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
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
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发表时间：
2005
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通讯作者：
Zhang Wenzheng
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作者：
Zhang Wenzheng
鄂尔多斯盆地晚三叠世延长组七段（简称长7）发育了一套优质的半深湖-深湖相烃源岩，其中延长组有机质含量最丰富。在5×104 km 2的面积上，单层厚度一般为5~25 m，累积厚度以10 ~ 50 m为主，最大可达80 m。详细的地球化学资料分析表明，长7优质烃源岩形成于水体深、盐度低、分层水体不明显的还原性沉积条件下，有机质主要来源于贫13 C的低级湖相有机质--碳酸盐岩，干酪根类型为Ⅰ-Ⅱ 1型，干酪根类型为Ⅰ-Ⅱ 1型，有机质类型为Ⅱ-Ⅲ型。有机质丰度高，残余TOC值一般为6%~ 14%，最高可达30%，有机质已处于成熟和高成熟演化阶段。烃源岩的S1+S2和氯仿沥青A含量低，饱和烃/芳烃比值低，排烃作用强烈。这套优质烃源岩的准确圈定，对该区低渗透油藏的油气勘探和深入认识油气存款机理具有重要意义。
A suit of high-quality source rock of semi-deep to deep lacustrine facies, which developed during the age of the Seventh Member of Yanchang Formation (Chang 7 for short) at Late Triassic in the Ordos Basin, has the most abundant content of organic matter in Yanchang Formation. On the area of 5×104 km2, its thickness of a single layer is commonly 5～25 m and the accumulative one is mainly from 10 m to 50 m, with a maximum of 80 m. The analyses of the detailed geochemical data show that the Chang 7 high-quality source rock was formed under the reductive sedimentary condition with deep water body, low salinity, and indistinct delaminating water body; the main organic matters were originated from alga, a low form of lacustrine organism poor in 13C; the kerogen is of type I-II1; the organic matter abundance is high and the residual TOC value is commonly 6%-14%, with a maximum value of 30%; and the organic matter has been in maturation and high maturation evolution stage. It is indicated that the source rock underwent violent hydrocarbon expulsion by low content of S1+S2 and chloroform bitumen A, and low ratio of saturated hydrocarbon to aromatic hydrocarbon. The precise delimitation of this suite of high-quality source rock is of great importance in oil exploration and deep understanding of petroleum deposit mechanism of low-penetrating reservoir in this region.