Bacterial Methanogenesis in Underground Waters

Methanogenic bacteria are widespread in various anaerobic ecosystems. Their biogeochemical activity in rocks and waters associated with commercial gas and oil deposits is of particular interest. Methanogenic bacteria numbering up to 250 cells$\text{ml}^{-1}$of water or$\text{g}^{-1}$of rock were found in underground waters and sedimentary rocks of Neocene-Quaternary deposits of the Caspian depression, rich in natural gas. Intensity of bacterial methanogenesis was$2.0-63.5\cdot 10^{-5}$ml$\text{CH}_{4}\text{l}^{-1}\text{d}^{-1}$in water or$\text{kg}^{-1}\text{d}^{-1}$in rocks. The δ^{13}\text{C}$value of methane dissolved in stratal water changed from -64.2 to -94.1‰, thus confirming the biogenic nature of methane in the ecosystem under study. Methanogenic bacteria were also found in stratal water and kern of the Bondyuzhskoe oil-bearing deposit (middle Volga region). Intensity of bacterial methanogenesis reached$22.7-30.5\cdot 10^{-5}$ml$\text{CH}_{4}\text{l}^{-1}$stratal water$\text{d}^{-1}$. Pure cultures of methane-forming bacteria, isolated from the flooding and stratal waters, grew actively in inorganic media on infinite sources of CO₂ and H₂. The δ^{13}\text{C}$value of methane from the Bondyuzhskoe deposit varied within the range -37.9 to -68.7‰. The results obtained make it possible to infer that part of the methane from the oil deposit under study is of bacterial origin.