NONLINEAR FLOW ANALYSIS OF METHANE IN LOW PERMEABILITY COAL SEAMS

Considering the wellbore storage and skin effects, a mathematical model of methane flowing in low permeability coal seams was presented with the starting pressure gradient. The analytical solutions for dimensionless bottom-hole pressure in Laplace space were obtained by Laplace transform and Green function method when the constant flow rate was specified in an infinitely large reservoir, and then converted to numerical solutions in real space by Stehfest numerical inversion method. The parameter sensitivity analysis has shown that the starting pressure gradient has no effect on the initial pressure behavior, but the ascending tendency of dimensionless bottom-hole pressure and its derivative curves becomes more obvious with increasing starting pressure gradient values in the middle-late production stage, that is, the starting pressure gradient has brought more serious influence to the methane flow in coal seams.