采空区垮落煤岩渗透特性研究

Study on permeability characteristics of caved coal and rock in goaf

地震法常用于分析采空区垮落煤岩孔隙率和渗透率的相关性,现有研究大多采用有效介质理论,将采空区垮落煤岩的各向异性和不均匀性转换为等效的介质参数,对粒径、孔隙率、空间特征等因素对地震波的影响考虑较少。以采空区垮落煤岩为研究对象,根据实际采空区垮落煤岩颗粒级配和孔隙率,制备了破碎煤岩样品,通过实验验证了其孔隙率和波长-粒径比与实际采空区垮落煤岩一致。在此基础上,通过实验分析了煤岩粒径、孔隙率、地震波频率等因素对波速、振幅衰减系数及渗透率的影响,结果表明:破碎煤岩中P波速度随孔隙率增大而减小,随粒径增大而增大,受地震波频率影响较小;振幅衰减系数随孔隙率增大而增大,随粒径增大而减小,孔隙率较大时更易受地震波频率影响;破碎煤岩的渗透率随孔隙率和粒径增大而增大,遵循Kozney-Carman方程,基于实验结果建立了采空区垮落煤岩渗透率预测公式,计算得现场采空区垮落煤岩渗透率为1 225×10^(-12)~178 930×10^(-12)m^(2);为消除粒径对地震波振幅衰减系数和煤岩样品渗透率的影响,提出单位波长振幅衰减系数(振幅衰减因子),并通过最小二乘法拟合得到振幅衰减因子与渗透率之间的经验关系式,为初步判断采空区垮落煤岩的渗透率提供了思路。

The seismic method is often used to analyze the correlation between porosity and permeability of caved coal and rock in goaf. Most of the existing studies adopt the effective medium theory, which convert the anisotropy and inhomogeneity of caved coal and rock in goaf into equivalent medium parameters. The influence of particle size, porosity, spatial characteristics and other factors on the seismic wave is less considered. Taking the caved coal and rock in goaf as the research object, the broken coal and rock samples are prepared according to the actual particle gradation and porosity of the caved coal and rock in goaf. The porosity and wavelength-particle size ratio of the caved coal and rock samples are verified to be consistent with those of the caved coal and rock in the actual goaf. On this basis, the influence of coal and rock particle size, porosity and seismic wave frequency on wave velocity, amplitude attenuation coefficient and permeability is analyzed through experiments.The P-wave velocity in broken coal and rock decreases with the increase of porosity, increases with the increase of particle size, and is less affected by seismic wave frequency. The amplitude attenuation coefficient increases with porosity and decreases with the increase of particle size, and is more easily affected by seismic wave frequency when porosity is larger. The permeability of broken coal and rock increases with the increase of porosity and particle size. According to the Kozney-Carman equation, the permeability prediction formula of coal and rock in goaf is established based on the experimental results. The calculated permeability of caved coal and rock in goaf is1 225× 10^(-12)-178 930×10^(-12)m^(2). In order to eliminate the influence of particle size on the amplitude attenuation coefficient of seismic wave and the permeability of coal and rock samples, the amplitude attenuation coefficient of unit wavelength(amplitude attenuation factor) is proposed. The empirical relationship between the amplitude attenuation factor and the permeability is obtained by least square fitting. The study provides a thought for preliminarily judging the permeability of caved coal and rock in goaf.