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我国在南海北部陆坡的细粒沉积物中首次钻获水合物样品,为深入了解这一特殊成藏体系的形成机制,本研究以钻探区域高精度的二维和三维多道地震资料为基础,通过精细的地球物理解释和地质分析,探讨了该天然气水合物系统的成藏控制因素.细粒沉积物天然气水合物系统中水合物的富集过程存在着三个特殊的控制因素:(1)大面积丰富的含甲烷流体的参与.南海北部深水盆地广泛存在的异常热流体活动促使深部的热解成因天然气或浅层的生物成因气运移到水合物稳定带,有利于水合物的发育.热流体活动表现为底辟和气烟囱构造,在地震剖面上,表现为地震声学模糊带、同相轴下拉或中断、顶部出现反射亮点,这些构造直抵水合物稳定带.在气烟囱或底辟构造顶部通常有BSR伴生,说明热流体活动与水合物成藏具有密切关系;(2)断裂构造的发育在水合物稳定带中细粒沉积物的成核和生长过程中具有重要的作用,一方面促进稳定带流体的垂向和侧向运移,另一方面,构造裂缝可能成为成核和生长过程的空间;(3)大型海底滑坡导致了地层中超压流体活动和构造裂缝的发育,从而促进了水合物富集.在上述研究基础上,提出了南海北部水合物钻探区高饱和度水合物成藏模式.
For the first time, hydrate samples were obtained from fine-grained sediments on the northern slope of the South China Sea. Based on the high-precision 2D and 3D multi-channel seismic data of the drilling area, in order to understand the formation mechanism of this special reservoir system, Through detailed geophysical interpretation and geological analysis, the controlling factors of hydrocarbon accumulation in gas hydrate system are discussed.The three specific controlling factors exist in the process of gas hydrate enrichment in fine-grained gas hydrate system: (1) Large-scale enrichment of methane-containing fluids The extensive presence of abnormal hydrothermal fluids in deep-water basins in the northern South China Sea prompted the deep pyrolysis of natural gas or shallow biogenic gas to migrate into the hydrate stable zone, contributing to hydrate development. The thermal fluid activity is characterized by the structure of diapirs and gas chimneys, which are characterized by the seismic acoustic fuzzy band, the pull-down or interruption of seismic events at the seismic section, the reflected bright spots at the top, and these structures reach the hydrate stability zone. At the top of the gas chimney or diapir structure Usually associated with BSR, indicating that thermal fluid activity and hydrate accumulation are closely related; (2) the development of fault structure in the hydrate stability zone fine particles On the one hand, it promotes vertical and lateral migration of fluids in the stable zone; on the other hand, structural fractures may become space for nucleation and growth process; (3) Large-scale seabed Landslides lead to the development of overpressure fluid activity and tectonic fractures in the strata, which promotes the enrichment of hydrates.On the basis of the above studies, a model of high saturation hydrate accumulation in the northern South China Sea hydrate drilling area is proposed.