Abstract:

Beginning with flow mechanism of coal methane,a mathematical model for coalbed methane reservoirs is established by utilizing the Langmuir isothermal adsorption equation to describe the desorption of methane from coal surface and the Fick's law to delineate the diffusion of methane in coal matrix and micropores.The calculated results of this model show that the productivity steps up with the increase of fracture half length and flow conductivity.However,when the fracture half length is increased to 100m and the fracture flow conductivity is beyond 20 μm²·cm,their effects upon the productivity becomes less evident.Molecular diffusion coefficient has no big influence over the productivity,while the permeability of cleaps,on the contrary,is closely connected with productivity changes.A rational selection of fracture half length and flow conductivity is strongly recommended when put a coalbed methane gas well into production.

Key words: fracturing, numerical simulation, productivity, coalbed methane