Hydrate Gas Reservoir Buck Exploitation Mechanism

Facing exhaustion of hydrocarbon resources in the late stage of this century, people have to make a search for a sort of new source of energy who is cleanliness and high efficiency. Natural gas hydrate is a sort of new energy resource which is drawn attention generally by all over the world in recent years. By reason of extensive distributing and a large amount of quantity, natural gas hydrate is recognized the most prospective energy source in the 21st century. It is considered as the substitute of conventional hydrocarbon resources by scientific and technological circles. So the research about exploitation of natural gas hydrate is very important significance. It can offer scientific academic support and technical review of feasibility for large-scale production of natural gas hydrate reservoir on location.By systemic researching and simulating experiment, the following results are achieved in this paper.1. On the basis of sufficient research on the models and theories of overseas, analyzing the relative merits of main methods to recover natural gas reservoir from natural gas hydrate, increasing formation temperature, injecting inhibitors and depressurization, it think that depressurization is the most economical and prospect method.2. The paper has established the new mathematical model on depressurization exploitation natural gas hydrate reservoir in porous medium. Natural gas hydrate reservoir is divided into three zones, dissociated zone, dissociated completely zone and hydrate zone; the new model thinks over the flow of natural gas and water, it also thinks over the change of temperature on simulating depressurization of natural gas hydrate reservoir.3. Through computing the new mathematical model, it achieves that pressure and temperature, cumulative gas production, cumulative water production, dissociation front location and hydrate saturation, gas saturation, water saturation in porous medium. Comparing the result of new model with experimental result of Berea sandstone, thematching is very good and it proves that the new mathematical model is right.4. The results of new model also indicates that during the depressurization of natural gas hydrate reservoir in porous medium, dissociation front moves outward with grow of time and reaches the boundary of porous medium; pressure drop and temperature drop of dissociation front location is sharp; the temperature drop of the dissociated zone and the dissociated completely zone is quicker than that of the hydrate zone, the cause is that the convective heat transfer of natural gas and water in the dissociated zone and the dissociated completely zone is larger than heat conduction of natural gas hydrate in the hydrate zone; along the direction of bottom hole in the dissociated zone, the hydrate saturation decreases gradually, gas saturation increases gradually, water saturation increases firstly and decreases later; water saturation has a wave crest and moves along with dissociation front, the cause is accumulation of water provisionally.5. After making research on sensibility of new model parameters, it draws a conclusion that cumulative gas and water production and dissociation front location increases with the increase of absolute permeability in porous medium, with the decrease of bottom pressure, with the increase of formation temperature.6. Formation mechanism of natural gas hydrate is observed, it makes experimental on making use of liquor to generate hydrate in porous medium. The paper inducts a new experimental facility in experimental program, which is stirring up clamper. It ensures that full contact and reaction of free natural gas and water making use of liquor to generate hydrate in porous medium.7. Based decomposition mechanism of natural gas hydrates, the paper makes experimental of depressurizing on natural gas hydrate reservoir in porous medium making use of the results of new model. Through simulation experiment, it can obtain cumulative gas and water production. The results of simulation experiment can provide experimental data for correctness test and improvement of new model.