Abstract:

According to 3D high-resolution seismic data, polygonal faults were discovered firstly in Qiongdongnan Basin of the northern continental margin of South China Sea by using the coherent slice and flattening technique. The polygonal fault is tensional fault system with small throws, which is of nontectonic origin. The polygonal fault in the deep-water area of Qiongdongnan Basin has a length from 150 meters to 1500 meters, an interval space from 50 meters to 3 000 meters, a fault throw from 10 meters to 40 meters and a dip from 50° to 90° in three layers. Qiongdongnan Basin underwent the syn-rift stage and the post-rift thermal subsidence stage. The tectonic faults were undeveloped in the post-rift stage, which leads to the absence of pathway between source rock and reservoir. The unfavorable migration system is one of the factors restricting oil and gas accumulation in the post-rift stage. The polygonal fault can efficiently serve as the pathway for linking source rock and reservoir to enhance hydrocarbon migration along the polygonal fault. So it is very favorable for oil and gas migration and accumulation in the post-rift stage of the northern South China Sea.

Key words: Qiongdongnan Basin, deep-water area, polygonal fault, oil-gas migration pathway, oil-gas accumulation

摘要：

在高精度的三维地震资料基础上,利用层拉平和相干切片技术,在南海北部琼东南盆地首次发现多边形断层。多边形断层是一种非构造成因的断距微小的张性断层。琼东南盆地深水区的多边形断层长度为150～1500m,间距为150～3000m,断距为10～40m,倾角为50°～90°,发育在3个层位。琼东南盆地可以分为裂谷断陷期和裂后热沉降期两个演化阶段;裂后热沉降期构造断裂不发育,缺乏连接烃源岩和储层的通道,不利的油气疏导系统成为制约该期成藏最主要的因素之一。多边形断层的存在可以有效地解决这个问题,它可作为油气运移的疏导体系,使下部生油层中的油气向上运移成藏,对南海北部裂后热沉降期油气运聚具有重要的意义。

关键词: 琼东南盆地, 深水区, 多边形断层, 油气运移通道, 油气成藏