One-dimensional study on gas production characteristics of methane hydrate in clayey sediments using depressurization method

Abstract

As a new kind of clean and high-energy resource, natural gas hydrate possesses promising prospects in exploitation and utilization. The characteristic of gas production in clay-rich sediments need to be further clarified for developing hydrates more safely and efficiently. To study the dissociation behaviors of methane hydrates in clayey sediments, a novel pressure retention system was applied to create both confined and unconfined environments using a one-dimensional visual hydrate simulator. Two types of methane hydrate deposits were simulated, of which were characterized by excess gas and excess water, respectively. Direct depressurization results showed that in confined environment, the increase of clay content in sediments will result in the decrease of gas phase permeability and gas production rate, but have negligible effect on the final gas recovery ratio. In unconfined environment, the infiltration of overlying seawater will result in the migration of fine-grained particles and extremely low gas recovery ratio. Moreover, the build-up of vertical pressure gradient was observed due to the occurrence of sediment compaction during depressurization process in clayey sediments. It is of significance to improve the effective permeability of the reservior and suppress water seepage for exploiting hydrate safely and efficiently.