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针对坚硬顶板难垮带来的冲击灾害,提出运用垂直层面预制裂缝定向水力压裂技术。运用RFPA-2D分析软件,模拟试件尺寸为300 mm×300 mm的砂岩预制裂缝水力压裂的裂缝扩展过程,以及预制裂缝的长度、方位角(α)及围压比(σH/σh)对裂缝扩展的影响。模拟结果表明:人工预制裂缝对裂缝的扩展起到导向作用,裂纹首先在预制裂缝的尖端产生并延伸;预制裂缝扩展方向的转向角随着围压比的减小而减小,最大主应力与最小主应力接近时,预制裂缝对裂缝扩展的导向作用最明显,预制裂缝扩展方向的转向角随着预制裂缝与最大主应力夹角的增大先增大后减小,预制裂缝的长度在20 mm以内对裂缝扩展方向的转向角影响较小;破裂压力随着围压比的增大而减小,随着预制裂缝与最大主应力夹角α的增大而增大,在α为0°~45°时增加缓慢,α大于45°时急剧增加,破裂压力随着预制裂缝长度的增加而减小。
In view of the impact disaster caused by the unbearable hard roof, we propose the use of the vertical fractured directional hydraulic fracturing technology. The RFPA-2D analysis software was used to simulate the crack propagation process of sandstone prefabricated fractures with the specimen size of 300 mm × 300 mm, as well as the length, azimuth (α) and confining pressure ratio (σH / σh) of prefabricated fractures The effect of crack propagation. The simulation results show that the artificial prefabricated cracks play a guiding role in the crack propagation. The crack is firstly produced and extends at the tip of the prefabricated crack. The steering angle of the prefabricated crack decreases with the decrease of the confining pressure ratio. The maximum principal stress When the minimum principal stress is close, the prefabricated crack has the most obvious guiding effect on the crack propagation. The steering angle in the direction of prefabricated crack growth first increases and then decreases with the increase of the included angle between the prefabricated crack and the maximum principal stress. The length of the prefabricated crack is between 20 mm. The fracture pressure decreases with the increase of the confining pressure ratio, and increases with the increase of the included angle α between the prefabricated fracture and the maximum principal stress. When α is 0 ° ~ 45 ° slow increase, a sharp increase when α is greater than 45 °, the fracture pressure decreases with the increase of pre-crack length.