International Journal of Coal Geology, Vol.206, 91-105, 2019
The influence of the thermal aureole asymmetry on hydrocarbon generative potential of coal beds: Insights from Raniganj Basin, West Bengal, India
The aim of the present study is to uncover hydrocarbon generation potential of an area intruded by lamprophyre dyke. Lamprophyre dyke induced a short-distance asymmetric thermal aureole in coal beds with more intense impact along the dip direction. Large ash yield, carbon content, lower volatile matter content, hydrogen indices, presence of natural coke, disordered kaolinite peaks, less pronounced aliphatic peaks, higher aromaticity under Fourier Transform Infra-Red spectroscopy (FTIR); highly rugged surface and large pores with the aid of Atomic force microscopy (AFM); abundant calcium carbonate mineral phases (calcite, dolomite, ankerite) and high temperature silica phases (tridymite, sanidine) under X-ray diffraction (XRD) are the consequences of pronounced thermal effect and expulsion of hydrocarbons. Furthermore, the estimated vitrinite reflectance (EVRo) calculated through maximum pyrolysis temperature (T-max) and measured mean random vitrinite reflectance (VRo) show the maximum difference in the heat-affected coal samples. In addition, parameters for source rock reconstruction and indices for quantification of FTIR spectra i.e. index of aliphaticity (IAL), index of aromaticity (IAR) and index for hydrocarbon generation (IHG) are introduced for coals. The distant (i.e. least-heat-affected) coals collected opposite to the dip direction of the coal bed have a higher potential for hydrocarbon generation. The igneous intrusion thus played a significant role in enhancing the maturity of the organic material, in turn, augmenting the hydrocarbon generation potential for targeting hydrocarbon plays of the area although at the expense of proximal samples.
Keywords:Raniganj Basin;Thermal aureole asymmetry;Lamprophyre dyke intrusion;FTIR indices;Rock Eval pyrolysis;AFM