Figure 1 shows the Fickian diffusion coefficients obtained from four different drilling tests in the Bulli coal seam. In these, the coal cuttings were washed out of the hole, sieved, and then desorbed. The desorption rate was analysed to produce the gas content and diffusion rate. The size ranges were 0.25 to 0.5 mm 0.5 to 1.0 mm, 2.0 to 4.0 mm and 4 + mm. The diffusion coefficients vary over two orders of magnitude.
