Wellbore annulus pressure model of vertical coalbed methane well

In order to calculate the pressure distribution of wellbore annulus of vertical coalbed methane well in each production stage,and provide guidance for the control pressure production in coalbed methane wells,combined with the domestic production of coalbed methane,the gas-liquid distribution of CBM vertical wells’wellbore at every production stages has been studied,which uses the production method of tubing drainage and annular production gas. The pure liquid flow occurs in the annulus only before the desorption of coalbed methane has been proposed. Only bubbly and slug flow occurs in the annulus at gas-liquid two-phase flow stage. And the gas rises in the annulus without carrying liquid. Based on this,using the hydrodynamics method,three wellbore annulus pressure models have been established. They are single-phase liquid pressure model,gas-liquid two-phase pressure model and single-phase gas pressure model respectively. Transition condition and solution steps of the model have been given. And at each production stage,the pressure distribution of wellbore annulus of vertical coalbed methane well can be calculated. Verified by a total of 71 groups of measured data,coming from 41 CBM wells,the average error of three models are 2. 70% ,7. 96% and 3. 80% . The wellbore annulus pressure model of vertical CBM well has reasonable accuracy and practicability.