川东地区侏罗系凉高山组页岩油气地质特征及勘探潜力

Geological characteristics and exploration potential of shale oil and gas in Jurassic Lianggaoshan Formation, eastern Sichuan Basin

  • 摘要: 四川盆地侏罗系凉高山组发育广覆式厚层富有机质页岩。近年来,在凉高山组凉一段页岩型、凉二段砂泥岩互层型两类储层中均获高产工业油气流,展现出良好的资源潜力,使凉高山组成为四川盆地浅层风险勘探的重要接替领域。采用全岩X-衍射、有机地化分析、扫描电镜等分析手段,结合成藏要素对比,探讨了川东地区凉高山组页岩油气成藏主控因素。凉一段页岩平均孔隙度为4.45%,储集空间以黏土矿物粒内、粒间溶蚀孔为主,局部发育有机孔、层理缝和高角度缝;页岩储层脆性矿物含量高,两向水平应力差适中,可压性好。有机碳含量等值线呈环带状分布,在垫江—梁平—忠县生烃中心总有机碳含量超1.8%;有机质类型以Ⅱ2型和Ⅲ型为主,平均有机质成熟度(Ro)为1.14%,整体处于成熟—高成熟阶段。“沉积控源、高压富集、裂缝疏导”为凉高山组页岩油气富集高产的三大主控因素,其中沉积控源、异常高压富集的优先级高于裂缝疏导。以优质页岩连续厚度、地层压力系数、微裂缝发育程度及脆性指数等参数为评价依据,建立了川东地区凉高山组页岩油气有利区评价标准。鉴于邻区勘探经验,建议纵向上以凉一段3小层优质页岩为主要目标,区域上重点关注忠县向斜、万县向斜等Ⅰ类有利区,对埋深大于2 500 m的向斜核部区开展地质—工程一体化勘探。

     

    Abstract: The Jurassic Lianggaoshan Formation in the Sichuan Basin is characterized by widely distributed, thick organic-rich shale. In recent years, high-yield industrial oil and gas flows have been obtained in shale reservoirs of the first member of the Lianggaoshan Formation (Liang 1) as well as sandstone and mudstone interbedded reservoirs of the second member of the Lianggaoshan Formation (Liang 2), showing good resource potential. The high yield makes the Lianggaoshan Formation an important successor field for shallow oil and gas exploration in the Sichuan Basin. Using whole rock X-ray diffraction, organic geochemical analysis, and scanning electron microscopy (SEM), combined with a comparison of accumulation elements, the main controlling factors of shale oil and gas accumulation in the Lianggaoshan Formation of the eastern Sichuan Basin were discussed. The average porosity of shale in Liang 1 member is 4.45%, with reservoir space mainly consisting of intragranular and intergranular dissolution pores of clay minerals, and locally developed organic pores, bedding fractures, and high-angle fractures. The shale reservoirs have high brittle mineral content, moderate two-way horizontal stress difference, and good compressibility. The total organic carbon (TOC) content isolines exhibit ring-shaped distribution, with TOC content exceeding 1.8% in the Dianjiang, Liangping and Zhongxian hydrocarbon generation center. Organic matter types are mainly type Ⅱ2 and type Ⅲ, with an average organic matter maturity (Ro) of 1.14%, generally in the mature to highly mature stage. Three main controlling factors were observed for shale oil and gas enrichment and high production in the Lianggaoshan Formation: (1) sedimentation, which controlled source, (2) overpressure, which promoted enrichment, and (3) fracturing, which facilitated migration. Among them, sedimentation-controlled source and abnormal overpressure-driven enrichment are more critical than fracturing in controlling oil and gas migration. Using parameters such as continuous thickness of high-quality shale, formation pressure coefficient, micro-fracture development degree, and brittleness index, the evaluation criterion for favorable areas of shale oil and gas in the Lianggaoshan Formation of the eastern Sichuan Basin was established. Based on exploration experience in adjacent areas, it is recommended to prioritize the three high-quality sublayers of Liang 1 member as the primary targets vertically, while focusing regionally on favorable type Ⅰ areas such as the Zhongxian and Wanxian synclines. An integrated geological and engineering exploration for core areas of the syncline with burial depth greater than 2 500 m should be conducted.

     

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