Evolution of Compressional Wave Velocity during CO2 Hydrate Formation in Sediments

Abstract

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 CO2 sequestered sediments or to understand the characteristics of CO2 hydrate formation in sediments. Furthermore, there are still only limited reliable laboratory results quantifying the P-wave velocity change in sediments that results from CO2 hydrate formation and accumulation processes. This study presents experimental measurements on the evolution of P-wave velocity as CO2 hydrate saturation increases in unconsolidated sediment. The measured data are compared with the simple yet robust asymptotic Gassmann model to estimate CO2 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 CO2 reservoirs after sequestration in deep marine sediments.