四川盆地东北地区吴家坪组海相页岩垂向有机质富集机制

Vertical organic matter enrichment mechanism of marine shales in the Wujiaping Formation, Northeastern Sichuan Basin

摘要

四川盆地开江-梁平海槽吴家坪组海相页岩有机质富集机制不明确,制约页岩气有利层段的识别与勘探选区部署。根据研究区DY1H井岩心资料,采用X射线衍射、总有机碳质量分数、微量元素与同位素等测试方法,分析四川盆地东北地区吴家坪组沉积环境与垂向有机质富集机制。结果表明:吴家坪组海相页岩纵向具有明显的三阶段分异特征,吴家坪组一段沉积时期处于火山活动初期,火山物质输入滞后,表现为陆源碎屑主导、弱氧化条件下的低效富集特征,总有机碳质量分数平均为1.20%;吴家坪组二段沉积时期为过渡阶段,火山风化营养输入与贫氧环境共同作用,促使有机质保存,总有机碳质量分数平均为5.40%;吴家坪组三段沉积时期为火山活动高峰期,在湿润气候与半封闭滞留盆地耦合背景下,形成“火山源营养输入-生物富集-滞留保存”三元高效富集机制,总有机碳质量分数平均为8.83%,陆源输入显著降低;揭示构造-气候-沉积环境多因素协同控制有机质富集规律。该结果为四川盆地深层页岩气勘探选区提供指导。

Abstract

The organic matter enrichment mechanism of marine shales in the Wujiaping Formation in the Kaijiang-Liangping Trough of the Sichuan Basin remains unclear, which restricts the identification of favorable shale gas intervals and the planning of exploration deployment. Based on core data from well DY1H in the study area, using X-ray diffraction, total organic carbon (TOC) content, trace element and isotope analyses, this study investigates the sedimentary environment and organic matter enrichment mechanism of the Wujiaping Formation in Northeastern Sichuan Basin. The results show that the marine shales of the Wujiaping Formation exhibit a clear three-stage vertical differentiation. During the deposition of the first member of the Wujiaping Formation, which was in the early stage of volcanic activity with a lag in volcanic material input, it is characterized by inefficient enrichment under terrigenous detrital dominance and weakly oxic conditions, with an average TOC content of 1.20%. The second member of the Wujiaping Formation represents a transitional phase, where the combined effect of nutrient input from volcanic weathering and dysoxic conditions promoted organic matter preservation, with an average TOC content of 5.40%. The third member of the Wujiaping Formation corresponds to the peak of volcanic activity. Under the coupled background of a humid climate and a semi-restricted stagnant basin, a ternary high-efficiency enrichment mechanism of “volcanic nutrient input-biological enrichment-stagnant preservation” was established, with an average TOC content of 8.83% and a marked decrease in terrigenous input. This reveals the dynamic patterns of organic matter enrichment under the synergistic control of tectonic, sedimentary, and climatic factors. These results provide guidance for deep shale gas exploration and block selection in the Sichuan Basin.

关键词

四川盆地 / 吴家坪组 / 海相页岩 / 火山活动 / 沉积环境 / 有机质富集机制

Key words

Sichuan Basin / Wujiaping Formation / marine shale / volcanic activity / sedimentary environment / organic matter enrichment mechanism

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基金资助

重庆市教委科学技术研究项目(KJZD-K202401503)