澳大利亚Vulcan次盆Puffin油田油气源与成藏

Hydrocarbon sources and accumulation in Puffin oilfield,Vulcan sub-basin,Australia

Puffin油田目前油气来源不明,主力烃源岩展布及主要生、排烃期不确定都制约了下一步勘探的进行。利用烃源岩二维生烃模拟以及生物标志物指纹对比等方法,揭示了下Vulcan组海相泥页岩是本区最为重要的一套烃源岩,白垩纪—中新世为主要生、排烃期;而本区的Plover组烃源岩普遍演化程度较高,在晚侏罗世已达到高成熟,生烃潜力差,对于成藏的贡献较为有限,属于次要烃源岩。成藏事件图反映出Puffin垒带上的圈闭主要形成于侏罗纪—白垩纪,中新世以前由于侏罗系以上地层断裂不发育,下Vulcan组主力烃源岩生成的原油主要在地堑中的侏罗系圈闭中聚集成藏。中新世末,区域性的构造挤压运动形成众多垂向断裂并且使早期形成的断裂体系活化,使得早期成藏的油气垂向调整到浅层的白垩系聚集成藏。因此,目前Puffin油田发现的白垩系油藏主要为次生油藏,为早期侏罗系油藏调整改造到浅部垒带上形成。

Hydrocarbon sources,distribution of the major source rocks and timing of hydrocarbon generation and expulsion are poorly understood in Puffin oilfield,constraining future exploration.Two-dimension hydrocarbon generation modeling and biomarker fingerprinting reveal that the Lower Vulcan marine shale is the most important source rocks in the study area and its peak hydrocarbon generation and expulsion occurred from Cretaceous to Miocene.In contrast,the Plover source rocks got over matured during the Late Jurassic,and contributed limited hydrocarbons due to its low capability of hydrocarbon generation.The events chart shows that the traps on the Puffin horst were mainly formed in the Jurassic-Cretaceous period.Before the Miocene,the hydrocarbon generated from the Vulcan source rocks mainly accumulated in the Jurassic traps in the graben as faults were undeveloped in strata above the Jurassic.At the end of Miocene,lots of vertical faults were created or reactivated by the regional tectonic compression,causing that hydrocarbons in the early pools vertically migrated to and accumulated in the shallow Cretaceous reservoirs.So oil in the discovered Cretaceous reservoirs is mostly secondary.