A novel three-dimensional natural gas hydrate physical simulation device was designed and developed for study the accumulation and exploitation of hydrate in sediment. The reactor with a capacity of 196 L was built to simulate three-dimensional macroscopic hydrate formation and dissociation behavior, and the maximum operating pressure is 32 MPa. Acoustic, electrical, and thermal properties at different positions can be collected in real-time to examine the state variation of hydrate-bearing sediment during the accumulation of hydrate or the production of natural gas. The preliminary experiment for hydrate accumulation using this device was performed where free methane continuously seeped through the sediment. The experimental results indicated that hydrate only formed and aggregated near the seepage path of fluids. The water saturation was an important for the distribution of hydrate.
Natural gas hydrate is a nonstoichiometric, crystalline, clathrate compound, which is formed by gas when contacted with water under high pressure and low temperature conditions. The hydrate is distributed through sea floor sediments below water depths that exceed 500 m, although water depths of 1–3 km are more common for known hydrate occurrences [Kvenvolden, 1993]. Since 1 m3 hydrate may contain more than 160 m3 natural gas, it has been deemed as an alternative energy in the future. Conservative estimates suggest that the amount of energy in hydrates is equivalent to twice that of all other fossil fuels combined. However, substantial volumes of methane hydrate margins also motivating speculations about a possible factor in global climate change and submarine geohazard [Kvenvolden, 1999; Sloan, 2003]. The obtained information in lab-scale apparatus may not equate to the reservoir forming process in seafloor. Seafloor conditions, such as the type of gas supply, the type of hydrate accumulation, and the geothermal gradient, are hard to be reproduced in small-scale apparatus.
