Organo-inorganic facets of shale gas reservoir of Jharia Basin of Damodar Valley, India

The Mahuda-Kapuria block of the Jharia Basin, Damodar Valley comprises thick shale sequences of Shibabudih (>180 m) in Barakar and Hariharpur shale (>40 m) in Barren Measures Formations. The ternary organic facies of maceral shown the trend of anoxification, resulting in higher maceration as a function of terrestrial-marshy depositional conditions. Subsequently, it supported the tissue preservation and carbon enrichment contributing to the formation of shale matrix. H/C vs O/C plot shown Type III/IV kemgen transformed from fluviohumid to dry terrestrial depositional conditions followed by diagenesis, cata- and metagenesis processes. Also, the range values of T-max (442-558 degrees C) and HI (25-345 mg HC/g TOC) confirms the significantly matured source rock having the input of dominantly type III/IV kerogen. The 51 and S2 specify (0.07-2.54 mg HC/g rock, 0.58-20.14 mg HC/g rock) the presence of substantial free/adsorbed hydrocarbon gases and uncracked hydrocarbon compounds. The large content of SiO2 , Al2O3, and Fe2O3 account for 85-95 % of the samples point towards granitic source rock of sediments. The high CIA and low ICV values denote the compositional maturity of the shale due to conversion of feldspars to Al-bearing clays through intense geochemical weathering and alteration. The positive trend of organic weight with Langmuir volume (V-L) and TOC specify the organic carbon present in shale mainly contributes to the formation of pore containing matrix system and adsorption of methane in shale pores. The mineralogy of shale directly controls the tensile strength, uniaxial compressive strength, Young's modulus, Poisson's ratio and brittleness of shale beds. Further, it is observed that the brittleness of shale beds exhibits higher axial strain with a small region of elastic behaviour by the influence of the hydrous property of kaolinite and illite. The proposed empirical EMBI for estimation of brittleness indicated moderate brittle characteristics of shale beds.