Creep properties of fractured hydrate-bearing sediments

Long-term extraction of natural gas hydrates can induce reservoir creep, leading to geological hazards such as submarine landslides and wellbore instability. The presence of widespread natural fractures can intensify this creep deformation by altering stress distributions, thereby significantly increasing engineering geological risks. However, the influence of key parameters on the creep behaviour of fractured hydrate-bearing sediments remains insufficiently understood. This study presents a systematic investigation into the creep properties of fractured and fracture-free hydrate-bearing sediments under various conditions, including effective confining pressures and hydrate saturations. It provides a reference for assessing the stability of fractured hydrate-bearing reservoirs. A comparative analysis of total creep strain, attenuation-creep strain, and rheological rate was conducted to elucidate the distinct mechanical responses of the two types of sediments. The results reveal that fractures fundamentally alter the sediment’s creep behaviour. In fractured sediments, key creep parameters exhibit a non-monotonic dependence on hydrate saturation, with total creep strain peaking at a critical saturation of approximately 20%. In contrast, the same parameters in fracture-free sediments show a consistent positive correlation with hydrate saturation. For both sediment types, the rheological initiation time increases with both effective confining pressures and hydrate saturation, indicating this relationship is independent of fracturing. Crucially, the total creep strain is predominantly governed by the attenuation-creep stage, regardless of fracture presence. This work improves the understanding of creep mechanics in fractured hydrate reservoirs and provides a critical theoretical basis for engineering geological safety assessments and the optimisation of hydrate extraction strategies.