Biomarker characteristics of certain crude oils and the oil-source rock correlation for the Kurdistan oilfields, Northern Iraq

Abstract

The study herein analysed crude oil and source rock samples from Kurdistan oilfields, northern Iraq using various biomarker ratios. Biomarker characteristics are used to provide information on source organic matter input, depositional environment and the correlation between crude oils and Chia Gara source rocks. The relevant data include normal alkane and acyclic isoprenoids distributions, terpane and sterane aliphatic biomarkers and distribution of the aromatic biomarkers naphthalenes, phenanthrenes, dibenzothiophene and methyldibenzothiophenes. The Kurdistan’s oils characterized by low Pr/Ph ratio (<1.0), a relatively high C35 homohopane index, high C27 regular steranes abundance, the presence of tricyclic terpanes and relatively high dibenzothiophene/phenanthrene ratios. These data indicated that the oils were derived from a carbonate source rock contain a mixture of aquatic (algal and bacterial) organic matter with a minor terrigenous organic matter contribution that were deposited in a marine environment under highly reducing conditions and generated at low maturity. The biomarker characteristics also suggest that the oils were derived from the Upper Jurassic–Early Cretaceous age Chia Gara carbonates.