soil is destroyed at the same time,the methane molecules on both sides begin to escape,and the methane molecules in the middle migrate in the soil.(6)The micro model of methane hydrate soil after environmental restoration is established and compressed.It is found that the mechanical properties of methane hydrate soil after environmental restoration are affected by the order of water molecules,and its micro mechanism is revealed.When water molecules are arranged in order,the strength of soil is high,and when water molecules become free water,the strength of soil decreases.