Study on gas drainage technique for combined seam with coalbed methane well in Tucheng Block of West Guizhou

in order to set up a gas crainage system suitable to the caled methane combined drainage well in Tucheng Block.based on the demo projec of the coal bed methane surface drainage in Tucheng Block.in combinaton with the combined seam drainage theory and the COMET3 numericalsimulaton method.thecoledmnethane geologic conditin and the gas drainage cure features ofthe gas production well vithin the bock were analized and the optimized measures of the combinedsean drainage fechrique were discussed.Theresults showed tht the water drainage rate should be seriously controlled at the intial water drainage stage.the height of the water level should be kept over 450 m and the fowing pressure value should be over 4.5 MfPa.T7he pressure buli-up margin shauld be controlld during the pressure build-up stage and the pressure built-up should be based on the certain level heigh pre-set.The fowing pressure reduced rate should be ighly conrlled at the pessure control and gas production stage and the sirulaton results showed that adrainage effect would be best when the fiowing pressuredail reducion was conral d at 0.010~0.015 MPal d. At the pressure control and stable producion stage,the retention time of the fiowin liqud lvel at the frt ay er should not be too ong andthe upper production layer could be actively and slowly exposed under the casing pressure of 0.5 MPa.At the productio attenuation stage,the flowing pressure in the third fractring secion should be kept n stable and the sinulation resuits showed that 0.7 MPa as a stablired pressure value would be favorableto the gas production