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凝胶压裂裂缝扩展规律及破裂机制试验研究

Experimental study on fractures propagation law and fractures mechanism of gel fracturing

  • 摘要: 水力压裂技术是常用的物理破岩方法之一,可解决坚硬岩石截割困难的问题,但其水压裂缝通常沿垂直于最小主应力的方向扩展,裂缝数量少且形态单一,影响矿山破岩效果和生产效率。为进一步提高矿山破岩效果,提出一种凝胶压裂的新型压裂技术。基于自研的煤岩体真三轴水力压裂模拟试验系统,开展纯水压裂、先纯水压裂后凝胶压裂及不同质量分数的凝胶压裂试验,采用电子压力记录仪实时监测试块破裂的压力信息,对比分析岩石破裂压力变化规律及对应的破裂行为;通过对比分析试块宏观破环特征,探究凝胶压裂的裂缝扩展规律,揭示凝胶压裂的破岩机理。研究结果表明:① 凝胶压裂可以增加试块破裂的裂缝密度,单位面积内裂缝总长度增加92.71%~216.67%,裂缝密度升高92.7%~216.97%,使裂缝形态更加复杂,为形成复杂缝网提供基础;② 凝胶压裂阶段压力存在长时间及大幅度波动,这是复杂裂缝形成的力学响应;③ 凝胶压裂可以缩小岩石破碎块度,使裂缝开度增大,其分支裂缝的数量明显多于纯水压裂,破岩效果明显优于纯水压裂;④ 凝胶压裂液质量分数越高,分支裂缝数量越多,压裂动力现象越明显。研究结果证明,凝胶压裂改变了传统水力压裂的裂缝扩展模式,在裂缝起裂扩展阶段封堵物质可以封堵先压裂缝,改变应力薄弱区起裂新裂缝,其岩石破裂效果明显优于纯水压裂。

     

    Abstract: Hydraulic fracturing is a widely used physical rock-breaking method to address the challenges in cutting hard rocks. However, conventional water-based fracturing typically generates fractures propagating perpendicular to the minimum principal stress direction, resulting in limited fractures quantity and simplistic morphology, which restricts rock-breaking efficiency and productivity in mining operations. To enhance rock fragmentation effectiveness, this study proposes a novel gel fracturing technique. Based on the self-developed true triaxial hydraulic fracturing simulation experiment system of coal and rock mass, pure water fracturing, gel fracturing after pure water fracturing and gel fracturing experiments with different mass fractions were carried out. An electronic pressure recorder was employed for real-time monitoring of specimen rupture pressures, enabling comparative analysis of pressure evolution patterns and corresponding fracturing behaviors. By comparing and analyzing the macroscopic fractures characteristics of the test block, the fractures propagation law of gel fracturing was explored, and the rock breaking mechanism of gel fracturing was revealed. The key findings demonstrate that: ① Gel fracturing significantly increases fractures density, enhancing total fractures length per unit area by 92.71%−216.67% and fractures density by 92.7%−216.97%, while creating more complex fractures networks; ② Prolonged and substantial pressure fluctuations during gel fracturing represent mechanical responses to complex fractures formation; ③ Gel fracturing reduces rock fragment size while enlarging fractures apertures, generating significantly more branch fractures than water fracturing, with markedly superior rock-breaking performance; ④ Higher gel concentration correlates with increased branch fractures and more pronounced fracturing dynamics. These results confirm that gel fracturing fundamentally alters conventional fractures propagation patterns through temporary sealing of initial fractures by blocking agents during fractures initiation and extension phases. This mechanism modifies stress distribution in weak zones to initiate new fractures, achieving substantially better rock fragmentation than water fracturing. The findings provide theoretical support for optimizing hydraulic fracturing techniques in hard rock excavation.

     

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