Focused Fliud-Flow Escape System And Sediments Deformation In Deep-Water Basins Of Northern South China Sea

The deep-water area of the Northern South China Sea (NSCS) is rich in hydrocarbon and gas hydrate resources. However, because the study of deep-water hydrocarbon and gas hydrate in NSCS is only carried out in recent several tens years, many important scientific and practical topics should be urgently studied. This thesis try to study the characteristics, classifications, influenced factors and their results (soft sediments deformation and mega-pockmarks) of focused fluid-flow escape systems in NSCS, including southern Qiongdongnan Basin, northern Zhongjiannan Basin and the deep-water area of Pearl River Basin, basing on high-resolution 3D seismic data, 2D seismic data, multibeam data and well data. Through the study, the thesis concludes that: (1) the focused fluid-flow escape systems in NSCS including tectonic faults, polygonal faults, carbonate dissolution, sandstone intrusion, igneous intrusion and pipes, and the escape systems such as, polygonal faults carbonate dissolution and sandstone, are first reported in NSCS; (2) documented the largest pockmarks in the worldwide. Here, these pockmarks are named mega-pockmarks. The average diameter of mega-pockmarks is above 1600 m and the average depth is ca. 100 m. The pockmarks are as the manifestation of fluid-flow escape on the seabed, which are important for the study of hydrocarbon exploration. The genesis of mega-pockmarks in the study area is caused by strong fluid-flow escape and bottom current together; (3) first documented a new type of soft sediment deformation. The soft sediment deformation is showed as depression-ridge structures on the seabed. The depressions are multi-kilometers in diameter and several tens meters in depth. Basing on careful observation and analysis of seismic data and multibeam data, we propose that this soft sediment deformation is attributed to fluid-flow escape and differential compaction, which are triggered by the earthquakes and uplifts related with the activities of Red River Strike-Slip Fault. The study of focused fluid-flow escape systems and soft sediment deformation is very important, because (1) they are usually related with hydrocarbon and gas hydrate accumulation and destroy and (2) they can cause seabed instabilities which should be considered when explorationists and engineers design wells and pipe locations.