Experimental Investigation of Coal Powder Transport and Deposition in Propped Fractures of CBM Well

To address the issue of excessive coal powder production during hydraulic fracturing, a series of experiments were conducted using the LD-1A proppant conductivity testing system. These experiments investigated fluid flow behavior at various velocities and with different concentrations of coal powder in a propped fracture. The study examined the transport, deposition, and production of coal powder under conditions of varying flow velocity, constant flow velocity, and intermittent flow. Experimental results revealed that there exists a critical velocity for coal powder transport, which varies significantly depending on experimental conditions. In fractures propped with 20–40 mesh quartz, the critical velocity for coal powder larger than 60 mesh is found to be 5.20 cm/min, while for coal powder larger than 140 mesh, it is 2.01 cm/min. The production of coal powder is influenced by a combination of factors including fluid velocity, proppant size, coal powder size, coal powder concentration, and production strategy. Coal powder can easily deposit within the propped fracture, leading to pore plugging in the proppant pack and significant damage to fracture conductivity. Effective management of coal powder through flowback after fracturing can mitigate such damage. Controlling flow velocity during the production process is also beneficial for reducing the generation, transport, and deposition of coal powder.