Dynamic influence law of coal powder migration and deposition on propped fracture permeability

The permeability damage of propped fracture caused by coal powder deposition is one of the important factors that affect the effect of coalbed methane drainage.Based on capillary tube bundle model and Carman-Kozeny formula,the permeability evolution model of propped fracture considering coal powder migration and deposition is established,and the coal rock conductivity test system is used to test the penetration of coal powder into propped fracture under different conditions,and the model is verified.The influence of coal powder deposition characteristics on the distribution of coal powder and permeability spatio-temporal evolution in the propped fracture are investigated in this study.The results show that along the migration direction of coal powder,the concentration of deposited coal powder in the propped fracture gradually decreases,and a large number of coal powder deposited in the entrance end of the fracture,leading to a greater degree of pore plugging at the entrance end of the fracture and a smaller degree of pore plugging in the fracture,and the permeability of the propped fracture decreases along the migration direction of coal powder.And with the increase of coal migration time,the concentration of suspended coal powder in the propped fracture first rises to the peak value,and then remains unchanged,the concentration of deposited coal powder continues to increase,the plugging degree of pores in the propped fracture increases and the permeability of the propped fracture decreases.With the increase of deposition rate coefficient of coal powder,it is more difficult to transport coal powder into the powder fracture,and the amount of deposited coal powder at the entrance of the propped fracture increases,the amount of coal powder entering into the propped fracture decreases,the concentration of suspended coal powder and deposited coal powder in the propped fracture decreases,the pore volume occupied by coal powder becomes smaller,and the permeability of propped fracture increases;as the dispersion coefficient increases,the coal powder is easier to migrate,and the amount of coal powder entering the propped fracture increases,the concentration of suspended coal powder and deposited coal powder in the propped fracture become higher,the pore volume occupied by coal powder becomes larger,and the permeability of propped fracture becomes smaller.