南海北部陆坡东沙海域海底丘状体气体与水合物分布

海底丘状体在天然气水合物发育区是一种常见的微地貌，对丘状体的研究有助于理解海底流体渗漏模式以及水合物的赋存规律。本文研究南海北部陆坡东沙海域天然气水合物发育区海底丘状体的特征及其与水合物的关系。研究所用的数据包括准三维多道地震数据、多波束数据以及浅地层剖面数据。在多波束海底地形图上，丘状体表现为局部的正地形，直径大约为300 m，高出周围海底约50 m。浅地层剖面上存在明显的声空白以及同相轴下拉现象，指示了海底丘状体气体的分布以及流体运移的路径。丘状体周围明显的BSR表明局部区域可能发育有水合物，水合物钻探结果也证实了这一推测。三维多道地震剖面上，丘状体正下方存在空白反射区域，这与泥火山的地震反射特征类似。但空白反射区域内存在强振幅能量，而且丘状体正下方存在连续的反射层，这表明该丘状体并非泥火山成因。综合钻探结果以及三维地震成像结果，认为水合物形成过程引起的沉积物膨胀以及海底碳酸盐岩的沉淀是形成该丘状体的主要原因。

Gas and gas hydrate distribution around seafloor mound in the Dongsha area, north slope of the South China Sea

Seafloor mound is common in gas hydrate reservoirs. The investigation of seafloor mound can help to understand the pattern of fluid seepage and the occurrence of gas hydrate. This paper investigated a seafloor mound in the Dongsha area, north slope of the South China Sea, where gas hydrate has been sampled. The data used include 3D seismic, multi-beam bathymetric and sub-bottom profiler data. On the multi-beam bathymetric data, seafloor mound manifests itself as an outstanding elevated morphologic feature, with height of ~50 m and diameter of ~300 m. Acoustic blanking zone in the sub-bottom profiler indicates the distribution of gas and the fluid migration pathway. Clearly observable BSR around the seafloor mound suggests the localized occurrence of gas hydrate, which is verified by the drilling program. Though acoustic blanking is also presented in the 3D seismic profiles, enhanced amplitude and continuous reflector directly beneath the mound indicates that the mound is probably not originated from mud volcano. Sediments expansion due to the formation of gas hydrate may be a better explanation.