Molecular Simulation Study Of CO 2 Replacement Gas Hydrate

In the face of severe situation that the conventional oil and gas resource cannot meet the world’s energy need gradually, the natural gas hydrate is gradually taken care by people as a new type of green energy. The natural gas hydrate is characteristic as abundant resource, widely distribution, high content of organic carbon and high density of burning energy. The development of natural gas hydrate is significant in alleviating the energy to be short and ameliorate the form using energy in China. CO2 exchange natural gas hydrate is a kind of important development form for natural gas hydrate, which has long received attentions. The processes of CO2 exchange natural gas hydrate are influenced by temperature and pressure, however, the law of it’s changing effected by temperature, pressure and the components of gas is not clear, therefore it is significant in developing natural gas hydrate to explore it.Although the traditional experiment methods can be used to research the change rules of the processes of CO2 exchange natural gas hydrate, they only can obtain the macro phenomenon, and they cannot explain the change mechanism in the angle of microscopic. With the help of computer technology, not only the macro phenomenon can be research, but also the change of structure and motivation of molecules can be research in the angel of microscopic. Thus, this paper stimulated the processes of CO2 exchange natural gas hydrate, and optimized the models of the processes, which is aimed to further explore the reaction mechanism of the exchange processes. Based on molecular kinetic theory, this paper establishes the 3 kinds of models:CO2-NGH, CO2/H2O-NGH and CO2/CH4-NGH. The particles radial distribution functions, mean square displacement and concentration profile of CH4, CO2 and H2O are determined by the numerical simulation, which was used to explore the effect of replacement components, temperature and pressure on the processes of CO2 exchange natural gas hydrate.The results show that:in the case of the pure CO2 is used to exchange the natural gas hydrate, the optimal temperature to generate the CO2 hydrate is between 280K-290K. The temperature has a little influence on the destruction of water cages, and a large amount of residual water cages exist after the decomposition of natural gas hydrate. After the CO2 is added by H2O or CH4, the decomposition rate of methane hydrate increases. The movement rate of CO2 increase, which make the CO2 enter inside of methane hydrate increases more easily. However the molecule of carbon dioxide become more difficult to generate the CO2 hydrate. The rate of the destruction of water cages in the hydrate slow down, and the movement rate of H2O as also. Along with the increase of concentration of CO2/H2O, the decomposition rate of methane hydrate is also increase, and the destruction rate of water cages is reduced. Along with the increase of concentration of CO2/CH4, the decomposition rate of methane hydrate is reduced, and the destruction rate of water cages is increase. In order to get better natural gas hydrate exploitation effect, and increase the speed of methane hydrate decomposition and carbon dioxide hydrate formation rate, we can add right amount of methane molecules in carbon dioxide in the actual production.