Abstract: Geochemical Approach to Identifying the Origin of Oil Spills: a Case Study From Nigeria

Sundararaman, P. and O. T. Udo - Chevron Nigeria Limited

For the past thirty years in Chevron, a geochemical fingerprinting technique has been used for oil-oil correlation. It is based on the principle that every oil has a unique chromatographic fingerprint. In recent years at Chevron Nigeria we have used this technique for identifying the source of oil spills. This geochemical approach helps in identifying the source of the problem and to take necessary action to correct. In some cases it has helped us to fight false claims. In this talk we illustrate the power of the geochemical technique using a recent example from the Western part of the Niger Delta.

An oil spill was reported in a creek near a village named Yaye in the Western part of the Niger Delta. This spill was reported in a place, which is 25 miles west of any existing production in the Niger Delta. A possible source could be the western-most production facility named Isan. The spilled oil sample was analyzed using Fused Silica Capillary Open Tubular (FSCOT) column chromatography and the chromatogram was compared with an oil from the Isan pipeline. The chromatographic fingerprints of the spilled oil were different from the Isan pipeline oil suggesting that the spill did not originate from the Isan facility. Close examination of the chromatographic fingerprint showed that this oil was different from any of the oil produced in Nigeria. This is based on the observation that the pristane/phytane ratio of the oil spill sample is 0.6, whereas the pristane/phytane ratio of over 200 oils from Nigeria is > 1.5. To further confirm this conclusion detailed biomarker analysis of the spill sample was carried out using the Gas Chromatography-Mass Spectrometry (GCMS) technique. The results of this analysis were compared with the analysis of over 200 oils from the Niger Delta. Comparison of the sterane and the hopane distribution of the oil spill sample with the oils from the Niger Delta further confirmed our hypothesis that the spill did not originate from any existing production in Nigeria.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil