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Comparison of microbial communities involved in souring and corrosion in offshore and onshore oil production facilities in Nigeria
Authors:Chuma Okoro  Seun Smith  Leo Chiejina  Rhea Lumactud  Dongshan An  Hyung Soo Park  Johanna Voordouw  Bart P Lomans  Gerrit Voordouw
Institution:1. Department of Biological Sciences, Caleb University, Lagos, Nigeria
2. Shell Nigeria Exploration and Production Company (SNEPCO), Lagos, Nigeria
3. Shell Petroleum Development Company (SPDC) of Nigeria, Port Harcourt, Nigeria
4. Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, ON, M1C 1A4, Canada
5. Department of Biological Sciences, University of Calgary, 2500 University Dr. NW, Calgary, AB, T2N 1N4, Canada
6. Shell Global Solutions International BV, 2280 AB, Rijswijk, The Netherlands
Abstract:Samples were obtained from the Obigbo field, located onshore in the Niger delta, Nigeria, from which oil is produced by injection of low-sulfate groundwater, as well as from the offshore Bonga field from which oil is produced by injection of high-sulfate (2,200 ppm) seawater, amended with 45 ppm of calcium nitrate to limit reservoir souring. Despite low concentrations of sulfate (0–7 ppm) and nitrate (0 ppm), sulfate-reducing bacteria (SRB) and heterotrophic nitrate-reducing bacteria (NRB) were present in samples from the Obigbo field. Biologically active deposits (BADs), scraped from corrosion-failed sections of a water- and of an oil-transporting pipeline (both Obigbo), had high counts of SRB and high sulfate and ferrous iron concentrations. Analysis of microbial community composition by pyrosequencing indicated anaerobic, methanogenic hydrocarbon degradation to be a dominant process in all samples from the Obigbo field, including the BADs. Samples from the Bonga field also had significant activity of SRB, as well as of heterotrophic and of sulfide-oxidizing NRB. Microbial community analysis indicated high proportions of potentially thermophilic NRB and near-absence of microbes active in methanogenic hydrocarbon degradation. Anaerobic incubation of Bonga samples with steel coupons gave moderate general corrosion rates of 0.045–0.049 mm/year, whereas near-zero general corrosion rates (0.001–0.002 mm/year) were observed with Obigbo water samples. Hence, methanogens may contribute to corrosion at Obigbo, but the low general corrosion rates cannot explain the reasons for pipeline failures in the Niger delta. A focus of future work should be on understanding the role of BADs in enhancing under-deposit pitting corrosion.
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