Organic Matter Enrichment Mechanism of Black Shale in Wufeng-Longmaxi Formations: A Case Study from Jiaoye 143-5 Well at Chongqing
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摘要: 上扬子地区五峰组-龙马溪组黑色岩系是我国南方重要的海相烃源岩,也是目前我国页岩气勘探开发的重要层位之一,前人对其有机质富集因素的综合分析和富集因素之间的关系研究较少.以渝东南武隆地区焦页143-5井为例,对五峰组-龙马溪组下段黑色岩系进行了地层学及古海洋环境的研究,探讨了古气候、火山活动、古海洋生产力和氧化还原特征及其在有机质富集中的作用.研究表明,TOC与强烈火山活动、缺氧古海洋环境、高古生产力和温暖古气候具有良好的正相关关系.这是由于强烈火山作用和陆源化学风化,大大提高了海洋中的营养盐含量,促使生物繁盛、生产力增高,并形成了缺氧硫化、富硅的海洋环境,从而为有机质富集提供了优良的条件.Abstract: The Wufeng-Longmaxi black shales were widely developed in the Yangtze region which was located in low latitude area during the Late Ordovician-Early Silurian. This marine shale succession is one of the most important hydrocarbon source rocks in South China and has attracted wide attention for shale gas exploration and development in China, which has been the focus for shale gas exploration. However, little is known about the synthetical factors controlling enrichment of organic matter and the relationships between them. In this study, it studies Well 143-5 in Wulong area of Southeast Chongqing to analyze the stratigraphic characteristics and paleomarine environments of the Wufeng-Lower Longmaxi shales, it discusses the paleo-climate evolution, volcanic activity, paleoproductivity, redox conditions and their relationships with organic matter enrichment. The results reveal that there are strong positive correlations between TOC content and strong volcanism, anoxic environment, high paleoproductivity, and warm paleoclimate. Due to strong volcanism and chemical weathering, nutrient content in the ocean was improved greatly, prompting the flourishing of animals and high productivity. At the same time, the marine environments became anoxic or euxinic, and rich in silicon. These paleoceanographic environments provided excellent conditions for organic matter enrichment.
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Key words:
- organic matter enrichment /
- shale gas /
- Sichuan Basin /
- Wufeng-Longmaxi formations /
- petroleum geology
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图 1 晚奥陶世全球及扬子板块(a、b)古地理图和五峰组-龙马溪组岩性柱状图(c)
图a据Zhou et al.(2015); 图b据Chen et al.(2004)
Fig. 1. Late Ordovician paleogeographic maps (a, b) and lithologic column of the Wufeng and Longmaxi formations (c)
图 2 焦页143-5井古海洋指标特征及演化阶段(SST据Melchin et al., 2013)
Fig. 2. Vertical variation characteristics of geochemical indexes for Jiaoye 143-5 Well (SST after Melchin et al., 2013)
表 1 焦页143-5井不同阶段TOC含量特征
Table 1. The characteristics of TOC content in different stages for Jiaoye 143-5 Well
TOC含量(%) 阶段一 阶段二 阶段三 阶段四 阶段五 阶段六 最小值 0.05 2.60 0.21 1.51 0.49 1.46 最大值 0.31 6.23 2.14 7.28 2.64 2.02 平均值 0.16 4.35 1.11 3.94 1.64 1.71 表 2 焦页143-5井不同阶段古海洋特征
Table 2. Paleooceangraphic characteristics for Jiaoye 143-5 Well
参数 阶段一 阶段二 阶段三 阶段四 阶段五 阶段六 TOC 低 高 低 高 中 中 古生产力 低 高 低 高 中 中 古氧相 氧化 缺氧 氧化 缺氧-贫氧 氧化 氧化-贫氧 生物硅 低 高 低 高 中 低 火山作用 无 强 无 强 无 无 古温度 高 波动 低 高 中-高 高 风化指数 高 高 低 中-高 中-高 高 陆源注入 高 低 低 中 高 高 沉积速率 低 低 低 低-中-高 中-高 高-特高 -
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