Effects of pressure and sea water flow on natural gas hydrate production characteristics in marine sediment

摘要

Natural gas hydrates (NGHs) widely exist in continental permafrost or marine sediment, and with a carbon quantity twice that of all fossil fuels combined, they are a potential energy source for the future. The efficient exploitation of NGHs has been a popular topic of research worldwide. Currently, existing NGH exploitation methods each present characteristic defect. In this study, by combining visualization studies with sea water phase migration, which is a crucial factor influencing NGH exploitation, the method of water flow erosion was utilized to enhance the driving force of methane hydrate (MH) dissociation. The influence of seawater migration on MH dissociation was systematically and visually studied by controlling different back pressures and seawater flow rates. There was no observed influence of temperature or pressure variation during the MH dissociation process. The results showed that the chemical potential difference between the hydrate phase and aqueous phase caused MH dissociation during the seawater flow process and that the rate of MH dissociation increased with decreasing backpressure and increasing water flow rate. It can be predicted that there will be no MH dissociation or time variations of absolute MH dissociation when the water flow rate is sufficiently low or high. The water migration, water phase permeability and MH dissociation strongly interacted with one another. This study combined a visualization study with theoretical analysis and first found that the gradient decrease of pressure difference lead to the increase of permeability during different stages of the seawater flow process.