南海北部神狐海域水合物储层沉积环境及其对水合物富集的指示意义

Sedimentary environment of gas hydrate reservoirs in the Shenhu area, northern South China Sea, and its implications for hydrate accumulation

  • 摘要: 绝大多数的海域天然气水合物资源蕴藏于深水细粒沉积物中,在水合物形成的理化条件及气源条件之外,沉积环境的变化对水合物的富集起到潜在的控制作用。本研究选取位于南海北部神狐海域的SH-W07-16站位,基于水合物饱和度数据,同时利用沉积物样品的粒度参数、全岩及黏土矿物组分、地球化学和生物组分数据,分析识别出水合物储层及非储层段的沉积过程及物源差异,分析沉积层段海平面、气候及季风等古海洋环境变化趋势,以期揭示沉积环境对水合物富集成藏的控制机理。研究结果表明,研究区水合物储层受细粒浊积过程控制,形成于气候寒冷、低海平面、冬季风盛行的冰期;而非储层受控于等深流等牵引流过程,形成于气候温暖、高海平面、夏季风盛行的间冰期;洋流活动影响不同沉积时期的物源供应,使得非储层段沉积物含有更多对水合物形成起到抑制作用的伊蒙混层,不利于水合物成藏。洋流、气候、季风等古环境变化通过引起沉积过程及物源的转换,影响储层及非储层之间沉积物组成来控制水合物形成,为揭示细粒沉积物中水合物富集成藏规律的研究提供了新视角。

     

    Abstract: The majority of gas hydrates occur in deep-water fine-grained sediments. Beyond the basic physical-chemical and gas source conditions, sediment mineral composition and sedimentary processes also play key roles in controlling hydrate accumulation and are closely linked to environmental changes. Hydrate saturation data from Site SH-W07-16 in the Shenhu area in the northern South China Sea were used to distinguish between hydrate-bearing and non-bearing layers; the sediment grain size, mineral composition, geochemical, and biological data were applied to analyze their differences in depositional processes and sediment sources, based on which past changes in sea level, climate, and monsoons were revealed to explore how these factors influence hydrate formation. Results show that hydrate-bearing layers are fine-grained turbidites formed during the glaciation period with cold climate, low sea levels, and strong winter monsoons. However, the non-hydrate layers formed under the influence of contour currents during interglaciation periods with warm climate, high sea levels, and dominant summer monsoons. Changes in ocean currents affected sediment supply, increasing I/S mixed-layer clays in non-hydrate layers, which hindered gas hydrate formation. Overall, variations in ocean currents, climate, and monsoon intensity regulate sedimentary processes and provenance, thereby controlling the accumulation of gas hydrates. This study presents a novel perspective on hydrate enrichment within fine-grained sediments.

     

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