The Effects of Hydrate on the Strength and Stiffness of Some Sands

Abstract

Gas hydrates can form more or less at the same time as seafloor sediment. They can have the effect of significantly stiffening and strengthening deep-ocean sediments. Subsequent increases in situ temperature or decreases in pressure may trigger hydrate dissociation, leading to large reductions in the strength and stiffness of the sediment and possible seafloor instability. Gas hydrate dissociation not only removes cementing. It also releases freshwater and significant amounts of trapped gas that are dependent on multiple factors such as type of sediment, available pore space, hydrate morphology, and hydrate saturation. The presence of pock marks in areas of known seabed instability suggests that hydrate dissociation may have been a factor in triggering failure at these locations. Having reviewed the mechanisms by which the strength and stiffness of seabed sediment may be changed during dissociation, this paper reports the results of laboratory testing to evaluate the effects of loss of hydrate cement on strength and stiffness, for a range of sand-sized materials with differing particle size, specific surface area, and particle shape, using a laboratory gas hydrate triaxial apparatus. The results suggest that both the strength and the stiffness of hydrate-cemented granular materials are affected significantly by the specific surface available for hydrate cementation and, to a certain extent, by the particle shape. Uniform coarse granular sediments of lower specific surface area can suffer significant loss of stiffness and strength upon hydrate dissociation, changing the sediment from dilative to contractive. Finer-grained sediments appear less affected by dissociation. Song et al. (2010) found the compressive strength of solid methane hydrate at À5°C to be 0.9 MPa under a 1-MPa confining pressure. For hydrate formed from ice/methane mixtures, at À5, À10, and À20°C, under back pressures of 2.5, 5, and 10 MPa, Yu et al. (2011) measured unconfined compressive strengths of between 1.2 and 3 MPa. It can be seen from the above that solid hydrate has the strength of ice, similar to that of a weak MADHUSUDHAN ET AL. 65

Cementation Failure Behavior of Consolidated Gas Hydrate‐Bearing Sand

“…It must be noted that there is a fracture in the hydrate cemented clusters of B‐2 in Figure . This indicates that not only the interconnected pores but also the solid skeleton will be compressed slightly during the linearity region, which explains the phenomenon whereby the presence of hydrates can enhance the stiffness of the specimen greatly even when the hydrate saturation is low (Hyodo, Li, et al, ; Madhusudhan et al, ; Masui et al, ; Miyazaki et al, ). First, at the initial stage of the deformation process, the hydrates in the specimen will also undergo a certain deformation, and this behavior will enhance the whole specimen stiffness since the stiffness of the hydrates is much greater than that of the hydrate‐free sediments (Ning et al, ; Waite et al, ).…”

A State-Dependent Constitutive Model for Gas Hydrate-Bearing Sediments Considering Cementing Effect

“…Masui et al [22] prepared two types of GHBS using percolated methane gas in a specimen of Toyoura sand mixed with powder ice and excessive water and later carried out a series of triaxial tests with different effective confining pressures. Yun et al [23], Miyazaki et al [24], Ghiassian et al [25], Liu et al [26], Madhusudhan et al [27] and Dong et al [28] conducted experimental studies on GHBS.…”

Introduction to Special Issue on Gas Hydrate in Porous Media: Linking Laboratory and Field‐Scale Phenomena

“…The situation might also apply at the base of the GHSZ, which is assumed to be the thermodynamic triple point (coexistence of vapor phase methane, hydrate, and dissolved methane). Just as specific surface plays a role in the locus of hydrate formation for fine‐grained sediments, the Madhusudhan et al () study demonstrates that the specific surface, grain morphology, and grain size affect the details of hydrate formation and cementation in various sands and thus differences in the behavior of these sands following hydrate dissociation.…”

“…Fine-grained particles that are mixed with coarser sediments can be mobilized under certain conditions and are also considered a component of pore fill in some cases. (2018) On the importance of advective versus diffusive transport in controlling the distribution of methane hydrate in heterogeneous marine sediments Lei and Santamarina (2018) Laboratory strategies for hydrate formation in fine-grained sediments (also fines) You and Flemings (2018) Methane hydrate formation in thick sandstones by free gas flow Effect of gas flow rate on hydrate formation within the hydrate stability zone Meyer, Flemings, DiCarlo, You, et al (2018) Experimental investigation of gas flow and hydrate formation within the hydrate stability zone Sahoo et al (2018) Presence and consequences of coexisting methane gas with hydrate under two phase water-hydrate stability conditions Almenningen et al (2018) Upscaled anisotropic methane hydrate critical state model for turbidite hydrate-bearing sediments at East Nankai Trough Ge et al (2018) Laboratory investigation into the formation and dissociation process of gas hydrate by low-field nuclear magnetic resonance technique Role of fines Han et al (2018) Depressurization-induced fines migration in sediments containing methane hydrate: X-Ray computed tomography imaging experiments Hyodo et al (2017) Influence of fines content on the mechanical behavior of methane hydrate-bearing sediments Jang et al (2018) Impact of pore fluid chemistry on fine-grained sediment fabric and compressibility Taleb et al (2018) Hydromechanical properties of gas hydrate-bearing fine sediments from in situ testing Geomechanical and hydraulic properties Spangenberg et al (2018) A quick look method to assess the dependencies of rock physical sediment properties on the saturation with pore-filling hydrate Madhusudhan et al (2019) The effects of hydrate on the strength and stiffness of some sands Kossel et al (2018) The dependence of water permeability in quartz sand on gas hydrate saturation in the pore space Gil et al (2019) Numerical analysis of dissociation behavior at critical gas hydrate saturation using depressurization method Cook and Waite (2018) Archie's saturation exponent for natural gas hydrate in coarse-grained reservoirs Zhou et al (2018) Upscaled anisotropic methane hydrate critical state model for turbidite hydrate-bearing sediments at East Nankai Trough Coupled numerical modeling Sánchez et al (2018) Coupled numerical modeling of gas hydrate-bearing sediments: From laboratory to field-scale analyses Kim et al (2018) Methane production from marine gas hydrate deposits in Korea: Thermal-hydraulic-mechanical simulation on production wellbore stabilit...…”