Organic Geochemistry And Source Rock Potential Assessment Of The Late Paleocene Patala Formation Margalla Hills Range,North Pakistan

Black shales of the Paleocene Patala Formation are proven source rocks for conventional hydrocarbons in southern Potwar Basin of Pakistan and are assumed to be effective source rocks towards north in the Margalla Hill Range of Pakistan.In this regard,the current study focuses on source rock geochemistry of the Paleocene Patala Formation to assess its source rock potential,organic matter types and thermal maturity levels in the Margalla Hill Range of north Pakistan.The present study is emphasized on an integrated approach of geochemical analysis and diagenetic setting of the Paleocene Patala Shale of Margalla Hill ranges,dominantly composed of dark grey shales yielding TOC values of 0.3-0.5%,while the dark carbonaceous shales are present in a very lesser amount,producing a TOC value of 0.6-0.69 wt.%.The S₂ value of rock eval shows poor potential with values ranging from of 0.015mg/g to 0.445mg/g with an average of 0.104mg/g rock.Source rock generative potential,kerogen types and thermal maturation of the analysed rock samples were unraveled by using Rock-Eval pyrolysis Tmax,TOC(total organic carbon)and vitrinite reflectance(R_o%)analyses.TOC analysis coupled with S₂ yield revealed poor to fair source rock quality encountered within the formation.The organic matter of the stratigraphic section appears to be kerogen type III.The average Hydrogen Index(HI)value is 67.17 mg HC/g TOC which is far greater that the upper limit of type III kerogen depicting that the hydrocarbons are composed of type III kerogen and some of the samples are over mature.The pyrolysis T_max vs Hydrogen Index(HI)showed mostly Type III kerogen dominated by thermally mature to over mature organic matter.The HI and genetic potential are low and revealed poor hydrocarbon generation potential of the formation.The S1 vs TOC plots confirm the indigenous nature of the hydrocarbons hosted by Patala Formation.The vitrinite reflectance outcomes indicated mature to mature source rock that's why the Paleocene Patala shale beds lying in dry gas zone.The HI and OI signatures and abundance of Type III kerogen are indicating dominance of terrestrial organic matter within the formation.Overall,the investigated Patala Formation exposed at the studied section of Margalla Hill Range,Pakistan acts as a poor source rock unit for liquid hydrocarbon generation but holds prospects for dry gas generation in the study area.