羌塘盆地托纳木地区上侏罗统索瓦组烃源岩特征

Characteristics of hydrocarbon source rocks in the upper Jurassic Suowa Formation in Tuonamu region, Qiangtang Basin

羌塘盆地托纳木地区的烃源岩主要为上侏罗统索瓦组一段—四段的灰岩和泥岩,烃源岩厚度较大。运用有机地球化学方法,分析了该区烃源岩的特征。该区烃源岩的有机碳含量和氯仿沥青“A”含量相对较低,有机质类型中等—较好,热演化程度中等—高成熟,生烃量巨大。烃源岩主峰碳主要以高碳数C25和C27为主,大部分具有较明显的重碳优势,但没有明显的奇偶优势,伽马蜡烷含量较低。综合分析表明,索四段碳酸盐岩和索三段泥岩为较好烃源岩,索三段和索二段的碳酸盐岩为中等—较差烃源岩,索二段泥岩、索一段泥岩与碳酸盐岩为较差的烃源岩。

Tuonamu region lies between the central uplift zone and northern Qiangtang Depression, where hydrocarbon source rocks are thick limestones and mudstones of 1-4 member of the upper Jurassic Suowa Formation. The characteristics of the hydrocarbon source rocks in this region are analyzed using organic geochemistry methods. In this region, the total contents of organic carbon and chloroform bitumen 'A' are relatively low. The organic material type is medium to good. The thermal evolution degree is medium to highly mature. Quanlity of hydrocarbon generation is large. The main carbon peak of the hydrocarbon source rocks is mainly C25 and C27 ,much of which has obviously heavy carbon advantage but no obvious odd/even predominance and has the lower content of gammaceranes. The comprehensive analysis shows that carbonate rocks in fourth member and mudstones in third member of Suowa Formation are good hydrocarbon source rocks, carbonate rocks in third and second member of Suowa Formation are medium to relative poor ones, mudstones in second member and carbonate rocks and mudstones in first member are relative bad ones.