Leading effect of the Seventh Member high-quality source rock of Yanchang Formation in Ordos Basin during the enrichment of low-penetrating oil-gas accumulation: Geology and geochemistry

摘要: A suit of high-quality source rock semi-deep to deep lacustrine facies, which developed during the age Seventh Member Yanchang Formation (Chang 7 for short) at Late Triassic in Ordos Basin, has most abundant content organic matter Formation. On area 5×104 km2, its thickness a single layer is commonly 5～25 m and accumulative one mainly from 10 50 m, with maximum 80 m. The analyses detailed geochemical data show that Chang was formed under reductive sedimentary condition water body, low salinity, indistinct delaminating body; main matters were originated alga, form organism poor 13C; kerogen type I-II1; abundance high residual TOC value 6%-14%, 30%; been maturation evolution stage. It indicated underwent violent hydrocarbon expulsion by S1+S2 chloroform bitumen A, ratio saturated aromatic hydrocarbon. precise delimitation this suite great importance oil exploration understanding petroleum deposit mechanism low-penetrating reservoir region.