We proposed a new gasification method to convert unused organic matter in sedimentary rocks to bio methane gas using microorganisms, known as Subsurface Cultivation and Gasification (SCG). Our approach uses hydrogen peroxide (H₂O₂) to decompose organic matter rapidly into usable substrates for methanogens. We previously reported that H₂O₂ would be useful for effective SCG at lignite, and conversion of organic matter from lignite into biogenic methane with the help of microorganisms is expected to be highly profitable. However, physical properties of the sedimentary rock are thought to change with the decomposition of sedimentary rock in the SCG method.

A series of one-dimensional compression tests were performed for artificial coal seams prepared using the lignite sampled from Tempoku coalfield in the northern Hokkaido to investigate the stability of coal seam during an industrial production of substrates for methanogens in the subsurface environment. H₂O₂ was used in the one-dimensional compression tests to produce lower-molecular-weight organic components as a substrate of methanogen. Moreover, H₂O₂ solution was repeatedly injected into the artificial coal seam under compressive pressure. Oxidative decomposition of the artificial coal seam produced a high yield of low-molecular-weight organic acids. However, settlement of the artificial coal seam subjected constant loading was dependent on concentration and injection amount of H₂O₂.

The biomethane deposits might become mechanically unstable during promoting decomposition of organic matter of coal seams, even if lignite has the greater resource potential for biomethane.

It is important to understand the long-term migration of radionuclides when considering rock engineering projects such as the geological disposal of radioactive waste. The network of fractures and pores in a rock mass plays a major role in fluid migration as it provides a pathway for fluid flow. The geometry of a network can change due to fracture sealing by some fine-grained materials over long-term periods. Groundwater usually contains finegrained minerals such as clay minerals, and it is probable that the accumulation of such minerals occurs within a rock fracture upon groundwater flow, thereby decreasing the aperture of a fracture and the permeability. It is therefore essential to conduct permeability measurements using water that includes fine-grained minerals to understand the permeability characteristics of a rock; however, this has not been studied to date. In the present study, we use a macro-fractured granite sample to investigate the change of permeability that occurs under the flow of water that includes two different amounts of clay. Findings showed that clay accumulated in a fracture and that the permeability (hydraulic conductivity) of the granite sample decreased over time, which was greater in for the higher clay content. We concluded that the accumulation of clay minerals in the fracture decreased the permeability of the rock. Furthermore, we consider that the filling and closure of fractures in rock is possible under the flow of groundwater that includes clay minerals.