Strengthening mechanism of cemented hydrate‐bearing sand at microscales

Abstract

On the basis of hypothetical particle‐level mechanisms, several constitutive models of hydrate‐bearing sediments have been proposed previously for gas production. However, to the best of our knowledge, the microstructural large‐strain behaviors of hydrate‐bearing sediments have not been reported to date because of the experimental challenges posed by the high‐pressure and low‐temperature testing conditions. Herein, a novel microtriaxial testing apparatus was developed, and the mechanical large‐strain behavior of hydrate‐bearing sediments with various hydrate saturation values (Sh = 0%, 39%, and 62%) was analyzed using microfocus X‐ray computed tomography. Patchy hydrates were observed in the sediments at Sh = 39%. The obtained stress‐strain relationships indicated strengthening with increasing hydrate saturation and a brittle failure mode of the hydrate‐bearing sand. Localized deformations were quantified via image processing at the submillimeter and micrometer scale. Shear planes and particle deformation and/or rotation were detected, and the shear band thickness decreased with increasing hydrate saturation.

Strength Estimation for Hydrate‐Bearing Sediments From Direct Shear Tests of Hydrate‐Bearing Sand and Silt

“…The results suggest that the shear failure tends to be in a more brittle manner in sediments with higher hydrate saturation and under lower stress state. Such a trend has also been observed in both laboratory synthesized specimens and pressure cores of naturally occurring hydrate‐bearing sediments (Yoneda et al, , ).…”

“…The two studies have many differences in terms of specimen size, shearing rate, and the inherent difference in naturally occurring versus laboratory synthesized samples; however, they share similarities in the testing method and the host sediment properties. The results from the two studies do not show significant discrepancy for specimens with similar hydrate saturation and stress condition, even though gas‐saturated hydrate‐bearing sediments tend to have higher strength than that of water‐saturated specimens (Hyodo et al, ; Yoneda et al, ). These findings imply that the peak strength of hydrate‐bearing sediments is mainly governed by the hydrate (both saturation and pore habits) and stress conditions.…”

Strain Rate‐Dependent Hardening‐Softening Characteristics of Gas Hydrate‐Bearing Sediments

“…The analysis of stress-strain behavior based on Rowe's stress-dilatancy theory suggests that GHs contribute a structuration effect in GHBS. This effect was substantial in water-limited systems with structuration strength (c′) up to 2 MPa at the onset of dilation and 1.6 MPa at peak strength (Figure 6b and supporting information Table S3), which was high compared to results from other experimental studies with GHBS (e.g., Choi et al, 2018;Ghiassian & Grozic, 2013;Yoneda et al, 2016). However, in water-saturated specimen c′ was substantially lower, reaching values of 0.4 MPa at the onset of dilation and 0.6 MPa at peak strength.…”

“…In the very recent past there have also been the first attempts to carry out studies on undisturbed pressure cores (Inada & Yamamoto, 2015;Santamarina et al, 2015;Yoneda et al, 2015b). Advanced geotechnical testing systems with tomographical techniques are increasingly being developed and used to analyze so far unresolved microstructures and micromechanical processes that constitute bulk stress-strain behavior in GHBS (Deusner et al, 2016;Yoneda et al, 2016).…”

Submarine landslides triggered by destabilization of high‐saturation hydrate anomalies

“…Parameter Values for Slope Stability and Rate and State Friction Model et al [2009]); it should be noted that the linear extrapolation we employ to account for increased cohesion at higher S h is not well-constrained, but consistent with the basic trend of strengthening behavior observed in deformation experiments [e.g.,Yoneda et al, 2016].…”