Time-lapse seismic is a widely used technology for monitoring the geological sequestration of carbon dioxide (CO₂), consisting of mapping its movement in the subsurface and of demonstrating that the CO₂ is safely stored in the reservoir (Xue and Ohsumi, 2004). In this work, the effect of CO₂ on P- and S-wave velocities was investigated. Laboratory measurements were performed with Castlegate sandstone both at seismic frequencies (1–155 Hz), and at ultrasonic frequency (around 500 kHz). Different CO₂ saturations between 2% and 10% were obtained by controlled depressurization of CO₂-saturated water with which the sandstone sample had been saturated with. At seismic frequencies, the results of the experiments revealed that P-wave velocity is strongly reduced in the presence of free gas CO₂ in the pore space, whereas at ultrasonic frequency, the P-wave velocity changed only slightly. Therefore, the presence of free CO₂ gas increased significantly the P-wave dispersion between seismic and ultrasonic frequencies. The S-wave velocity, on the other hand, was hardly affected by the pore fluid at seismic frequencies. At seismic frequencies, P- and S-wave velocities were consistent with the Biot–Gassmann model. The P-wave velocity dispersion and corresponding attenuation were simulated by applying the Cole–Cole model. The transition frequency was found around 200 kHz.

延时地震技术是监测二氧化碳（CO ₂）地质隔离的一种广泛使用的技术，包括绘制其在地下的运动以及证明CO ₂安全地存储在储层中（Xue and Ohsumi，2004）。 。在这项工作中，研究了CO ₂对P波和S波速度的影响。实验室测量是使用Castlegate砂岩在地震频率（1-155 Hz）和超声频率（约500 kHz）上进行的。通过控制CO ₂降压可获得2％至10％的不同CO ₂饱和度-砂岩样品已被饱和的饱和水。在地震频率下，实验结果表明，在孔隙空间中存在自由气体CO ₂时，P波速度会大大降低，而在超声频率下，P波速度仅会发生轻微变化。因此，游离CO ₂气体的存在显着增加了地震和超声频率之间的P波色散。另一方面，S波速度几乎不受地震频率下的孔隙流体的影响。在地震频率下，P波和S波的速度与Biot–Gassmann模型一致。利用Cole–Cole模型模拟了P波速度色散和相应的衰减。发现过渡频率约为200 kHz。