Experimental verification of a prediction model for hydrate‐bearing sand

Pinkert, Shmulik; Grozic, J. L. H.

doi:10.1002/2015jb012320

Cited by 17 publications

(15 citation statements)

References 18 publications

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“…Several mechanical models developed for MHBS assume that the increase of strength, stiffness, and dilatancy observed in these sediments is mainly governed by bonding or cementation between the hydrate crystal and the sediment grains (Table ). However, recent pore‐scale observations and geomechanical investigations evidence the lack of true cohesion in MHBS and suggest that the mechanical response of these sediments may not necessarily be governed by sediment bonding/cementation, but rather to kinematic constrictions at pore/grain scale during shearing. In this paper, we develop a new mechanical constitutive model that does not consider hydrate‐bonding effects in its formulation but assumes that the reduction of sediment available void volume and the increase of sediment elastic stiffness during pore invasion with hydrate can explain the greater mechanical properties observed in MHBS.…”

Section: Introductionmentioning

confidence: 99%

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

Fuente

Vaunat

Marín‐Moreno

2020

Num Anal Meth Geomechanics

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SUMMARY Recent pore‐scale observations and geomechanical investigations suggest the lack of true cohesion in methane hydrate‐bearing sediments (MHBSs) and propose that their mechanical behavior is governed by kinematic constrictions at pore‐scale. This paper presents a constitutive model for MHBS, which does not rely on physical bonding between hydrate crystals and sediment grains but on the densification effect that pore invasion with hydrate has on the sediment mechanical properties. The Hydrate‐CASM extends the critical state model Clay and Sand Model (CASM) by implementing the subloading surface model and introducing the densification mechanism. The model suggests that the decrease of the sediment available void volume during hydrate formation stiffens its structure and has a similar mechanical effect as the increase of sediment density. In particular, the model attributes stress‐strain changes observed in MHBS to the variations in sediment available void volume with hydrate saturation and its consequent effect on isotropic yield stress and swelling line slope. The model performance is examined against published experimental data from drained triaxial tests performed at different confining stress and with distinct hydrate saturation and morphology. Overall, the simulations capture the influence of hydrate saturation in both the magnitude and trend of the stiffness, shear strength, and volumetric response of synthetic MHBS. The results are validated against those obtained from previous mechanical models for MHBS that examine the same experimental data. The Hydrate‐CASM performs similarly to previous models, but its formulation only requires one hydrate‐related empirical parameter to express changes in the sediment elastic stiffness with hydrate saturation.

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Section: Introductionmentioning

confidence: 99%

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

Fuente

Vaunat

Marín‐Moreno

2020

Num Anal Meth Geomechanics

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“…The results indicated that: different GHBS preparation methods such as gas saturated method and water saturated method lead to obvious differences in the mechanical behavior; the GH existence mode in the pores of sediments varies with the increase of GH saturation, leading to the transition of the deformation from shear shrinkage to shear dilatancy. Constitutive models were established to describe the mechanical behaviors of GHBS by using linear elastic or nonlinear elasto-plastic models, such as the Discrete Element Method, Duncan-Chang model, Cam-clay model [16][17][18][19][20]. Those models can consider two or three phases in GHBS, but are incapable of describing the effects of GH dissociation.…”

Section: Introductionmentioning

confidence: 99%

Mechanical properties of gas hydrate-bearing sediments during hydrate dissociation

Zhang

Luo

et al. 2017

Acta Mech. Sin.

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The changes in the mechanical properties of gas hydrate-bearing sediments (GHBS) induced by gas hydrate (GH) dissociation are essential to the evaluation of GH exploration and stratum instabilities. Previous studies present substantial mechanical data and constitutive models for GHBS at a given GH saturation under the non-dissociated condition. In this paper, GHBS was formed by the gas saturated method, GH was dissociated by depressurization until the GH saturation reached different dissociation degrees. The stress-strain curves were measured using triaxial tests at a same pore gas pressure and different confining pressures. The results show that the shear strength decreases progressively by 30%-90% of the initial value with GH dissociation, and the modulus decreases by 50%-75%. Simplified relationships for the modulus, cohesion, and internal friction angle with GH dissociated saturation were presented.

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“…Refs. [70,71] propose that kinematics might govern the increase in strength observed in hydrate-bearing sands. Alternatively, [41] propose that the greater strength and dilatancy observed in MHBS can be explained by densification and stiffening of the host sediment due to pore invasion by hydrate.…”

Section: Stress -Strain Behavior Of Mhbsmentioning

confidence: 99%

Thermo-Hydro-Mechanical Coupled Modeling of Methane Hydrate-Bearing Sediments: Formulation and Application

2019

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We present a fully coupled thermo-hydro-mechanical formulation for the simulation of sediment deformation, fluid and heat transport and fluid/solid phase transformations occurring in methane hydrate geological systems. We reformulate the governing equations of energy and mass balance of the Code_Bright simulator to incorporate hydrate as a new pore phase. The formulation also integrates the constitutive model Hydrate-CASM to capture the effect of hydrate saturation in the mechanical response of the sediment. The thermo-hydraulic capabilities of the formulation are validated against the results from a series of state-of-the-art simulators involved in the first international gas hydrate code comparison study developed by the NETL-USGS. The coupling with the mechanical formulation is investigated by modeling synthetic dissociation tests and validated by reproducing published experimental data from triaxial tests performed in hydrate-bearing sands dissociated via depressurization. Our results show that the formulation captures the dominant mass and heat transfer phenomena occurring during hydrate dissociation and reproduces the stress release and volumetric deformation associated with this process. They also show that the hydrate production method has a strong influence on sediment deformation.

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Experimental verification of a prediction model for hydrate‐bearing sand

Cited by 17 publications

References 18 publications

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

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

Mechanical properties of gas hydrate-bearing sediments during hydrate dissociation

Thermo-Hydro-Mechanical Coupled Modeling of Methane Hydrate-Bearing Sediments: Formulation and Application

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