弹性波在中粒砂岩内传播衰减特性分析

为研究弹性波在岩石介质传播过程中的衰减特性,利用超声波传感器监测弹性波在中粒砂岩圆柱体内传播不同距离后的波形变化特征,通过频谱转换、数理统计、曲线拟合分析了特征参数的变化规律。研究表明:弹性波信号经滤波模数转化后,频率在100~500kHz的信号随着传播距离的增大,时域波形图和频谱图在振幅上都出现了衰减趋势,且信号中高频成分比低频成分衰减显著。频谱重心频率随传播距离增大按照线性趋势降低,变化趋势比主频稳定,更能全面反映信号的频率衰减特征,采用波形对比法得到的弹性波在中粒砂岩内传播的衰减系数为0.016dB/cm。在实验室尺寸范围内,绝对能量按照负指数规律衰减最为显著,幅值和振铃计数出现稳定线性衰减趋势,而上升时间有增加的趋势。波形参数的衰减趋势和敏感程度对于现场微震和室内声发射试验由传感器信号反演破裂源特征有一定的指导作用。

Study on the Attenuation of Elastic Wave Propagating in Medium-grained Sandstone

In order to study the attenuation characteristics of elastic wave, ultrasonic sensors are used to monitor wave propagating variation in medium-grained sandstone by the combined method of frequency spectral conversion, mathematical statistics and curve fitting. The results show that, after analog-digital conversion and filtering, the frequency of elastic wave is between 100~500 kHz, and the amplitude obviously decreases as the propagation distance increases in both frequency and time domain, and the high frequency components are attenuated more seriously than the low frequency components. Centroid frequency linearly decreases with the increasing propagating distance, and it shows more signal messages with stable variation than the main frequency. The attenuation coefficient in the sandstone acquired by waveform comparison method is 0.016 dB/cm. In the lab dimension, as the propagating distance increases, absolute energy decreases following a law of negative exponential change, and amplitude and ring counts stably decrease as linear trend, but the rise time trends to increase. Understanding the attenuation characteristics and sensitive degree of elastic wave is meaningful for inversing failure source characteristics in microseism monitoring and acoustic emission experiments.