Experimental Study in Laboratory on consolidation and gas production behavior during Dissociation of Methane Hydrate by Depressurization

Methane hydrate (MH) is one of the potential resources of natural gas in the near future, because large amount of MH exists in marine sediments or in permafrost regions worldwide. Depressurization process is regarded as the most effective process for gas recovery from the viewpoint of gas productivity and economical efficiency, compared with the other in-situ dissociation processes of MH. However, increase of effective stress during depressurization causes consolidation of MH sediments and permeability reduction. As a result, decrease of gas productivity is also supposed. Therefore, it is very important to understand the behavior in MH reservoir, especially in developing the extraction system for MH, and when considering the environmental impacts due to the development. We conducted an experimental study on consolidation and gas production behavior during MH Dissociation by Depressurization. In a real MH field, it is supposed that vertical consolidation of sediments occurs whereas gas and water flow in horizontal direction. For the purpose of considering porosity change due to consolidation and MH dissociation, the special type of experimental apparatus was designed. To reproduce the real flow condition of gas and water, we used disc shape samples as simulated MH sediment. Horizontal radial flow in porous media during MH dissociation was constructed whereas vertical load system was used to simulate rock pressure conditions in real MH sediment. We changed initial temperature, dissociation pressure, MH saturation, and sand grain size as experimental parameter to clarify the effect of these parameters on MH dissociation, consolidation, and dissociated gas production.