To derive the seepage rule and to make the productivity prediction of ultra-short radius radial horizontal well for coal-bed methane（CBM） exploitation

a fluid-solid coupling mathematical model was developed under the conditions of basic assumptions

a weak solution equation was formulated in certain boundary conditions and initial conditions and a set of program was developed with Matlab to show the variation of pressure field

velocity field and gas production in vertical shaft and radial-branch horizontal wells after 1000 days mining of CBM.The simulation results show that in certain production region and mining time

the scale of coal reservoir pressure drop is broadened

the disturbance of gas velocity field is strengthened

the area of pressure funnel drop is extended

the supply area and the desorption area of CBM grows largely

the desorption capacity and the stable production capacity are strengthened and the production increases substantially along with the increasing number of radial horizontal wells.Meanwhile

the growth rate of the gas production declines

thus there exists an optimum value for the number of radial horizontal wells.Effective pressure relief of ultra-short radius radial horizontal well in the CBM exploitation is shown in the simulation and it is significant to the choice of CBM industrial production increase technology and arrangement of drilling plan.