Multi-analytical assessment of shale gas potential in the West Bokaro Basin, India: A clean energy prospect

Abstract

Shale gas, a type of unconventional natural gas found within shale formations, has emerged as a significant source of energy globally. The West Bokaro Basin, part of the Damodar Valley, is known for its rich coal deposits and complex geological history. The basin's stratigraphy includes significant coal-bearing formations interbedded with shales, which may be potential sources of shale gas. The key formations in the basin include the Barakar Formation, which is the primary coal-bearing unit, and the Raniganj Formation, which contains substantial shale intervals. These formations exhibit varying thicknesses, organic content, thermal maturity, and mechanical strength, all of which are critical factors influencing shale gas potential. The assessment of shale gas potential in the West Bokaro Basin involves evaluating the organic richness, thermal maturity, pore characteristics, geochemistry, and mineralogy of the shale formations. Apart from organic richness and thermal maturity, the shale formations must be friable, as they generally lack natural permeability. This study aims to present a comprehensive analysis of the prospects of shale gas in the West Bokaro Basin based on the organic petrography, geochemistry, mineralogical study, Fourier Transform Infrared Spectroscopy (FTIR) analysis, and low-pressure N₂ adsorption analysis. The dark color, greasy touch, and high total organic carbon (TOC) content (5.88 %–22.84 %) provided an initial clue for the shale's potential as a source rock. Results from organic petrographic analysis suggest that these shales contain kerogen type Ⅲ, which is a known indicator of gas-prone zones. The random vitrinite reflectance (R_o, 0.80 %–0.91 %) and the temperature of maximum pyrolysis yield (T_max, 434–448 °C) indicate that the organic matter has attained the sufficient thermal maturity required for the generation of hydrocarbons. FTIR and X-ray diffraction (XRD) analyses identified inorganic entities and high quartz content in the shale samples, confirming their friability. The brittleness index (BI) calculated using X-ray fluorescence (XRF) data showed BI values above 0.48, indicating that the shales are brittle, which is advantageous for hydraulic fracturing. The high quartz content in the shale might act as a natural proppant, enhancing gas extraction efficiency. These findings suggest that the West Bokaro shales hold promise for economically viable shale gas production.