Geomechanically Sustainable Gas Hydrate Production Using a 3D Geological Model in the Ulleung Basin of the Korean East Sea

Although various simulation studies on gas hydrate production have been conducted, a single vertical well in the cylindrical system has been adopted in most research. However, this system has a limited ability to predict commercial production in gas hydrate reservoirs. In order to facilitate commercial production, a field-scale reservoir model with a multi-well system must be constructed using geological data, such as seismic data, well logging data, core data, etc. The depressurization method is regarded as a practical production strategy because it has high levels of production efficiency and economical effectiveness. However, this method can lead to subsidence due to the increased effective stress. In this work, we studied a production simulation strategy for commercial gas hydrate production. A three-dimensional geological model with a realistic field scale is constructed using seismic and well logging data from the Ulleung Basin of the Korean East Sea. All of the grids are refined in the I and J direction, and the grids near the production well are very small to consider realistic hydrate dissociation. The cyclic depressurization method is adopted for the increase in the geomechanical stability, rather than the non-cyclic depressurization method. Various case studies are conducted with alternating bottomhole pressures for the primary and secondary depressurization stages over 100 days. Geomechanical stability is significantly enhanced, while cumulative gas production is relatively less reduced or nearly maintained. In particular, all cases of the cumulative gas production at 6 MPa during the secondary depressurization stage are similar to the non-cyclic case, while the geomechanical stabilities of those cases are restored. This study is thought to have contributed to the development of technology for commercial gas hydrate production with a geomechanical stability study using a reservoir-scale model with a multi-well system.