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四川盆地南部长宁与威远区块是我国页岩气主要产区之一,主要产气层上奥陶统五峰组—下志留统龙马溪组富有机质页岩厚度介于20~40 m,具有良好的可对比性,然而,从笔石地层的角度分析后发现,上述2个区块黑色富有机质页岩的沉积时间和沉积速率均存在着明显的差异。为此,应用沉积学、生物地层学、地球化学和矿物学等研究手段,开展了上述2个区块8口钻井的岩心描述和笔石生物地层划分等工作。研究结果表明:(1)长宁地区的富有机质页岩主要沉积于WF1—LM4笔石层段,而威远地区则主要沉积于LM1—LM8笔石层段,二者富有机质页岩的沉积时间差异较大;(2)受广西运动的影响,富有机质页岩的沉积中心不断向北(威远地区)迁移,越靠近南部的海岸线,富有机质页岩沉积结束的时间就越早;(3)威远地区局部缺失观音桥组下部和部分笔石带,发育水下古隆起(赫南特冰期或已隆出水面),其边界目前尚未明确,影响了富有机质页岩的沉积,在该区域进行页岩气勘探部署需格外谨慎。
The Changning and Weiyuan blocks in the southern Sichuan Basin are one of the major shale gas producing areas in China. The thickness of organic-rich shale in Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation ranges from 20 m to 40 m, However, from the perspective of the penolith strata, it is found that there is a significant difference between the deposition time and the deposition rate of the black organic-rich shale in the two blocks above. To this end, the sedimentology, bio-stratigraphy, geochemistry and mineralogy and other research methods to carry out the core of the two blocks 8 drilling described and lithosphere biostratigraphy division and so on. The results show that: (1) the organic-rich shale in Changning area is mainly deposited in the WF1-LM4 penolith, while the Weiyuan area is mainly deposited in the LM1-LM8 penolith, and the deposition time of the organic-rich shale (2) Due to the influence of Guangxi movement, the sedimentary center of organic-rich shale migrates continuously to the north (Weiyuan area), and the nearer to the southern coastline, the earlier the sedimentation of organic-rich shale ends; (3) ) In the Weiyuan area, the lower part of the Guanyinqiao Formation and part of the pen-lithosphere, the development of the underwater paleohigh (Hernández glaciation or the surface water has been extended), the boundary is not yet clear, affecting the deposition of organic-rich shale, Shale gas exploration and deployment in the region should be used with great care.