Geomechanical Behaviors of Hydrate-Bearing Sediments in the Ulleung Basin

A possibility of methane hydrate presence in the Ulleung Basin of the Korean East Sea was suggested by Korea Institute of Geoscience and Mineral Resources early 2000s. A pilot production project is being planned as the world's second offshore hydrate production project. The water depth of the Ulleung Basin is 1500–2300 m; however, the hydrate occurrence zone is detected at relatively shallow depth (about 100–200 mbsf) for gas hydrate production. Moreover, the basin sediments exhibit high porosity, high compressibility and low permeability through the core samples and logging data. Therefore, there is high risk of geomechanical stability problems such as marine landslides, seafloor subsidence, and wellbore instability. In this study, the numerical modeling using the finite difference method is conducted to simulate methane hydrate production from the Ulleung Basin by depressurization method. The coupled mechanical-flow-thermal model incorporates the processes of hydrate dissociation, pore fluid flow, thermal advection, and geomechanical behaviors of hydrate-bearing sediments. The results indicate firstly the spatial distribution of the pore pressure and hydrate saturation, and secondly the volumetric strain in the area of the well head, and finally the degree of subsidence at seafloor during the production period (14 days).