多孔質体におけるメタンハイドレートの生成・分解挙動―メタンハイドレート貯留層の浸透率評価に関する研究 Ｉ―

Abstract

In order to obtain fundamental data for the evaluation of permeability in methane hydrate reservoir, we have conducted experimental and analytical studies on the behavior of formation and dissociation of methane hydrate in porous media and the change in permeability in the process of formation and dissociation. The experimental apparatus for permeability measurement was originally designed and manufactured. Very uniform methane hydrate reservoir was achieved by the method of gas injection into sand column. The artificial sample of sand column with methane hydrate was satisfactory for the experiment of absolute permeability measurement. As a result of the experiment, it was found that the formation rate of methane hydrate in porous media depends on the particle size distribution of sands composing porous media. The interfacial condition between methane gas and pore water was an essential parameter of formation. In an experiment of dissociation of hydrate by the injection of hot water, the increase of permeability in methane hydrate reservoir was observed as a function of time. The large decrease in permeability was also obtained as a result of reformation due to flow of dissociated gas in porous media. The apparent absolute permeability drastically decreased as the hydrate saturation in sand column becomes lower. The values of the permeability in the case of hydrate saturation 40 % were 1/30 to 1/50 compared with the original values without any hydrate formation in porous media.