220 / 2018-07-08 18:09:54

Investigation of self-sealing of upward boreholes using drilling cuttings to enhance coal-bed methane recovery

coal-bed methane, failure mechanism; upward borehole; drilling cuttings; self-sealing

矿井瓦斯与煤与瓦斯突出 > 煤矿瓦斯

Underground coal-bed methane (CBM) drainage plays an important role in coal-mine gas accidents prevention, environmental protection, and clean energy supply. Drainage through an upward borehole is commonly used in underground CBM extraction. Effective sealing of such boreholes is key to improve drainage efficiency. A new self-sealing technology for upward boreholes using drilling cuttings is proposed in this paper. The failure mechanism of upward borehole sealing was first analyzed. An experimental system for simulating the self-sealing of upward boreholes by drillings was established, and some critical parameters, such as particle size distribution and movement of the drillings, were investigated. The results indicated that most deposited particles exhibited small voids and were compacted to have low permeability. The small-scale particles entering cracks in the plastic zones around the boreholes at a high speed could prevented the air from flowing into the boreholes through some fractures. The angle of repose tended to increase until the borehole cross-sections were covered. Fine particles, accounted for a high proportion, were more likely to contact with the borehole walls, thereby preventing leakage at this interface. The field application constructed in the No. 8 coal mine in Pingdingshan, shown that the gas concentration of 10 trial boreholes were great, which proves that self-sealing method could effectively block air leakage channels in upward boreholes and ensures sealing efficiency.