Biomarker Distributions to Constrain the Origin of Organic Matter in Two Crude Oil Samples from the Murzuq Basin, Libya

Abstract

The aim of this search is to describe the origin of precursors of crude oils collected from Murzuq Basin fileds, based using geochemical method. Two crude oil samples collected from wells B1 and H1 in the NC115 concession of the Murzuq Basin, Libya, were analyzed. An analytical technique Gas chromatography (GC) joined with mass spectrometry (MS) was used to characterize key hydrocarbon biomarkers, including n-alkanes, isoprenoids, tricyclic and tetracyclic terpanes, hopanes, and steranes. The n-alkane distribution (C₁₅–C₂₅ dominance, CPI ≈ 1.0) and the ratios Pr/Ph = 1.21–1.13 and i-C₁₆/n-C₁₅ < 0.5 indicate deposition under sub-oxic to anoxic marine conditions with a minor terrestrial input. Hopane and sterane parameters (H31S/H31R ≈ 1.8; Sterane/Hopane = 0.42–0.58) further support a mixed algal– bacterial source deposited in a marine to fluvio-deltaic environment. Overall, the biomarker evidence suggests that the hydrocarbons of crude oils produced mainly from aquatic algal and bacterial biological precursors with a portion of terrestrial input, generated under reducing conditions within the Silurian age source rocks of the Murzuq Basin.