Radiotracer Assay of Microbial Processes in Petroleum Reservoirs

Oilfield microbial communities exist under conditions of hampered exchange of water and mass and at a constant temperature; they are independent of the modern atmosphere and sunlight and may be considered closed or semi-closed systems. Crude oil is the main source of organic matter in this ecosystem. Microbial growth in reservoirs can be limited by the low content of phosphate and ammonium nutrients [1,2]. Formation waters usually contain no dissolved oxygen and nitrate, while sulfate and other oxidized sulfur compounds are present, as well as carbonate. Sulfate reduction, methanogenesis, and acetogenesis are therefore probably the major metabolic processes occurring in such ecosystems. Since microbial processes are very slow due to low water exchange and scarcity of biogenic elements, oil in the reservoirs is preserved for geological periods. Activation of water exchange resulting from geological processes or anthropogenic activity returns the buried organic matter of petroleum into the biogeochemical cycles. Present-time biogenic processes of petroleum transformation and the relevant microorganisms are relatively poorly studied.