Consolidation deformation of hydrate-bearing sediments: A pore-scale computed tomography investigation

Abstract

Consolidation deformation is prevalent in hydrate-bearing sediments due to oceanic currents, the erection of jack-up drilling rig platforms, depressurization exploitation, etc. However, the microstructural behavior of hydrate-bearing sediment during consolidation remains unclear because of experimental challenges. Herein, using a novel microfocus X-ray CT-based triaxial testing apparatus, we present a series of results to reveal the microstructural evolution of hydrate-bearing sediment using the pixel-tracking technique at the submillimeter level. Initially, a stepped cone-shaped incremental displacement distribution with a relatively large deformation was observed, a rapid decline in the total number and radii of pores was noted, and the hydrate-sand interfacial area was greatly enlarged. Later, only some scattered large incremental displacement zones were found, the decline in the total number and radii of pores slowed, and the increase in the hydrate-sand interfacial area also slowed. The deformation pattern inside the hydrate-bearing sediment presented a strong relationship with the hydrate saturation; however, no obvious hydrate crushing occurred within 3 MPa of effective confining pressure, either visually or quantitatively. The consolidation could lead to a more complex pore system and lower coordination number between the pore and the throat, which led to a decrease in absolute permeability.