Trace metals characterisation of Niger delta kerogens

Ten trace elements were determined by graphite furnace atomic absorption spectrometry (GFAAS) in fifteen kerogen samples from five wells obtained from the paralic sequence Agbada formation in the Niger delta basin. The concentrations of the elements (As, Cd,, Cr, Co, Cu, Fe, Mn, Ni, Pb and V) determined ranged from 0.374 to 667.340 ppb with a mean value of 77.434 ppb (%RSD < 5) for the kerogen samples analysed. These metals were selected for analysis for exploration and environmental considerations. The concentrations of the metals in the kerogen were in excess of those obtained for the Niger delta oils except for Ni and V, which followed the expected trend (i.e. there should be more trace metals in the kerogen than in the oil since kerogen is a precursor of petroleum). The results indicate that concentrations of the metals decrease with depth. Also, concentrations of the metals decrease with increase thermal maturity of the kerogens. Although, this trend could be altered in horizons with low organic richness. The ratios calculated from the metals are comparable with those obtained for the Niger delta oils and indicate that the kerogens were derived from terrestrial origin. Kerogens of similar organic matter type from different geographic sedimentary basins can be distinguished by the fingerprints of their metal contents. (c) 2006 Elsevier Ltd. All rights reserved.