Strength of Laboratory Synthesized Hydrate‐Bearing Sands and Their Relationship to Natural Hydrate‐Bearing Sediments

Abstract

The strength of hydrate‐bearing sediments is an important input parameter for numerical simulations for evaluating the long‐term future gas production from these sediments and the risks associated with such activities on the environment. Studies on laboratory synthesized, and natural, hydrate‐bearing coarse‐grained soils exhibit similar behavior, where increasing hydrate saturation increases specimen strength and stiffness with the corresponding development of peak stress, postpeak strain softening and tendency for sample dilation, which is suppressed with increasing effective stress, although strength is increased. For synthesized specimens, hydrate growth at grain contacts leads to “cementing” behavior and the largest increase in strength, which is subdued when hydrate growth is prevented at these locations. Sample disturbance in natural samples lead to lower strength and stiffness compared to laboratory synthesized samples. Unconfined compression shear tests on natural samples highlight the strong “cementing” effect of gas hydrates on coarse‐grained soils. The strength of natural sediments appears strongly correlated with particle size and clay content, with smaller particle and increasing clay content reducing strength for a given hydrate saturation. The strength parameters, friction angle, and cohesion appear to depend on sample type. For synthesized specimens, friction angle was reasonably independent of hydrate saturation while cohesion increased in an exponential manner, with the largest increase occurring when hydrate growth is at particle contacts. In contrast, friction angle appeared to increase with a corresponding reduction in cohesion for natural hydrate‐bearing sediments. However, these observations may be related to sample disturbance and stress conditions under which the data were acquired.

Mechanical behaviors of hydrate-bearing sediment with different cementation spatial distributions at microscales

“…In this study, both specimens show a slight strain-softening phenomenon, which is consistent with the triaxial test results for remolded hydrate-bearing sandy specimens (Dong et al, 2019(Dong et al, , 2020, which is due to the failure of hydrate cementation under high stress (Priest and Hayley, 2019).…”

“…A large number of geomechanical experiments have been conducted on hydrate-bearing cores and remolded hydrate-bearing specimens from the laboratory and field to evaluate their geomechanical characteristics, and they are influenced by many factors, such as the hydrate saturation ( Hyodo et al., 2013b , 2014 ), effective confining pressure ( Choi et al., 2018 ; Hyodo et al., 2013a ), fines content ( Lee et al., 2010 ) and other factors ( Iwai et al., 2018 ; Li et al., 2019b ). Detailed literature reviews about geomechanical research on hydrate-bearing sediments have been comprehensively discussed elsewhere ( Priest and Hayley, 2019 ; Yan et al., 2020 ). Nevertheless, the vast majority of studies did not consider the hydrate cementation spatial distribution influence on the mechanical behavior of hydrate-bearing sediments due to the lack of an effective nondestructive technique.…”

Effect of Cylindrical THF Hydrate Veins on the Undrained Behavior of Fine‐Grained Soils

“…The Mohr-Coulomb strength parameters (c' and ϕ') from previous tests were obtained from hydrate-bearing sands where the hydrate is disseminated within the pore space. The strength of the hydrate bearing sands in these cases were observed to be strongly dependent on σ' 3 regardless of hydrate saturation (see Priest & Hayley, 2019). Thereby leading to a constant or increasing ϕ' with increasing hydrate saturation.…”

“Ester”—A new ring-shear-apparatus for hydrate-bearing sediments

“…29,30 The application of these newly developed technologies during a number of hydrate expeditions offshore Japan, India, and China resulted in a strongly increased number of strength tests on natural hydrate-bearing sediment samples. 25,[30][31][32][33][34] However, besides hydrate saturation and hydrate distribution, other parameters such as clay content, grain size, distribution, etc. influence the sediment strength properties.…”