Summary
A water-soluble methane gas is observed in the sedimentary basins. For an example, it is known around Lake Biwa and Sagara oil field (Shizuoka prefecture). According to some researches, the methane is generated from carbon materials by the activities of methanogenic bacteria.
This study is carried out for the system development, that CO2 will be injected into the sedimentary basins and methane gas generated by methanogenic bacteria.
(1) Geological survey of sedimentary basin containing methane
Drilling research of sedimentary basin at the coastal plain of Lake Biwa was performed for investigation of geological structure, origin of methane. The five layers including water-soluble methane were observed up to the depth of 184m. The ages of all sedimentary layers were estimated to be less than 780,000 years. Based on analysis of isotopic ratio, methane would originate from CO2 by microbial activity.
(2) Microbiologic study of methanogenic bacteria
Soil samples in methane-bearing formation around Lake Biwa were used as sources of microbial DNA for microbiological analysis of methane-producing mechanism in the formation. DNA was extracted from several soil samples from different depth, composition of microorganisms in these samples were compared based on the band patterns in DGGE analyses, and amplified partial 16S rDNA were sequenced to determine the origin of the each band. As the result, sequences of methanogenic archaea and archaea found in methane hydrate-bearing deep marine sediments were detected. Generation of methane from the soils of methane-bearing formation was not observed, but these results support the notion that methane in methane-bearing formation of Lake Biwa is originated from microbial activities.
(3) Estimation of the CO2-methane converting system
Based on simulation study, the conditions of the CO2 methane converting system were estimated. The system would require (1) the high threshold pressure in seal layer,
(2) the property
of pore structure for keep in low of specific gas-permeability. And flow rate of
ground water
in CO2 storage layer will be kept in low less than methane produce
rate by microbial
activity.
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