Mitigation Technologies for Wellbore Blockage Caused by Coal Powder Ejection from Surface Wells in Mining-Disturbed Areas: A Case Study

<title>Abstract</title> <p>Surface wells drilled in mining-disturbed areas are an effective means for pressure-relief gas drainage. In soft, outburst-prone coal seams, however, high-pressure gas can carry coal powder into the wellbore, causing severe plugging and a consequent decline in drainage efficiency. Intense mining disturbance, low coal strength, and high gas pressure were identified as the primary contributing factors. High-pressure gas flushing was applied to alleviate the blockage. Results show that flushing is most effective when the working face is positioned directly beneath the well, yielding an average peak gas flow rate of 30.9 m³/min and sustaining a rate above 10 m³/min for 57.5 days. A standpipe installed inside the slotted pipe was also tested, but coal powder continued to enter through the drain holes, rendering this approach ineffective. A third alternative—fitting a metal mesh filter around the slotted pipe—was subsequently proposed. Laboratory tests indicated that while the mesh effectively retained coal powder, it also reduced gas flow; a 1.0 mm mesh size was identified as optimal. In field applications, wells 1024-2 and 1024-3, equipped with the 1.0 mm mesh, achieved an average peak flow rate of 27.29 m³/min and maintained a flow above 10 m³/min for 45.5 days, confirming satisfactory performance in mitigating wellbore plugging.</p>