Abstract
Studying the strength and deformation properties of sediments containing gas hydrates is one of the key problems during the process of hydrate resource exploitation. In this paper, considering the effects of temperatures (−5, −3, −1 °C), confining pressures (0.5, 1, 2 MPa) and porosities (40%, 80%) on the dynamic modulus characteristics of sediments containing methane hydrates, several dynamic loading experiments were conducted. The results show that the sediment structure was more easily destroyed under a larger amplitude of dynamic loading. According to the dynamic stress–strain curves, the skeleton curves of the sediment samples were obtained, and it was shown that the deformation behaved with elastic characteristics in the initial stage, and then plastic deformation increased gradually and played a leading role with the increase in external loading. The maximum dynamic elastic modulus of sediments was reduced under the conditions of higher temperature and porosity, and effectively enhanced under higher confining pressure. Finally, on the basis of the Hardin–Drnevich equivalent model, and considering the influences of temperatures and confining pressures on model parameters, a viscoelastic constitutive model applied to analyze the dynamic modulus characteristics of sediments containing methane hydrate was established. The comparison showed that these calculated values of sediments’ dynamic elastic modulus accorded quite well with the experimental values.
Highlights
As a new type of clean energy, natural gas hydrates are widespread in marine sediments and under permafrost regions [1]
The dynamic modulus experiments of hydrate-bearing sediments, process, the stress–strain relationship was consistent with the deformation characteristics of previous every dynamic load amplitude remained stable during each stage of the vibration experiment
Before the samples were subjected to the dynamic loading at any stage of the dynamic modulus experiment process, the stress–strain relationship was consistent with the deformation characteristics of previous static triaxial compression experiments; that is, the deformation of hydrate-bearing sediment samples still behaved with elastic-plastic characteristics [32]
Summary
As a new type of clean energy, natural gas hydrates are widespread in marine sediments and under permafrost regions [1]. Based on synthetic hydrate samples in the lab and a small amount of sediment cores while drilling, researchers conducted triaxial compression tests, and studied the effects of hydrate saturation, confining pressures, temperatures, pore pressures, porosities, and cemented types on the static mechanical characteristics [13,14,15,16,17]. Researchers investigated the effects of hydrate dissociation on the static mechanical characteristics of sediments containing hydrates, and the results show that the sediments’. Further research indicated that different locations of hydrate particles in the pores, for instance, suspended and cemented types had great effects on the acoustical characteristics of sediments, and the hydrate saturation only affected the S-wave velocity of sediments when the saturation was above. Previous work systematically studied the dynamic strength properties of sediments containing gas hydrates, and the sediments’ cohesion and friction angle values were obtained [31]. According to the experimental data, a dynamic viscoelastic constitutive model applying to methane hydrate-bearing sediments was established
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