Cementation Failure Behavior of Consolidated Gas Hydrate‐Bearing Sand

Abstract

The macromechanical properties (strength, stiffness, stress-strain relationship, etc) of the hydrate-bearing sediment are often correlated with the hydrate cementation failure behavior. In this study, a consolidated drained triaxial shear test with X-ray computed tomography was conducted on a hydrate-bearing sediment with a hydrate saturation of 32.1% under 3 MPa effective confining pressure for revealing the cementation failure behavior. The hydrate occurrences were clearly identified to be cementing, grain-coating, prepatchy cluster and patchy cluster. The cementation failure behavior (morphology), deformation evolution (quantitative statistics), and localized shear deformation at different regions of stress-strain curve were observed and analyzed using computed tomography. In the linearity region, the hydrate-cemented clusters moved as a whole, while small hydrate particles would aggregate to the periphery of the clusters. The noncemented sand particles move disorderly during this process. Localized deformation occurred perfectly exhibit an antisymmetric bifurcation pattern. In the plasticity region, the specimen starts to deform plastically; an internal shear band occurs in the specimen. The hydrates begin to shed from the periphery of the cemented structure, and the grinding effect of hydrates begins to occur between sand particles. However, the shedded hydrates will not enter and fill the neighboring pores but hind the movement of sand particles structurally near the original position. In the yielding region, the hydrate-cemented cluster structure is completely damaged and crushed into small pieces; a shear band with a determined thickness and inclination angle was observed.

Pore‐Scale Investigation Of Methane Hydrate‐Bearing Sediments Under Triaxial Condition

“…In all experiments, the specimens get bulged under axial loading, additional example in Seol et al (), rather than developing a dominant shear plane, as observed in some previous experiments (Higo et al, ; Wu et al, ; Yoneda et al, ). Development of a dominant shear plane is accompanied with lateral movements of the loading piston and high degree of discontinuity at specimen surface where it intersects the shear plane.…”

Microstructure Evolution of Hydrate‐Bearing Sands During Thermal Dissociation and Ensued Impacts on the Mechanical and Seepage Characteristics

“…However, it has to be admitted that the partial volume effect would affect the thresholding segmentation to some extent (Soret & Bacharach, 2007). In the CT study relating to hydrate, this issue is usually solved by substituting some of the substances to anthor with a large difference in grayscale (like substituting NGH with XeH in this study) to make the grayscale range larger for reducing this impact (Chaouachi et al, 2015; Wu et al, 2020; Yang et al, 2016). In this paper, the pores are thought to be determined by Xe without Xe hydrate, during the pore parameter analysis and absolute permeability calculation.…”

“…Xenon gas (Xe) was used to generate xenon hydrates (XeH) due to its high X-ray 10.1029/2019JB019103 Journal of Geophysical Research: Solid Earth attenuation coefficient in comparison to NGH for enhanced phase contrast in obtained CT images. Meanwhile, the physical characteristics (such as structure type, stoichiometry, and adiabatic bulk modulus) are quite similar between XeH and NGH (Chaouachi et al, 2015;Ning et al, 2012;Wu et al, 2020). Additionally, XeH requires a much lower equilibrium pressure compared to NGH and thus makes the CT experiment which is conducted in a limited space safer (Chaouachi et al, 2015).…”

Pore‐Scale 3D Morphological Modeling and Physical Characterization of Hydrate‐Bearing Sediment Based on Computed Tomography

“…First, the REV was segmented into the sand phase and pore space phase according to the gray value, and the segmentation threshold was determined by repeatedly comparing the calculated and the real volumes. The specific method can be found in our previous study (Wu, Li, Liu, Sun, et al, 2020). The porosity of the REV was 36.4%, which was similar to that of the field investigation (Yoneda et al, 2017).…”

“…When the consolidation was completed, a CT scan was conducted with a voxel size of 44 μm. More details about the specimen preparation process can be found in our previous study (Wu, Li, Liu, Sun, et al, 2020).…”