Hydrocarbon potential, source correlation, and paleoenvironmental reconstruction of the Jurassic interval in the Zey Gawra Oilfield, Kurdistan Region, Iraq

A comprehensive geochemical analysis for the Sargelu, Naokelekan, and Najmah formations cutting rock and crude oil samples from Z1, Z3, and Z5 wells of Hawler Block, Kurdistan Region, Iraq have been studied for source rock evaluation. Depending on the total organic carbon (TOC) content from pyrolysis analyses, the Sargelu and Naokelekan formations are regarded as very good source rocks, and fair source rock for the Najmah Formation. The organic matter in the Sargelu Formation is characterized by types II and mixed II and III kerogens. However, the Naokelekan and Najmah formations are characterized by type II kerogen. The Sargelu and Naokelekan formations’ organic matters are at mature stages; hence, in the oil window, whereas Najmah Formation’s organic matter is at immature stage. Pyrolysis study shows that the Sargelu Formation is oil and gas prone, while the Najmah and Naokelekan formations are oil prone. The biomarkers and bulk properties of the selected oils from Gas Chromatography (GC) and Gas Chromatography-Mass Spectroscopy (GC/MS) analysis show that they originated by the same source rocks. The geochemical characteristics indicate a carbonate source in a reducing environment for the studied formations and oils. Based on the oleanane index, tricyclic terpane indices, C28S/C29S ratios, and gammacerane index, the relative age of the oils and cuttings of Sargelu, Naokelekan, and Najmah formations is Middle to Late Jurassic and deposited under moderate saline condition. The biomarkers parameters show evidence that molecules from the cutting rocks of the Sargelu and Naokelekan formations are related to the oils in Z1, Z3, and Z5 wells. However, they are not related to the Najmah Formation.