Geochemical and Organic Petrographic Characteristics of Coal From Hangu Formation, Dara Adam Khel, NW Pakistan

Abstract

The present study focuses on ultimate, proximate and, organic geochemical analyses of Hangu Formation, Dara Adam Khel, Khyber Pakhtoonkhwa, Pakistan. Organic geochemical analyses include TOC, Rock-Eval pyrolysis, organic petrography, and vitrinite reflectance study. The proximate analysis shows moisture content ranging from 0.3 to 1.1%, ash from 6.3-22.3%, volatile matter from 7.9 to 12%, fixed carbon from 64.6 to 84.9%, with mean values of 0.68, 12.45, 10.1, and 76.77 %. The total carbon ranges from 62.0 to 81.9 % and the total sulfur ranges from 2.6 to 12 %, having an average values of 61.16, and 6.9 %. It is evident from the proximate study that the analyzed coal has a low percent of moisture content, volatile matter, and a medium percentage of Fixed carbon, which place the studied coal in a low volatile bituminous rank. The sulphur percent from the ultimate analysis is high and may have adverse effects, causing corrosion to machinery and makes the environment polluted. The TOC value of the coals, shales and coaly shales are 3.5 to 83.3 wt.% indicating very goodexcellent source rock for hydrocarbon generation. According to organic geochemical analysis, the kerogens are of type III and IV which belong to terrestrial sources. The petrographic study showed different maceral such as vitrinite (collinite and gelocollinite), followed by inertinite (inertodetrinite). The dominance of vitrinite macerals contributes to gas-prone-type III kerogen. On the base of HI vs TOC plot, the analyzed samples have gas generation potential. This is supported by the thermal maturity, which lies in the mature stage, as indicated by vitrinite reflectance values of 0.71-0.91%.