Pore structures and fractal dimensions in Early Permian Barakar shales of Rajmahal Basin, Jharkhand, India

Abstract

The proximate, low-pressure N2 sorption, X-ray diffraction, and organic petrography parameters have been used to delineate the pore structures and fractal dimensions in the Barakar shales of Rajmahal Basin, India. The information has been utilized for the assessment of shale gas reservoir and to know about the mode of occurrence and storage capacity of shales for the entrapment of methane (CH4). The studied shales are characterized by high fixed carbon contents (10.14-46.09 wt.%) and contain significant abundance of brittle minerals, like quartz (6.0-51.6%) and mica (1.0-41.2%). The petrographic observations show that the studied samples comprise of numerous laths of vitrinite (collotelinite and vitrodetrinite) and semifusinite macerals and quartz grains. The data of low-pressure N2 sorption analysis indicates the shales encompass mainly meso- to macropores and microfractures. The total pore volume, average pore size, and multipoint BET surface area of the studied shales vary from 0.012 to 0.023 cc/g, 8.295 to 10.840 nm, and 5.752 to 10.390 m2/g respectively. Two types of fractal dimensions (D1 and D2) have been calculated by using FHH (Frankel-Halsey-Hill) method from the N2 adsorption isotherm. The high values of fractal dimensions (2.1949 < D1 < 2.4837 and 2.6668 < D2 < 2.7247) are indicating the highly rugged pore surface or complexity in the pore structures.