本煤层分段水力造穴钻孔抽采半径考察试验研究

Investigation and experimentation research on extraction radius of segmented hydraulic cavitation borehole in mining-coalbed

针对本煤层分段水力造穴钻孔抽采半径定义不明确、难以确定的问题,以古城煤矿3号煤层为背景,开展本煤层分段水力造穴钻孔抽采半径考察现场试验研究,结合不同试验钻孔的瓦斯抽采流量现场监测,运用瓦斯储量法考察了本煤层分段水力造穴钻孔和普通钻孔的抽采半径,获得了不同类型试验钻孔的抽采半径时变规律以及本煤层分段水力造穴对瓦斯抽采半径的扩大作用。结果表明:①在相同抽采时间内,前进式本煤层分段水力造穴钻孔和后退式本煤层分段水力造穴钻孔的抽采瓦斯纯量平均值分别是普通钻孔的3.08倍和3.79倍,抽采半径分别是普通钻孔的2.14~5.62倍和2.58~5.88倍,本煤层分段水力造穴钻孔能够显著提高钻孔瓦斯抽采纯量,有效扩大钻孔瓦斯抽采半径,且后退式本煤层分段水力造穴钻孔的扩大作用更加显著;②普通本煤层抽采钻孔和本煤层分段水力造穴钻孔的瓦斯抽采半径均具有时变特性,即抽采半径随着抽采时间的延长而相应扩大,并逐渐趋于某一极限值;抽采240 d后,普通钻孔的抽采半径基本达到极限,60 d内仅增长了0.01 m左右,钻孔瓦斯流量逐渐衰竭,而本煤层分段水力造穴钻孔的抽采半径仍能随时间延长而有效增长,瓦斯流量仍保持稳定,说明本煤层分段水力造穴钻孔的有效抽采时间和钻孔抽采寿命比普通本煤层钻孔更长。

Aiming at the problem of unclear definition and the difficulty to determine the drilling radius of segmental hydraulic cavity drilling in coal seam,taking No.3 coal seam in Gucheng Coal Mine as the engineering background,the field test study on the drilling radius of hydraulic hole drilling in coal seam was carried out.In conjunction with on-site monitoring of gas drainage flows from different test boreholes,the gas reserve method was used to investigate the extraction radius of the hydrodynamic cavity boreholes and ordinary boreholes in this coal seam.The time varying law of the extraction radius of different types of experimental boreholes and the increase of gas extraction radius from the hydrometric boreholes in coal seam were obtained.The results show that:①In the same extraction time,the average extraction quantities of the forward-type coal seam segmented hydraulic hole-drilling boreholes and the backward-type coal seam segmented hydraulic hole-drilling boreholes are 3.08 and 3.79 times higher than that of ordinary boreholes.And the gas drainage radius of progressive and retrusive hydraulic cavitation boreholes in coal seam are 2.14~5.62 times and 2.58~5.88 times higher than that of ordinary boreholes.The segmental hydraulic cavity drilling can significantly increase the pure volume of drilling gas extraction and effectively expand the drilling gas extraction radius and the lifting effect of the backward type coal seam segmented hydraulic cavern drilling is more significant;②The gas drainage radius of both the ordinary extraction borehole and the segmental hydraulic cavity borehole have time-varying characteristics,i.e.the drainage radius increases with the extension of time,and gradually tends to a certain limit value.After 240 d of drainage,the extraction radius of ordinary borehole basically reaches the limit,and only increased by about 0.01 m within 60 d,the gas flow in the borehole gradually depleted,and the extraction radius of segmented hydraulic cavitation borehole in coal seam can be still be effectively increased with time,and the gas flow rate remains stable,indicating that the effective extraction time and the extraction life of the segmental hydraulic cavity borehole is longer than that of a normal borehole.