Oil-Oil Correlation of the North-Central Niger Delta Basin: Implications for Production, Exploration and Petroleum System Modelling

Abstract

The Niger Delta Basin is a prolific hydrocarbon province, traditionally considered to host a single petroleum system largely derived from terrestrial organic matter; however, recent studies indicate the presence of multiple petroleum systems and distinct oil families across the basin. Despite its importance, detailed organic geochemical data and oil–oil correlation studies for the North Central Niger Delta remain limited. This study aims to characterize organic matter source, lithology, maturity, depositional setting and biodegradation, determine whether or not one or more source rocks was or were responsible for the accumulation of the oils in the reservoirs, and elucidate oil charge history, geochemical variability and exploration potential. Geochemical evaluation was conducted on thirteen crude oil samples (BW1–BW7 and ND1–ND6) collected from the North‑central Niger Delta basin. API gravity of the study oils was determined using a thermal hydrometer and Gas chromatography–mass spectrometry tool was applied to assess organic matter (OM) source, thermal maturity, depositional environment and biodegradation level. Parameter cross‑plots performed with Microsoft Excel 4.6 were used to establish oil–oil correlations within the basin. Sterane cross‑plots (C28/C27 αββR versus C27/C29 αααR), C27–C29 sterane distributions and the 1‑methylphenanthrene/9‑methylphenanthrene ratio reveal a mixed OM origin (Type II/III kerogen) for both BW and ND oils, with some BW samples dominated by marine algal input and most ND samples showing stronger terrestrial influence. Saturated biomarker maturity ratios (C29 versus C30 αβ/(αβ + βα) hopanes) indicate attainment of the early oil window, while aromatic indices (MPI‑3 and calculated %Ro) suggest medium to high maturity. Dibenzothiophene/Phenanthrene versus Pristane/Phytane and API gravity versus Pristane/Phytane indicate that a few BW oils were deposited in fluvio‑deltaic settings under oxic conditions. Other BW samples originated from marine shale–lacustrine environments under anoxic conditions, whereas most ND oils were sourced from marine carbonate and marl facies deposited in an oxic setting. Pr/n-C17 versus Ph/n-C18 suggests non‑to‑mild biodegradation for BW oils and moderate to high biodegradation for ND oils, attributed to fault‑controlled migration and mixing histories.