南海北部陆架南北卫浅滩的成因及油气地质意义

世界范围内的陆架调查已经清楚,陆架浅滩是普遍发育于陆架区的一种海底地貌类型。在中国陆架上发育多个知名浅滩,这些浅滩和现今动力条件处于动态平衡状态,为现今潮流沉积体系。然而,南海北部陆架的南北卫浅滩在地貌上被称为陆架浅滩,但其成因却和其他陆架浅滩有着根本不同。根据地震剖面解释结果,本文指出,南海北部珠江口东南陆架上发育的南卫滩、北卫滩和惠州滩都属于构造地形,其下部各对应一个底辟构造。这3个底辟构造并不是孤立的,而是在深部属于同一个较大的背冲构造。这个背冲构造位于南北卫滩的下方,其上几个突出的底辟,则和本文讨论的南卫滩、北卫滩和惠州滩相对应。南卫滩、北卫滩和惠州滩在成因上具有统一的深部背景,从而在平面上构成一个统一的底辟系统,本文称为南北卫滩底辟系统。该底辟系统以北卫滩为中心,包括南卫滩、惠州滩和陆丰滩,形成一个大致呈圆形,直径约50km的区域。在构造上,该底辟系统位于珠一坳陷和东沙隆起之间。南北卫滩底辟系统的发育起因于东沙隆起后在南海东北部形成的挤压应力环境。底辟系统的发育活化了惠陆-东沙含油气系统的输导层,并重新调整了油气运移的势差和势梯度,在环绕南北卫滩底辟系统一定距离的圆周上形成一个有利于油气聚集的环带。已知的油气田基本分布于这个环带上。下一步的油气勘探方向应该考虑围绕这个环带重点展开。同时,应该考虑在南北卫滩底辟系统的中心带内开展气藏的勘探工作。

Formation and Petroliferous Effect of Nanbeiwei Shoal on the northern South China Sea Shelf

Worldwide continental shelves have been investigated and shelf shoals are a kind of submarine geography commonly developed within continental shelf areas.Several known shoals have been developed within Chinese continual shelf.These shoals have set up a dynamic equilibrium system with present dynamic conditions,forming a modern tidal current deposit regime.However,the Nanbeiwei shoal on the shelf of the northern South China Sea is named continental shelf shoal,but its genesis is completely different from other continental shoals.Based on the seismic data,this paper indicates that Nanwei,Beiwei,and Huizhou shoals developed within the east and south shelves belong to structural landform,with each shelf corresponding to one underlying diaper.They do not occur independently but belong to relative larger thrusting structure at depth.The thrusting structure is located beneath the Nanwei and Beiwei shoals with several diapers,which respond to the Nanwei,Beiwei and Huizhou shoals discussed in this study.The Nanwei,Beiwei and Huizhou shoals have the same deep setting,constituting a united diapir system on plane,and this study names it Nanbeiwei shoal diapir system.This diapir sytem forms roughly round shape with Beiwei at center and Nanwei,Huizhou and Lufeng around the margin,and is confined within an area of 50 km in diameter.Tectonically,the diapir system rests between Zhuhai depression and Dongsha uplift.Development of the Nanbeiwei diapir system is attributed to a compressed stress setting in the northeast of South Sea by the Dongsha uplift.This system activated transport layer of the Huilu-Dongsha petroleum system,and re-adjusted potential difference and gradient of oil and gas migration,forming a preferential zone for hydrocarbon accumulation near to the diapir system.The known oil and gas fields are basically distributed around this zone.Therefore,future oil and gas exploration should aim at this zone,as well as within the central area of the Nanbeiwei diapir system.