东濮凹陷盐滑脱变形构造及其在油气勘探中的意义

东濮凹陷北部老第三纪时期发育了巨厚的盐岩沉积,构成了盐滑脱变形构造发育的物质基础。持续的拉伸应力作用,导致盐层上覆盖层差异沉降形成伸展型强制性褶皱。同时,由于盐层下伏层各次级断块的不断掀斜作用,盐层下滑剪切应力增大并超过了盐的抗剪强度,从而引发上覆盖层中犁式滑脱断层发育,以及在盐滑脱断层的上盘发育滚动背斜。盐滑脱变形构造这一特殊构造组合不仅为油气运移提供了良好的通道,而且也为油气聚集成藏提供了众多类型的含油气圈闭。如东濮凹陷已发现的断块油气藏、伸展型强制性褶皱拱顶圈闭油气藏、盐滑脱断层下盘圈闭油气藏、反向牵引断层圈闭油气藏及滚动背斜圈闭油气藏等。东濮凹陷北部盐滑脱变形构造的发育,形成了该凹陷中央隆起区的油气富集区。

Detached deformational salt structures and the significance in petroleum exploration in Dongpu depression

Thick salt deposits were developed in Paleogene in the northern Dongpu depression. Under sustained stretching stress, extensional forced folds were formed in the overlying formations of salt beds due to their differential subsidence.At the same time, continuous down-tilting of the secondary fault blocks in the underlying formations resulted in increasing of downslide shear stress and even exceeding the shear strength of salt beds, thus listric detached faults were formed in the overlying beds,and rollover anticlines were formed in the upper wall of salt detached faults. The detached deformational salt structures would not only constitute good migration pathway but also provide various traps for hydrocarbon accumulation,such as oil and gas reservoirs in fault block traps, extensional forced fold traps, rollover anticlinal traps, traps in the footwall of the detached faults and reverse drag fault traps in Dongpu depression. The development of detached deformational salt structures led to the formation of hydrocarbon enrichment in the central uplift zone of Dongpu depression