Controlling mechanism of shale palaeoenvironment on its tensile strength: A case study of Banjiuguan Formation in Micangshan Mountain

The sedimentary environment largely controls the thickness, distribution, organic carbon content, geochemical, and petrophysical characteristics of the shale. Thereby, the mechanical properties of the shale are indirectly influenced. Along these lines, in this work, the tensile strength + acoustic emission (AE), and total organic carbon (TOC) were systematically explored. In addition, X-ray fluorescence spectroscopy (XRF), inductively coupled plasma mass spectrometry (ICP-MS), as well as other experiments were performed on the marine shale of the Banjiuguan Formation in the Micangshan Mountain to identify the tensile strength and geochemical characteristics of the shale. As a result, its Brazilian cleavage damage mechanism was examined, and the control mechanism of the tensile strength of the shale was revealed. From the acquired results it was demonstrated that 1) the tensile strength of the shale ranged from 14.03 to 25.62 MPa, with an average value of 20.84 MPa; 2) The sedimentary environment of shale has an influence on its mineral morphology and content. 3) The total organic carbon (TOC) content in shale has a certain influence on its tensile strength, but it is not the main controlling factor. Additionally, diagenesis of shale also influences its mechanical properties. 4) The sediment source and palaeosalinity have a strengthening effect on shale, while palaeo-climate and palaeo-redox conditions have a constraining effect. This study can provide theoretical guidance for the prediction and production efficiency of shale gas favorable areas.