Geochemical Investigation of Trace Metals in Crude Oils from Some Producing Oil Fields in Niger Delta, Nigeria

The geochemical investigation of trace metals in crude oils from some producing oil fields in the Niger Delta, Nigeria, was carried out to ascertain the petroleum source rocks and organic matter deposits. The concentrations of trace metals in crude oil samples obtained from eight producing fields from Niger Delta, Nigeria, were analyzed using a ۷۰۰ model Perkin Elmer atomic absorption spectrophotometer. The results showed the following ranges for the trace metals: Cu (۰.۰۱–۰.۰۴ mg/kg), Fe (۰.۰۵–۵.۹۰ mg/kg), Ni (۰.۰۹–۰.۷۲ mg/kg); and V (۰.۰۰۸–۱.۰۵ mg/kg). Pb and Zn were lower than ۰.۰۱ mg/kg. Trace metal ratios such as V/Ni, V/Fe, and (V/V + Ni) were used to unravel the genetic correlation among the oils. All the crude samples except the sample from Nembe South-۲ have a V/N ratio lower than ۱.۰, indicating that the organic materials produced the petroleum source rock. A cross plot of V/Ni revealed two genetic families for the crude oils, derived from a terrestrial and marine origin, which was confirmed by the ternary plot of V, Ni, and Fe, discriminating the crude oils from the producing fields into two distinct groups. The V/(Ni + V) of smaller than ۰.۵ showed that most crude oils were deposited in an oxic environment. A cross-plot of V/(Ni + V) and V/Fe showed a weak correlation, suggesting that it could not substitute for the V/Ni ratio in determining the origin and depositional environment of crude oil samples. Therefore, an in-depth knowledge of the concentration of trace metals, especially vanadium and nickel, within an environment during oil exploration is essential in developing new oil locations.

Keywords:

anoxic , marine , oxic , Organic material , Petroleum , Rock , Source , terrestrial