Occurrence and geochemical significance of fluorene and alkylfluorenes in crude oils and source rock extracts from Niger Delta basin, Nigeria

Abstract

The crude oils and their source rocks from Niger Delta basin, Nigeria were investigated by optical microscopy for the maceral compositions and by gas chromatography - mass spectrometry (GC-MS) for the composition, distribution and abundances of saturated and aromatic biomarkers. The data obtained showed that the rock samples and crude oils were formed from the mixed input of terrestrial and marine organic matter, and deposited under oxic to sub-oxic conditions in a lacustrine-fluvial/deltaic environment. The aliphatic maturity parameters calculated for the source rocks and oil samples showed that they have immature to early mature; and early oil window maturity respectively, whereas aromatic maturity ratios indicated that they were within immature to peak of oil generation and beyond; and peak to late oil generative window, respectively. The crude oils and source rocks were characterized by the dominance of C 2 -fluorenes over other alkylated homologues. The predominance of C 2 fluorenes over other alkylated homologues might have been influenced by source facies and depositional environments. The relative percentages of fluorenes (FLs %), dibenzofurans (DBFs %) and dibenzothiophenes (DBTs %) values for the rock samples range from 9.36 to 38.04 %, 35.82–71.60 % and 10.02–42.52 %, respectively, while the crude oils have ranges of values from 18.91 to 56.38 %, 24.90–72.34 % and 5.99–19.02 %, respectively. These values showed that the crude oils and source rocks originated from the mixture of organic matter (terrestrial and marine) with higher contribution from terrestrial organic matter and deposited in a marine/brackish-saline lacustrine/swampy environments. The abundance and distribution of fluorenes and its derivatives were found to be effective in determining the origin and depositional environments of crude oils and source rocks in the Niger Delta Basin, Nigeria.

Applying biomarkers as paleoenvironmental indicators to reveal the organic matter enrichment of shale during deep energy exploration: a review

“…10 Plot of Pr/n-C 17 against Ph/n-C 18 ratios of oils from Niger Delta. 18,141 are potential precursors of botryococcanes, and long-chain nalkanes to freshwater (lacustrine) sediments since it exists as two physiologically distinct clonal races. 142 For the rst time in an Australian crude oil, biomarkers found in coastal bitumens from the western Otway Basin conrmed the presence of substantial amounts of botryococcane.…”

“…8,9 The source facies can be distinguished by comparing structurally similar chemicals in sediments and crude oils with their likely biological precursors. 8,9,17,18 The thermal history of the oil can be reconstructed by altering the biomarker structure. 3,17,18 Some biomarkers are biochemical processes or environmental indicators.…”

“…8,9,17,18 The thermal history of the oil can be reconstructed by altering the biomarker structure. 3,17,18 Some biomarkers are biochemical processes or environmental indicators. Triterpenoids and steroids were thoroughly investigated.…”

“…Fig.14A cross plot of dibenzothiophene/phenanthrene (DBT/P) and pristane/phytane (Pr/Ph) ratios for the Niger Delta oils 18,212. Fig.15Cross plot of C 27 /C 28 20R TAS versus C 26 /C 28 20S TAS for Niger Delta crude oils 215,217.…”

Biological Marker Fingerprints of Crude Oils from Three Oilfields in the Central Niger Delta: Implication to Source Input, Conditions of Deposition, and Thermal Maturation

“…Oil samples from the Central Niger Delta show a high proportion for the oleanane index (0.64 to 0.95), recommending Tertiary matured source rocks with extremely high contribution of terrigenous materials, and a fulfillment of the equilibrium point of oil generation (Table 1). Ogbesejana et al [50] reported a matured to immature and early maturation status for the Niger Delta crude oils and source rocks respectively. The C31/C30 hopane proportion has been utilized to separate marine and terrestrial source organic matter.…”