地層内バイオメタン生成に関する宗谷夾炭層での有機物分解促進に関する検討

Abstract

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.