The primary objective during Phase 4 was to initiate the research and establish the course of action for a long-term study. Because striking developments were observed in the research related to methanogenesis in geological formations, this area was made the primary focus of research. We targeted sedimentary rocks commonly found in the northern Hokkaido area, such as siliceous rock and lignite, to examine the generation process of biomethane in geological formations, and to determine control and evaluation methods for this process; we also conducted research to identify key parameters contributing to the development of an in situ model. Based on the above-mentioned information, in FY 2014, the Subsurface Microbiology Research Group, Groundwater Environment Research Group, and Sedimentary Rock Research Group each investigated several research topics concerning field science related to biomethane generation in geological formations and the development of underlying technology, as described below.
　To assess the initial state of the underground methanogenic environment, the Subsurface Microbiology Research Group joined ongoing work at the underground facility of the JAEA’s Horonobe URL to obtain comprehensive microbial community structural analyses from groundwater specimens obtained primarily from the Koetoi Formation (siliceous rock); this work demonstrated the microbes that produce hydrogen as well as that produce methane or acetic acid from hydrogen was highly abundant in the Koetoi Formation. These groups also conducted long-term cultivation tests using groundwater collected from the Horonobe URL, using cultivation models that imitated in situ conditions, verifying that it is possible to cultivate microbes that produce acetic acid or methane using hydrogen as substrate. In addition, the third new low-temperature-resistant methane-producing microorganism isolated from the groundwater of Horonobe URL, Methanosarcina subterranea, was recognized internationally in FY2014. These results show that the Horonobe URL is an internationally important site in the field of subsurface microbiological research. The Group also set about to improve cultivation methods and expand culture collection for anaerobic microbes thought to be involved in the initial methanogenic process, that is, the decomposition of persistent organic matter in sedimentary rocks.
　The Groundwater Environment Research Group researched the origin of methane in geological formations and the process required to generate a substrate for methanogenesis. Specifically, they used boreholes in the Sarufutsu mining area of the Tempoku coalfields to analyze interstitial water and gas in cores and groundwater of the lignite formations, clarifying that the interstitial water in deep areas originated from seawater (based on the elevated iodine concentration in groundwater), and showing that methane in the cores and groundwater was mainly of microbial origin. The team also collected methane found in open and closed system gaps in cores of Cretaceous rocks from the Kushiro Coal Mine, and measured the carbon isotope ratios of this methane. They discovered that methane found in closed pores was of thermogenic origin, whereas methane found in open pores was of microbial origin. Analyses of organic matter in coal and sedimentary rock indicated that polymerized materials in the humin that accompanied oxidative weathering changed into humic acids. In parallel with this field research, the Group conducted reaction tests for lignite and low-concentration hydrogen peroxide; these tests clarified that the mass of gases, particularly carbon dioxide, discharged during the reaction varies depending on the reaction temperature; the concentration of each organic acid and aromatic moieties at the end of the reaction tests were similar, regardless of the difference in reaction temperature, and the concentration of hydrogen peroxide shows an almost inverse correlation between the gas discharge amount and the concentration of each organic acid.
　The Sedimentary Rock Research Group conducted research on rock mass dynamics and geotechnical issues in biomethane production and recovery in sedimentary rock. Based on previous research by each H-RISE group, the Group proposed a biomethane ore deposit production method, Subsurface Cultivation and Gasification (SCG), as a practical biomethane production technology. To determine the environmental impact on sedimentary rock formations during the decomposition of organic matter, the Group encouraged the use of hydrogen peroxide in the decomposition of organic matter in sedimentary rock, evaluating the chemical properties of solvents over time and their effects on the internal structure of sedimentary rocks. The Group carried out immersion tests, using a hydrogen peroxide aqueous solution on samples of lignite from the Soya coal-bearing formations collected in the Sarufutsu mining area of the Tempoku coalfields to investigate the chemical properties of solvents and changes in the appearance of the samples. Using a micro-focus X-ray CT scanner, the Group investigated changes to the internal structure of lignite over time during immersion in the hydrogen peroxide solution. The Group also investigated the effects of failure and deformation on the permeability of sedimentary rock, using the lignite sample described above with elemental analysis by X-ray fluorescence, pore distribution measurements with a mercury intrusion porosimeter, and uniaxial compression tests to evaluate the physical and mechanical properties of lignite.