松辽盆地“T_2”断裂密集带成因机制及控藏机理——以三肇凹陷为例

The genetic mechanism and accumulation mechanism of "T_2" fault dense zone in Songliao Basin:In Sanzhao depression

松辽盆地T_2反射界面高密度断层与扶杨油层油气"倒灌"运聚成藏关系密切,其成因机制备受地质学家关注,存在构造成因和水力断层等多种假说。本文系统研究了"T_2"断层几何学特征,认为该断层以南北展布方向为主、断距和延伸长度幂律分布、密集成带、与断陷期断层呈"似花状"组合模式、部分断层多期活动,该断层有别于超压周期性释放产生的非构造成因的多边断层,为典型的构造成因断层。T_2高密度断层和密集带的成因可以归结为3个因素:1)坳陷期松辽盆地强烈拉张发生在青山口组沉积时期,泥岩低剪切强度导致构造破碎,是高密度断层形成的前提;2)基底—断陷期断裂、火山口和基岩隆起作为早期薄弱带,控制着坳陷期断裂的形成且密集成带,是高密度断层形成的根本原因。3)塑性泥岩在坳陷期发生水平拆离作用,导致断陷期断裂与坳陷期断裂上、下不衔接,T_2和T_1断层上、下贯通较少,这是造成仅T_2反射层发育高密度断层的有力保障。构造反转期三肇凹陷整体活动较弱,断裂密集带边界断层选择性活动,向上延伸到T_(06)反射层以上,反转期活动的断层正赶上青山口组烃源岩大量生排烃时期,这些断层为扶杨和葡萄花油层有利的通道断层,控制着扶杨和葡萄花油层油气的运聚成藏与分布。

In Songliao Basin, high density fault in T2 reflecting interface and ＂decanting＂ migration and accumulation in Fuyang reservoir are closely relate, its genetic mechanism are highly concerned from the geologists, there are a variety of hypotheses of tectonic origin and hydraulic fault. This paper systematically study on the geometry of the ＂T2 ＂ fault, the dominant N-S trending fault, the power-law distribution characteristics of displacement and length, dense zone,＂ flower-like＂ composite pattern with fault in rifting, characteristics of the multi-phase activity in the part of the fault are different from non-tectonic origin polygonal fault which generate from overpressure cyclical release, is typical tectonic origin fault. The causes of the high density fault and dense zone in T2 can be attributed into three factors： first, Songliao depressed basin has strong strenching during the Qingshankou deposited, the low shear strength in mudstone lead to fracture,is the premise of high density fault formation; second, basement- rifting fault,volcanic vent and uplifted bed rock as early weak belts, control the formation of the depressed fault and dense zone, is the primary cause of the high density fault formation ; third, plastic mudstone detachment horizontal during depression, making the rifting fault and the depressed fault can＇t link up, T2 and T~ fault lack of perforation, this is the favorable security for development of the high density fault in only T2 reflecting layer. The activity of the overall Sanzhao depression in tectonic inversion period is weak, polygonal fault in fault dense zone selective activity, extends upwardly to above T06 reflection layer, the fault in inversion is active during the source rock generate and expulse abundance hydrocarbon, these faults are advantageous channel fault for Fuyang and Putaohua oil layers, control the migration, accumulation and distribution of the Fuyang and Putaohua reservoir.