Abstract Due to the complicated reservoir conditions in the oceanic methane hydrate (MH) reservoir in the Nankai Trough, Japan, the gas production rate for the economical extraction had not been achieved during the current field production tests in 2013 and 2017 using vertical wells. Therefore, this study aimed at the application of the horizontal wells to the oceanic MH production in the Nankai Trough. Since there existed three sub-hydrate-bearing layers with different physical properties (i.e., initial hydrate saturation, porosity, and intrinsic permeability) in the reservoir, some possible well configurations including single horizontal well patterns and dual horizontal well patterns were designed based on a multilayered geological model simulating the real oceanic MH reservoir in the Nankai Trough. Then, the effectiveness of these two kinds of well designs was verified via long-term simulations of the oceanic MH production by simple depressurization, and the optimal well configuration for each design was recommended. Furthermore, a combined method of depressurization and hot water injection was also tested based on the dual horizontal well pattern, and the sensitivity analyses indicated that a favorable gas production rate of 8.64 × 105 m3/day could be obtained within the first year, even under a relatively low injection temperature of 40 °C and a relatively small injection rate of 2 kg/s/m of well.

中文翻译：

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水平井在日本南海海槽大洋甲烷水合物生产中的应用

摘要 由于日本南海海槽大洋甲烷水合物（MH）储层条件复杂，目前2013年和2017年的直井现场试采尚未达到经济开采的产气率。因此，本研究旨在将水平井应用于南海海槽大洋MH生产。由于储层中存在三个具有不同物理性质（即初始水合物饱和度、孔隙度和固有渗透率）的亚水合物含水层，因此设计了一些可能的井网配置，包括单水平井网和双水平井网。模拟南海海槽真实海洋MH储层的多层地质模型。然后，这两种井设计的有效性通过对海洋 MH 生产的长期模拟通过简单降压得到验证，并推荐了每种设计的最佳井配置。此外，还基于双水平井网试验了降压和注热水联合方法，敏感性分析表明，即使在低气压下，第一年也可以获得8.64×105 m3/d的有利产气量。相对较低的注入温度为 40 °C，注入速度相对较小，为 2 kg/s/m 井。