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根据近年天然气水合物地质、地球化学和地球物理调查资料,结合2013年钻孔成果,分析南海东北部陆坡海底甲烷渗漏特征及其对水合物成藏的影响,探讨了水合物成因模式。研究表明,南海东北部陆坡海底存在高通量甲烷渗漏体系,甲烷渗漏引起的地质、地球化学指标异常非常明显。大量块状、脉状、结核状渗漏型水合物也被发现,其成因应与高通量甲烷渗漏有关。其典型成因模式是高通量甲烷以游离态渗漏方式沿断层或裂缝体系向浅部地层运移,以气烟囱形式在稳定带的不同部位形成渗漏区,甲烷在气烟囱顶端或侧翼聚集而形成水合物矿藏。影响水合物成藏的断层主要为长期活动的继承性正断层、层间断层以及与海底滑塌密切相关的活动断层,气烟囱对渗漏型水合物成藏有明显的控制作用。
According to the data of gas hydrate geology, geochemistry and geophysical survey in recent years, combined with the drilling results in 2013, the characteristics of methane leakage in the seabed in the southeastern South China Sea and its influence on hydrate accumulation are discussed, and the genesis pattern of hydrate is discussed. The results show that there is a high flux methane seepage system in the sea floor of the southeastern part of the South China Sea. The geological and geochemical indicators caused by methane seepage are very obvious. A large number of massive, vein and tubercular seepage hydrates have also been found, which should be related to high flux methane seepage. The typical causative mode is that high-flux methane migrates along the fault or fracture system to shallow formations in the form of free-state leakage, forms a seepage zone in different parts of the stable zone with gas chimneys, and methane accumulates at the top or flanks of the gas chimney Formation of hydrate deposits. The faults that affect the accumulation of hydrates are mainly inherited normal faults, interlaminar faults and active faults closely related to the submarine slump, and the gas chimneys can obviously control the formation of leakage hydrates.