Gas Production System From Methane Hydrate Layers by Hot Water Injection Using Dual Horizontal Wells

Abstract

Abstract In this study, we investigate a system of gas production from methane hydrate layers involving hot water injection using dual horizontal wells. Physical and numerical models simulating the gas production process from methane hydrate layers within a hot water chamber are proposed. Experiments with scaled two-dimensional physical models using an imitated hydrate layer (NaHCO3 ice formation) were performed to investigate fluid flow characteristics and production performance. The thermal simulator was used to simulate experimental chamber growth and field production. Numerical simulations for the processes were successfully performed with a two-component (water and oil or methane hydrates), three-phase (water, methane hydrates and methane gas) and three-dimensional model, matching the physical model. Results of the history-matched numerical simulations were in good agreement with data on production and chamber shapes obtained using the Intermediate3-Stone1 wettability model. Simulations of field production using dual horizontal wells 500 m in length were performed to evaluate cumulative gas production over 3 years of injection with 500 × 103 kg/day of hot water, which varied from 5 × 106 to 9 × 106 std m3. The production process appears economical, in view of the expected convective heat transfer from the chamber boundary and buoyancy force on dissociated methane gas. Introduction Recent studies confirm that conserved methane hydrate deposits in sedimentation layers at a depth of more than 200 to 300 m from the bottom of the sea floor can be utilized as novel natural gas resources. In-situ hydrate decomposition into water and gas is required to produce methane gas economically from these layers, since methane hydrate is a type of non-mobile solid energy resource. To trigger methane hydrate decomposition, decompression or temperature increase out of the equilibrium zone is necessary, while heat should be supplied for continuous dissociation. Accordingly, new gas production systems that supply heat continuously into the methane hydrate layers have been reported. The conventional methods of gas production to date include depressurization, inhibitor injection and thermal recovery.