Investigating seismic dispersion and attenuation characteristics of loosely compacted marine sandstone is essential in reconciling different geophysical measurements (surface seismic, well logging and ultrasonic) for better characterization of a shallow marine sandstone reservoir. We have experimented with a typical high‐porosity and high‐permeability sandstone sample, extracted from the Paleogene marine depositional setting in the Gulf of Mexico, at the low‐frequency band (2–500 Hz) as well as ultrasonic point (10⁶ Hz), to investigate the effects of varying saturation levels on a rock's elasticity. The results suggest that the Young's modulus of the measured sample with adsorbed moisture at laboratory conditions (room temperature, 60%–90% humidity) exhibits dispersive behaviours. The extensional attenuation can be as high as 0.038, and the peak frequency occurs around 60 Hz. The extensional attenuation due to moisture adsorption can be dramatically mitigated with the increase of confining pressure. For partial saturation status, extensional attenuation increases as increasing water saturation by 79% with respect to the measured frequencies. Additionally, the results show that extensional attenuation at the fully water‐saturated situation is even smaller than that at adsorbed moisture conditions. The Gassmann–Wood model can overall capture the P‐wave velocity‐saturation trend of measured data at seismic frequencies, demonstrating that the partially saturated unconsolidated sandstone at the measured seismic frequency range is prone to be in the relaxed status. Nevertheless, the ultrasonic velocities are significantly higher than the Gassmann–Wood predictions, suggesting that the rocks are in the unrelaxed status at the ultrasonic frequency range. The poroelastic modelling results based on the patchy saturation model also indicate that the characteristic frequency of the partially saturated sample is likely beyond the measured seismic frequency range.

中文翻译：

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弱固结海砂岩频率相关弹性特性的实验研究：部分饱和的影响

研究松散压实的海洋砂岩的地震波散和衰减特性对于调和不同的地球物理测量结果（地表地震，测井和超声）至关重要，以便更好地表征浅层海洋砂岩储层。我们已经对典型的高孔隙率和高渗透率砂岩样品进行了实验，该样品是从墨西哥湾古近纪海相沉积环境中提取的，其低频频段（2-500 Hz）以及超声点（10 ⁶Hz），以研究饱和度变化对岩石弹性的影响。结果表明，在实验室条件（室温，60％–90％湿度）下，水分被吸附的被测样品的杨氏模量表现出分散的行为。扩展衰减可能高达0.038，峰值频率出现在60 Hz附近。随着围压的增加，由于水分吸收而引起的延伸衰减可以大大减轻。对于部分饱和状态，相对于测得的频率，随着水饱和度增加79％，延伸衰减会增加。此外，结果表明，在完全水饱和的情况下的延伸衰减甚至比在吸附水分条件下的延伸衰减小。Gassmann-Wood模型可以整体捕获地震频率下测得的数据的P波速度饱和趋势，表明在地震频率范围内部分饱和的未固结砂岩很容易处于松弛状态。然而，超声速度明显高于Gassmann-Wood的预测，这表明岩石在超声频率范围内处于无松弛状态。基于斑块饱和度模型的孔隙弹性建模结果还表明，部分饱和样品的特征频率可能超出了测得的地震频率范围。表明在测得的地震频率范围内部分饱和的疏松砂岩很容易处于松弛状态。然而，超声速度明显高于Gassmann-Wood的预测，这表明岩石在超声频率范围内处于无松弛状态。基于斑块饱和度模型的孔隙弹性建模结果还表明，部分饱和样品的特征频率可能超出了测得的地震频率范围。表明在测得的地震频率范围内部分饱和的疏松砂岩很容易处于松弛状态。然而，超声速度明显高于Gassmann-Wood的预测，这表明岩石在超声频率范围内处于无松弛状态。基于斑块饱和度模型的孔隙弹性建模结果还表明，部分饱和样品的特征频率可能超出了测得的地震频率范围。