Geochemical evaluation of Niger Delta sedimentary organic rocks: a new insight

Abstract

A geochemical evaluation of Niger Delta organic matter was carried out using supercritical fluid extraction (SFE) sample preparation procedure. Comparison of geochemical significance of gas chromatographic data of rock extracts of SFE with those of Soxhlet extraction method from previous studies was made in order to establish the usefulness of SFE in geochemical exploration. The assessment of geochemical character of the rock samples from the comparison and interpretation of other geochemical parameters were used to give more insights into understanding the source rocks characteristics of onshore and shelf portions of the Niger Delta Basin. The results of the gas chromatographic (GC) analysis of the rock extracts across the lithostratigraphic units show that Pr/Ph, Pr/nC 17 , Pr/nC 18 , CPI and odd/even preference ranged from 0.07 to 12.39, 0.04 to 6.66, 0.05 to 13.80, 0.12 to 8.4 and 0.06 to 8.12, respectively. The Rock-Eval pyrolysis data and geochemical ratios and parameters calculated from the GC data showed that most of the samples are mature and have strong terrestrial provenance while a few samples have strong marine provenance. The few marine source rocks are located in the deeper depth horizon. Pr/Ph and standard geochemical plots indicate that most of samples were derived from organic matter deposited in less reducing conditions, i.e. more of oxidizing conditions while a few samples have predominantly influence of reducing conditions. The results of trace metal analysis of older samples from Agbada Formation also indicate marine and mixed organic matter input deposited in less reducing conditions. The results obtained in this study are comparable with those obtained from previous studies when Soxhlet extraction method was used and also indicated the presence of more than one petroleum systems in the Niger Delta.

Quantitative diamondoid analysis indicates oil cosourcing from a deep petroleum system onshore Niger Delta Basin

“…% to 4.22 wt. % (Akinlua and Torto, 2011). However, Doust and Omatsola (1990) point out that the beds with high TOC content are always very thin and commonly insignificant based on their studies on core samples from different wells in the basin.…”

“…However, Doust and Omatsola (1990) point out that the beds with high TOC content are always very thin and commonly insignificant based on their studies on core samples from different wells in the basin. The HI values of the thermally immature shales are also very low (e.g., 50-160 mg HC/g TOC) with an average value of 90 mg HC/g TOC (Bustin, 1988), 38 to 239 mg HC/g TOC (Akinlua and Torto, 2011). This shows that they have potential to generate gas and some oil (Baskin, 1997).…”

Occurrence and Distribution of Carbazoles and Benzocarbazoles in Tertiary Niger Delta Source Rocks

“…The HI values are comparable to the values reported by other authors for source rocks from the same basin (Udo et. al., 1988;Akinlua and Torto, 2011).…”

Paleoenvironment and Its Control of the Formation of Oligocene Marine Source Rocks in the Deep-Water Area of the Northern South China Sea

“…However, in continental margin basins, terrigenous organic matter (TOM) input is also a significant factor on marine source rock formation. , Influenced by river-delta systems, TOM may contribute to marine source rocks in continental margin basins, as is the case in the Congo Basin and Niger Delta Basin. , These basins are located below the estuaries of large rivers, which may bring abundant TOM along with nutrients into the basin, giving rise to ocean surface plankton booms . However, a large number of detrital materials transported by rivers can also dilute marine productivity …”