P-wave velocity evolution and interpretation of seepage mechanisms during CO2 hydrate formation in quartz sands: Perspective of hydrate pore habits

Abstract

The hydrate-based CO2 storage (HBCS) is a promising technology for controlling CO2 emissions. A comprehensive understanding of the hydrate pore habits and seepage mechanism of hydrate-bearing sediments (HBSs) could provide a theoretical basis for HBCS. In the study, the hydrate occurrence characteristics, water migration and P-wave velocity response during hydrate formation in quartz sands are investigated. In addition, a new theoretical equation that relates P-wave velocity to permeability is presented. The digital core of porous media containing hydrate is also established, and the seepage characteristics during hydrate formation are revealed by numerical simulation. The results show that hydrates are preferentially generated in large pores and initially appear in a non-cementing pore-filling pattern, while an annular flow path for water is formed in quartz sands during hydrate formation. The hydrate morphology is changed from a pore-filling pattern to a patchy pattern at a critical hydrate saturation of around 3–7% for quartz sands with various particle diameters. The formation sites and spatial heterogeneity of hydrates can be depicted by the evolution pattern of streamlines. The results of the experiments indicate that the new semiempirical model is effective for estimating the permeability from the P-wave velocity of HBSs. These findings offer significant theoretical and practical insights for HBCS in porous media.