Abstract
A total of 56 cuttings samples of Sargelu and Kurrachine formations from different wells (Ain Zalah, Baiji, and Jabal Kand) in northern Iraq have been investigated in this study. Both the Sargelu and Kurrachine formations were examined using Rock-Eval pyrolysis to assess the richness of organic matter and thermal maturity level. The Sargelu Formation Have Total Organic Carbon wt.% ranged from 0.22–2.52 wt.%, average 1.26 wt.% in Ain Zalah Well, and between 0.57–8.90 wt.%, average 2.95 wt.% in Baiji Well, and between 0.81–11.80 wt.%, average 5.01wt.% in for Kand Well. It is considered a potential source rock based on total organic carbon content. total organic carbon wt. % in Ain Zalah and Kand in the Kurrachine Formation is considered poor source rock with a total organic carbon content of 0.17, 0.39 wt. %, respectively, while in Baiji Well is considered moderate source rock with total organic carbon content 0.53 wt. %. The Rock-Eval data are not always sufficient to define the kind of organic matter through the use of the van Krevelen diagram because HI and OI are affected by both matrix mineralogy and the kerogen mixture. For accurate assessments of the source rocks, gas chromatography has been relied on, which provides a direct indication of the kerogen type as well as the type of hydrocarbons that kerogen can generate during maturity. Gas chromatography analysis indicates that all selected samples contained type II kerogen. The highest value of the TAS/ (MAS+TAS) ratio was found in Ain Zalah samples (Sargelu Formation), and this result indicates the occurrence of an aromatization process with increasing thermal maturation.
Highlights
Petroleum source layers are fine-grained, silicate rocks rich in clay or dark-colored carbonate rocks that have generated and expelled hydrocarbon effectively (Leythaeuser, 2005)
In the analyzed samples that they studied, carbonate is richer in organic matter and more oil-prone than silty mudstones and carbonaceous shales (Abdula et al, 2017); Edilbi et al (2019) in their study on the potential of source rocks and basin modeling of the Kurrachine Formation concluded that the formation consists of mixed types ІІІ and ІІ-ІІІ kerogen, and the values of Tmax show that the organic matter is mature
The parameters obtained by Rock-Eval pyrolysis include S1, S2 (Hydrocarbon compound generated by the cracking of Kerogen during pyrolysis, S3 (Carbon dioxide released during the thermal cracking of kerogen), and Tmax (Maximum temperature at highest amount of S2 generation)
Summary
Petroleum source layers are fine-grained, silicate rocks rich in clay (mudstone, shales) or dark-colored carbonate rocks (marlstones, limestone) that have generated and expelled hydrocarbon effectively (Leythaeuser, 2005). Jassim and Al-Gailani (2006) studied petroleum systems in the Triassic and Jurassic; Al-Ameri et al (2009) in their study on the palynofacies of the upper units of Kurrachine and Baluti formations concluded that the organic matter within the Kurrachine Formation consists of thermally mature mixed kerogen types ІІ and ІІІ; Abdula (2010 and 2015) identified two types of kerogen (ІІ and ІІІ) in the Sargelu Formation and he showed through the pyrolysis analysis that complete organic carbon is decreasing towards the north and northeast areas of Iraq; Al-Badry investigated geochemistry and stratigraphy of Jurassic formations in northern Iraq in 2012 and concluded that Chia Gara, Naokelekan, and Sargelu formations are all good source rocks for generating and producing hydrocarbons. The aim of this research is to evaluate the potential of the source rocks by determining the type of kerogen using gas chromatography and to assess the rock maturity in the Sargelu and Kurrachine formations
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