Study On The Mechanism Of Natural Gas Hydrate Decomposition Based On Molecular Dynamics Simulation

Natural gas hydrate,which is similar to ice in structure,is formed by natural gas and water under high pressure and low temperature.Since its discovery,its effective exploitation has become a long-term research hotspot in the industry.In this paper,the molecular dynamics method is used to simulate the dissociation process of s I methane hydrate.The Materials Studio simulation software is used to analyze the temperature and pressure through the crystal configuration,potential energy change,mean square displacement and radial distribution function of the system.Regarding the influence of hydrate stability,the specific movement process of each atom during hydrate decomposition was obtained from a microscopic point of view,and the mechanism of hydrate decomposition by two conventional methods,thermal injection method and inhibitor method,was studied.Taking sI natural gas hydrate as the research object,firstly,the influence of temperature change on the stability of hydrate is studied: the decomposition of hydrate at the temperature of 190K-290 K is explored: when the system temperature is in the range of 190K-210 K,the hydrate crystal The dissociation of hydrate is not obvious;as the temperature continues to increase,when the temperature is 230 K,the configuration,potential energy,mean square displacement and radial distribution function of the hydrate all change significantly.At this time,the hydrate gradually dissociates.The dissociation temperature is between 210K-230K;when the temperature rises to 290 K,the methane molecules and water molecules in the system are clearly stratified,the structure and form of the hydrate crystals disappear completely,and the hydrates are basically completely dissociated at this time.Secondly,the influence of pressure changes on the stability of hydrates is studied: when the system pressure is in the range of 25-45 MPa,the hydrate crystals can still maintain a stable form,and no obvious dissociation is found;when the pressure drops to 15 MPa,The clathrate structure of hydrate has been deformed and broken,and methane molecules escaped from the cavities to form clusters,so the decomposition pressure of hydrate is between 15MPa-25 MPa.The simulation uses the NVE ensemble and the NVT ensemble to achieve the setting of two conditions of closed adiabatic and stable heat injection.When under the closed adiabatic condition,the decomposition of hydrate can only consume the potential energy of the system itself to achieve decomposition.The potential energy of the system gradually decreases.When the closed system itself cannot meet the heat required for hydrate decomposition,the complete hydrate structure in the system can exist stably.When under the condition of stable heat injection,the stable and sufficient heat supply from the outside can cause the hydrate to continue to decompose until it is completely decomposed.The continuous decomposition of hydrate requires a stable supply of heat,which lays a theoretical foundation for the feasibility of heat injection to produce hydrates.The effect of inhibitors on the decomposition of hydrates has been simulated.The results show that the crystal structure of hydrates can stably exist in the pure hydrate system without adding any substances;and when a certain amount of hydrate is added to the system In the case of inorganic salt solution,the hydrate layer will dissociate layer by layer until it is completely dissociated.At a concentration of 20%,the dissociation effect of KCl is better than that of NaCl.