Thermal controls of lamprophyre sill on hydrocarbon generation outlook of shale beds in Raniganj basin, India

Abstract

The present work highlights the role of lamprophyre sill on the potential of hydrocarbon generation of shale beds. Here, the authors had systematically collected seven shales for detailed investigations of thermal impact provided by lamprophyre sill both along the dip and opposite to the dip directions of the shale beds. Proximate, ultimate, Rock Eval pyrolysis, organo-petrographic, vitrinite reflectance, Fourier Transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and X-ray diffraction (XRD) analyses were performed. Authors have also introduced new parameters like index of aliphaticity (IAL), index of aromaticity (IAR) and index for hydrocarbon generation (IHG) for precise quantification of FTIR spectra of shales, which in turn helpful in indicating the influence of thermal aureole on shale beds. The results indicate more distinct thermal alterations in the heat-affected shales collected along the dip direction of the shale beds owing to more pronounced and extensive thermal impact of lamprophyre sill in the dip direction. The estimated vitrinite reflectance (EVRo) and mean random vitrinite reflectance (VRo) show maximum difference in the heat-affected shales. Low genetic potential (GP), IHG indicate poor potential for heataffected shales along the dip due to intense thermal influence. In contrast, the fairly-affected shales collected opposite to the dip of the bed have higher GP, IHG and hence considered to be excellent source material. The mesopores present in the fairly-affected shales held good amount of hydrocarbons and thus suitable for hydrocarbon exploration and exploitation. The igneous intrusion improves the overall the general maturity of the area although at the expense of the reduction of the hydrocarbon generation potential of the proximal samples.