利用高精度的三维地震资料,在非洲下刚果盆地上新统-更新统识别出一种多边形断层系统.它们在地震剖面上为微小断距的张性断层,主要发育在深水、半深水环境中沉积的细粒泥质岩中.利用地震相干技术,显示其平面特征为多边形形状;断层无优势走向,属非构造成因;在一个断层层段内,具有上密下疏的特征.研究区多边形断层的形成模式是:顶部泥岩层细粒沉积物正常压实,形成致密层,阻止了下部泥岩层收缩流体的排泄,造成欠压实状态,逐渐形成多边形断层.随着地层的演化,还可以在已发育断层层位之下发育新一轮的多边形断层,同时引发上方原先的多边形断层再次活动.多边形断层的发育程度主要取决于沉积物颗粒的大小和矿物成分,随着颗粒的减小和蒙脱石含量的增加,多边形断层的发育程度会增强.多边形断层不仅可以作为油气运移的通道,而且还可以使油气沿断层向上运移后形成气水化合物,对后期的油气成藏产生封盖作用.

Based on high-resolution 3D seismic data, a sort of polygonal fault systems has been identified in Pliocene-Pleistocene strata in Lower Congo Basin. Within the seismic sections, the polygonal fault systems are characterized by small extensional faults,which develop in pelagic or hemipelagic sedimentary environment with fine-grained mud-dominated sediments. Within the seismic-time coherent slices, polygonal shapes are identified in map view. The orientations of the polygonal faults are almost isotropic, which indicatesa non-tectonic origin. In an identical highly-faulted interval, it is characterized by dense in the upper and rare in the lower. The development mechanism for the polygonal fault systems is inferred to be that due to the volumetric contraction induced by syneresis during early burial of compaction of fine sediments at the top, dense layers formed and resisted against the drainage of fluid out from undercompacting muds tone in the lower, which gradually resulted in polygonal faults. With evolution of strata, new polygonal faults could develop under previous polygonal faults and simultaneously the upper polygon faults would be active once again. The factors dominating the development of polygonal fault systems are mainly the sizes of sediment grain and the composition of minerals. With decreaing grains and increasing montmorillonite, polygon faults will develop further in the extent. Polygonal faults not only can be as pathways of hydrocarbon migration but also form overpressure that seals hydrocarbon to escape.