Migration patterns of coal powder in coal reservoirs during the well drainage

The study on the transport patterns of coal powder the formulation of measures to reduce the output of coal powder are the key for the high and stable productivity of coalbed methane (CBM) wells. Based on the kinematic and dynamic analysis of coal particles in coal reservoir channels, the mathematical model of coal moving with liquid was developed. And the effects of coal powder size and channel radius on coal powder migration were analyzed based on the data of site investigation. The results show that the critical flow rate for coal particle characterizes the eigen values of coal powder produced from CBM well. The coal particle moves while its flow rate reaches to the critical value. With the progressive decrease of the size of powder and channel radius, the critical flow rate of powder coal migration decreases gradually, and coal particles move more easily, the output of powder coal of CBM well will increase. The increase of coal powder size and decrease of angle α between centroid connection and channel lead to rougher channel wall and higher critical flow rate. The critical flow rate of powder coal migration increases gradually, reducing the output of coal powder in CBM well. The systematic and quantitative analysis of coal powder migration in coal reservoir was completed for the first time, which will provide the reasonable basis for controlling the output of powder coal in CBM well and adopting the reasonable operating methods of gas drainage and extraction.