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<p>This research assesses the hydrocarbon potential, kerogen classification, and thermal maturity of the Upper Jurassic-Lower Cretaceous Chia Gara Formation cuttings samples from the T well (ca. 2780–2880&#xa0;m depth), central Iraq. Geochemical analysis comprised total organic carbon (TOC) determination, Rock-Eval 6 pyrolysis, gas chromatography (GC), and gas chromatography–mass spectrometry (GC–MS). Our results indicate that the Chia Gara Formation is characterized by TOC values ranging from 1.3 to 11.4 wt% with an average of 4.47 wt%. Notably, higher TOC concentrations are observed in the lower stratigraphic section. Rock-Eval pyrolysis Hydrogen and Oxygen indexes (HI and OI) results reveal predominance Types I and II kerogens, implying a primary contribution from marine organic matter. The distributions of normal alkanes, acyclic isoprenoids (pristane and phytane) and biomarker ratios, including regular steranes and terpanes (tricyclic terpane ratios, homohopane index and C<sub>35</sub>/C<sub>34</sub>), together with aromatic hydrocarbons, suggest a predominantly marine deposition setting under anoxic environment with little terrestrial input. Thermal maturity parameters, including Tmax (ca. 426–436&#xa0;°C), production index (PI) (ca. 0.05–0.09), C<sub>32</sub> homohopane ratio (0.58–0.60), C<sub>29</sub> sterane isomerisation ratios, and methylphenanthrene index (MPI; 0.59–0.75), show that the organic matter is marginally to early mature and mid-mature. These integrated geochemical data corroborate that the Chia Gara Formation is qualified as a good to excellent petroleum source rock with substantial hydrocarbon generation potential specifically within its lower part.</p>

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Some organic geochemical characteristics of the upper Jurassic–lower Cretaceous Chia Gara formation in Central Iraq: insights from TOC, rock-eval pyrolysis, saturated and aromatic biomarkers

  • 期刊论文

  • 发表日期：

    2026年3月17日

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  • Seror S. AL-Jubouri,
  • Mohamed W. Alkhafaji

摘要

This research assesses the hydrocarbon potential, kerogen classification, and thermal maturity of the Upper Jurassic-Lower Cretaceous Chia Gara Formation cuttings samples from the T well (ca. 2780–2880 m depth), central Iraq. Geochemical analysis comprised total organic carbon (TOC) determination, Rock-Eval 6 pyrolysis, gas chromatography (GC), and gas chromatography–mass spectrometry (GC–MS). Our results indicate that the Chia Gara Formation is characterized by TOC values ranging from 1.3 to 11.4 wt% with an average of 4.47 wt%. Notably, higher TOC concentrations are observed in the lower stratigraphic section. Rock-Eval pyrolysis Hydrogen and Oxygen indexes (HI and OI) results reveal predominance Types I and II kerogens, implying a primary contribution from marine organic matter. The distributions of normal alkanes, acyclic isoprenoids (pristane and phytane) and biomarker ratios, including regular steranes and terpanes (tricyclic terpane ratios, homohopane index and C35/C34), together with aromatic hydrocarbons, suggest a predominantly marine deposition setting under anoxic environment with little terrestrial input. Thermal maturity parameters, including Tmax (ca. 426–436 °C), production index (PI) (ca. 0.05–0.09), C32 homohopane ratio (0.58–0.60), C29 sterane isomerisation ratios, and methylphenanthrene index (MPI; 0.59–0.75), show that the organic matter is marginally to early mature and mid-mature. These integrated geochemical data corroborate that the Chia Gara Formation is qualified as a good to excellent petroleum source rock with substantial hydrocarbon generation potential specifically within its lower part.