Experimental study on the influence of hydrate formation process on the elastic properties of consolidated rock

ABSTRACT Knowledge of the influence of gas hydrates on the elastic characteristics of a formation is beneficial for improving the understanding of gas hydrate seismic exploration. An experimental setup for gas hydrates was developed to measure P- and S-waves during the gas hydrate formation process. Ultrasonic experiments were conducted on the synthesized samples. The results of the experiments were as follows. Variations in pore pressure and elastic waves correlated well with the hydrate formation process. P- and S-wave amplitudes decreased when methane was injected into the samples. The amplitudes of P- and S-waves increased with hydrate saturation. A comparison between the experimental data and theoretical models indicated that the hydrate exhibited cementing morphologies when the saturation was less than 9%. When the saturation ranged from 9% to 40%, the hydrate exhibited a frame-strengthening morphology. These morphological transitions were accompanied by systematic changes in wave velocity and VP/VS ratio. Furthermore, a coupled attenuation effect from hydrate and free gas was identified. Although hydrate formation reduced amplitude attenuation, gas enhanced it, particularly for P-waves. In the later stages of hydrate formation, P-wave amplitude declined despite continued hydrate growth, whereas S-wave amplitude remained elevated owing to its lower sensitivity to gas. This attenuation dominance shift highlights the relationship between hydrate morphology, elastic properties, and attenuation characteristics, offering insights into hydrate reservoir evaluation.