Simulation Study on UBGH2-6 Deposit in the Ulleung Basin Considering Hydrate Bearing Sediments and Saturation Distribution Characteristics

Reservoir simulation models with a heterogeneous distribution of hydrate saturation were built based on the complex geology model of the UBGH2-6 deposit in the Ulleung Basin, Korea. Because of the hydrate production by the depressurization method, 74.6% of the cumulative gas production was produced from a thin layer (less than 0.2 m) with low hydrate saturation. A reservoir simulation was performed to evaluate the effect of hydrate saturation and thin-layer structure on gas production. In the case of homogeneous distribution of hydrate saturation, the gas can be produced from all sand layers because of the increasing effective permeability with decreasing hydrate saturation. Production analysis based on various thin layer structures revealed a decrease in the cumulative gas production by 40% after removal of a thin layer with thickness of 0.1 m from the base model. As the radius of the thin layer increases, the hydrate dissociation front can be propagated more by increasing the influence radius of the bottomhole pressure. Considering the proportion of gas production in the thin layers, a detailed investigation of thin layers as the production target is required to establish a strategy for gas hydrate production in the UBGH2-6 deposit.