川南寒武系筇竹寺组新类型页岩气富集主控因素

Main controlling factors of new-type shale gas enrichment in Cambrian Qiongzhusi Formation, southern Sichuan Basin

  • 摘要: 基于四川盆地寒武系筇竹寺组页岩岩心、测井及地震等资料,采用薄片分析、扫描电镜、有机与无机地球化学、吸附—解吸等测试方法,结合北美圣胡安盆地Mancos页岩类比分析,系统研究新类型页岩气藏形成条件及富集主控因素。结果表明:(1)井研地区筇竹寺组以含有机质页岩为主,TOC含量 < 1%,沉积相为浅水缓坡相,是发育输导层的有利相带;(2)新类型页岩气藏具有“两低一大四高”特征,即低TOC含量、低泊松比、大孔径、高长英质含量、高无机孔隙、高含气量、高杨氏模量;(3)在源储压差驱动下,深水相烃源岩生成的天然气可向孔隙结构更优的浅水相含有机质页岩输导层运移并富集;(4)新类型(输导层型)页岩气藏有别于龙马溪组富有机质连续型页岩气藏,具有“沉积成岩控源储、输导保存控富集”的二元富集规律。研究成果明确了新类型页岩气富集机理,可为有利勘探目标优选提供地质依据。

     

    Abstract: Based on shale core, logging, and seismic data from the Cambrian Qiongzhusi Formation in the Sichuan Basin, the study used methods including thin-section analysis, scanning electron microscopy, organic and inorganic geochemistry, and adsorption–desorption tests. Combined with a comparative analysis of the Mancos shale in the San Juan Basin, North America, it systematically investigated the formation conditions and main enrichment controlling factors of new-type shale gas reservoirs. The results showed that: (1) The Qiongzhusi Formation in the Jingyan area was dominated by organic-bearing shale with total organic carbon (TOC) content < 1%. It developed sedimentary facies at the shallow-water gentle slope zone, which was favorable for the development of carrier beds. (2) The new-type shale gas reservoir exhibited the characteristics of "two lows, one large, and four highs": low TOC content, low Poisson's ratio, large pore size, high felsic content, high inorganic poro-sity, high gas content, and high Young's modulus. (3) Driven by source-reservoir pressure differences, natural gas generated from deep-water source rocks migrated and accumulated in the shallow-water organic-bearing shale carrier beds with more favorable pore structures. (4) The new-type carrier bed shale gas reservoir was different from the organic-rich continuous shale gas reservoir of the Longmaxi Formation, and exhibited a dual enrichment mechanism of source and reservoir controlled by sedimentation and diagenesis, and enrichment controlled by migration and preservation. The research results clarify the enrichment mechanism of new-type shale gas and provide a geological basis for the selection optimization of favorable exploration targets.

     

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