Abstract
There are practical and financial difficulties to measure gas permeability of coal seams. So we tried to evaluate gas permeability of a coal seam using permeabilities of small lump coal samples.From the results of measurement it was shown that; 1) Gas permeabilities of coal samples are distributed between very wide range, i.e. 10-7-100 darcy. 2) They fit to log-normal distribution. 3) In parallel or perpendicular direction of a seam, gas flow range has not significant difference.From the results it was unsuitable to estimate coal seam gas permeability by using arithmetic mean of these permeabilities. So we used two and three-dimensional model of coal seam consisted of random elements whose permeabilities are distributed as in samples. We made simulating calculation about gas flow in the model.Gas permeabilities of coal seams which were gained in this way are nearly same values with logarithmic means of sample permeabilities and showed good agreements with easiness of gas drainage in the colliery and values measured by other persons.
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