It was previously supposed that natural methane gas accumulations were mainly tied up with oil pools. However, five years ago Russian and Swiss geologists discovered natural gas accumulations in underground horizons, where oil fields were few, and the hot salt solutions were circulating. Nadezhda Verkhovtseva from Lomonosov Moscow State University believes that the fuel gas is evolved by archaebacteria inhabiting underground water.
The analysis of stratal water from the Vorotilovskaya deep well (seventy kilometers north of Nizhny Novgorod) has confirmed that. "Methane-evolving archaebacteria have been discovered in the specimen from the depth of 1.5 through 4.5 km," said Verkhovtseva. "They live at 30-80° C in solutions saturated with calcium, sodium and magnesium chlorides and sulfates.
The sources of carbon and hydrogen are different in the underground solutions. They are mainly produced by microorganisms destructing organic materials. A quarter of solute carbonic acid is provided by the carbonate strata. Microorganisms, which reduce sulfates, nitrates and nitrites, compete for hydrogen with methane bacteria. Since these microorganisms are hundreds of times less in number, methane-producing archaebacteria naturally have the advantage in absorbing the solute carbonic acid and hydrogen.
The underground water evolves fuel gas as intensely as the oil water does. Therefore, the increased quantity of carbonate and hydrogen in the stratal water is the evidence of close methane occurrence. In the researchers' opinion, these showings suppose to indicate the natural gas accumulation findings.
Results of the research may entail the revision of theories explaining the occurrence of underground carbon accumulations. The natural gas fields do not necessarily accompany oil pools, because the underground water easily circulates and methane may accumulate in cavities and other interstice. So, new hydrocarbon accumulations can be found even in well-explored areas.