Gas production from methane hydrate sediment layer by thermal stimulation with hot water injection

A gas production system from methane hydrate layer by hot water injection using a pair of dual-horizontal wells has been proposed. Experiments with physical and numerical reservoir models have been carried out in order to simulate gas production characteristics with the system. In the experiments, the reservoir models consisting with ice of NaHCO₃ aqueous solution formed in glass-bees porous medium were used to express the dissociation heat of methane hydrate by melting one of ice. Gas production at dissociation front of methane hydrate was simulated by gas generation with a chemical reaction of NaHCO₃ included in the ice and HCl mixed in hot water injected at ice melting front. In the system, a dissociated region including the dual horizontal wells filled with hot water, named as hot water chamber, was generated to produce gas continuously. The gas production rate has the maximum peak just after breakthrough of injected water between dual horizontal wells, then it declined and gas was produced by almost constant rate. We have successfully developed the numerical model, and matched the history of physical gas production. Moreover, numerical simulations of gas production by the hot water injection into a Nankai Trough sediment layer model using a pair of dual horizontal wells 500m in length were carried out for a methane hydrate reservoir of 20 m in layer thickness, 46% of average methane hydrate saturation, 100 and 25 md in horizontal and vertical absolute permeabilities, respectively. The cumulative gas production is simulated as 5 × 10⁶ std-m ³ for initial two years. Furthermore, a new gas production scheme, which uses four pairs of dual horizontal wells in radian arrangement in a methane hydrate sediment layer with area of 1kmx1km located at Nankai Trough, has been presented and evaluated with the numerical simulation as the cumulative gas production for 15 years is 1.3×10⁸ std-m³.