【摘要】 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.更多还原

【Abstract】 Gas hydrate samples were obtained firstly in China by drilling on the northern margin of South China Sea (SCS).To understand the formation mechanism of this unique accumulation system,this paper discusses the factors controlling the formation of the system by accurate geophysical interpretation and geological analysis,based on the high precision 2-D and 3 D multichannel seismic data in the drilling area.There are three key factors controlling the accumulation of the gas hydrate system in fine grain sediment:(1) large volume of fluid bearing methane gas joins the formation of gas hydrate.Active fluid flow in the northern South China Sea makes both thermal gas and/or biogenic gas migrate into shallow strata and form hydrate in the gas hydrate stability zone (GHSZ).The fluid flow includes mud diapir and gas chimney structure.They are commonly characterized by positive topographic relief,acoustic turbidity and push-down,and low reflection intensity on seismic profiles.The gas chimneys can reach to GHSZ,which favors the development of BSRs.It means that the active fluid flow has a close relationship with the formation and accumulation of gas hydrate.(2) The episodic process of fracture plays an important role in the generation of gas hydrate.It may provide the passage along which thermogenic or biogenic gas migrated into gas hydrate stability zone (GHSZ) upward.And it increases the pore space for the growth of hydrate crystal.(3) Submarine landslide induced the anomalous overpressure activity and development of fracture in the GHSZ.The formation model of high concentration gas hydrate in the drilling sea area was proposed on the basis of above analysis.更多还原