Experimental Study On Influence Factors Of Coal Acoustic Velocities And Mechanism Analysis

Acoustic logging and seismic exploration are the main means of detecting underground minerals. The research on the influence factors of coal acoustic velocities is very important for coal exploration. In this paper, eight species of coals with native structures from different regions are selected for study. The experimental tests are applied as the main investigation means, which measure the coal acoustic velocities under different pressures, temperatures and saturation conditions. At the same time, we measured the principle parameters of the coal, such as its industrial components, apparent density, porosity, permeability, total organic carbon content, vitrinite maximum reflectance and inorganic minerals. The results show that coal acoustic velocities are positively proportional to apparent density, coal rank and also the ash component. The P-wave velocity increases after the saturation of coal, shear wave velocity does not change significantly. Temperature has no obvious effect on the acoustic velocity of coal. Coal exhibits velocity anisotropy,which decreases with the increase of pressure and saturation degree.Based on the relationships among measured acoustic velocities, the maximum reflecticity of coal vitrinite and apparent density, this paper comes up with a coal rank identification method using compressional-to-shear-wave velocity ratio and elastic modulus, which is an effective solution to the problem of quantitative determination of coal rank. Based on the S-wave velocity of coal,P-wave velocity and density, this paper also proposes a method of S-wave velocity prediction by P-wave velocity and apparent density, which provides a possibility for estimating the dynamic moduli of coal.