水力压裂对煤层应力影响的实验研究

Experimental Study on the Effect of Hydraulic Fracturing on the Stress of Coal Seam

为了研究水力压裂过程中注水压力和周围煤层应力的变化规律,在实验室开展了相似材料模拟实验,结果表明:注水压力的增加、煤体破裂的速度均受地应力影响,地应力越大,注水压力越大、煤体破裂的速度越慢;距注水孔半径75 mm圆形区域内为钻孔水力压裂实验的卸压范围,注水后煤体应力往深部方向转移;裂隙以水力压裂孔为中心,沿半径方向延伸分为3个等级,即半径40 mm圆形区域内裂隙范围最大,40~65 mm圆环区域裂隙范围次之,65~80 mm圆环区域裂隙范围最小。根据实验结果,在小庄煤矿40201工作面开切眼以内200 m区域进行现场应用,抽采瓦斯浓度相比常规抽采提高了20%,钻孔抽采瓦斯流量相比常规抽采提高了40%。

In order to study the variation law of water injection pressure and surrounding coal seam stress during hydraulic fracturing,the experiments simulation with similar materials were carried out in the laboratory. The results showed that the increase of the injection pressure and the rupture velocity of coal body are affected by crustal stress. The greater the crustal stress,the greater the water injection pressure,the slower the rupture velocity of coal body. Pressure relief range of drilling hydraulic fracturing test is within a circular area with a radius of 75 mm which taking the water injection hole as the center,the stress of coal body is transferred to the deep direction after water injection; the fracture is divided into three grades that centered on hydraulic fracturing hole and extended along the radius. The fracture is the largest within the circular area with a radius of 40 mm,followed by that of the circular area with a radius from 40 mm to 65 mm,and it is the smallest when the area with a radius from 65 mm to80 mm. According to the experimental results,the field application was carried out within 200 m area of cutting hole in the 40201 working face of Xiaozhuang Coal Mine,the concentrations of gas extraction increase by 20% compared to conventional extraction,the gas flow rate of borehole extraction is 40% higher than that of conventional extraction.