ORGANIC GEOCHEMICAL CHARACTERIZATION AND SHALE GAS POTENTIAL OF THE PERMIAN BARREN MEASURES FORMATION, WEST BOKARO SUB-BASIN, EASTERN INDIA

Anuradha Tewari¹, Suryendu Dutta^1* and Tanmoy Sarkar²

¹ Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai-400076, Maharashtra, India.

² RI-3, Central Mine Planning & Design Institute Limited, Gondwana Place, Kanke Road, Ranchi-834008, Jharkhand, India.

^* Corresponding author, email: s.dutta@iitb.ac.in

This study investigates the shale gas characteristics of the Permian Barren Measures Formation (Gondwana Supergroup) in the West Bokaro sub-basin of the Damodar Valley Basin, eastern India. A total of 23 core shale samples collected from a borehole located in the western part of the sub-basin were analysed using organic geochemical techniques and scanning electron microscopy. The samples are black carbonaceous shales composed chiefly of quartz, mica and clay minerals.

Rock-Eval pyrolysis data show that the analysed samples contain a mixture of Type II and Type III kerogen with TOC values of 2.7 to 6.2%. Rock-Eval T_max values ranging from 443 to 452 °C correspond to calculated vitrinite reflectance of approximately 0.8-0.9%. A cross-plot of hydrogen index versus T_max indicates that the samples have reached peak oil to wet gas maturities. A pristane/n-C₁₇ versus phytane/n-C₁₈ cross-plot, together with biomarker parameters such as the dominance of C₂₉ over C₂₇ and C₂₈ steranes and high moretane/hopane ratios (0.22-0.51), demonstrate that the shale samples contain terrigenous organic matter deposited in a suboxic environment.

Scanning electron microscopy images of shale samples show the presence of a complex, mostly intergranular pore network. Both micropores (>0.75µm) and nanopores (<0.75µm) were observed. Some pores are elongated and are associated with layer-spaces in sheet silicate minerals; others are non-elongated and irregular in shape. The organic geochemical parameters and the observed pore attributes suggest that the Barren Measures Formation has good shale gas potential.

Key words: Barren Measures Formation, Gondwana Supergroup, Permian, Damodar Valley Basin, India, shale gas, black shales, organic geochemistry, pore structure.

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