Fundamental Study on Gas Production from Sediments Containing Natural Gas Hydrates

点击翻译按钮获取中文摘要

The researchers have studied the dissociation behavior of hydrates in sediments by experimental and modeling approach, considering the depressurization technique of gas production from hydrate sediments.Two experimental apparatuses were constructed. One was designed for measuring formation and dissociation rates of hydrate in a cell. The experiment using xenon gas showed that it took several hours to reach equilibrium state after the start of formation and dissociation of hydrate. The hydrate number of formed xenon hydrate was higher than its theoretical value. Another apparatus was designed for measuring the decrease in gas permeability with hydrate formation in porous media. The change in gas permeability with hydrate saturation was mathematically modeled from the experimental results using a core packed with 710-840 mum glass beads. Although the method for forming hydrate in the core was established, the dissociation rate of hydrate in the core could not be measured because the total pore volume was too small for accurate measurement of gas flow rate.Regarding to modeling study, a numerical program was developed for predicting phase behavior of methane-water mixture. For predicting gas production performance from porous media containing hydrates, two numerical programs were developed. One was based on phase-equilibrium theory, and another was based on dissociation kinetics of hydrate. From model calculations using these programs, the dissociation behavior of hydrate in a one-dimensional core was studied. The calculations showed that the three factors would affect the dissociation rate of hydrates in sediments : heat conduction from the surroundings ; the dissociation rate of hydrate crystals ; and permeability of sediments.