Evaluation of gas resource potentiality, geochemical and mineralogical characteristics of Permian shale beds of Latehar-Auranga Coalfield, India

The plots of hydrogen index (39.54-821.45 mg HC/g TOC) with calculated VRo (0.29-1.05%) and Tmax (414-456 °C) are signifying types I, II, III and IV kerogen in the shales prone to generate oil, wet and dry gas placed in immature to mature regions. The positive linear correlation of the VL with kaolinite and illite contents suggests that mainly clays contribute to the formation of shale matrix. The SEM images show six types of pore: i) lenticular open pores along the fissility, ii) altered pores due to weathering, iii) intergranular pores, iv) intermingled pores between crystal lattices, v) partially filled pores associated with clays and minerals, and vi) evolved pores by cracking of the organic compounds. The values of porosity and permeability have been measured under reservoir simulated confining pressure, and are ranging from 0.87-8.18% and 0.08-1.45 mD, respectively. This shows poor connectivity between the pores and fracture mechanisms controlled by the clay and minerals. It is summarized that the studied shales of Latehar-Auranga Coalfield have a low to moderate gas potential, based on their in-situ gas, TOC content (1.28-16.26 wt%), sorption capacity, Tmax values and thermal maturity. Moreover, the significant residual volume, low porosity and low permeability are the most critical properties for shale gas resource development at the Latehar-Auranga coalfield.