Gas hydrate is one of the new energy resources because of vast amount of reservoirs in marine sediments. Recently, research and developments for the gas hydrate production have been conducted in some countries. To evaluate the production from the reservoirs, it is necessary to understand the behavior of dissociation in-situ condition. However, the rate of dissociation of gas hydrate has been unknown, especially in the situation of pore space of marine sediments. In this paper, the rate of dissociation of methane hydrates occupied in pore space is discussed. Based on the microscopic observation using Raman spectrometer, the mechanism of dissociation in pore space has been clarified. The rates of gas hydrate dissociation were measured under various unstable conditions, such as pressure decrease and heat stimulation. Dissociation model to simulate the interaction between hydrate crystals and pore space was considered on the basis of the experimental results. Through the above discussion, the estimation method for dissociation rate of methane hydrates was developed and validated. The simulation results using the developed model agree well with the data obtained from bulk-scale experiments.
Methane hydrate is ice-like solid substance in which water molecule structure contains embedded methane molecules under low-temperature and high-pressure conditions. Three major extraction methods of gas hydrates from the reservoir in marine sediments has been proposed, such as depressurization, thermal stimulation and inhibitor injection. These are all based on the in-situ dissociation process of gas hydrates that is transformed into methane gas and water. Fig.1 shows the production image for gas hydrates from marine sediments. Only methane gas can be produced from the reservoirs in marine sediments. To evaluate the productivity of methane gas from the reservoirs, it is necessary to understand the phenomena of dissociation and to estimate the rate of dissociation in the environment of marine sediments.