当阳复向斜上组合生烃潜力及其含油气系统

Hydrocarbon-generating Potential and Petroleum System of Upper Assemblage of Dangyang Synclinorium

当阳复向斜上组合存在志留系、二叠系及下三叠统三套烃源层,以碳酸盐岩及泥质岩为主。以志留系底部厚约50m的黑色页岩生油条件最好,在王家湾剖面有机碳含量平均达3.77％;次为二叠系碳酸盐岩,全区有机碳平均含量为0.36％。干酪根碳同位素特征和扫描电镜特征均显示该区烃源岩母质类型主要为I型和Ⅱ型。有机质热演化程度普遍较高,应以天然气勘探为主。利用“二维源岩评价系统”软件进行了盆地模拟,三套烃源层的累积生烃强度为56.89×10~8m^3/km^2。总体分析,当阳复向斜烃源岩厚度大,生烃量大,具备寻找大、中型气藏的气源条件。推测上组合有两个含油气系统:早期成藏含油气系统,关键时刻为早燕山末期,气源充足,但保存条件相对较差;晚期成藏含油气系统,关键时刻为喜马拉雅末期,保存条件好,但气源不足。研究重点应以早期成藏含油气系统为主。

There are three sets of source rooks, Silurian, Permian and Lowe Triassic, in upper assemblage of Dangyang Synclinorium. The dom- inant source rooks are carbonate rock and shale. 50m black shale ir the bottom of Silurian is regarded as the best source rook, the aver- age organic-carbon content may reach up to 3. 77% in Wangjiawar section; Permian Carbonate rock is the ,second one. The regional or- ganic-carbon content is 0.36% on an average. The predominanl kerogen of the source rocks is type I and II verified by carbon iso- tope of kerogen and SEM. Owing to high evolution of organic matte the main target in this region is gas survey. The three sets of source rocks add up to 56. 9×10~8m^3/km^2 of hydrocarben-generating strength by 2D source rock assessment system. Two petroleurr systems are inferred in upper assemblage of Dangyang Synclinori- um: the early peel-forming petroleum system rich in gas source bul poor in preservation, whose critical moment is the end of early Yan- shan movement; the later pool-forming petroleum system good ir preservation but poor in gas source, whose critical moment is the end of Himalayan movement. It is considered that the stress of the study should be put on early pool-forming petroleum system.