Study On The Migration Law Of Pulverized Coal In Wellbor

Pulverized coal deposition in the well is one of the important cause of coal bed methane(CBM)downhole failures.In view of the low efficiency,leakage and stuck pump failures caused by Pulverized coal deposition in CBM wellbore,the migration rule of pulverized coal in CBM wellbore was studied.According to the production conditions of CBM Wells in zhaozhuang coalmine of Qinshui Basin,a transient model of the solid-liquid two-phase flow of coal powders in the pumping rod and tubing annulus area was established,and the Euler model in FLUENT software was used to simulate the migration of pulverized coal particles in the fluid.Through the simulation of the continuous flow of pulverized coal and the processing and analysis of the results,the critical carrying velocity of the pulverized coal at different particle sizes was obtained.The critical carrying velocities of 40 mesh,60 mesh,80 mesh,100 mesh and 120 mesh coal powders were 2.46508cm/s,1.57108 cm/s,0.84562 cm/s,0.53107 cm/s and 0.39826 cm/s,respectively.The influencing factors of the critical carrying velocity of pulverized coal were analyzed.and the results showed that the particle size and shape of pulverized coal particles,the concentration of pulverized coal and the borehole diameter of CBM drainage well all have different effects on the critical carrying velocity of pulverized coal particles.Through the simulation of pulverized coal particles with different sizes and different flow rates,the amount of coal powders discharged at different particle sizes and the critical amount of coal powders discharged at the maximum particle size were obtained.The simulation results showed that the amount of coal powders discharged in wellbore decreases with the increase of pulverized coal particle size and increases with the increase of well fluid velocity.When the flow rate of well fluid was 0.06071 m/s(the average daily water production of zhaozhuang mining area is 10 m~3/d),the discharge amount of coal powder with a particle size of 60 mesh and below exceeded 85%,and the coal powder discharge effect was better.When the particle size of the coal powders was 10 mesh,the critical flow rate of the coal powders discharge was 0.17m/s,and when the daily water production was controlled above 28m~3/d,the coal powders discharge effect was better.Through the analysis of the flow characteristics of the CBM well during the drainage process and the drainage characteristics of each drainage stage,combined with the critical carrying velocity of the coal powder particles and the migration law of the coal powder particles in the wellbore,the drainage volume of the CBM well during the drainage process Reasonable design method.The research results provide a reference for the development of the drainage system of CBM well in Zhaozhuang mining area.