An integrated geochemical study was performed for the assessment of the hydrocarbon potential, environment of deposition, thermal maturity and the organic matter’s source of the Chichali Formation in the Kohat sub-basin of Pakistan. The analytical techniques used included the total organic carbon (TOC), Rock–Eval (RE), organic petrography, column chromatography (CC) and gas chromatography mass spectrometry (GC–MS). The quantity of the organic matter (i.e., TOC), Rock–Eval parameters (such as the original hydrogen index, oxygen index and T_max) and maceral analyses revealed that the shales of the Chichali Formation have poor to good petroleum source potential with Kerogen type II presently shown as type III (hydrogen index, oxygen index and T_max) due to thermal maturation and with higher marine organic matter. The extracts of the rock samples have high amount of short-chain n-alkanes with high ratios of tricyclic terpanes to hopanes (TCT/H), C₂₇ to C₂₉ stranes and low ratios of pristane to phytane (Pr/Ph), C₁₉/C₂₃ TCT and C₂₀/C₂₃ TCT. These ratios and lack of terrestrial biomarker (oleanane) are pointing toward algal/marine organic source deposited under anoxic environment. The dibenzothiophene-to-phenanthrene ratios (DBT/P) versus Pr/Ph cross-plot also confirms the anoxic environment with sulfate poor mixed shale/carbonate lithology. The drill cuttings show relatively high maturity compared to outcrop samples indicated by n-alkanes ratios, isoprenoids vs n-alkanes cross-plot, methyl-phenanthrene index (MPI-1), methyl-dibenzothiophene ratios and absence of saturate biomarkers. All the above findings reveal that the Chichali Formation had mature algal source with anoxic environment of deposition and may prove to be a poor to good hydrocarbon source rock.

中文翻译：

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巴基斯坦开伯尔-普赫图赫瓦省科哈特盆地的奇查里组综合地球化学研究

进行了一项综合的地球化学研究，以评估巴基斯坦Kohat盆地中的奇恰里组的碳氢化合物潜力，沉积环境，热成熟度和有机物来源。所使用的分析技术包括总有机碳（TOC），Rock–Eval（RE），有机岩相学，柱色谱法（CC）和气相色谱质谱法（GC-MS）。有机质的数量（即TOC），岩石-Eval参数（例如原始氢指数，氧指数和T _max）和宏观分析表明，奇卡里组页岩在含干酪根的条件下具有差至良好的石油来源潜力II型目前显示为III型（氢指数，氧指数和T _max）是由于热成熟和海洋有机质含量较高。岩石样品的提取物中含有大量的短链正构烷烃，其中三环萜烷与hop烷的比例高（TCT / H），C ₂₇至C ₂₉烷烃的比例高，而rist烷与植烷的比例低（Pr / Ph），C ₁₉ / C ₂₃ TCT和C ₂₀ / C ₂₃TCT。这些比率和缺乏陆地生物标志物（油烷）指向在缺氧环境下沉积的藻类/海洋有机源。二苯并噻吩与菲之比（DBT / P）与Pr / Ph交会图也证实了缺氧环境，其页岩/碳酸盐岩的混合岩性差。与由正构烷烃比，类异戊二烯对正构烷烃的交点图，甲基菲指数（MPI-1），甲基-二苯并噻吩比率和不存在饱和生物标志物指示的露头样品相比，钻屑显示出相对较高的成熟度。以上所有发现表明，Chichali组藻类资源成熟，具有缺氧沉积环境，可能是劣质至优质的烃源岩。