华北东部地区盆地叠合特征与古生界生烃史

华北东部地区下古生界沉积了海相碳酸盐岩潜在的烃源岩,上古生界发育良好的煤系气源岩。由于经历了多期次、不同规模盆地的多种样式的叠合,其间又经历多期次的抬升、剥蚀与改造,因此,不同地区的古生界烃源岩生烃史具有显著的差异。地层对比和上古生界RO特征指示研究区北部的济阳坳陷具有较厚的三叠系原始沉积,三叠纪盆地的叠合对古生界烃源岩生烃史具有重要影响。依据盆地叠合方式、上古生界热演化程度,将上古生界生烃史划分为三叠纪、侏罗纪—白垩纪、早第三纪以来等3个阶段,分别对应生烃史的早期、中期和晚期,早期浅埋、中期抬升、晚期深埋型地区的“二次生烃”潜力大,如济阳坳陷和东濮凹陷。上古生界盆地的均衡面式叠合使下古生界的热演化程度比上古生界至少高0.3%以上,因此,在三叠纪末下古生界基本达到生烃高峰,在一定程度上损耗了其原始有机质并降低其“二次生烃”潜力。

Basin Superimposing Characteristics and Hydrocarbon Generation History of Paleozoic Source Rock in the East Part of the North China

In the east part of the North China,there are potential carbonate source rock of sea facies of Lower Paleozoic and good coal formation source rock of Upper Paleozoic.Undergoing multiple types of superimposing process of basins with multiple episodes and different scales,and experiencing uplift,erosion and change of multiple episodes among the superimposing episodes,Paleozoic source rock in different areas has different(hydrocarbon) generation histories.Strata calibration and R_O data indicate that there should be Triassic deposition of big thickness in Jiyang depression,and superimposing process of Triassic basins is crucial for hydrocarbon generation history of Paleozoic source rock.With basin superimposing model and evolution grade of Upper Paleozoic referred,the generation history of Paleozoic source rock is divided into three stages,Triassic as the early stage,Jurassic to Cretaceous as the middle stage,and since Early Tertiary to now as the late stage.The areas such as Jiyang depression and Dongpu sag with imbedding histories of shallow imbedding in the early stage,(uplift) in the middle stage and deep imbedding in the late stage have big potentials of secondary hydrocarbon generation.The balanceable surface superimposition of Upper Paleozoic basin makes R_O of Lower Paleozoic higher than Upper Paleozoic,and the difference is more than 0.3%.So in the end of Triassic,Lower Paleozoic source rock achieved hydrocarbon generation peak,which expensed the initial organic matter and reduced the potentials of secondary hydrocarbon generation to some extent.