Energy Science & Engineering (Feb 2022)
The effect of particle size and hydrate status on dynamic mechanical properties of hydrate‐bearing sediments
Abstract
Abstract Dynamic mechanical properties of natural gas hydrate (NGH) reservoirs are extremely important owing to their critical role in drilling safety and reservoir stability during NGH development. However, the comprehensive influence of reservoir skeleton and hydrate status on the dynamic mechanical properties of hydrate‐bearing sediments (HBS) has rarely been reported. In this study, three types of sandy sediments with different particle size were simulated. A customized resonant column system was used to synthesize HBS and to test the dynamic mechanical properties of the HBS under the conditions of different confining pressures and shear strains. In addition, the dynamic mechanical responses of the hydrate‐free and hydrate‐dissociated specimens were comprehensively studied to further demonstrate the dominant role of hydrate status and skeleton‐hydrate interactions on the dynamic mechanical properties of HBS. The results show that the shear moduli of the HBS specimens increase exponentially with an increase in confining pressure and decrease in amplitude strain. However, the damping ratios decreases with an increase in confining pressure and decrease in amplitude strain. With an increase in the median particle size (D50) of the simulated sediments, the shear moduli tend to increase, whereas the damping ratios decreas. In addition, the hydrate occurrence decreases differences in moduli between fine‐, medium‐ and coarse‐skeleton specimens, and the enhancement effect of hydrate on the mechanical properties of the specimen is the maximum for the fine sediment specimens. Interestingly, we find that the modulus of the hydrate‐dissociated specimen is relatively smaller than that of the hydrate‐free specimen, which implies that the structure of the sediments could be rearranged and weakened due to the hydrate formation‐dissociation processes.
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