Abstract
The present study aims to investigate the origin, type, thermal maturity and hydrocarbon generation potential of organic matter and paleo-depositional environment of the Early Paleocene (Danian) Hangu Formation outcropped in the Kala-Chitta Range of Northwest Pakistan, Eastern Tethys. Organic-rich shale and coal intervals were utilized for geochemical analyses including TOC (total organic carbon) and Rock–Eval pyrolysis coupled with carbon (δ13Corg) and nitrogen (δ15Norg) stable isotopes. The organic geochemical results showed that the kerogen Type II (oil/gas prone) and Type III (gas prone) dominate the investigated rock units. The TOC (wt%) and S2 yield indicate that the rock unit quantifies sufficient organic matter (OM) to act as potential source rock. However, the thermal maturity Tmax°C marks the over maturation of the OM, which may be possibly linked with the effect attained from nearby tectonically active Himalayan Foreland Fold-and-Thrust Belt system and associated metamorphosed sequences. The organic geochemical analyses deciphered indigenous nature of the OM and resultant hydrocarbons. The δ13Corg and δ15Norg stable isotopic signatures illustrated enrichment of the OM from both marine and terrestrial sources accumulated into the Hangu Formation. The Paleo-depositional model established using organic geochemical and stable isotopic data for the formation supports its deposition in a shallow marine proximal inner shelf environment with prevalence of sub-oxic to anoxic conditions, a scenario that could enhance the OM preservation. Overall, the formation holds promising coal and shale intervals in terms of organic richness, but due to relatively over thermal maturation, it cannot act as an effective source rock for liquid hydrocarbon generation and only minor amount of dry gas can be expected. In implication, the results of this study suggest least prospects of liquid hydrocarbon generation potential within Hangu Formation at studied sections.
Highlights
The organic-rich shales and coals bearing stratigraphic sequences are widely distributed in Cenozoic and Mesozoic rock records (Petersen 2006; Friederich et al 2016) and these sedimentary units generate and expel much of1 3 Vol.:(0123456789)Journal of Petroleum Exploration and Production Technology the porous and permeable reservoir rock unit (Kassem et al 2021; Radwan 2021; Radwan et al 2021b; Shehata et al 2021), whereas the unconventional hydrocarbon reservoirs are sharing the same source and reservoir rock unit (Radwan et al 2020, 2021a)
Organic geochemical analyses (TOC wt% and Rock–Eval pyrolysis) coupled with stable isotopic proxies were performed on the organic-rich shale and coal samples of the Early Paleocene (Danian) Hangu Formation in the
Kala-Chitta Range of Northwest Pakistan to assess its source rock potential that resulted into the following conclusions;
Summary
The organic-rich shales and coals bearing stratigraphic sequences are widely distributed in Cenozoic and Mesozoic rock records (Petersen 2006; Friederich et al 2016) and these sedimentary units generate and expel much of1 3 Vol.:(0123456789)Journal of Petroleum Exploration and Production Technology the porous and permeable reservoir rock unit (Kassem et al 2021; Radwan 2021; Radwan et al 2021b; Shehata et al 2021), whereas the unconventional hydrocarbon reservoirs are sharing the same source and reservoir rock unit (Radwan et al 2020, 2021a). The hydrocarbon bearing, Tertiary coal and organic-rich shale deposits are reported worldwide for instance in the Gippsland Basin of Australia, Guasare Basin of Venezuelan, Columbus Basin of West Indies, Malaysia, Vietnam, Myanmar, China and Indus Basin of Pakistan (Boreham et al 2003; Shah 2009; Alias et al 2012; Hakimi et al 2013; Abbassi et al 2016; Escobar et al 2016; Friederich et al 2016; Khan et al 2018) Such prospective rock units need detailed studies for hydrocarbon potential assessment using Rock–Eval pyrolysis, TOC analysis, isotopic proxies and organic geochemistry (Boreham et al 2003; Hao et al 2011; Makeen et al 2015; Yandoka et al 2015; Abbassi et al 2016; Niu et al 2019). The investigation of coals and organic-rich shales as hydrocarbon resource is an attractive option to cope with rising energy demands and provide excellent research opportunities to tackle with associated organic geochemical and depositional complexities
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