Advanced Applied Geology

Advanced Applied Geology

Biomarker characteristics of the Asmari reservoir oil in the Dezful Embayment, southwestern Zagros Fold–Thrust Belt, Iran

Authors
Mehdi Mazarei 1
Maryam Khosravi 1
Morteza Tabaei 1
Mohammad Ali Salehi 2
Buyuk Gorbani 3
1 Department of Mining Engineering, Isfahan University of Technology, Isfahan, Iran
2 Department of Geology, Faculty of Sciences, University of Isfahan, Isfahan, Iran
3 Department of Organic Geochemistry, Earth Sciences Research Institute, Research Institute of Petroleum Industry, Tehran, Iran
10.22055/aag.2026.52340.2573
Abstract
This study investigates the geochemical characteristics of oils from the Asmari reservoir in the Dezful Embayment using biomarker parameters. The results indicate that oil from the Nargesi Field contains the highest proportion of saturated hydrocarbons and exhibits superior quality compared to the other studied oil samples. A comprehensive suite of biomarker parameters, including Pr/Ph, DBT/phenanthrene, CPI, TAR, oleanane/C30H, Gam/(Gam+C30H), δ13C values of asphaltenes, C27–C29 steranes, C26–C28 triaromatic steroids, Pr/n-C17 and Ph/n-C18 ratios, as well as Gam/(Gam+C30H) versus Pr/Ph plot, indicates that all studied oils were generated from source rocks deposited in a marine depositional environment dominated by Type II kerogen. Based on the oil classification diagram, the studied oils are classified as paraffinic and paraffinic–naphthenic types. Thermal maturity parameters, including C29 ααα sterane 20S/(20S+20R), C29 steraneββ/(αα+ββ), Ts/(Ts+Tm), CPI, C32 22S/(22R+22S), MDR, and TAS (Total Triaromatic Steranes), demonstrate that all studied samples are thermally mature and fall within the main oil window to peak oil generation stage. Among the investigated oils, the Nargesi sample exhibits the highest level of thermal maturity. The DBT/phenanthrene versus Pr/Ph diagram indicates that the source rocks of all studied oils are of carbonate–marl facies. In addition, the C29/C30 hopane versus C35/C34 hopane diagram indicates that the source rocks of most studied oils are of carbonate–marl facies, whereas those of some oils are of carbonate–shale facies. The C28 steranes versus C28/C29 steranes plot suggests a predominantly early Cretaceous–Tertiary age for the source rocks, which is consistent with the oleanane/C30H ratios and carbon isotope data.
Keywords
Biomarker
Asmari
Dezful Embayment
Gas chromatography
Gas chromatography–mass spectrometry
Subjects
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Advanced Applied Geology
Volume 16, Issue 2
Summer 2026
Pages 193-213