Organic and inorganic geochemistry of northwestern Niger Delta oils

Abstract

A detailed geochemical study of oil samples from an onshore field in the Niger Delta was carried out for their characterization and correlation. The samples were analyzed using Gas Chromatographic (GC), Gas Chromatographic-Mass Spectrometric (GC-MS) and Inductively Coupled Plasma-Mass Spectrometric (ICP-MS) analytical techniques. The results showed that CPI, Pr/Ph, Pr/nC 17 , Ph/nC 18 and odd/even ratios ranged from 0.91 to 1.17, 3.07 to 6.04, 0.39 to 0.80, 0.14 to 3.30 and 1.33 to 1.39 respectively. The concentration levels of Co, Cr, Cu, Fe, Ni and V ranged from 0.9 to 32, 6.2 to 24, 3.31 to 19.4, 11.4 to 1241, 26.3 to 144 and 11.0 to 29.7 pbb respectively. The Pr/nC 17 vs. Ph/nC 18 plot revealed two oil types; non-degraded and minor degraded oils, which were derived from organic matter deposited in transitional environments. This suggests that both oil types have identical source rocks. Also, CPI values of 0.91 to 1.17 indicated that the oils are thermally mature. Biomarker data also discriminated the oils into two groups on the basis of biodegradation and revealed that the oils are mature and generated at almost the same thermal maturity level. The results of Ni vs. V, Co/Ni vs. V/Ni cross plots and cluster analysis similarly revealed identical two oil types. The similarity in the results of both organic and inorganic geochemistry of these oils shows that an integrated organic and inorganic geochemical data provide a reliable tool for the evaluation, characterization and correlation of crude oils.

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

“…These values suggest different levels of anoxic and oxic conditions during the deposition of the sediments in the Niger Delta Basin, with intermediate conditions prevalent. This is in a good agreement with previous studies (Okoh and Nwachukwu 1997;Akinlua et al 2007). In all these studies, it has been noted consistently that the prevailing environment of deposition in the Niger Delta is transitional.…”

“…Most of the geochemical data available from the onshore and shelf of Niger Delta suggests one super-family of oil in the Delta from one source type, which should suggest one petroleum system (a terrigenous system) for the basin (Ekweozor and Okoye 1980;Bustin 1988;Rooney et al 1998;Matava et al 2003;Akinlua et al 2007). Abundant of higher plant input to the source kerogen is believed to characterize the superfamily of oils as evident from the presence of high Pr/Ph ratio, high oleanane indices and high %C 29 steranes in the oils studied.…”

Determination of Metal Ions in Crude Oils

“…Trace metals have been used as a tool to understand the depositional environments and source rock (AlberdiGenolet and Tocco, 1999). The metal ions and their ratios have been observed as a valuable tool in oil-oil correction and oil-source rock correlation studies (Barwise et al, 1990), (Akinlua et al, 2007). The trace metals are also indicated as biomarkers of the source rocks (Odermatt and Cruriale, 1991).…”

Trace Metals Geochemistry of Crude Oils from Umutu/Bomu Fields in South West Niger Delta Nigeria

“…It may also involve digenesis from organic molecules as well as metals derived from different biogenic (biomass) and abiogenic (Weathering of minerals) sources. Metals of proven association with organic matter may be used as reliable correlation tools (Akinlua et al, 2007). Nickel, Vanadium and Cobalt (usually referred to as biophile elements) are such examples.…”

“…These trace metals are simply a reflection of those picked up during migration or in the reservoir, and incorporated directly into oils in form of porphyrin complexes (species) in petroleum source rocks from the biomass and formation during sedimentation (Akinlua et al, 2007). It may also involve digenesis from organic molecules as well as metals derived from different biogenic (biomass) and abiogenic (Weathering of minerals) sources.…”