Geochemical fingerprinting of western offshore Niger Delta oils B.O. Ekpo a, b, * , N. Essien c , P.A. Neji b , R.O. Etsenake d a Exploration Research and Services Section, Research & Development, NNPC, Port Harcourt, Nigeria b Environmental & Petroleum Geochemistry Research Group (EPGRG), Department of Pure and Applied Chemistry, University of Calabar, Calabar, C.R. State, Nigeria c Department of Geology, University of Calabar, P.M.B. 1115, Calabar, Nigeria d Renewable Energy Research and Services Section, Research & Development, NNPC, Port Harcourt, Nigeria ARTICLE INFO Keywords: Oil fingerprinting Organic geochemistry Niger Delta Nigeria ABSTRACT This study reports the findings based on analyses of saturated (normal alkanes and aliphatic isoprenoid) hydro- carbons and biomarkers in twenty four (24) crude oil samples from western offshore Niger Delta of Nigeria using gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and carbon isotopy. The major ob- jectives were to apply reservoir geochemistry and oil fingerprinting to characterize the oils in order to determine their origin and to identify the existence of reservoir continuity and/or compartmentalization. Results from this study using the distributions of normal alkanes, tricyclic and tetracyclic terpanes as well as source specific maturity and facies controlled biomarker ratios of the oils including pristane/phytane (Pr/Ph), Pr/n-C 17, Ph/n-C l8, C 31 :22S/(22S þ 22R) homohopane, C 29 :αα(20S/(20S þ 20R)) steranes, moretane/C 30 -Hopane and Ts/(Ts þ Tm), showed that the entire crude oil samples from three reservoir units are the same, the differences are small. The oils originated from same source rocks which were deposited under oxidizing condition with mixed marine/ terrigeneous organic source inputs and thermal maturity. This genetic classification is supported by stable carbon isotopic compositions (δ 13 C) of the hydrocarbon fractions and multivariate statistical (Principal Component and Cluster) analyses. Geochemical, fingerprinting and multivariate statistical data provided corroborative evidence of a single compartment with vertical and lateral reservoir continuity across the fault complex within the studied fields. This information can be utilized by geologists and petroleum engineers in solving production related problems such as optimising hydrocarbon production via drilling horizontal wells to arrest the reservoir communication that occurs with existing vertical wells. 1. Introduction A major consideration in the management of both brown field and green field is how to maximize the amount of recoverable petroleum. In green discoveries, much attention is devoted to delineating the reservoirs before full scale development is undertaken. For instance, in accurate reservoir modeling, geologist and engineers seek for data on core mate- rials, detailed analyses of the sediments and well logs. Often ignored or partially utilized is the chemical composition of the oils. It is a common observation that oil within a continuous reservoir has a uniform hydro- carbon composition when sampled away from the oil/water and oil/gas contacts, and oils in separate reservoirs almost always have measurable compositional differences (Kaufman et al., 1990). Owing to the fact that oils within a field usually have a similar geologic history (e.g. similar source and maturation), the differences may not be detected by bulk properties such as viscosity, gravity, sulfur and isotopic composition. Therefore, the most successful tool for the measurement of the molecular composition of the oils is gas chromatography. The chemical composition of oil measured using gas chromatography is often thought of as a fingerprint and characteristics of a particular reservoir. For example, fingerprinting technology can be used to resolve reservoir development and production engineering challenges such as determining if a reservoir penetrated by a particular well is the same reservoir as has been penetrated by other well. This technology region- ally has assisted in the determination of the size or the extent (reservoir continuity) and volume of a field and has also been useful in planning the development of a field and specifically the number and location of wells required to drain the field. Oil geochemistry (oil fingerprinting) applied to reservoir continuity assessment in a diverse range of geological set- tings include a wide range of field sizes, structural environments, reser- voir lithologies, and oil types (Slentz, 1981; Kaufman et al., 1990; Hwang and Baskin, 1994; Hwang et al., 1994; Sundararaman et al., 1995; Ross * Corresponding author. Exploration Research and Services Section, Research & Development, NNPC, Port Harcourt, Nigeria. E-mail address: basseyekpo10@yahoo.com (B.O. Ekpo). Contents lists available at ScienceDirect Journal of Petroleum Science and Engineering journal homepage: www.elsevier.com/locate/petrol https://doi.org/10.1016/j.petrol.2017.10.041 Received 26 April 2017; Received in revised form 6 October 2017; Accepted 14 October 2017 Available online 17 October 2017 0920-4105/© 2017 Elsevier B.V. All rights reserved. Journal of Petroleum Science and Engineering 160 (2018) 452–464