Transient pressure analysis of horizontal well for coalbed methane

The mathematical models of the pseudo-steady state percolation of horizontal coalbed methane(CBM) well may be obtained by use of the gas pseudo-pressure to replace the pressure in Langmuir adsorption formula.Owing to the fact that the flow equation of permeability's depending on the change in pore pressure is of strong nonlinearity,the models may be solved by use of regular perturbation method and Laplace transform and the zero-order perturbation solution can be obtained through numerical inversion.The change rule of pseudo-pressure along with the changes in the deformation,adsorption,fracture storage and interporosity flow is discussed.All of these results indicated that the pseudo-steady state double-log pressure derivative curve may show "V" shape which can be influenced by storage ratio and adsorption coefficient,the present time of "V" shaped curve can be influenced by channelling coefficient,as wll as the permeability deformation coefficient can only influence the later stage shape of curves.