A gas production system from methane hydrate (MH) sediment layers by combination method with hot water injection and bottom hole pressure control at production well using radial horizontal wells has been proposed.

Firstly, gas production characteristics by the depressurization method with bottom hole pressure control have been evaluated by numerical simulations of cylindrical homogeneous MH layer model. The cumulative production gas amount or MH recovery ratio were limited with the pressure reduction from MH equilibrium pressure, because the sediment pressure must be suppressed to keep mechanical stability of sediment layers under the sea bottom. Furthermore, effects of numerical bock modeling and averaging physical properties of MH layers have been discussed as those numerical simulation errors against the original deposit model show a safety side results to evaluate economic issues in gas amount and production rate.

By applying the present production system with combining hot water injection and bottom hole pressure control, the numerical simulation results showed that dissociated region including two wells filled with hot water, named as hot water chamber, is expanded outer ward from the area center of MH layer with continuous gas production. The simulations on gas production by injecting 85°C hot water into the MH layer with 1km× 1km and 20m in thickness by using four pairs of dual horizontal wells 500m in length were carried out. It was found that 2MPa pressure reduction from MH equilibrium pressure made the gas production 2.2 times compared with the case of hot water injection only without pressure reduction control.

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