Numerical Studies Of Methane Gas Production From Hydrate Decomposition By Depressurization In Porous Media

As a kind of potential new sources of energy, the research of gas hydrates has been focused around the world. The relevant knowledge system is being perfected with the extension of research and in-depth. With the tireless efforts of all relevant scholars, the numerical simulation research of the hydrate formation and decomposition got great development. Many mathematical models have been proposed, and obtained a good validation and application. However, the model of considering the ice phase generated is relatively insufficient. And most scholars ignored the ice phase for a variety of reasons in research.On the basis of summarizing the existing model, this study established a one-dimensional mathematical model for methane hydrates decomposition by depressurization in porous media. And this model contains four phase (water phase, gas phase, hydrate phase, ice phase) and three constituents (water, gas, hydrate). Using the finite difference method (FDM) discrete mathematical model and numerical model was established. A computer program was written for solving the numerical model. This paper focuses on the ice generation and distribution characteristics through changing the parameters of the relevant settings, and analyzes the ice with the pressure, temperature, permeability, cumulative gas production and related parameters influence each other. At the same time, the influence factors and features of the cumulative gas production and the instantaneous gas generation rate are analyzed.The results show that, as time goes on, generation of ice phase increases gradually in the hydrates decomposition process, and they concentration distribution in mining wells near the side area. The ice makes the absolute permeability decline, makes the instantaneous gas generation rate at the early stage decline, and makes the local pressure rise. In a word, ice phase is unfavorable factors in the process of mining. Mining well pressure obviously influences on the formation of ice, and the pressure is less, the generated ice is more at the same time the same position. Hydrate decomposition sediment itself characteristics is to determine the main factors of mineral deposits of gas production and gas production rate, which includes the hydrate saturation, reservoir porosity, permeability, etc.. The greater the hydrate saturation and reservoir porosity is, the greater cumulative gas production rate and instantaneous gas rate is. The increase of the absolute permeability can raise gas generation rate, but it do not affect the final cumulative gas production.