利用石膏产状研究汶东盐湖相沉积与烃源岩特征

Application of Occurrences of Gypsum Minerals in Saline Lacustrine Facies Analysis and Source Rocks Organic Geochemistry Evaluation:A Case Study of Wendong Subdepression

根据石膏矿物类型和产状以及其它相标志,对汶东凹陷汶ZK16钻孔的古近系盐湖相地层进行了沉积相分析,并结合有机地球化学分析,对不同沉积相的烃源岩开展了地球化学评价。汶东凹陷石膏矿物组合较好的反映了古盐湖沉积环境、水深、盐度和底水含氧量等的变化,不同的石膏矿物组合对应着不同的沉积相和不同质量的烃源岩,其中干化泥坪相和盐化泥坪相石膏矿物组合以分散胶结状和结核状为主,其烃源岩有机质丰度较低,发育非烃源岩到差烃源岩;干盐湖相石膏矿物组合以肠状石膏和透镜状石膏为主,烃源岩有机质丰度较高,发育好到优质烃源岩;而深水盐湖相石膏矿物以纹层状石膏为主,烃源岩有机质丰度高,总体达到优质烃源岩的标准。据此,建立了盐湖相烃源岩的发育模式。该模式对于中国第三系盐湖烃源岩,特别是高演化程度的盐湖相烃源岩原始烃源岩类型研究具有重要的指导意义。

Based on the occurrences and characteristics of the gypsum and other markers,the sedimentary facies of the Paleogene saline lacustrine deposits in Wendong subdepression was studied,and the source rocks of different facies were evaluated according to the organic geochemistry analysis.It shows that the association of gypsum minerals reflects the changes in sediment environment,lake water depth,lake water salinity and bottom oxygen content etc.,and possesses close relationship with sedimentary facies and source rocks development.Accordingly we established the saline lacustrine facies and source rocks development model.The saline mudflat and dry mudflat facies is dominated by disseminated,cemented and nodular gypsum minerals,the source rocks belong to no or poor source rocks with low organic abundance.The playa facies is dominated by enterolithic and lenticular gypsum minerals,has relatively high organic abundance and can form good to excellent source rocks. The saline deep lake facies is dominated by laminated gypsum minerals and can develop excellent source rocks with high organic abundance.This is of great significance in Paleogene saline source rocks evaluation of China.