Mechanism of crack-oriented of hydraulic fracture and its technique in mine
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摘要:
针对井下煤层水力压裂裂缝扩展无序导致抽采效率低的问题，提出水力压裂裂缝导向方法，即采用高压水射流割定向缝导向裂缝起裂及扩展。在压裂孔周边合理布置导向钻孔，压裂孔及导向钻孔均采用水射流割缝技术在煤孔中形成定向缝隙。在地应力作用下缝隙尖端形成剪切破坏区，在内水压的作用下裂缝在缝隙尖端起裂；通过计算射流割缝缝隙水平延长方向最大主应力方向得出，裂缝在尖端起裂后沿水平方向延伸；在此基础上研发了裂缝导向技术工艺，即钻孔布置工艺、封孔工艺及压裂工艺，并成功应用于典型低透气性煤层；试验结果表明：该方法能够导向裂缝的延伸，压裂半径为25 m以上；抽采数据表明瓦斯抽放平均浓度为68%，单孔平均抽放纯量为0.037 m 3/min；采用裂缝导向技术后相比普通孔瓦斯抽放纯量提高了11.26倍，抽放浓度提高了2.12倍。
Abstract:
Drainage is inefficient of coal seam treated by hydraulic fracture due to disordered propagation of fracture. Therefore, we propose a novel approach of fracture-oriented via slotting a slitting in coal seam by high pressure water jet. Firstly，boreholes-oriented are drilled around the borehole of hydraulic fracture. Then we slot the coal seam via high pressure water jet. Finally，we carry out hydraulic fracture in the borehole. Shear destruction area which is formed under geostress is located on crack tip. And crack propagates along horizontal direction because the major principal stress direction is horizontal. Besides，we develop the technique of crack-oriented and apply it in typical low permeability coal seam. The results show that the technique is efficient. The diameter of hydraulic fracture is larger than 25 m，the concentration of gas drainage is 68% on average，and the gas flow is 0.037 m 3/min. The concentration and flow of gas increase 2.12 times and 11.26 times respectively comparing to those of traditional technique.
