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

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.