Quantitative evaluation of shale brittleness based on statistics: Taking shale of Niutitang Formation in western Hubei as an example
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摘要: 【研究目的】页岩储层的脆性是反映页岩气储集层压裂品质的参数之一，对压裂难易程度和压裂缝网形态有着重要的影响。【研究方法】对鄂西黄陵背斜南翼五口钻井进行了系统采样和全岩矿物及黏土含量测试、主微量元素含量测试、声学力学联测实验等分析测试，利用聚类分析和主成分分析法对页岩脆性进行了定量评价。【研究结果】矿物与岩石脆性密切相关，利用聚类分析方法可以定量表征泥页岩中有效脆性矿物成分和非有效脆性矿物成分；利用主成分分析法建立了基于岩石力学、矿物组分和元素成分的脆性指数综合定量评价公式，形成鄂西地区牛蹄塘组页岩层段的脆性指数剖面。【结论】微地震监测及压裂施工结果显示，新建立的脆性指数剖面能准确指示页岩的高脆性层段，与压裂结果吻合较好。Abstract: The brittleness of shale reservoir is one of the parameters reflecting the fracturing quality of shale gas reservoir, which has an important influence on the degree of difficulty of fracturing and the shape of fracture network. [Methods] In order to accurately evaluate the brittleness characteristics of Niutitang Formation shale reservoir in Western Hubei, systematic sampling, whole rock mineral and clay content test, main and trace element content test, acoustic mechanics joint test and other analytical tests were carried out on five wells in the south wing of Huangling anticline in Western Hubei. The quantitative evaluation of shale brittleness was carried out by cluster analysis and principal component analysis. [Results]There is a close relationship between minerals and rock brittleness, and the cluster analysis method can quantitatively characterize the effective brittle mineral composition and non-effective brittle mineral composition in shale; The comprehensive quantitative evaluation formula of brittleness index based on rock mechanics, mineral composition and element composition is established by using principal component analysis method, which forms the brittleness index profile of Niutitang Formation shale section in Western Hubei. [Conclusions]The results of microseismic monitoring and fracturing show that the newly established brittle index profile can accurately indicate the high brittle layer of shale, and the fracturing effect is good.
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