Geochemical fingerprinting of western offshore Niger Delta oils

This study reports the findings based on analyses of saturated (normal alkanes and aliphatic isoprenoid) hydrocarbons 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 objectives 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 + 22R) homohopane, C-29:alpha alpha(20S/(20S + 20R)) steranes, moretane/C-30-Hopane and Ts/(Ts + 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 (delta C-13) 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.