松辽盆地三肇凹陷青一段多边形断层的发育及其油气地质意义

摘要

松辽盆地青一段发育大量密集分布的小型张性断层系，其成因一直以来颇受争议。本文选取松辽盆地三肇凹陷为研究区，通过新连片三维地震剖面精细解释及沿层相干切片分析等手段，详细描述了三肇凹陷青一段密集张性断裂系统的剖面和平面特征，提出：①青一段张性断裂系主体为非构造成因的多边形断层，其成因可能是由青山口组青一段泥岩超压幕式排烃破裂所导致，同时盆地构造反转活动对断层发育特征具有重要影响；②凹陷内多边形断层主要发育于嫩江组沉积末期，明水组沉积末期盆地强烈构造反转致使早期形成的多边形断层再活动，且对部分多边形断层的发育进行改造；③多边形断层起到沟通青一段烃源岩和分别位于其上部与下部的葡萄花、扶杨2个油气储层的作用，是凹陷内油气成藏的重要运移通道；④嫩江组沉积末期，超压使油气通过多边形断层从青一段短距离向下部扶杨储层“倒灌”运聚成藏；明水组沉积末期，超压导致油气沿重新开启的多边形断层向上部葡萄花储层或向下部扶杨储层运移聚集形成油气藏，同时垂向延伸较长的多边形断层对下部扶杨油藏可能具有一定的破坏作用。%Numerous small-scaled, extensional faults occur densely in the mudstone layer of the Qingshankou 1st member (Qn1) in Songliao Basin. Its attribute and genetic mechanism are highly concerned but still controversy. The high-resolution 3D seismic datasets of a new block that covers most of the Sanzhao sag of Songliao Basin is studied., The characteristics of the profile and plane geometry of the extensional fracture system in the Sanzhao sag were depicted in detail through fine seismic interpretation using coherent technology. Based o the results, we proposed that:(1) The extensional fault system is mainly polygonal fault, which probably resulted from rupture pressure related to the episodic hydrocarbon-expulsion from the mudstone of Qn1. However, the tectonic inversion in Songliao Basin may also contribute to the formation and development of the polygonal fault system;(2) The polygonal faults were mainly formed by the end of deposition period of the Nenjiang Formation, and some experienced vertical direction propagation caused by the strong tectonic inversion at the end of deposition period of the Mingshui Formation; (3) The polygonal faults connect the Qn1 hydrocarbon source rock with the underlying Fuyang oil layer and the overlying Putaohua oil layer, and thus are important migration channels for the oil and gas accumulation; (4) Until the end of deposition period of the Nenjiang Formation, hydrocarbon generated in the Qn1 mainly migrated downward into the underlying Fuyang oil layer via the small polygonal faults rather than upwards to the Putaohua oil layer. On the contrary, by the end of deposition period of the Mingshui Formation, the oils from Qn1 source rock can migrate either downward into the Fuyang oil layer or upward into the Putaohua oil layer. It is noteworthy that the vertical propagation of the polygonal faults induced by the tectonic inversion might also damage the Fuyang accumulations formed earlier.