煤矿井下穿层水力压裂钻孔布置优化分析及应用

Optimization Analysis on Hydraulic Fracturing Crossing Borehole Layout and Its Application in Coal Mine

为解决重庆地区低透气性松软煤层瓦斯抽采的难题,提出煤矿井下穿层水力压裂技术,分析得出其增透主要是高压水在煤体裂隙尖端产生拉应力增高区促使原始裂隙扩展、次生裂隙形成的过程,借助数值模拟对不同孔距的穿层水力压裂煤体塑性破坏区随注入高压水压力的变化规律进行研究,得到重庆逢春煤矿7号煤层起裂压力为33～35MPa,而延伸压力略低于起裂压力,拟合出不同孔径下水力压裂有效范围与注入高压水压力的指数曲线,并将研究成果应用于该矿底板巷瓦斯抽采工程.结果表明：水力压裂后煤层在走向、倾向上单孔压裂有效范围分别达到60m和50m,煤层透气性系数提高195～370倍,瓦斯抽采纯量提高3.5倍,瓦斯抽采浓度提高5倍.

To resolve the problem of gas drainage difficulty in soft coal seam with low permeability in Chongqing area, a new technology by hydraulic fracturing across coal seams was proposed, it was concluded from the analysis that the process of the permeability enhancement included the original crack expansion and the secondary crack formation in the tensile stress concentration area produced at the crack tip. Study was made on the variation law of the plastic failure zone of the coal body by hydraulic fracturing across seams with the pressure of the injected high-pressure water with the help of numerical simulation. It was found that the fracture initiation pressure of No. 7 coal seam in Fengchun Coal Mine was 33 ~35 MPa and the extension pressure was slightly lower than the initiation pressure. The exponential curve of the hydraulic fracturing radius and the injection pressure was fitted out, which was applied to gas pre-drainage engineering in a floor roadway. The application results showed that the effective range of hydraulic fracturing along the strike and inclination respectively reached 60 m and 50 m, the permeability of coal seam raised by 195 ~370 times, the gas drainage volume increased by 3. 5 times and the gas drainage concentration increased by 5 times.