乌石凹陷东区古近系断裂系统与油气成藏

Palaeogene Fault System and Hydrocarbon Accumulation in East Wushi Sag

乌石凹陷东区古近系复杂的断裂系统一直是制约油气勘探成败的关键因素,通过对研究区内断裂体系的期次、组合方式、成因及演化的系统分析,认为凹陷东区的演化经历了3个阶段、形成3套断裂系统:即古新世—早始新世的弱裂陷、始新世中晚期的强裂陷以及渐新世的走滑弱伸展3个阶段。3套断裂系统:断开长流组流三段(T100—T86)的早期断裂体系、断开流二段涠洲组(T83—T60)的晚期断裂体系以及断开整个古近系地层的(T100—T60)继承性断裂体系,并识别出伸展构造、走滑及反转等构造样式。同时分析了断裂体系对烃源岩的展布、沉积体系的充填演化、圈闭的形成、分布以及油气的运聚等方面的控制作用,从各成藏要素的时空配置上分析认为中央隆起带和北部掀斜断块是有利的勘探区。研究成果对研究区下一步油气勘探、目标评价优选与地质研究等具有一定的指导和参考意义。

Paleogene complex fault system has always been a key factor in the success of oil and gas exploration in East Wushi Sag. In this article the time of faults movement, their classification and the structural evolution are studied. The results show that the evolution of East Wushi sag can be divided into weak rifting stage in Paleocene -Early Eocene, strong rifting stage in Middle-Late Eocene and strike-slip weak stretching stage in Oligocene. Besides, 3 sets of fault systems can be recognized： the early fault system formed in Changliu Formation to Liushagang Section 3 Formation sedimentary stage（T^00-Ts6）, the late fault system formed during Liushagang Section 2 Formation to Weizhou Formation sedimentary stage（Ts3--Tr0） and succession fault system formed in all the Palaeogene time （T100-T86）. In addition, stretching structure, strike-slip structure and inversion structure have been found in study area. While the tectonic controls on the distribution of source rock and the filling evolution of sediment systems has been discussed, as well as the fault activity impacts on the trap formation, distribution, and the accumulation of hydrocarbon. Based on the analysis of the elements of reservoir formation, the central uplift and the north tilted fault block are the favorable prospecting areas. And the research has some guidance and reference value for the future oil and gas exploration, target evaluation and preference, and geological research.