南黄海盆地北部坳陷北凹油气成藏特征的再认识

New View on Hydrocarbon Accumulation Characteristics of the North Sag,North Depression of the South Yellow Sea Basin

南黄海盆地北部坳陷北凹是一个大中型的中、新生代沉积凹陷,经过四十余年的油气勘探,至今仍无商业油气发现,仅发现诸城1-2一个含油气构造。北凹的油气勘探存在诸多问题,其中是否发育优质烃源岩、烃源岩能否生烃、油气是否运移至储层是关系到北凹油气勘探的基础地质问题。在对北凹主要烃源岩分析评价的基础上,采用流体包裹体系统分析技术,对北凹油气成藏特征展开研究。研究认为,北凹存在白垩系泰二段主力烃源岩,为中深湖相,生烃指标较好,分布面积较大,且现今已经成熟并排烃,生烃中心位于ZC-A井区。油气通过断裂发生垂向运移,已充注至始新统戴南组储层。流体包裹体荧光观察结果及显微测温结果均表明戴南组至少存在两期油充注,第一期发生在35 Ma左右,第二期为现今。

The South Yellow Sea basin is a large size Mesozoic and Cenozoic sedimentary basin. Hydrocarbon exploration in this basin has been carried out for more than four decades, but no commercial hydrocarbon discovery has been obtained so far, with only one oil bearing structure Zhucheng 1-2 has been discovered. There are a lot of basic geological problems to be solved in this basin, including whether the excellent quality source rocks are well developed, whether hydrocarbon has been generated from the source rocks, and whether hydrocarbons can migrate into reservoirs. Based on evaluation results on source rocks, the hydrocarbon accumulation characteristics in the North Sag have been studied with fluid inclusion technique in this paper. The result showed that the second member of Taizhou formation is the main source rock, being semi-deep lacustrine facies, and distributes widely. The main source rocks have mature and large amount of oil and gas have been expulsed from the main source rocks. The hydrocarbon generation center was located in Well Block ZC-A. Hydrocarbon has migrated along faults and filled into the Eocene Dainan Formation. The results show that there were two phases of hydrocarbon charge at least in the Dainan formation based on the study results of fluorescence observation of fluid inclusion and the microscopic temperature measure. The first phase hydrocarbon charge happened in about 35 Ma, and the second charge happened at present.