# Physical Simulation Experiment for Visualizing Pulverized Coal Transport in Propped Fractures
## 3 Results and Discussion
### Analysis of the Migration Pattern of Pulverized Coal with Various Particle Sizes  
Under the experimental conditions of 16-20 mesh proppant, a replacement rate of 200 mL/min, and agglomerated fracturing fluid as the transport fluid, notable differences in the injury rate of proppant fracture conductivity, the amount of pulverized coal output, and the displacement time of the equal-volume solution occur between the coal transport cases with different pulverized coal particle sizes (80-100 mesh and 100-150 mesh, Figure 7).  
Figure 6: Experimental results of pulverized coal migration at various displacement speeds.  
When the particle size of pulverized coal is 80-100 mesh, the variation range of crack inflow capacity injury rate is 3.4-56.8%. There is a sharp increase in the injury rate of propped fracture conductivity in the fourth cup, indicating severe blockage in the propped crack, and a sharp decrease in the crack inflow capacity. When the particle size of pulverized coal is 100-150 mesh, the variation range of the crack inflow capacity injury rate is 2.4-7.8%, showing a slowly increasing trend. However, the variation is more gradual than that under 80-100 mesh, suggesting that the injury caused by 100-150 mesh pulverized coal to the propped fractures' inflow capacity is much smaller than that of 80-100 mesh pulverized coal.  
The variation range of the pulverized coal output at a pulverized coal particle size of 80-100 mesh is 52.4-69.7 mg, showing a trend of gradual increase, followed by a decrease. This indicates that the propped fractures experience pulverized coal deposition and slight clogging as the replacement experiment progresses, with the pulverized coal clogging the propped fractures to form serious blockage when replacing the fourth cup of liquid, leading to a sudden decrease in the output of pulverized coal. When the particle size of pulverized coal is 100-150 mesh, the variation in the pulverized coal output ranges from 107.4 to 155.9 mg, also showing a slow increase followed by a sudden decrease, but the amount of pulverized coal output is significantly higher than that under pulverized coal of 80-100 mesh.  
When the particle size of pulverized coal is 80-100 mesh, the variation range of the equal-volume solution displacement time is 88-197 s, with a sharp increase observed in the fourth cup, indicating severe blockage in the propped fractures. When the particle size of pulverized coal is 100-150 mesh, the change range of the displacement time of the equal-volume solution is 58-90 s, showing a slowly increasing trend. There is no sharp increase in the fourth cup, indicating the absence of serious blockage in the propped fractures. The displacement time is notably reduced compared with that under 80-100 mesh.  
The analysis above indicates that when the particle size of pulverized coal is larger, the damage to the propped fracture inflow capacity is significantly greater than that under smaller particle sizes. Additionally, the output of pulverized coal is lower, and the transportation output time is longer.