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

The concentrations of trace metals in crude oil samples obtained from eight producing fields from Niger Delta Nigeria were analyzed using a 700 model Perkin Elmer Atomic Absorption Spectrophotometer. Results showed the following ranges for the trace metals, Cu (0.01- 0.04 mg/kg); Fe (0.05 – 5.90 mg/kg); Ni (0.09 – 0.72 mg/kg); V (0.008 – 1.05 mg/kg). Pb and Zn were < 0.01 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. Results showed that all the crude samples except sample from Nembe South-2 have a V/N ratio < 1 indicating the organic material that 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. This was confirmed by the Ternary plot of V, Ni and Fe which discriminated the crude oils from the producing fields into two distinct groups. The V/(Ni+V) of < 0.5 shows that most of crude oil were deposited in an oxic environment. A cross-plot of V/(Ni+V) and V/Fe showed a weak correlation which suggests that it cannot be used as a substitute for the V/Ni ratio in determining the origin and depositional environment of crude oil samples. Therefore, in-depth knowledge of the concentration of trace metals especially vanadium and nickel within an environment during oil exploration is very essential in developing new oil locations.