中国华南陡山沱组烃源岩的形成机制与分布预测

震旦系(埃迪卡拉系)陡山沱组是成冰系(南华系)极端冰期事件结束后首次沉积的泥岩和碳酸盐岩地层,大规模的海侵活动导致在全球广泛发育富有机质黑色页岩,可能是未来深层油气和页岩气勘探的重要烃源岩层.中国华南陡山沱组烃源岩分布广泛,由于受古构造格局、沉积相带等因素影响,烃源岩非均质性强、平面上分布差异大.本文在前人研究基础上,结合3个剖面的有机地球化学、古生物学和沉积地球化学等分析,对比华南10个典型剖面,分别对陡二段和陡四段烃源岩的沉积环境开展分析对比,认为陡二段烃源岩形成于海侵背景下的贫氧环境,陡四段烃源岩形成于海退背景下的缺氧滞留环境;多细胞藻类和疑源类是主要有机质母源.不同相带对比研究表明,台地相烃源岩主要发育在陡四段(TOC平均值为3.61％),斜坡相烃源岩在陡二段(TOC均值为2.20％)和陡四段均发育(TOC平均值为3.66％).烃源岩质量和厚度明显受控于沉积环境和古裂陷地质结构等.结合露头和钻井资料,对华南陡山沱组烃源岩分布及厚度开展预测和编图,提出了优质烃源岩分布的有利区域,为深层油气勘探和页岩气富集区预测提供了依据.

Formation mechanism and distribution prediction of source rocks in the Ediacaran Doushantuo Formation, South China

Doushantuo Formation is the first interglacial deposited at the end of the glacial event of the Cryogenian. Extensive transgression resulted in the development of organic rich black shale all over the world, which is an important source rock for deep oil and gas exploration at present. The widely distributed Doushantuo Formation source rocks in South China are affected by tectonism and sedimentary facies, resulting in large differences in spatial distribution and strong heterogeneity in source rocks, posing a challenge to oil and gas exploration and prediction. On the basis of previous studies, combined with the analysis of organic geochemistry, paleontology and sedimentary geochemistry of three profiles, this study compared 10 typical profiles in South China, and concluded that in the Doushantuo Formation, 2nd Member and 4th Member developed source rocks. The analysis of redox environment shows that the source rocks of the 2nd Member of Doushantuo Formation are formed in dysoxic environment in a transgressive background, and the source rocks of the 4th Member are formed in anoxic environment in regressive background. Multicellular algae and acritarcha are the main source materials. The comparative study shows that the platform facies mainly develops in the 4th Member source rocks (TOC average value is 3. 61%), the slope facies mainly develops in the 2nd Member (TOC average value is 2. 20%) and the 4th Member source rocks (TOC average value is 3. 66%). Based on a large number of analysis data and profile correlation, it is considered that the thickness and quality of source rock are obviously controlled by paleo- depression and redox environment. Based on the outcrop and drilling data, the thickness distribution of the source rocks in the Doushantuo Formation of South China (the 2nd Member+the 4th Membe r) is predicted. A favorable area for excellent source rock distribution is proposed providing a basis for deep oil and gas exploration and prediction of shale gas- rich areas.