# Physical Simulation Experiment for Visualizing Pulverized Coal Transport in Propped Fractures
## 3 Results and Discussion
### Analysis of the Migration Patterns of Pulverized Coal at Various Displacement Speeds  
Under the experimental conditions, where the proppant size ranges from 16 to 20 mesh, the pulverized coal particle size is between 100 and 150 mesh, and the transport fluid is agglomerated fracturing fluid, notable differences are observed in the injury rate of proppant fracture inflow capacity, the amount of pulverized coal output, and the time taken for equal-volume solution repulsion during experiments conducted at different repulsion velocities (100 mL/min, 200 mL/min, and 300 mL/min) (Figure 6).  
At a replacement speed of 100 mL/min, the injury rate of fracture inflow capacity ranges from 0.58% to 5.08%, with variation rates of 3.9, 2.0, and 1.1 times, demonstrating a gradually slowing increasing trend. With an expulsion rate of 200 mL/min, the variation range of fracture inflow capacity injury rate is 2.35-7.78%, with variation rates of 1, 1.49, and 2.23 times, indicating a steady upward trend. When the expulsion rate is 300 mL/min, the variation range of fracture inflow capacity injury rate is 5-44.12%, with variation rates of 1, 2.19, and 4.03 times, showing a significant increasing trend. The cumulative values of fracture inflow capacity injury rate for the three driving speeds are 12.55%, 15.97%, and 65.06%, suggesting that the injury rate of fracture inflow capacity increases with the rise in driving speed.  
517.2 mg, and 485.2 mg, indicating that pulverized coal output tends to increase and then decrease with the increase in driving speed.  
(3) Equal-volume solution displacement time.  
At a displacement rate of 100 mL/min, the displacement time of the equal-volume solution ranges from 169 s to 177 s, demonstrating a slowly increasing trend. This suggests a gradual increase in the migration of the carrier fluid within the propped fractures. When the displacement speed is 200 mL/min, the displacement time of the equal-volume solution varies from 85 s to 90 s, also showing a slowly increasing trend, although more gently than at 100 mL/min. This indicates that with the increase in displacement speed, the migration of the carrier fluid within the propped fractures slows down, suggesting that the displacement speed can counteract the influence of some adverse factors on fracture conductivity. At a displacement speed of 300 mL/min, the displacement time of the equal-volume solution ranges from 60 s to 102 s. The displacement time increases noticeably from the beginning of the second cup and rises sharply from the third cup to the fourth cup, indicating significant blockage occurring in the propped fractures.  
The analysis above indicates that excessively fast displacement speeds can result in premature blockage formation, leading to damage to fracture conductivity. Conversely, excessively slow displacement speeds can prolong the migration and output time of the carrier fluid, which is unfavorable for drainage operations. Both fast and slow displacement speeds can impact the output of pulverized coal to some extent. Therefore, determining the critical displacement speed for the prevention and control of pulverized coal is paramount.