Knowledge of the mechanical properties of clathrate hydrates is central for studying the mechanical properties of hydrate-bearing sediments, their associated applications in wellbore stability, exploitation in stratum deformation, geological disaster prevention, and risk assessment of CO₂ buried in oceans. However, because of the limited understanding of hydrate formation conditions and limited methods to investigate these, the understanding of the mechanical properties of hydrates is still poor and even controversial to some extent. This paper reviews current experimental and theoretical results on mechanical properties of hydrates, and discusses the typical difficulties faced in this area. On the experimental side, the most important problem is obtaining pure hydrate samples. Theoretically, the essential origin of the mechanical properties has not been explained in terms of molecular interactions. The hope is to resolve these issues by combining novel macroscopic experiments and microscopic methods. In order to avoid difficulties caused by impurities, it is proposed to use molecular dynamics simulations. This technique can be used to reveal the nature of the mechanical characteristics of hydrates at the molecular and nanometre scale. The goals of this paper are to establish a bridge between the micromechanical nature and the macromechanical properties of hydrates, and to lay a solid theoretical basis for the study of the mechanical properties of hydrate-bearing sediments. These goals are important for the future safe and efficient exploitation of natural hydrates, hydrate-induced seabed geological disaster prevention, the safety of CO₂ geological burial, and the deployment of a reliable long-term seabed-borehole coupled hydrate observation system in the integrated Ocean Drilling Program.

The low permeability of silty hydrate reservoirs in the South China Sea is a critical issue that threatens safe, efficient, and long‐term gas production from these reservoirs. Hydraulic fracturing is a potentially promising stimulation technology for such low‐permeability reservoirs. Here, we assess the gas production potential of a depressurization horizontal well that is assisted by the hydraulic fracturing using numerical simulation according to field data at site SH2 in this area. In addition, the number of horizontal wells drilled is discussed if commercial production is to be performed at this site. The results show that the production potential can be significantly stimulated at the early production stage by adopting hydraulic fracturing in this reservoir due to a better depressurization effect. However, the increase in gas recovery gradually decreases with the continuous dissociation of gas hydrates, and the evolution trend is similar to that in a reservoir without stimulation during later periods of gas production because the dissociation front gradually moves away from the fractures. From the perspective of production potential, using a horizontal well scheme assisted by the hydraulic fracturing technology for gas recovery from a hydrate deposit can sharply reduce the number of operation wells, shorten the drilling operation time, and boost the economic efficiency. The horizontal well scheme may be an effective way to increase the gas yield if the application of quickly deployed horizontal wells and hydraulic fracturing techniques in such hydrate reservoirs greatly increases in the near future.

Despite observations of massive methane release and geohazards associated with gas hydrate instability in nature, as well as ductile flow accompanying hydrate dissociation in artificial polycrystalline methane hydrates in the laboratory, the destabilising mechanisms of gas hydrates under deformation and their grain-boundary structures have not yet been elucidated at the molecular level. Here we report direct molecular dynamics simulations of the material instability of monocrystalline and polycrystalline methane hydrates under mechanical loading. The results show dislocation-free brittle failure in monocrystalline hydrates and an unexpected crossover from strengthening to weakening in polycrystals. Upon uniaxial depressurisation, strain-induced hydrate dissociation accompanied by grain-boundary decohesion and sliding destabilises the polycrystals. In contrast, upon compression, appreciable solid-state structural transformation dominates the response. These findings provide molecular insight not only into the metastable structures of grain boundaries, but also into unusual ductile flow with hydrate dissociation as observed during macroscopic compression experiments.

Fine‐grained sediments host more than 90% of gas hydrates on Earth. However, the fundamental properties of hydrate‐bearing silty and clayey sediments are much less understood than those of hydrate‐bearing sands, mainly due to the experimental challenges in synthesizing gas hydrate in fine‐grained sediments in the laboratory as the way they form in nature. This study forms tetrahydrofuran (THF) hydrate in kaolinite, visualizes the hydrate distribution and morphology using X‐ray computed tomography, and uses P and S waves to characterize the formed hydrate‐bearing clayey sediments. The results show that THF hydrate formed in clay is innately segregated and heterogeneous, no longer as a pore constituent as in sandy sediments. Hydrate nucleation, growth, and distribution in clays are dominated by the thermal condition and constrained by water activity and mass transport, which can result in low stoichiometric‐solution‐to‐hydrate conversion ratios of approximately 0.4–0.7. Thus, the estimation of hydrate volume in clays based on the mass of stoichiometric solution can be erroneous. The heterogeneity in hydrate‐bearing clays imposes challenges in wave velocity based characterization. The bulk elastic properties of hydrate‐bearing clays can be well predicted using the self‐consistent model. Specimens with higher hydrate volume fraction VF_h show higher wave attenuations Q⁻¹, highlighting the dominant role of THF hydrate in the wave attenuation of hydrate‐bearing clays. The results suggest that Q_p⁻¹ = 0.08 + 0.4VF_h = 2Q_s⁻¹, which underlines the potential of using wave attenuation based methods to quantify the hydrate volume fraction in clayey sediments.