Gas Production and Settlement Deformation of Nondiagenetic Hydrate during Depressurization: A Triaxial Investigation under Multifactorial Control

To investigate the deformation characteristics of nondiagenetic hydrate under depressurization, this study conducted triaxial tests systematically controlling hydrate saturation (Sh), sediment matrix, depressurization procedure, and effective axial stress (σ1′). Gas production and axial deformation were monitored in real time, revealing the settlement deformation characteristics of nondiagenetic hydrate-bearing sediments under multifactor control. The results show: (1) The hydrate decomposition process is characterized by three stages: “undecomposed, rapidly decomposed, continuously decomposed”. (2) Increased Sh significantly enhanced total gas production and axial deformation. Conversely, coarser sediment matrix particles significantly reduced axial deformation while exerting negligible influence on total gas yield. (3) Larger depressurization magnitudes intensified settlement deformation. However, drastic temperature drops could trigger secondary hydrate formation and redissociation, reducing dissociation efficiency. (4) Lower σ1′ reduced the amount of deformation. As dissociation is primarily governed by thermodynamic phase equilibrium, variations in stress have a limited impact on total gas production. These results elucidate the critical influence of reservoir matrix properties and depressurization strategies on gas production and deformation in nondiagenetic hydrate reservoirs, providing a theoretical basis for their safe exploitation.