Evolution of Compressional Wave Velocity during CO_2 Hydrate Formation in Sediments

摘要

While the acoustic wave-based survey is considered to be one of the most effective and promising means for monitoring the behavior of particulate/discrete geomaterials, the P-wave velocity has scarcely been used to monitor the long-term behavior of CO_2 sequestered sediments or to understand the characteristics of CO_2 hydrate formation in sediments. Furthermore, there are still only limited reliable laboratory results quantifying the P-wave velocity change in sediments that results from CO_2 hydrate formation and accumulation processes. This study presents experimental measurements on the evolution of P-wave velocity as CO_2 hydrate saturation increases in unconsolidated sediment. The measured data are compared with the simple yet robust asymptotic Gassmann model to estimate CO_2 hydrate saturation (volume fraction of hydrate in pore space) in sediments. Given that in situ techniques to measure acoustic waves are well-established for the exploration of deep oceanic sediment, the methodology presented in this paper for estimating hydrate saturation is of potential significance in the monitoring of the long-term behavior of CO_2 reservoirs after sequestration in deep marine sediments.