The 3D seismic data acquired in the central Qiongdongnan Basin, northwestern South China Sea, reveal the presence of shallow gas hydrate, free gas, and focused fluid flow in the study area, which are indicated by multiple seismic anomalies, including bottom simulating reflectors, polarity reverses, pulldowns, minor faults, and gas chimneys intensively emplaced within the shallow strata. A new cold seep is also discovered at approximately 1520 m water depths with an ~40 m wide crater in the west part of the study area. Water column imaging, seafloor observation, and sampling using the remotely operated vehicle “Haima” demonstrate ongoing gas seepages and shallow gas hydrates at this site. Thermogenic gas in the study area migrates from the deep reservoir through the gas hydrate stability zone along deep faults and gas chimneys, forms shallow gas hydrate and free gas, and sustains localized gas seepage within this cold seep. The results provide insight into the relationship between shallow gas hydrate accumulation and deep hydrocarbon generation and migration and simultaneously have important implications for hydrocarbon explorations in the Qiongdongnan Basin, northwestern South China Sea.

中文翻译：

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南海西北部琼东南盆地集中流体流动、浅层天然气水合物与冷渗流

在南海西北部琼东南盆地中部采集的三维地震数据揭示了研究区存在浅层天然气水合物、游离气和集中流体流，这些地震异常表现为底部模拟反射层、极性倒转、下拉、小断层和集中分布在浅层中的气烟囱。在研究区西部约 1520 m 水深处还发现了一个新的冷渗漏，有一个约 40 m 宽的陨石坑。使用遥控车“海马”进行水柱成像、海底观测和采样，展示了该地点正在进行的气体渗漏和浅层天然气水合物。研究区热成因气沿深部断层和气烟囱从深部储层运移通过天然气水合物稳定带，形成浅层天然气水合物和游离气，并在该冷渗流中维持局部气体渗流。研究结果有助于深入了解浅层天然气水合物成藏与深层油气生运移之间的关系，同时对南海西北部琼东南盆地油气勘探具有重要意义。