4:45 PM - 5:00 PM
[MIS26-11] Simulation of methane hydrate formation in coarse-/fine-grained sediments in the Nankai Trough, Japan
Keywords:Simulation, Methane hydrate, Nankai Trough
Abstract
The morphology and formation process of methane hydrate are affected significantly by the characteristics of sediments. In coarse-grained sediments, methane hydrate is formed by pore filling, while in fine-grained sediments, methane hydrate usually forms segregated lenses, veins, and nodules by replacing rock particles. At IODP Site C0002, Kumano forearc base, in the Nankai Trough, a gas bearing reservoir about 100 meters below the hydrate stability zone is discovered by logging analysis, which is used as methane source responsible for the hydrate accumulation in the numerical model. The formation of methane hydrate in coarse-grained sediments is constrained by the salt concentration in pore water, so the distribution of methane hydrate saturation is related to the distribution of salts in aqueous phase under phase equilibrium state, and the simulation results of methane hydrate distribution are consistent with the results of logging curve analysis. On the other hand, the formation mode of methane hydrate in fine-grained sediments can be determined by calculating the relative magnitude of effective stress and capillary pressure. The short-range migration theory model and patchy hydrate saturation (whereby zones with 100% pore-space hydrate saturation are embedded in hydrate-free sediments) are used to explain the profile of saturation of methane hydrate in fine-grained sediments.
The morphology and formation process of methane hydrate are affected significantly by the characteristics of sediments. In coarse-grained sediments, methane hydrate is formed by pore filling, while in fine-grained sediments, methane hydrate usually forms segregated lenses, veins, and nodules by replacing rock particles. At IODP Site C0002, Kumano forearc base, in the Nankai Trough, a gas bearing reservoir about 100 meters below the hydrate stability zone is discovered by logging analysis, which is used as methane source responsible for the hydrate accumulation in the numerical model. The formation of methane hydrate in coarse-grained sediments is constrained by the salt concentration in pore water, so the distribution of methane hydrate saturation is related to the distribution of salts in aqueous phase under phase equilibrium state, and the simulation results of methane hydrate distribution are consistent with the results of logging curve analysis. On the other hand, the formation mode of methane hydrate in fine-grained sediments can be determined by calculating the relative magnitude of effective stress and capillary pressure. The short-range migration theory model and patchy hydrate saturation (whereby zones with 100% pore-space hydrate saturation are embedded in hydrate-free sediments) are used to explain the profile of saturation of methane hydrate in fine-grained sediments.