Dynamic model for bottomhole flowing pressure in initial stage of CBM wells drainage and its application

Bottomhole flowing pressure is one of the key parameters that affect gas production of coalbed methane (CBM) wells, how to control the change of the bottomhole flowing pressure to increase the gas production of coalbed methane well is a problem worth considering. Based on the radial seepage theory, two dynamic prediction models are established, one is under the condition of infinite outer boundary with inner boundary of regular production and the other is non-regular production, and the change law of the bottomhole flowing pressure is finally revealed under the condition of regular production and non-regular production in the early stage of the drainage. Results show that the flowing bottomhole pressure reduces with the drainage time by the negative logarithm law under the condition of regular production and the flowing bottomhole pressure reduces with the displacement by the negative linear law in the condition of non-regular production. The prediction and analysis of the prediction model were applied in 6 CBM wells of Shizhuangnan block in the early stage of the drainage. It turns out that the predicted result fits the actual situation well.