Mechanism Of Soluble Organic Matter Influencing On Coal Gas Storage And Transport Properties

Gas extraction is a fundamental measure for preventing gas disaster. However, during extraction, the problem such as gas flow attenuation rapid, the low amount of pure gas, etc. often confuses us, which also causes the difficulty to prevent gas disaster. Complex pore structure and coal composition are the key influencing factors that decide gas transport from the microscopic pore of coal seam. In the paper, based on coal structure and composition, the methods of theoretical analysis and experimental simulation and test were used, pore characteristics and the structural parameters of raw and residual coals and their adsorption、diffusion and percolation characteristics were systematically studied. The mechanism between the soluble organic matter and coal pore were deeply analyzed, and then the influence mechanism of soluble organic matter on coal adsorption and diffusion and percolation characteristic were discussed.Four coal samples(long-flame coal, gas coal, coking coal and anthracite) were extracted with tetrahydrofuran(THF) solvent at 50°C and atmospheric pressure by microwave-assisted extraction. And then the extractions(soluble organic matter) and extraction tailings(residual coals) were obtained. The soluble organic matters were analyzed via the Gas Chromatography/Mass Spectrometry(GC/MS). The extractions mainly include hydrocarbons and oxygen compounds, especially for the aromatic hydrocarbons.Pore surface features and pore structure parameters of raw and residual coals were respectively scanned by the scanning electron microscope(SEM) and tested via mercury intrusion and gas adsorption(N2, CO2) method. The changing law of pore characteristics and structural parameters for raw and residual coals were comparatively analyzed. And their variations were quantitatively study analyzed with the fractal theory. After extraction, coal pore structure was simplified and the proportion of micropores was reduced.The methane isothermal adsorption experiments of raw and residual coal were carried out at different temperatures(20 °C, 30 °C and 40 °C). Based on several common adsorption theoretical models and adsorption thermodynamic theory, the rules of methane adsorption characteristic parameters, surface free energy change value, methane adsorption characteristic curve and isosteric adsorption heat were respectively analyzed. From the view of thermodynamics, the interactions between methane and raw and residual coals were analyzed, and the essential differences about methane adsorption for raw and residual coal were revealed. After extraction, the coal adsorption capacity reduced.Methane irradiation and radial seepage tests of raw and residual coals were carried out. The change law of the amount of methane emission, the speed of methane emission, emission coefficient and permeability were deeply analyzed. After the soluble organic matter was dissolved by the solvent, the pore structure of coal could be simplified, the diffusion resistance was reduced, coal permeability channels were enlarged and speepage resistance was reduced. And all these would be conducive to methane tansport from the coal matrix.Based on raw and residual coals pore structure, adsorption properties, diffusion characteristics and permeability,the effect of soluble organic matter on the coal pore was deeply analyzed. The method of “increasing”(adding diesel) and “decreasing”(extracting) organic matter was creatively used to prepare coal samples. The differences of adsorption isotherm curves for raw coals, their residues and coals added diesel were analyzed, and mechanism of soluble organic matter affecting on their adsorption properties was discussed. And then the effect mechanism of soluble organic matter on methane diffusion and seepage in the coal was analyzed. Finally the mechanism of soluble organic matter influencing on coal storage and transport properties was revealed. The research results have certain guiding significance for the further development of related technology to control the coal microcosmic pore structure.