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低渗透煤层中的煤层气抽放是一个世界性难题，目前尚没有有效的解决办法。文章针对低渗透煤层提出了采用水力割缝技术提高煤层渗透性的方法，介绍了特大煤样条件下的钻孔和水力割缝两种排放煤层气的对比试验研究。试验结果表明：煤样的煤层气排放符合艾黎经验公式，可以使用该公式对煤层中的煤层气排放进行预测。与钻孔排放相比，水力割缝排放煤层气，会随埋深不同而发生不同程度的煤层气突出，从而提高煤层气的排放速度和排放量，缩短排放时间。相同埋深的煤层，割缝后，煤层气初期排放速度急增，约为钻孔的2～2.5倍；随着煤层埋藏深度的增加，水力割缝对提高煤层的渗透性作用越明显。这些结论对低渗透煤层的煤层气抽放与开采有参考价值。

TESTING STUDY OF OUTSIZED COAL SAMPLES CUTTING AND DRILLING TO DISCHARGE COAL-BED GAS

It is an international problem to recover the coal bed gas from coal formation with low permeability. There is no effective way to solute it now. Aiming to the coal formations with permeability, the hydraulic cutting technique is proposed to improve the permeability of coal formations. The comparison tests are described for the drilling and hydraulic cutting methods to discharge coal bed gas with outsized coal samples. The test results show the coal bed gas discharging follows E.M. Airey  experiential formula. The formula can be used to predict the coal bed gas discharge in coal formations. Comparing to the drilling method, with hydraulic cutting to discharge coal bed gas, the gas outburst will happen at different level as the buried depth varies, which will increase the discharge rate and volume of coal bed gas and shorten the discharge time. Cutting the coal formation at the same depth, the discharge rate increases rapidly in the initial stage and is about 2 — 2.5 times to that by drilling. The effect of hydraulic cutting to improve the permeability of coal formations is more obvious as their buried depth increases. The conclusions are helpful to discharge and recover coal bed gas from coal formations with low permeability. (Financed by the project of the National Natural Science Foundation, No. 50404017, 50134040, 50174040)