Study on drainage system of coalbed methane well based on drainage rate

In order to analyze the drainage system's influence the production capacity of the coalbed methane well, based on the actual drainage data of the coalbe d methane vertical well in Shizhuang South Block of Qinshui Basin, the production capacities of the coalbed methane wells under different drainage rate were compared and an analysis was conducted on the drainage system in different drainage stage. The results showed that the fast drainage rate would reduce the radius of the draina ge, would cause a quick sensitive effect, would make the crack closed and would reduce the production capacity of the coalbed methane well. Based on the drainage ra te, the drainage process of the coalbed methane well could be divided into three stages. An initial gas production stage when the dynamic liquid level dropped down to t he seam roof nearby could make the dynamic liquid level slowly drop with the liquid supply capacity of the strata and the drop rate would be 5~ 10 m/ d suitably. A sta ble pressure waving stage which control the flow pressure of the well bottom could control the casing pressure stabilized within0. 2 ~ 0. 4 MPa and the gas production at the stage would cause unstable up and down waving and the unstable time would be long. At the pressure reduction and production increasing stage, when the gas p roduction was obviously reduced, the dynamic liquid level would steadily drop to the seam floor, the casing pressure would be reduced and finally the pressure would b e stabilized around 0.02 MPa. The gas production of the coalbed methane well at this stage would be increased anyhow and a max gas production potential would be p layed.