Estimating stress percolation patterns in hydraulic fractured Gondwana coal using Raman spectroscopy

The present article discusses the importance of combining the laboratory hydraulic fracturing (HF) method with Raman spectroscopy to estimate stress percolation patterns. In order to demonstrate this idea, Gondwana coal (GC) samples of India are employed. The GC samples are taken perpendicular and parallel to the bedding plane direction for the studies. Raman spectroscopy characterization is performed on GC samples to predict the nature of (i.e., tensile or compressive) stress percolation patterns on the fractured samples. Based on the shift in the D-band of Raman spectra the nature of stress percolation patterns is predicted. The proposed method calculates onset and shift in the plastic yielding during HF depending on the nature of stress. A relation between the D-band shift of Raman spectra against the radial crack propagation is estimated considering the geochemical variations for mode I fracture. In general, the fracture modes refer to the decomposition of the crack tip stresses, if the applied stress is orthogonal to the local plane of the crack surface it is referred to as mode I fracture. It was observed that, in perpendicular directions, the GC sample possessed a tensile stress percolation pattern in contrast to the parallel direction.