Quantitative evaluation of shale brittleness based on statistics: Taking shale of Niutitang Formation in western Hubei as an example

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.