Role of critical state framework in understanding geomechanical behavior of methane hydrate‐bearing sediments

Abstract

A proper understanding of geomechanical behavior of methane hydrate‐bearing sediments is crucial for sustainable future gas production. There are a number of triaxial experiments conducted over synthetic and natural methane hydrate (MH)‐bearing sediments, and several soil constitutive models have been proposed to describe their behavior. However, the generality of a sophisticated model is questioned if it is tested only for a limited number of cases. Furthermore, it is difficult to experimentally determine the associated parameters if their physical meanings and significance are not elucidated. The objective of this paper is to demonstrate that a simple extension of the critical state framework is sufficient to capture the geomechanical behavior of MH‐bearing soils from various sources around the world, while the significance of each parameter is quantified through variance‐based global sensitivity analyses. Our results show that the influence of hydrates can be largely represented by one hydrate‐dependent parameter, pcd′, which controls the expansion of the initial yield surface. This is validated through comparisons with shearing and volumetric response of MH‐bearing soils tested at various institutes under different confining stresses and with varying degrees of hydrate saturation. Our study suggests that the behavior of MH‐bearing soils can be reasonably predicted based on pcd′ and the conventional critical state parameters of the host sediments that can be obtained through typical geotechnical testing procedures.

A densification mechanism to model the mechanical effect of methane hydrates in sandy sediments

“…The set of critical state parameters characterizing the behavior of pure Toyoura sand (ie, hydrate‐free sediment) (Table ) has been calibrated here using the stress‐strain curve and the volumetric response of the host specimen used for the synthetic formation of cementing hydrate ( S h = 0% in Figure C). For the calibration process, values adopted in previous publications that also model the mechanical response of Toyoura sand have been used as a reference . In addition, the different void ratios of 0.6 and 0.75 reported for the cementing and pore‐filling specimens, respectively, have also been considered in the simulations (Table ).…”

“…The results presented in this section have been validated against the outputs from three other mechanical models for MHBS (Figure ). The comparison is satisfactory and shows that despite the simplicity of the densification mechanism, the Hydrate‐CASM performs similarly to models that require more than one hydrate‐related empirical parameter in their formulation.…”

“…Model comparison between the results from Hydrate‐CASM, Sánchez et al, Hyodo et al, and Uchida et al models against the experimental data from Hyodo et al Stress‐strain behavior and volumetric response for hydrate‐bearing sediments with (A) S h =24.2%, (B) S h =35.1%, and (C) S h =53.1% subjected to triaxial shear under confining effective stress of 5 MPa [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…The Hydrate‐CASM is applied here to robust and well‐described published experimental data that cover the most relevant conditions related to MHBS behavior, including a wide range of hydrate saturations, several hydrate morphologies, and confinement stress. These data have also been used in the calibration of previous mechanical models developed for MHBS, which give us the opportunity to compare and validate our results. The model performance is found satisfactory over a wide range of test conditions and evidence the capability of the Hydrate‐CASM model at capturing both the trend and magnitude of the stress‐strain and the volumetric response of synthetic MHBS.…”

Upscaled Anisotropic Methane Hydrate Critical State Model for Turbidite Hydrate‐Bearing Sediments at East Nankai Trough

“…The soil material within each core sample was assumed to be a homogenized continuum with isotropic mechanical properties. Uchida et al (2016) demonstrated that the MHCS model is sufficient to capture the geomechanical behavior of the hydrate-bearing sediments tested at various institutes under different confining stresses and with varying degrees of hydrate saturation. Therefore, the MHCS model was used to simulate the triaxial tests and match the mechanical response curves with the laboratory triaxial test results.…”