超声纵波在孔隙砂岩中的传播特性实验*

为了深入研究不同入射频率下超声波纵波在砂岩中的传播特性，以灰、红、褐砂岩为研究对象，开展了基于50 k Hz、100 kHz、200 kHz、500 kHz和1000 kHz入射频率的超声波纵波测试。提取纵波波速、幅值衰减系数、主频幅值、波形能量这些声学参数，结合入射频率和砂岩孔隙率进行传播特性的相关性分析。结果表明，在3种砂岩中，纵波波速随入射频率增大呈非线性增长趋势，砂岩种类不同，波速增长规律也不同；波形能量和主频幅值随入射频率呈指数关系降低；灰、红砂岩纵波波速随孔隙率越大，下降速率越大，褐砂岩在同级孔隙率下波速差异性明显。建立了基于3种砂岩的入射频率和幅值衰减系数的回归方程；基于200 kHz的入射频率，建立了砂岩孔隙率于波形能量的回归方程，实际测试中建议采用200 kHz作为入射频率，可较好兼顾检测的灵敏度和探测距离。研究成果为建立声学参数与砂岩抗压强度之间的内在联系提供了更多数据支撑，为实际物探测试中超声波入射频率的选择提供参考。

The propagation characteristics of ultrasonic P-wave in sandstone at different incidence frequencies

In order to study the propagation characteristics of ultrasonic longitudinal waves in sandstone under different incident frequencies, the ultrasonic longitudinal wave tests based on the incident frequencies of 50kHz, 100kHz, 200kHz, 500kHz and 1000kHz were carried out with gray, red and brown sandstone as the research objects. Acoustic parameters such as wave velocity, amplitude attenuation coefficient and dominant frequency amplitude are extracted, and the correlation analysis of propagation characteristics is carried out by combining incident frequency and sandstone porosity. The results show that in the three kinds of sandstones, the longitudinal wave velocity increases nonlinearly with the increase of incident frequency, and the growth law of the longitudinal wave velocity is different with different kinds of sandstones. The amplitude of waveform energy and dominant frequency decreases exponentially with incident frequency. The longitudinal wave velocity of grey sandstone and red sandstone decreases with the increase of porosity, and the difference of wave velocity of brown sandstone under the same porosity is obvious. The regression equations based on the incident frequency and amplitude attenuation coefficient of three kinds of sandstones are established. Based on the incident frequency of 200kHz, the regression equation of sandstone porosity and waveform energy is established. It is suggested that 200kHz should be used as the incident frequency, which can give consideration to the detection sensitivity and detection distance. The research results are helpful to analyze and understand the acoustic characteristics of sandstone, and provide reference for rock quality prediction and geophysical testing.