Strength characteristics of fractured methane hydrate-bearing sediments

Abstract

A large number of fractures have been discovered in natural gas hydrate (NGH) reservoirs on land and under the seabed worldwide, and the presence of these fractures may trigger deformation and instability of the reservoirs during NGH extraction. However, the specific impact of fractures on the mechanical properties of NGH reservoirs is still unknown at present. Based on these, this paper studies the strength characteristics of fractured hydrate-bearing sediments (FHBSs) and fracture-free hydrate-bearing sediments (FFHBSs) during shear processes under different effective stresses and hydrate saturations, and compares the stress–strain relationships, failure strengths, cohesion and internal friction angle between FHBSs and FFHBSs. The research indicates that under the same condition, the strength of FFHBSs is generally higher than that of FHBSs. In the absence of gas hydrates, the cohesion and internal friction angle of FHBSs are the same as those of FFHBSs. As the hydrate saturation increases (20% and 40%), the cohesion of FHBSs is lower than that of FFHBSs, while the internal friction angle of FHBSs is larger than that of FFHBSs. The research in this paper enhances the comprehension of the mechanical behavior of FHBSs and provides theoretical guidance for reducing the risk of geological disasters during NGH extraction.