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Recently, the possibility of realizing a subsurface bio-reactor has been realized since microbial methanogenesis has been confirmed in diverse subsurface environments such as coalbeds or petroleum reservoirs. We propose a new gasification method for use in subsurface environments, known as the Subsurface Cultivation and Gasification (SCG). SCG was devised based on the production of biogenic methane gas in subsurface environments. This approach employed hydrogen peroxide to decompose organic matter rapidly. Conversion of organic matter from source rocks into biomethane with the help of microorganisms is expected to be highly profitable. In this study, a series of batch tests using a hydrogen peroxide (H2O2) solution were performed on lignite to estimate the potential of low-molecular-weight organic acid production. The effects of several factors on the production of low-molecular-weight organic acids have been considered, such as, concentration of H2O2, temperature, liquid-solid ratio, and specific subsurface area of lignite. It was found that the quantity of low-molecular-weight organic acids depended on temperature, liquid-solid ratio, and specific subsurface area of lignite; however, there isn't a unique relationship between them and the H2O2 concentration. Moreover, the mass of lignite reduced remarkably when batch tests were performed with a high concentration of H2O2. If H2O2 is to be injected into a target seam with the SCG method, we should estimate the optimum H2O2 concentration to produce low-molecular-weight organic acids with taking into consideration the mechanical stability of the target seam as well as the subsurface environmental chemical reaction with a geological improvement.

We propose a new gasification method that converts unused organic matter in sedimentary rocks to bio methane gas through the use of microorganisms, known as Subsurface Cultivation and Gasification (SCG). SCG was devised based on the product ion of biogenic methane gas in subsurface environments completely without a mining process of coal. With the goal of developing a method to produce biogenic methane gas in subsurface environments, this approach employed hydrogen peroxide to decompose organic matter rapidly. Conversion of organic matter from source rocks into bio-methane with the help of microorganisms is expected to be of high profitability. In northern Hokkaido, several coal seams called Soya coal-bearing formations form the Tenpoku coalfield. These seams consist of lignite, coaly shale, and tuff. This coalfield has not been mined since 1972. SCG will enable gas production from this source, thereby allowing the utilization of an unused resource in this area. In this study, immersion tests using a hydrogen peroxide solution were performed on lignite and coaly shale to estimate the quantity of low-molecular-weight organic acids and the producing potential for biogenic methane gas. Laboratory tests of both physical and mechanical properties were also performed on the lignite. Before the immersion tests, a pyrite in the coal was analysed by both the X-ray Fluorescence Analysis and the X-ray diffraction. Decomposition of organic matter using hydrogen peroxide depended on the amount of pyrite in the coal. The oxidative decomposition of lignite, which contains minimal pyrite, produced a high yield of lowmolecular-weight organic acids as substrates for methanogenic microorganisms, whereas there was no correlation between the yield of them and material characteristics of lignite. If SCG is used in the coal seams of Soya coalbearing formations, the methanogenic potential of minimal-pyrite-containing lignite should be greater than that of coaly shale, which contains much more pyrite.