LAUSR

Abstract Shale brittleness is one of the essential parameters for shale gas reservoir evaluation. Based on correlation analysis between triaxial test and XRD results of shale samples from Wufeng-Longmaxi formations in Shuanghe outcrop area in Sichuan Basin, south western China, we propose a new mineralogical brittleness index from brittle minerals. This study shows three important results: (1) The simple sum of brittle minerals is not significantly correlated to the mechanical brittleness index, indicating the former may be a questionable estimator of shale brittleness. (2) Considering the bulk modulus of the different brittle minerals, a new mineralogical brittleness index, as a function of brittle minerals with respective weighting coefficients, is proposed, and this new index is significantly correlated to the mechanical brittleness index. (3) The new mineralogical brittleness index is used in a case study for its effectiveness, in characterizing shale brittleness. With a large amount of XRD data available from laboratory for calibrating the logging interpretation of mineralogical compositions, the new mineralogical brittleness index has a good reliability and its application has proved to be valuable.