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煤层静态致裂增透技术的钻孔布置优化研究

Optimization of drilling arrangement for static fracturing and penetration enhancement technology in coal seams

  • 摘要: 为了提高低透气性煤层静态致裂增透效果,优化致裂钻孔布置方式,采用实验室实验和数值模拟相结合的方法,基于COMSOL软件构建煤体静态致裂过程中的应力-损伤耦合数值模型,研究钻孔布置方式对静态致裂效果的影响,揭示不同施工参数下煤体的应力场演化和损伤区分布。研究结果表明:双孔致裂产生的膨胀压力叠加效应显著增强了煤层致裂效果,在导向孔布置方式下煤体内部存在自由面,可以引导裂隙扩展的方向,裂隙扩展更为显著; 在静态致裂过程中损伤区演化受膨胀压力、布孔方式及弹性模量3个因素影响,膨胀压力增大,加速应力拐点迁移,导致煤体弹性模量下降并出现损伤区; 在静态致裂后期,含导向孔及预制裂缝布置方式下形成的损伤区面积分别为5.98、4.78 m2,相较于单孔布置方式分别提高了2.3倍和1.8倍; 在双孔基础上增设导向孔,损伤区面积从5.47 m2增至5.98 m2,说明布置导向孔和预制裂缝均能显著提高煤体的致裂效果,其中“双孔+导向孔”的复合布孔方式致裂效果最好。

     

    Abstract: In order to improve the effect of static fracturing and penetration enhancement in low permeability coal seams and optimize the fracturing distribution method, a static fracturing stress-damage coupling model was constructed based on COMSOL software by combining laboratory experiments and numerical simulation, and the influence of the drilling arrangement on the effect of static fracturing was investigated, which revealed the evolution of the stress field and the distribution of the damage zone of the coal body under different construction parameters. The results show that: the superposition effect of expansion pressure generated by double-hole fracturing obviously enhances the fracturing effect, and the existence of free surface inside the coal body under the guided hole arrangement can guide the direction of fracture expansion, which makes the fracture expansion more significant; the evolution of the damage zone in the process of static fracturing is affected by the expansion pressure, the parameters of hole arrangement and the elastic modulus, and the increase of expansion pressure accelerates the migration of the stress inflection point, which results in the decrease of the elastic modulus of the coal body and the emergence of the damage zone. In the late stage of static fracturing, the area of the damage zone with guided holes and prefabricated cracks is 5.98 m2 and 4.78 m2, respectively, which is 2.3 times and 1.8 times higher than that of the single-hole arrangement, and the area of the damage zone is increased from 5.47 m2 to 5.98 m2 by adding guided holes on top of the double-hole arrangement, which indicates that the arrangement of guided holes and prefabricated cracks can significantly improve the fracturing effect of the coal body. The fracturing effect of "double holes+guide holes" is the best.

     

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