造穴-CO_(2)气相压裂复合技术造缝卸压增渗机理研究

Research on mechanism of fracture formation,pressure relief,and permeability enhancement with composite technology of cavitation and CO_(2)-frac

我国煤矿煤与瓦斯突出灾害严重,目前增透主要采用静力型技术和动力型技术,不同程度地解决了瓦斯治理难题。为获得更好的复合造缝卸压增渗效果,开发出造穴-气相压裂复合技术,综合采用185 MPa高压力CO_(2)冲击煤样、数值模拟、光纤应变监测3种技术手段,研究造穴-气相压裂复合技术的瓦斯治理机理。结果表明:①煤样在CO_(2)气相压裂应力波作用下,在煤基质表面新形成损伤坑(DM)和三翼型裂隙(TRW)典型显微构造。②煤层在静力型和动力型荷载复合作用下近钻孔中心范围内煤层中原始的裂隙被重新打开,形成以钻孔为中心的放射状多尺度、张剪性破坏为主的裂缝,该裂缝能够充分均化应力集中区,并使得煤层产生不可逆的破坏,其应力扰动范围为24 m。③在有效的气相压裂-造穴复合技术影响范围内,造穴孔有助于提高气相压裂应力波的能量利用效率,避免能量耗散在无效的震动区,充分导通压裂孔与造穴孔多尺度裂缝,使得煤层裂缝区域范围大、连续性强、卸压充分。研究为解决煤层低渗、难抽、高地应力的问题提供了参考。

Coal mine disasters caused by coal and gas outbursts are severe in China.Currently,static and dynamic technologies are mainly used to address the difficult gas control problem.The gas control mechanism of the composite technology of cavity making and gas phase fracturing is studied by comprehensively using three technical methods:185 MPa high pressure CO_(2) impact coal sample,numerical simulation,and fiber optic strain monitoring.The research results indicate that①under the action of CO_(2) gas phase fracturing stress waves,typical microstructures such as damage pits(DM)and three wing cracks(TRW)are newly formed on the surface of the coal matrix in coal samples.②Under the action of static and dynamic loads,the original fractures in the coal seam within the range near the borehole center are reopened along the direction of vertical fracture,forming a radial multi-scale,tensile-dominant fracture with the borehole as the center.The fracture can fully equalize stress concentration zones and cause irreversible damage to the coal seam,with a stress disturbance range of 24 m.③Within the influence range of effective gas phase fracturing hole making composite technology,hole making holes help to improve the energy utilization efficiency of gas phase fracturing stress waves,avoid energy dissipation in ineffective vibration areas,fully connect the multi-scale fractures of the fracturing hole and hole making hole,making the coal seam fracture area wide,continuous,and fully depressurized,which fundamentally solves the problem of low permeability,difficult extraction,and high ground stress in the coal seam.