Microscale assessment of 3D geomechanical structural characterization of gondawana shales

The microscale characteristics of gray and black shale samples collected from two different locations of Singrauli coalfield, Madhya Pradesh, India were investigated using scratch tester and Raman stress mapping. The failure events were analyzed for the entire scratch track. The areas of critical point were identified based on the acoustic emission, tangential force measurement along with characterization methods Scanning Electron Microscopy (SEM) and Raman spectroscopy. The SEM studies at the critical points indicate the failure in black and gray shale are completely different. The critical points are analyzed by confocal Raman spectroscopy for measuring the Raman spectral shifts and Raman stress mapping. The Raman spectra of disordered D band are used for quantifying the stress in the entire scratch track. Micro scratch test performed in different directions along with critical point regions of black and gray shale is compared. Raman spectral shifts of D band are measured and compared for the strained regions. This reveals the 2D Raman imaging of black and gray shale as a proxy for characterizing the stress inversion. Correspondingly the Raman peak intensity ratios along with full width at half maximum (FWHM) were calculated for the critical regions.