海洋浅表层天然气水合物成藏特征

按照天然气水合物形成的气体疏导方式划分，渗漏系统是海洋浅表层天然气水合物藏形成的主要模式。关键成藏要素包括温压场、气源等，温压场主要控制天然气水合物成藏的平面分布和纵向分布；海底热流低值区有利于形成天然气水合物，但在海底热流超高的海域，只要有充足的气源供给，在高甲烷通量区深海浅表层也可以形成天然气水合物藏，而且往往与泥火山、气烟囱等特殊地质体伴生，形成致密的数米厚层状天然气水合物藏。浅表层天然气水合物藏气源主要是有机热解成因气，一般其深部均发育有成熟的含油气盆地，有烃源层广泛分布，并且干酪根发生过明确的生烃过程，形成的热解甲烷气通过断层、气烟囱等破碎带垂向运移通道渗漏上升，在温压场控制的相平衡区形成天然气水合物藏，因此，海底热流值较高的海盆也是浅表层天然气水合物藏形成的有利海域。

CHARACTERISTICS OF SHALLOW GAS HYDRATES ACCUMULATION IN THE SEA

Based on the migration ways of the gas responsible for the gas-hydrate formation, the leaking-type accumulation system is the major model for the formation of the shallow gas-hydrate reservoirs, and it would be influenced by multiple critical controlling factors including temperature-pressure field, gas source, et al. The temperature-pressure field mainly influences the gas-hydrate distribution in plane view and vertical section. The area with low heat flow is favorable for the formation of gas hydrates, while the deep-sea area with very high heat flow and high-flux methane can also deposit dense, thick-bedded (up to several meters) shallow gas-hydrate if there are abundant gas supply, and this type of gas-hydrate reservoirs are generally accompanied with special geological bodies, such as mud volcanoes and gas chimneys. The gas responsible for the shallow gas-hydrate formation is dominated by organic pyrolysis gas, since shallow gas-hydrate reservoirs are generally presented above mature oil- and gas-bearing basins, in which source rocks are widespread and characterized by the kerogen having defined hydrocarbon generation processes, and the generated pyrolysis methane would migrate upwards along the broken zones like faults, gas chimneys, and then form gas-hydrate at the shallow layers where temperature-pressure fields are appropriate for the gas-hydrate deposition, thus the deep-sea basin with very high flow can also be favorable for the formation of the shallow gas hydrates.