Microorganisms living in the harsh environment present in oil field reservoirs are known to cause souring, plugging, and corrosion. A field survey was therefore conducted in an oil field located in Northern Germany that is producing out of the Valanginian sandstone of the Lower Cretaceous. The production started more than 50 years ago and there are still over 80 water injection and production wells active. The reservoir is located at a depth of 3600 to 4500 ft. Microbiological diversity was high in fresh core samples with 21 genus identified. Sulfate-reducing prokaryotes were dominating the microbial population and included species of Desulfosalsimonas propionicica, Desulfoto¬maculum geothermicum, Desulfonatronovibrio magnus, and Archaeoglobus fulgidus. Other species found were oil-degrading species of Orenia sp., Gracibacillus sp., Paraliobacillus quinghaiensis, Halanaerobium alcaliphilum, and methane-producing Methanoculleus sp. and Methanolinea tarda. Yet, microbial numbers were not exceeding 10^4 cells/g in the fresh cores and were not detectable in the fluids at the wellhead. Salt contents, reservoir temperature, and available nutrients did not facilitate growth and detrimental effects of the production facilities were not significant. Molecular microbiological methods provided valuable data for assessment of souring, microbiological influenced corrosion, oil degradation and subsurface monitoring can be correlated to the reservoir conditions.


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