High quality source rocks in trough facies of Upper Permian Dalong Formation, Sichuan Basin

Source rocks in trough facies of the Upper Permian Dalong Formation of the Sichuan Basin were assessed by field observations and measurements in outcrop areas as well as from logging and core/cutting analysis from drilling sites. The results show that in the Dalong Formation, the black shale and sapropelite facies have an average TOC of 5.86%, with the maximum value up to 24.31%, making them high quality hydrocarbon source rocks. Dark cryptite, with a TOC of 0.77% (on average) is also a good hydrocarbon source rock. A dark silicate, with TOC of only 0.13% on average, has no potential to generate hydrocarbons. Since the source rocks are much evolved, the content of chloroform bitumen “A” extracts tend not to be high. The (S1+S2) value of source rocks in the Dalong Formation are low, with only 4.36 mg/g on average. The major macerals of Kerogen of the Dalong Formation are sapropels, averaging 71.5%. Kerogen is mainly Type II1, and a little belongs to II2. The flourishing of pelagic organisms during deposition of the Late Permian Changxing Formation, slow deposition rate of the Dalong Formation and an anoxic and calm deep water depositional environment are the key controlling factors for accumulation, preservation and generation of organic matter in this part of the basin.

摘要： 通过四川盆地上二叠统海槽相大隆组露头区野外观察测量和钻井区测井及岩心、岩屑分析，对大隆组烃源岩进行评价。研究表明，大隆组黑色泥质岩、腐泥岩TOC平均值为5.86%，最高可达24.31%，是一套优质烃源岩；大隆组暗色泥晶灰岩TOC平均值可达0.77%，也是很好的烃源岩；大隆组暗色硅质岩TOC平均值仅为0.13%，不具备生烃能力。由于烃源岩演化程度较高，氯仿沥青“A”含量总体不高。大隆组烃源岩（S1＋S2）值总体也比较低，平均值仅4.36 mg/g。烃源岩干酪根显微组分以腐泥组为主，干酪根主要为Ⅱ1型，少量为Ⅱ2型。晚二叠世长兴组沉积期浮游类生物繁盛、大隆组沉积速率缓慢以及缺氧、安静的深水沉积环境是有机质富集、保存、形成优质烃源岩的主要控制因素。图6表2参12