ABSTRACT: Underground to inseam (UIS) borehole gas drainage is of significance for improving mining safety and turning hazardous methane into a clean gas resource. However, in the horizontal UIS borehole sealing by adopting cement-grout-based sealing method, an upper gap frequently occurs in the sealing section after cement-grout solidification, which could potentially be an air-leakage path and consequently decrease drainage efficiency. Despite extensive previous investigations on borehole sealing, very few studies have been reported in addressing the upper gap issue to enhance drainage performance. In this study, the air-leakage flow models in concentric ring and off-centre ring seal gap of horizontal borehole were established. Then by adopting new expansive composite sealing (ECS) material, a double-phase-grouting (DPG) sealing method was developed to seal the upper gap. Based on theoretical fundamentals of seal-gap leakage, procedures and explanations of DPG sealing method were discussed. Finally, coalmine field trials were conducted to examine effects of DPG sealing method. Results show that: (1) there are positive correlations between air leakage quantity into borehole and the gap width, borehole diameter, pressure differences and eccentricity ratio. While the air leakage amount is negatively related to fluid viscosity and sealing-section length; and (2) because of adopting ECS material and the second-phase grouting specially designed for upper gap sealing, DPG sealing method is capable of sealing upper gap well to improve sealing quality. It mainly reflects in increasing drained gas concentration and prolonging the period of high-methane-concentration drainage. In comparison with traditional sealing method, the mean gas flow with DPG sealing method averagely rises by 30%. Outcomes of this study are expected to provide an effective way to solve upper gap issue and enhance drainage performance of horizontal UIS boreholes.

中文翻译：

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双相注浆封堵水平井下瓦斯抽采钻孔性能提升保障煤矿安全清洁瓦斯资源

摘要：地下至内煤层（UIS）钻孔瓦斯抽采对于提高采矿安全和将危险甲烷转化为清洁的天然气资源具有重要意义。然而，在采用水泥浆基封堵方法的水平UIS钻孔封堵中，水泥浆固化后的封堵段经常出现上部间隙，这可能成为漏气通道，从而降低排水效率。尽管之前对钻孔密封进行了广泛的调查，但很少有研究报告解决上部间隙问题以提高排水性能。本研究建立了水平井眼同心环和偏心环密封间隙的漏气流动模型。然后通过采用新型膨胀复合密封（ECS）材料，开发了一种双相灌浆（DPG）密封方法来密封上部间隙。基于密封间隙泄漏的理论基础，讨论了DPG密封方法的程序和解释。最后，进行了煤矿现场试验，以检验 DPG 密封方法的效果。结果表明：（1）井内漏风量与间隙宽度、井眼直径、压差和偏心比呈正相关。而漏气量与流体粘度和密封段长度呈负相关；(2)由于采用ECS材料和专为上部间隙密封设计的二相灌浆，DPG密封方法能够很好地密封上部间隙，提高密封质量。主要体现在提高抽放瓦斯浓度，延长高甲烷浓度抽放周期。与传统密封方式相比，DPG密封方式的平均气体流量平均提高30%。该研究成果有望为解决上层间隙问题和提高UIS水平钻孔的排水性能提供有效途径。