Abstract
Two crude oils from Rivers and Delta States, Niger Delta Nigeria, samples A and F respectively, and their binary mixtures at different compositions, samples B, C, D, and E, were geochemically characterized using bulk properties and aliphatic hydrocarbon distributions. Results of density and API gravity, which classified samples A, B, C, D as light oils and samples E, F as medium oils, were observed to increase and decrease with increase in the composition of oil sample F respectively. The composition of the saturates, from 68.00 to 71.10%, suggest high maturity of the oil samples which did not show a relationship to the compositional mix of the two Niger Delta crude oils. Bimodal distribution of n-alkanes in samples A and B with a slight prominence of the short chain suggest marine source with significant terrestrial input, while the prominence of the long chain n-alkanes in sample F, which suggest a terrestrial source, progressively increased in samples C, D, and E. Pr/Ph ratios from 2.37 to 2.70 suggest source rocks deposited in an oxic environment. Ratios of Pr/nC17, from 0.94 to 1.20, and Ph/nC18, from 0.39 to 0.53, suggest shale source rocks with terrestrial higher plant input. From these results, the geochemical characteristics of the individual Niger Delta crude oils were exhibited by their binary mixtures. However, density, API gravity, n-alkane distribution, Pr/nC17 and Ph/nC18 ratios were expressed relative to the compositional mix of the two Niger Delta crude oils.
Highlights
Correlation studies of crude oils require parameters that discriminate a homologous suit of oils from another [1]
It was observed that the densities of the crude oil samples increased with increase in the composition of oil sample F
Samples A, B, C, and D have high American petroleum institute (API) gravities (> 35°) which classify them as light crude oils, while samples E and F are classified as medium crude oils
Summary
Correlation studies of crude oils require parameters that discriminate a homologous suit of oils (oils from the same source) from another [1]. This is primarily accomplished using bulk properties such as American petroleum institute (API) gravity, compound class fractions - saturates, aromatics, resins and asphaltenes (SARA) and distribution of aliphatic hydrocarbons (AHCs) from C8 to C40 normal alkanes (nalkanes) including the isoprenoids pristane and phytane [2, 3, 4]. The stability of asphaltenes in organic deposition during petroleum production, processing, and refining is related to the SARA composition of crude oil and cannot be associated with only one fraction [9]. Nwadinigwe et al (2017) showed that despite API gravities of three Nigerian Niger Delta crude oils, Kokori 34.19°, Afiesere 37.76° and Nembe 39.39°, indicated light oils, the aromatics/saturate ratios ascertained Kokori with the lowest ratio of 0.092 will cause more problem by asphaltene deposition in the refinery than the other oils [10]
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