Simulation Study Of The Seepage Characteristics Of Porous Media Containing Hydrate And Hydrate Dissociation

Natural gas hydrate，as a kind of rich reserves, high energy density,combustion clean potential energy source, is concerned by more and morecountries. So now many countries have already started the study of natural gashydrate, and the research contents include natural gas hydrate productiontechnology and hydrate application technology. And it has made greatprogress.Natural gas hydrate exists in the ocean floor or in the permafrost. However,natural gas hydrate decomposition is a complex process which is influenced bymany factors, and it is difficult to exploit natural gas hydrate. The permeabilityin the natural gas hydrate reservoir is one of the key parameters in estimating thegas production performance and the flow behavior of gas and water duringdissociation. In this study, a numerical simulation method is proposed tocalculate the microcosmic dissociation of natural gas hydrate based on the porenetwork model and seepage mechanics, and the multiphase flow characteristicand the effect of relative permeability of gas and water on natural gas hydratedissociation were studied。 The phase shift of natural gas hydrate with different pore size distributionand hydrate saturation was simulated based on a three-dimensional pore network.Darcy’s law as the theoretical basis of the study and the research method of fluidmechanics were applied to study permeability variation of hydrate-bearingporous media under different hydrate formation position. It is found that whetherhydrate is generated in the pore center or generated on the wall surface, theincrease of hydrate saturation lead to the decrease of permeability. And thedecrease amplitude of the permeability of hydrate formation in the pore center isgreater than generated on the wall surface.The relative permeabily of gas, water were also studied on the conditonswith different porosity of porous medium, different hydate saturation anddifferent hydrate formation characteristic in porous media. The results show thatthe relative permeabily decreases more slowly with hydrate formation on thepore wall surface than it does with hydate locating center of pore. And theisotonic point of relative permeabily with mode of hydrate on pore wall surfaceis more high. At the same time, the relative permeability can not vary withporosity of porous media and hydate saturation no matter the pore wall modeand the pore center mode.The sensitive factors were studied for dissociation charactersitic of hydatebearing porous meida inmicro-scale level. The results suggest that intrinsickinetic constant, porosity, initial temperature, outer pressure，initial saturationsare sensitive for natural gas hydrate production, and the effect of the pore size distribution may be ignored.The contents which include the relation of permeability with natural gashydrate saturation and natural gas hydrate dissociation characteristics in porousmedia were studied based on the method of simulation. All of research willprovide supports for determination of the natural gas hydrate product.