Trace element geochemistry of kerogens from the central Niger Delta

Abstract

Trace elements in kerogens isolated from shale samples obtained from oil wells in the central Niger Delta were determined using atomic absorption spectrometry, with the aim to determine the depositional environment and source of the organic matter. The results showed that the concentrations of the elements in the kerogens ranged from 1.50 to 6470.00 ppm and 3.50 to 7946.00 ppm for Wells X and Y, respectively. In both wells, Fe was the most abundant element, while cobalt had the least concentration. Nickel had an enhanced concentration over vanadium in Well X, while the reversed was the case in Well Y. The distribution patterns of the trace elements indicate that most of the kerogens from the two wells have similar origin. The geochemical ratios calculated from the concentrations of the trace elements revealed kerogens from Well X have terrestrial organic matter input, while kerogens from Well Y have both mixed marine/terrestrial organic matter and terrestrial inputs. The concentrations of the trace elements also revealed that the organic materials of samples from Well X were deposited under oxic conditions, while those from Well Y were deposited under oxic–suboxic conditions.