Quantitative analysis of the wave attenuation pattern and wave properties of coal samples with varying degrees of water saturation

To investigate the influence of water content on P-wave attenuation patterns and wave properties in coal samples, we conducted comprehensive P-wave measurements on untreated coal specimens throughout the complete water absorption process. The experimental design focused on determining how water saturation and porosity affect peak P-wave amplitude. Subsequently, the quality attenuation factor of P-waves in coal specimens with varying water saturation is calculated inversely using the Brune model and grid search method, and the influence of porosity and water saturation on the quality attenuation factor is examined. Finally, the P-wave characteristics of coal specimens with different water saturation are analyzed using wavelet packet, empirical mode decomposition (EMD), and multifractal techniques. Our results demonstrate that peak P-wave amplitude decreases consistently with increasing water saturation and porosity. Notably, while amplitude variations occur across coal samples with different porosity values, the magnitude of these fluctuations diminishes as water saturation increases, indicating a stabilizing effect of water content on amplitude variability. By utilizing the Brune grid and grid search methods, it is possible to accurately invert the quality attenuation factor of P-wave attenuation in coal samples. The decrease in water saturation and porosity leads to a reduction in the quality attenuation factor, which is directly related to the maximum amplitude. Analyzing waves with varying water saturation through wavelet packet and EMD analysis reveals that as the water saturation of coal specimens increases, the proportion of high-frequency components in the wave gradually diminishes, causing the high-energy frequency band to continuously shift toward lower frequencies. The findings indicate that pore liquid not only speeds up the reduction rate of energy in all frequency ranges of the wave but also the absorption loss of high-frequency signal is higher compared to low-frequency signal. Coal samples with varying water saturation exhibit multifractal properties in their waves. Furthermore, as water saturation increases, the range of deviation for the generalized information dimension of the wave decreases, suggesting a decrease in the multifractality of the wave with increasing water saturation. As water saturation increases, the Δf(a) of the P-wave gradually rises, suggesting a gradual decrease in P-wave energy and stronger wave attenuation with increasing water saturation.