The determination method of coal gas drainage radius based on methane flow state

Based on the Reynolds number,the fluid flow state can be divided into four types: non-linear seepage with high velocity,linear seepage,non-linear seepage with low velocity,and diffusion.The drainage redius was calculated by Darcy law in the linear seepage zone.Based on the reservior pressure and starting pressure gradient,the low velocity non-linear seepage zone was been determined.The calculation result is similar to the measurement under coal mining in Hongling area of Anyang coal district.