Ultrasonic Transmission Experiment Research on Igneous Rocks Under Dry and Saturated Conditions

To investigate changes in seismic wave propagation in different types of igneous rocks under dry and water-saturated conditions, this study employed CT scanning to characterize the microstructural development of three distinct igneous rock types. Laboratory measurements were then performed to determine the density, porosity, permeability, and compressional and shear wave travel times of the rock cores in both dry and water-saturated states. The results show that water content significantly affects the waveforms in both the time and frequency domains. For rocks with developed pores and fractures, the propagation of seismic wave energy is impeded under water-saturated conditions, causing faster attenuation of ultrasonic waves while high-frequency components are retained. For dense rocks, the amplitude of the initial wave segment decreases, the middle-segment amplitude increases, and the tail wave undergoes significant attenuation under saturated conditions, with frequency components in the 50–100 kHz range being filtered out. Furthermore, higher water content leads to lower shear-wave amplitudes and more severe attenuation. These findings contribute to the proper use of acoustic logging data for understanding the microstructure and water content characteristics of igneous rock reservoirs.