Laboratory measurements of ultrasonic wave reflectivity of gas-charged layer in the vicinity of seafloor

摘要

Recent observation in the gas leakage area demonstrates that the gas-charged sedimentary layer where the bubbles are stored can affect the reflectivity of seismic data.Although existing studies demonstrate the increase of reflectivity at the sea floor from a gas-charged layer in a low-frequency range(i.e.,seismic frequency),there are few scientific observations in a high-frequency range(i.e.,ultrasonic frequency).We aim to find out the characteristics of the reflectivity from the gas-charged layer through laboratory experiments.This is because the broadband frequency response of the reflectivity from the gas-charged layer allows us to more understand the characteristics the gas-charged layer.Through the study of the waveform and amplitude information observed in the laboratory study,we found that in the reflection of ultrasonic waves,when there are bubbles in the sediment pouring into the water,the amplitude appears to decrease.Due to the existence of air bubbles in the sediment,multiple interfaces with varying acoustic impedances are generated,resulting in an overall increase in amplitude.