苏北盆地白驹凹陷油气富集规律与成藏模式

Hydrocarbon enrichment patterns and pooling modes in Baiju sag,Subei Basin

白驹凹陷洋心次凹自2005年投入勘探以来,已发现多个小断块油气藏。为认识其油气富集与成藏模式,提高勘探成功率,以油气富集规律与成藏模式分析为主线,通过烃源岩评价及成熟期分析、圈闭类型划分,研究了断层对油气成藏的控制作用、岩浆岩活动与油气成藏的关系。结果认为:①白驹凹陷洋心次凹发育成熟的古近系泰州组陆相湖盆泥质烃源岩,其油气具有晚期成藏的特点,渐新世末的盐城期是陆相油气源的主要运移、聚集及成藏期,断裂形成的复杂小断块圈闭类型是油气聚集的主要场所;②贯穿生油深洼的大断层是沟通主力油源区的主要油气通道,油气以断层和砂体为运移通道,就近运移与聚集成藏;③成藏类型为岩性+断块、断块+岩性等的多种圈闭组合的小断块层状砂岩低渗高凝油藏,岩浆活动有利于提高地温梯度,对油气运移、聚集不起破坏作用。结论指出:洋心次凹进一步勘探的重点应以泰州组一段为主,阜宁组一段为辅,若在"油源、储层、圈闭"三者配置条件好的地区找到匹配比较理想的圈闭,将有希望获得新的油气发现。

Several small fault block oil/gas reservoirs have been discovered in Yangxin subsag of the Baiju sag since its exploration started in 2005.In order to understand the hydrocarbon enrichment patterns and pooling modes and to improve the success ratio of exploration,we study the control action of faults on hydrocarbon accumulation and the relationship between magmatic activity and hydrocarbon accumulation through evaluation of source rocks,analysis of their maturity stage,and classification of trap types.The following conclusions are obtained.①The Yangxin subsag in the Baiju sag has well-developed mature shaly source rocks of lacustrine facies in the Paleogene Taizhou Formation and is featured by late hydrocarbon accumulation.Migration and accumulation of hydrocarbons sourced from the continental source rocks occurred mainly in the Yancheng stage at the end of Oligocene.The complex small fault block traps are the major habitats for hydrocarbon accumulation.②Large faults rooted deep in hydrocarbon kitchen link the major oil source with the reservoirs.The hydrocarbons migrate along faults and sandbodies and accumulate in nearby traps after short migration.③The reservoir types are small fault block-bedded sandstone reservoirs with low permeability.They are formed by various trap combinations such as lithology + fault block,fault block + lithology,and so on.The magmatic activities are favorable for enlarging geothermal gradient,with no negative effects on hydrocarbon migration and accumulation.It is clearly pointed out that the second member of the Taizhou Formation should be the primary target for further exploration in the study area,while the second member of Funing Formation should be the secondary target.If ideal trap combinations exist in the areas with favorable timing of source rocks,reservoirs and traps,it is highly possible to get new oil/gas discoveries.