枯渇油層への圧入ＣＯ２と地下微生物作用による原油のメタン変換研究

Abstract

Inpex and Chugai Technos have been working since 2006 to study methane-producing technology using microbes inhabiting depleted oil fields. The concept and mechanism of microbial methane conversion are depicted as follows.First, hydrogen producing microbes (bacteria) prompt to produce hydrogen from residual petroleum components in the depleted reservoir. Next, methane-producing microbes (methanogens) are concerned in generating methane from the hydrogen and carbon dioxide injected for geological sequestration.The research team in Inpex and Chugai Technos has successfully isolated samples of hydrogen- and methane-producing microbes from the depleted oil fields in Japan (10 hydrogen producing thermophilic bacteria and 4 methane producing thermophilic archaea). It was confirmed that continuous methane production took place using indigenous microbes in the reservoir brine and crude oil as a carbon source with 10 mol% of CO2.Produced gas (methane, carbon dioxide) and concentration of acetic acid indicate that there are 2 reaction pathways from oil to methane. One is the acetoclastic methane producing pathway, another is hydrogentrophic methane producing pathway.Furthermore, from the result of methane producing experiments using isolated microbes, we found there was some syntrophic cooperation between hydrogen producing bacteria and methanogen (methane producing archaea). We must investigate the suitable combination of these microbes in order to get an effective methane production.The next step will be to evaluate the way to enhance the capability of methane-producing microbes and to identify an effective and efficient process of producing methane in the actual reservoir (porous media) condition.If successful, it will be a big step toward building a carbon cycling system that converts residual oil in depleted oil fields into environmentally friendly methane.