低频条件下煤岩地震波频散与衰减参数的试验测量与分析

Experimental measurement and analysis of seismic wave dispersion and attenuation parameters in coal and rock under low-frequency conditions

  • 摘要: 波速频散和能量衰减等参数对煤炭精细勘探与开发具有重要意义。应力-应变低频测试技术为实现包含地震波频段的跨频段测量提供了策略。针对该技术存在的信号噪声干扰大和测试精度要求高等问题,文中通过系列方法予以优化。以神府、临兴地区的4块煤岩样为例,在低频段(4~1 000 Hz)及不同温度和围压条件下,测试其频散与衰减特性,并借助Chapman模型分析影响因素。结果表明:①利用有限冲激响应(FIR)带通滤波器并结合快速傅里叶变换(FFT)等方式,有效提升了信噪比和相位差提取精度,显著改善了设备性能。②煤岩弹性参数随围压非线性增加;纵横波速度随围压增大而提高,随温度升高略有降低;衰减峰值随围压增加而降低,随温度升高而增高,且特征频率基本不变。实测数据与Chapman模型的拟合效果良好,验证了该模型的适用性。③衰减峰值与煤岩孔隙率及含水饱和度成正比,孔隙率的影响更加显著;流体黏度、渗透率、含水饱和度的变化与弛豫时间相关,是影响频散和衰减特征频率的主因。

     

    Abstract: Wave velocity dispersion and energy attenuation are key parameters for precise coal exploration and development. Low-frequency stress-strain testing provides a strategy for realizing cross-band measurements, such as seismic bands. This study implemented a series of optimization to address the challenges of high signal-noise interference and high testing accuracy requirement in such test systems. Using four coal samples from Shenfu and Linxing areas, we measured and analyzed the dispersion and attenuation characteristics of coal rock seismic waves in the low-frequency band (4-1 000 Hz) under varying temperatures and confining pressures. Experimental data were interpreted using the Chapman model to discuss the factors influencing these characteristics. Results show that: ① System performance was significantly enhanced by employing the Finite Impulse Response(FIR) bandpass filter and Fast Fourier Transform(FFT), which improved signal-to-noise ratio and the accuracy of phase difference extraction. ② The elastic parameters of coal rock increased nonlinearly with confining pressure. Both P- and S-wave velocities rose with increasing confining pressure, but decreased slightly with rising temperature. The attenuation peak decreased with higher confining pressure, and increased with temperature, while the eigenfrequency remained unchanged. The Chapman model shows a good fit with the measured data, confirming its applicability. ③ The attenuation peak was positively correlated with the porosity and water saturation of coal rock, with porosity exerting a more significant influence. Variations in fluid viscosity, permeability and water saturation were related to relaxation time, which is the main cause of dispersion and attenuation eigenfrequency.

     

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