Impact of Drainage Parameters on Coal Fines Production in CBM Wells: A Long-Term Monitoring Study of Liulin Block, Ordos Basin, China.

Coalbed methane (CBM) horizontal wells often experience significant coal fines production during the drainage process, which disrupts efficient CBM extraction. This study monitored key drainage parameters such as gas and water production rates, bottomhole flowing pressure, and casing pressure over an extended period. We analyzed fluid samples containing coal fines to understand their concentration, particle size distribution, and morphology. By correlating these findings with drainage parameters, we identified factors influencing coal fines production and the variation patterns in coal fines concentration. The results revealed that the concentration of produced coal fines ranged from 0.01 to 6.14 g/L, with particle sizes ranging from 0.63 to 704.00 μm. Rapid and continuous increases in production and gas release led to an increase in coal fine concentration and particle size. Conversely, slow, intermittent production increases and stable gas production helped reduce coal fines production. Additionally, pump start-stop cycles resulted in instantaneous increases in coal fines production. Notably, coal fines produced at the wellhead exhibited better roundness than those from workover operations. The smooth surface consists mainly of organic components, while the rough surface minerals are mainly kaolinite, calcite, quartz, illite, and pyrite. By advocating for a "continuous, slow, stable, and long-term" drainage approach, accidents such as screen clogging and pump blockage can be reduced.