Abstract The lithological characteristics of subsurface formations control the variations in the permeability. Herein, the effect of lithological rhythm on gas production was numerically investigated for depressurization applied in a confined hydrate reservoir. The lithological rhythm structures from simple uniform, positive, and reserve rhythms to complex composite rhythms were designed. The water-to-gas ratio showed that economic feasibility of all rhythms varied with the expansion of the hydrate dissociation region. The depth of high permeability region affected the hydrate dissociation and temperature recovery. Therefore, the gas production rate of positive rhythm was higher than that of the uniform and reverse rhythms, while the reverse rhythm was economically more suitable in the later stages of the production. Furthermore, the gas and water production rates decreased with the increase in the permeability contrast. The number of composite rhythmic layers negligibly affected the gas production rate, while it significantly affected the hydrate saturation distribution, indicating an increasing hydraulic connectivity in the lateral direction that may lead to water breakthrough. Moreover, the rhythmic structures significantly affected the gas production rate and the economic feasibility, and controlled the developed depth of high hydraulic connectivity. Therefore, minor and large seepage pathways could form in a complex rhythm reservoir.

中文翻译：

---

密闭水合物储层直井减压岩性节律对采气动态的影响

摘要 地下地层的岩性特征控制着渗透率的变化。在本文中，数值研究了岩性节律对产气量的影响，以应用于承压水合物储层中的减压。设计了从简单的均匀、正向、储备韵律到复杂的复合韵律的岩性韵律结构。水气比表明所有节律的经济可行性随着水合物分解区域的扩大而变化。高渗透区的深度影响水合物的解离和温度恢复。因此，正节律的产气率高于均匀节律和逆节律的产气率，而逆节律在生产后期在经济上更适合。此外，产气率和产水率随着渗透率对比的增加而降低。复合韵律层的数量对产气速率的影响可以忽略不计，而对水合物饱和度分布有显着影响，表明横向水力连通性增加可能导致水突破。此外，节律构造显着影响产气速率和经济可行性，控制高水力连通性的开发深度。因此，在复杂的韵律储层中可能会形成大小不一的渗流路径。表明横向水力连通性增加，可能导致水突破。此外，节律构造显着影响产气速率和经济可行性，控制高水力连通性的开发深度。因此，在复杂的韵律储层中可能会形成大小不一的渗流路径。表明横向水力连通性增加，可能导致水突破。此外，节律构造显着影响产气速率和经济可行性，控制高水力连通性的开发深度。因此，在复杂的韵律储层中可能会形成大小不一的渗流路径。