准噶尔盆地东北缘乌伦古坳陷油气成藏的构造制约

Structural constrain to hydrocarbon accumulation in the Wulungu depression of the Junggar Basin

近年来随着地质工作的不断深入,在乌伦古坳陷发现丰富的油气资源。然而与盆地其余地区相比,其油气勘探开发程度仍较低。本文通过构造特征和断裂发育过程对乌伦古坳陷油气成藏规律进行了系统研究。研究区发育3套烃源岩,其中石炭系滴水泉组和巴塔玛依内山组烃源岩最为重要,索索泉凹陷中心为乌伦古坳陷的石炭系烃源岩生油中心。乌伦古坳陷油气藏的形成受控于逆冲断裂而呈带状分布,是逆冲断裂控制的油气聚集带。断裂活动自北往南变新,断裂活动期次与烃源岩生烃高峰期相匹配,沟通油源的深大断裂是油气运移的主要通道。浅部发育反冲断层,主要分布在斜坡区的喀拉萨伊断裂附近,对早期油气起到破坏作用。研究区断裂系统在平面上自北往南可分为根部带、中部带和前锋带,受断裂活动影响,构造圈闭和油气藏形成时期逐渐变新,层位逐渐变浅,类型由断层相关变为褶皱相关。

As geological investigation of the Wulungu depression in the Northeast Junggar Basin goes on in recent years, rich oil and gas resources are founded in the depression. But compared with the other part of the basin, the investigative level of oil and gas in the Wulungu depression is still low. This article systematically explores the law of oil and gas accumulation based on the structural characteristics and fault evolution. The Wulungu depression developed three sets of source rocks. The Dishuiquan Group and Batamayineishan group of Carboniferous dark mudstone is the most important source rock. According to the structural characteristics and evolution, the piedmont of Kelameili Mountain is the favorable oil and gas accumulation areas. The Wulungu depression is the oil-gas accumulation zone controlled by thrust faults, the oil and gas reservoirs in this area are characterized by zonal distribution along the NW-striking faults. The active deep-seated faults are the major hydrocarbon migration paths; the shallow faults mostly distributed in the Kalasayi fault, may damaged the early oil and gas reservoirs but benefit to the formation of secondary reservoirs in some degree. As the tectonic migration from north to south, the fault intensely active period matched well with the hydrocarbon generation. Structural traps in the root zone in the north developed from Late Indocinian stage to Early Yanshan stage, the main hydrocarbon reservoir types are faulted noses and faulted blocks related to the thrusting and secondary lithofacies reservoirs. Structural traps in the front zone in the south formed at Middle-Late Yanshan stage, the main hydrocarbon reservoir types are fault- related bends, fault-propagation folds, angular unconformity reservoirs and lithofacies reservoirs, but most of them are damaged by normal faulting during Himalayan period.