DEM investigation on macro and micro mechanical properties of methane hydrate-bearing sediments considering dissociation

The cementing effect of methane hydrates on sediment reservoirs is weakened during the dissociation process, leading to a series of engineering disasters such as deformation and landslides in hydrate reservoirs. However, under external loading conditions, the motion of sediment particles and the evolution of contact force chains, resulting in insufficient discussion on the failure modes of hydrate cementation. Therefore, an improved bond contact model (I-PB) and a hydrate decomposition simulation method were proposed, enabling biaxial shear simulations and field-scale hydrate extraction simulations. The results indicate that the I-PB contact model effectively captures the tensile, compressive, and shear failure modes of hydrate cementation bonds under decomposition and deviatoric stress conditions. As the hydrate cementation failure intensifies, the sediment particles shift from axial displacement to radial displacement, and the hydrate sediment samples transition from axial compression to radial expansion. At the field scale, as the reservoir stress increases from 10 MPa to 30 MPa, the hydrate cementation failure increases from 31% to 85%, exacerbating the rotational tendency of sediment particles and resulting in increased vertical and horizontal displacement of the hydrate reservoir. This research provides a theoretical basis and reference value for the safe extraction of hydrates in field operations.