There have been several field tests worldwide to recover natural gas from marine gas hydrate reservoirs. The resulting intrinsic characteristics of the sediments are recognized as the major challenge hindering the large-scale gas production; of particular interest is the heterogeneous spatial distribution of natural gas hydrates in the sediments. Open issues still remain on mimicking the locally varying reservoir and revealing its role in the production process. Here in this work, reservoirs with a heterogeneous distribution of gas hydrates were prepared by controlling the uneven distribution of moisture in the fine natural sediments drilled from the South China Sea; special interest was put in the effects of the well location and depressurization schemes on the gas production performance. The results showed that the production efficiency in the heterogeneous reservoirs was significantly weakened compared with the homogeneous case; this was ascribed to the ununiform distribution of methane hydrates and pore fluids and a resulting locally different energy demand. Consequently, the production behavior showed a strong dependence on the depressurization location. A wellbore arranged in the layer with a high permeability can help improve the gas production efficiency by up to 38.25%. This yet resulted in an uneven temperature distribution; the rapid gas production and methane hydrate dissociation decreased the reservoir temperature to −3.33 °C. Further applying a cycling and step-wise depressurization could raise the minimum reservoir temperature up to 1.12 °C. Whereas, relieving temperature decline only through consuming the sensible heat in the reservoir and the surroundings was found to seriously weaken the gas production rate; an external heat supply was thus suggested in the hydrate-abundant regions for efficient gas production. Our findings expand the understanding of the spatially varying gas production behavior from the vertically heterogeneous hydrate-bearing fine marine sediments and may guide the operation of well location and depressurization schemes for field production in similar reservoirs.

从海洋天然气水合物储层中回收天然气，世界范围内进行了多项现场试验。由此产生的沉积物固有特征被认为是阻碍大规模天然气生产的主要挑战；特别令人感兴趣的是沉积物中天然气水合物的异质空间分布。模拟局部变化的储层并揭示其在生产过程中的作用仍然存在悬而未决的问题。在这项工作中，通过控制从南海钻探的细天然沉积物中水分的不均匀分布，制备了天然气水合物分布不均匀的储层；特别关注井位和减压方案对天然气生产性能的影响。结果表明，与均质情况相比，非均质油藏的生产效率明显减弱；这归因于甲烷水合物和孔隙流体的不均匀分布以及由此导致的局部不同的能源需求。因此，生产行为表现出对减压位置的强烈依赖。布置在高渗透层的井眼可提高产气效率达38.25%。这仍然导致温度分布不均匀；快速产气和甲烷水合物分解使储层温度降至-3.33 °C。进一步应用循环和逐步减压可以将最低储层温度提高到 1.12 °C。然而，发现仅通过消耗储层及周围的显热来缓解温度下降严重削弱了产气量；因此，建议在水合物丰富的地区使用外部供热，以实现有效的天然气生产。我们的研究结果扩展了对垂直非均质含水合物精细海洋沉积物的空间变化天然气生产行为的理解，并可能指导类似储层中油田生产的井位和减压方案的操作。