Diffusional Analysis of Seam Gas Emission in Coal Mines

CIM Bulletin, 1971


Seam gas flow in coal mines takes place through a medium which has both capacity and resistance and can therefore be expressed in terms of the bas ic diffusion equation, provided that the characteristics of the system can be adequately described. It may be possible to lump the variations from point to point in a seam together as an effective diffu sivity. The paper discusses the characteristic flow-time patterns for various types of openings and the particular features of coal and seam which influence the diffusiv ity. Two field experiments are described in which gas make to a heading and to a borehole were measured in a mine for which considerable data on coal sorption properties were available. Incremental gas flow measured from the borehole experiment predicted the actual flow from the heading measurements remarkably well. The effective permeability adjacent to the face was much higher than expected from the properties of the coal. The incremental flow measurements to a horizontal (in-seam) borehole showed a striking picture of advancing 'relaxation' behind the face which is not discernible by other exp.erimental means
Keywords: analysis, Australian Coal Association, borehole, colliery, numerical analysis, permeability, Boreholes, Coal, Desorption, experiment, Experiments, flow, Permeability, Pressure