The role of hyperthermophilic prokaryotes in oil fields

Deep geothermally heated oil stratifications represent newly recognized non-volcanic islands of microbial life at extremely high temperatures, some 3,500 m below the surface. Samples of produced fluids contain high concentrations of various anaerobic extremely thermophilic and hyperthermophilic archaea and bacteria, indicating the presence of complex microbial communities in situ. The isolates consist of heterotrophs and facultative and obligate chemolithoautotrophs, some of which are able to use crude oil in their energyyielding reactions. They belong to the genera Archaeoglobus, Thermococcus, Pyrococcus, Methanococcus, Methanobacterium, Thermotoga, Thermosipho, and Thermodesulfobacterium. Most isolates are members of species already known from hot springs and hydrothermal vents. They may have entered the reservoirs through natural routes such as faults and oil seeps or by sea water injection. A great deal are sulfidogens and may, therefore, participate in reservoir "souring" at temperatures previously considered too high for biochemical reactions.