Heat-assisted production strategy for oceanic methane hydrate development in the Nankai Trough, Japan

Abstract

The heat-assisted production strategy was considered to be an effective approach for the oceanic methane hydrate (MH) development. In this study, the combined method of depressurization and hot water injection was applied to the multilayered MH reservoir in the Nankai Trough, Japan, by using dual horizontal wells. Some possible well placements by placing the two wells in the same sublayer and different sublayers were designed in this study, and their effectiveness on the gas recovery enhancement was verified via long-term simulations of the oceanic MH production. It was found that when the two wells were placed in different sublayers, with some horizontal distance and the injection well locating above the production well, a favorable average gas production rate of 2.0 × 106 m3/day could be obtained, and was up to 100 times of that confirmed during the 2013 offshore MH production test in the Nankai Trough (2.0 × 104 m3/day), which indicated the high efficiency of the method proposed in this study. Furthermore, sensitivity analyses on the well locations suggested that the production well should be placed near the bottom of the hydrate reservoir, and a mild well spacing should be carefully determined, both to promote the heat transfer in the reservoir by making the maximum use of the injected hot water, and obtain a higher gas production rate.