Phase 4 identified two specific targets for study:
(1) Research related to biomethanation of organic matter found in geological formations: evaluation of methods related to biological processes to release methane harbored in siliceous rocks and lignite formations, and the storage ability, subterranean transfer characteristics, and relevant parameters for the development of an in situ model.
(2) Research related to underground fixation of CO2: isolation of organisms that can be utilized for the biological fixation of CO2, and improved understanding of the void structures and geochemical characteristics of siliceous and lignite formations in which CO2 storage occurs.
　To implement this program, we conducted the following research.
　To investigate the characteristics and geological effects of sedimentary rock, we developed a method for evaluating the significant features of those rocks on the mechanical properties of methane gas development and geological CO2 storage in the subterranean environments, identified as the priority research areas in the long-term plan. We also continued our research on the effects of destruction and deformation on the properties of rocks and investigated detail structures based on thin piece structures. Research on the mechanical properties of soft rocks and the influence of pore fluids required the development of indoor test methods to obtain clearance elasticity parameters, applying methods developed in FY 2011 to rocks such as Horonobe siliceous rock, and accumulating relevant data on the studied formations.
　Research on subsurface microbial environments and their effective utilization involved increasing the number of survey points for the 140-m and 250-m underground tunnels of the JAEA shaft, and improving the accuracy of the 16S rRNA gene library of the subterranean microorganisms at Horonobe. The search for, and identification of the functions of, the methanogenic microorganism group is a priority research topic in the long-term plan, as part of an effort to acquire basic knowledge needed to improve the efficiency of methanogenesis as part of the study on biomethanation of underused organic matter in geological formations; we identified the community structure characteristics and major methanogenic microbes of the microbial communities that produce methane from siliceous rock and coal, and which we discovered last year. In collaboration with the Groundwater Environment Research Group, we also evaluated microbial influences on the molecular structure of humic substances that are major components of the organic matter in geological formations.
　In order to identify the substrate formation process of methanogenic microorganisms, we conducted research related to the subterranean migration of underground water and gas and to the broader groundwater environment, clarifying the composition of organic matter in rock via instrumental analyses, and investigating the elution tendencies of organic acids having a high degree of microbial reactivity. We also conducted collaborative research with the Subsurface Microbiology Research Group in line with these objectives. We also identified the carbon and hydrogen isotopic ratios of methane and amino acids in the groundwater of the Horonobe area.