Organic Geochemical Assessment of Jurassic Source Rock from Duhok, North Iraq

Abstract

In the Northern Iraq, the Jurassic oil shales are widely distributed. The studied samples were collected from Sehkanyian, Sargelu and Naokelekan formations in Banik area, about 25 km due NE of Zakho town, Duhok Governorate, North Iraq. The hydrocarbon potentiality parameters, including type and amount of bitumen and kerogen, and thermal maturity of 72 samples as well as two oil samples were assessed by using Rock-Eval/TOC pyrolysis and GC/GCMS techniques. In general, Sargelu Formation samples have PI values below 0.1 and Tmax values varying between 437 and 449, suggesting immature to early mature stage of thermal maturity of oil. They can be considered as good to excellent source, where TOC content ranges from 0.06 to 28.57 with an average of 4.69%. The Naokelekan Formation samples can also be considered as an excellent source rock with TOC content ranges from 5.39% to 25.55%, averaging 17.77%, while the Sehkanyian Formation has no potential (TOC below 0.09%). The samples of Sargelu and Naokelekan formations contain both kerogen types I and II indicating marine organic matter mainly derived from algae and phytoplanktonic organisms proposing typical oil source kerogen. The extracted bitumen samples from Sargelu Formation show diagnostic ratios of Pr/Ph, Pr/nC17 and Ph/nC18 for generation of oil at an early thermal maturity stage. The low Pr/Ph ratio of the analyzed two oil samples from Jeribe and Sargelu formations together with the low Pr/n-C17 and Ph/n-C18 suggest that the oils was generated from a source rock containing mainly marine organic matter deposited under reducing conditions.