Characteristics of coal powders adhering to wall in process of deep coalbed methane exploration

Key words:  deep coalbed methane  coal adhesion  maximum particle size  adhesion test

Abstract:

In view of the relatively high ground temperature in deep coal seams, and considering the influence of such factors as the well fluid velocity, the pipe wall roughness and the well fluid temperature, the adhesion mechanism of pulverized coal on the pipe wall of deep coal seams was analyzed, and the formulas to calculate the maximum particle radius of the coal powders adhering to the wall in the process of deep coalbed methane exploration were deduced. The pulverized coal adhesion rotating coupon test was carried out to reveal the characteristics of pulverized coal adhesion to the wall of deep coal seam exploration. The results show that the adhesion characteristics of pulverized coal are mainly affected by such factors as the well fluid flow rate, the pipe wall roughness and the temperature. When the other conditions remain unchanged, and when the flow rate of the well fluid increases to 1.5 m/s and above, the coal particles with the radius greater than 20 μm will no longer cause adhesion. When the tube wall roughness is reduced from 32 μm to 16 μm, the maximum particle size of coal powders decreases from 40 μm to 20 μm. Decreasing the temperature from 40 ℃ to 20 ℃ can reduce the maximum adhesion particle size from 26 μm to 20 μm. This analysis uncovers the reason for the more serious problem of pulverized coal adhesion in deep coalbed methane wells, and it lays a foundation for economically and effectively solving the problem of coal adhesion on pipe walls and proposing reasonable drainage strategies.