Methane Production From Marine Gas Hydrate Deposits in Korea: Thermal-Hydraulic-Mechanical Simulation on Production Wellbore Stability

During methane production induced by depressurization, significant mechanical responses of hydrate-bearing sediment (HBS) such as large volume contraction and subsidence can possibly be generated. Moreover, this phenomenon is further exacerbated by strength and stiffness reduction in the HBSs as hydrate dissociation advances. As a result, the highest compressive strength is concentrated in the vicinity of the production wellbore. Therefore, it is essential to address and evaluate the mechanical responses of HBSs and conduct a stability analysis of the production well during depressurization and hydrate dissociation to prevent the destruction of production facilities and consequent leakage of methane gas. In this study, a reservoir-scale thermal-hydraulic-mechanical coupled simulation using FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) was conducted to evaluate the mechanical responses of HBSs and the stability of a wellbore during methane production by depressurization at the Ulleung Basin. The structural design and mechanical properties including the dimensions of wellbore components and interface properties related to the interaction behavior between the sediment and wellbore were considered in the three-dimensional model.