Molecular Dynamics Simulation Of Methane Hydrate Decomposition In Porous Media

According to statistics, natural gas hydrate resource is the 21st century the most potential energy. Because of the weak cementation, conventional hydrate exploitation methods are no longer applicable. Gas reservoir which is out of control would not only cause massive gas leakage and climate warming, but also cause shipwreck, aircraft crash and environmental pollution.The discussions in this dissertation focus on the possible thermal conductivity mechanisms for dissociation process and diffusion effect of structure I methane hydrate.The dissociation process of structure I methane hydrates are investigated, and the possible mechanism of hydrate bulk dissociation is discussed. The bulk dissociation process of methane hydrate is considered to be comprised of two steps. The first is the process associated with the diffusive behavior of host molecules (water molecules), which in turn leads to the increase of crystal distortion. The hydrate cavities will start to break as crystal distortion is too severe to maintain the lattice structure. The second stage is such a process in which methane molecules will escape from the broken hydrate cavities. The first stage is found to be the key for hydrate dissociation. The mechanism presented here supports the hypothesis proposed by Kim at a molecular level.The dissociation process and diffusion effect of structure I methane hydrates in porous media are investigated, such as:density distribution, radial distribution function (RDF), the mean square displacement (MSD)and the diffusion coefficient structural and dynamics properties of hydrate. We use NVT ensemble and NPT ensemble study decomposition and diffusion effects of methane hydrate in the dioxide silica surface. The main purpose of this thesis is to investigate the dissociation and diffusion mechanism of gas hydrates. Research shows that in the porous media decomposition rate of hydrate is higher than the pure hydrate. So in certain pressure and temperature, driving force of the decomposition of gas hydrates in porous medium will be higher than pure methane hydrate.The decomposition process and thermal conductivity of methane hydrates in porous media are investigated. Owing to the characteristic that the stability of hydrate is quite sensitive to temperature changes, it is necessary to research on the thermal conductivity of the hydrates. In addition, faced with the low thermal conductivity characteristics of the hydrate, it is essential to strengthen its thermal conductivity. Research has shown that, the porous media of different pore sizes are introduced into the thermal conductivity of hydrate fields. It can be ascertained that the porous media of different pore sizes have strengthened the role of the thermal conductivity of hydrates. Considering the hydrates in nature is not exist alone, always accompanied by other materials such as quartz sand, ice etc. So the hydrates in the compound system of transmit heat function was studied. The textual research is particularly aims to study the thermal conductivity of hydrate in porous media (namely hydrate-porous media system), which is further study the mechanism of thermal conductivity of hydrate, to provide method for the exploitation transportation and utilization of hydrate.