Gas chromatographic analysis of whole oil samples: implications for biodegradation in the Niger Delta

Résumé

The levels of biodegradation of five whole oil samples from five oil fields in the Niger Delta were assessed using a high-resolution gas chromatography. The results show that all the samples are at different levels of degradation ranging from slight to heavy. The crude oils from Fs, Bs and Qe fields had undergone extensive to heavy degradation, while those from Ai and Ea fields had undergone slight to moderate degradation. The low paraffinic content values in the samples suggest that the n -paraffins have been degraded and reduced consistently. The aromatic fractions (C 14 –C 18 ) have been reduced slightly, though the 3-Methylhexane component was observed to show strong resistance to the bacterial attack even at deeper fields. These levels of biodegradation show indications that they could be caused by the degrading anaerobic bacteria present in the deep reservoir and/or by the influx of meteoric water, especially for the Bs crude, which is from an onshore field. As this degradation continues to deplete the light hydrocarbon components, the residual heavy components such as sulfur and asphaltenes are gradually concentrated, while the API gravity is consequently lowered.

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