Numerical Simulation On Natural Gas Production From Hydrate Decomposition By Depressurization

There are many problems about energy shortage and environment worsens, developing efficient and clear energy resource is the only way to solve those problems. Natural gas hydrate extensive distributing in the earth and vast amount of quantity, an it is recognized the most prospective energy in the 21st century. So the research about exploitation of natural gas hydrate is very important significant.The three methods being explored for hydrate production are thermal stimulation, depressurization and inhibition injection, it think that depressurization is the most economical method, but it is must be study in-depth about the exploitation efficiency of depressurization and the problem will encounter in the gas hydrate exploitation process.In order to research depressurization, the following work will be down in this paper:1. Sufficient research many gas hydrate depressurization exploration model, analyzing the characteristics and limitations of those model, which set a foundation of establish a more perfect, real model of gas hydrate depressurization exploration.2. A 2-D simulator for gas hydrate depressurization exploration is developed, which is think of the decomposition thermodynamics, decomposition kinetic, and two phase flow and heat transfer.3. During the production of the reservoirs, the relationship between pressure distribution and radius is logarithm relation, so in the direction of radius use irregular grid to improve precision, in the direction of vertical use uniform grid, using center-difference discrete the space and using backward-difference discrete the time, the pressure is solved implicate(Gauss—Seidel block iteration method)first, the saturation is solved explicitly next, followed by implicit solution(Gauss-Seidel block iteration method) of the temperature.4. Through computing the laboratory-scale gas hydrate dissociation, it is shows that for only different outlet pressure, the lower the outlet pressure, the faster the dissociation of gas hydrates, and the longer the dissociation time, the greater the gas production, and the lower of the reservoir temperature when the dissociation stop. And for only different initial temperature, the higher initial temperature, the faster the dissociation of gas hydrates, the greater the gas production, but the same of the reservoir temperature when the dissociation stop. When the dissociation stop, there are many gas hydrate can not dissociation.5. Through computing the field-scale gas hydrate dissociation, it is shows that the gas hydrate near the outlet is complete decomposition, but there are still a large number of gas hydrate doesn't dissociation in the reservoir. A higher initial temperature leads to a higher gas hydrate dissociation rate, and a lower outlet pressure leads to a higher gas hydrate dissociation rate.6. For any scale, the outlet pressure and initial temperature are the very important factor effect gas hydrate dissociation.7. Gas hydrate in the reservoirs can not dissociation completely by only using depressurization, so this paper give a new method to exploration gas hydrate using solar energy firstly, the exploration sketch is present and the exploration process is detail described.8. A simple simulator for exploration gas hydrate using solar energy is developed, the result indicates that the energy provided by solar is enough.