Phase 5 (FY 2015 to FY 2017) aims to examine the generation process, control method, and evaluation method of biomethane in geological formations related to sedimentary rocks in the northern Hokkaido area, and to extract the parameter which contributes to the development of in situ model. Though 2017 is the last fiscal year of the Phase 5, it was decided that the tasks of the Phase 6 would also be carried out partially in advance in consideration of the progress situation of the research. Therefore, the research on field science and elemental technology development for the achievement of the above goal was carried out in each of Subsurface Microbiology Research Group, Groundwater Environment Research Group, and Sedimentary Rock Research Group. The outline of researches and results in this fiscal year is as described below.

　The Subsurface Microbiology Research Group conducted a monitoring survey of microbial community structure in groundwater of lignite formations in Sarufutsu mining area of the Tempoku coalfields using water sampling equipment installed in the preceding fiscal year, and confirmed that the dominance rate of anaerobic methanogenic archaea increased and the dominance rate of aerobic bacteria decreased. As a result, it was verified that groundwater close to the in situ condition could be collected by the new water sampling equipment. Furthermore, phylogenetic analysis and culture experiments using the mcrA gene as a molecular marker revealed that hydrogenotrophic methanogenic archaea play an important role in methanogenesis in in situ ligite formations. For the culture model, the Group experimentally verified the methanation of the solution after the reaction of lignite and hydrogen peroxide by the H-RISE microbial consortium that has been subcultured for many years in our research institute, and revealed that the addition of lignite powder as a solid phase greatly promoted the methanogenesis. In addition to the above experiment, the Group planned and designed the culture experiment using the high-pressure culture equipment assuming the ground pressure in the field, and the examination of the culture condition was started. For the decomposition experiment of methane source materials in geological formations, further detailed analysis using pyrolysis-GC/MS analysis was carried out following the previous year. In addition, by the experiment using the radioisotope, the important knowledge which led to the elucidation of humic substance decomposition mechanism under the anaerobic condition was obtained.
　The Groundwater Environment Research Group has clarified that microbial origin methane is present at high concentrations in the meteoric water recharge zone of the Sarufutsu mining area of the Tempoku coalfields. The Group also discussed the cause, and pointed out that the main causes are, through meteoric water recharge, thermodynamically accelerated bacterial fermentation reaction by promoting advection of fermentation reactants, and activated methanogens by advection (supply) of the feed (fermentation reactants) of methanogens to methanogenic sites. For the Cretaceous formation in the Kushiro area, the Group identified the thermal denaturation history of the Cretaceous formation from the vitrinite reflectance, and showed that the amount of coal oil production was greatest near the depth of 2500-m, and the core sample at the depth of 200-m - 1150-m contained thermogenic origin gas with an organic carbon concentration of about 0.05 - 0.5%. In addition, the Group carried out the analysis of groundwater sampled from hot spring facilities which can be classified into iodine hot springs in Hokkaido and boreholes of Hamasato area, and clarified that dissolved methane contained in iodine hot springs in Hokkaido is mainly hydrogen substrate microbial origin and a part is thermogenic origin related to organic substances. In the elemental technology development research, the relation between coal quality and hydrogen peroxide reactivity was analyzed, and it was clarified that the lower the thermal maturity of coal, the faster the reaction rate with hydrogen peroxide, the greater the amount of dissolved organic matter and organic acid generated, the smaller the amount of gas generated in the reaction process, and the larger the ratio of CO₂ to oxygen in the generated gas.
　The Sedimentary Rock Research Group conducted various physical and mechanical tests on lignite to clarify the mechanical properties of sedimentary rock during industrial biomethane production in geological formations. The sedimentary rock samples were lignite collected from the outcrop and the borehole core of Sarufutsu mining area of the Tempoku coalfields. To evaluate physical properties of lignite in the organic matter decomposition promotion, elastic wave velocity measurement using the ultrasonic pulse method were carried out. Similarly, needle penetration test and uniaxial compression test were conducted to evaluate the mechanical properties. In this study, the Group focused on the cleat development direction in lignite, and examined the effect of structural anisotropy. Furthermore, the Group is trying to construct the test system for the permeability evaluation of lignite in organic matter decomposition. Also, for the development of biomethane production technology in sedimentary rock formations, in order to obtain the design data of in situ testing, the Group reproduced the in situ sedimentary environment, promoted the organic matter decomposition in the sedimentary rock using hydrogen peroxide, and evaluated the chemical properties of the solvent over time and the compression properties of the sedimentary rock. In addition, the Group proposed a test method to estimate the amount of low molecular weight organic acids produced from lignite by the injection of hydrogen peroxide into geological formations.