Acoustic properties and model analysis of sandy gas-bearing sediments

The acoustic properties of marine sediments are significantly affected by bubbles in the sediments.A double-probe acoustic measurement system was developed to study the acoustic properties of sandy gas-bearing sediments in the laboratory,which can simulate the in-situ stress condition of the sediments.The size distribution of bubbles in sand samples was obtained by CT scanning test,and the resonance frequency range of the bubbles is determined.As the increase of gas content in sediments,the compression wave speed decreases exponentially,and the attenuation coefficient increases exponentially.The sound speed of the sediment becomes faster and the attenuation coefficient becomes smaller with the increase of initial stress.When the measuring frequency is 250 kHz,the gas content in fine sand sediments with an effective confining pressure of 100 kPa is 0%-1.18%,the sound speed is 1745-976 m/s,and the attenuation coefficient is 57-224 dB/m.When the effective confining pressure is 200 kPa,the sound speed is 1773-1011 m/s,and the attenuation coefficient is 41-192 dB/m.The predicted values of the three acoustic models are compared with the experimental results.Although the occurrence state of gas bubbles and the reflection of acoustic waves at the solid,liquid,and gas interfaces have been considered,the in-situ stress of the sediments also needs to be considered in the theoretical model of gas-bearing sediments.