Abstract Integrated three-dimensional seismic, logging, sediment cores, and geochemical testing data were collected from Guangzhou Marine Geological Survey 3 and 4 hydrate drilling expeditions and used in this study for a comprehensive investigation of the geological and geophysical features and accumulation mechanism of hydrates in the first offshore gas-hydrate production test region (GHPTR) in the Shenhu area of the South China Sea. Seismic signatures indicative of disseminated hydrates and free gas include the bottom simulating reflector (BSR), gas chimney, and mud diapir associated with enhanced seismic reflections, acoustic blanking, masking, and chaotic appearance have been observed. The acoustic travel-time responses, density, and compensated neutron three porosity log analysis, high-precision grid tomography inversion analysis, and constrained sparse spike inversion confirm the presence of free gas below the gas-hydrate-bearing zone (GHBZ). Free-gas-bearing zones have significantly different p-wave impedances and low-velocity anomalies than the overlying GHBZ and surrounding strata. These anomalous zones are controlled by the structural attitude of the reservoir strata, which are characterized as inter-bedded stratigraphic units. Variations in the type and geological characteristics of the hydrocarbon migration pathways were observed between sites W18 and W19 on the western ridge and sites W11 and W17 on the eastern ridge in the GMGS study area. The efficiency of gas migration in the western ridge may be higher than that in the eastern ridge, resulting in variations in hydrate gas types, thickness of the GHBZ, and gas migration flux and accumulation. Except for site W11, hydrates were recovered below the structure I inferred BSR at sites W17, W18, and W19. The gas-hydrate stability zone calculations reveal that the structure I hydrate stability zone differs from the BSR depth and is generally shallower than the base of the logging anomaly, indicating the coexistence of structure I and II hydrates. The BSR is not indicative of the BGHSZ; it is rather regarded as a transitional indicator of structure I and II gas hydrates in the GHPTR. The appearance of free gas and hydrates below the structure I inferred BSR indicates that the Shenhu area is characterized by a complex hydrate formation and accumulation system resulting from the supply of biogenic and thermogenic gases. Despite fine-grained host sediments predominating the GHPTR, the coupling of favorable conditions including efficient hydrocarbon generation, sufficient gas supply, multiple pathways for gas migration, and relatively high reservoir porosity have led to the development of highly saturated gas-hydrate accumulations within relatively thick sedimentary sections, which demonstrates a significant resource potential.

中文翻译：

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南海北部神狐海域第一个海上天然气水合物生产试验区天然气水合物的地质地球物理特征及成藏控制

摘要 本研究收集了广州海洋地质调查局三、四水合物钻探综合三维地震、测井、沉积岩心、地球化学测试数据，综合研究了广州海洋地质调查局水合物地质地球物理特征及成藏机制。南海神狐海域首个海上天然气水合物生产试验区（GHPTR）。表明弥散水合物和游离气的地震特征包括底部模拟反射器 (BSR)、气烟囱和与增强的地震反射、声学消隐、掩蔽和混沌外观相关的泥底辟。声波走时响应、密度和补偿中子三孔隙度测井分析，高精度网格层析成像反演分析，约束稀疏尖峰反演证实了含天然气水合物带 (GHBZ) 下方存在游离气体。与上覆的 GHBZ 和周围地层相比，含游离气区具有显着不同的 p 波阻抗和低速异常。这些异常带受储集层构造姿态控制，表现为互层地层单元。GMGS研究区西部山脊W18、W19站点与东部山脊W11、W17站点间油气运移路径类型和地质特征存在差异。西脊的天然气运移效率可能高于东脊，导致水合物气体类型、GHBZ厚度、气体运移通量和聚集发生变化。除了站点 W11，在位点 W17、W18 和 W19 处，在 I 推断的 BSR 结构下方回收了水合物。天然气水合物稳定带计算表明，Ⅰ型水合物稳定带与BSR深度不同，一般比测井异常基底浅，表明Ⅰ型和Ⅱ型水合物共存。BSR 并不代表 BGHSZ；它被认为是 GHPTR 中 I 型和 II 型天然气水合物的过渡指标。构造Ⅰ推断BSR下方有游离气和水合物的出现表明神狐地区具有复杂的水合物形成和聚集系统，由生物气和热气供给形成。尽管细粒宿主沉积物在 GHPTR 中占主导地位，但有利条件的耦合包括有效的碳氢化合物生成，