Mechanical Behavior of Layered Heterogeneous Hydrate-Bearing Sediments: Insights from Triaxial Experiments and Numerical Modeling

Abstract

The mechanical behavior of natural gas hydrate-bearing sediments (HBS) is critical for safe and efficient gas production. However, marine HBS commonly exhibit layered heterogeneity caused by spatial variations in clay distribution and hydrate saturation (Sh), whose effects on stress transfer and failure mechanisms remain poorly understood. In this study, triaxial shear tests were conducted on three types of heterogeneous HBS with a montmorillonite-bearing interlayer (HBShet-M), an illite-bearing interlayer (HBShet-I), and a low-hydrate-saturation interlayer (HBShet-Sh). An elastoplastic finite-element model based on the Mohr–Coulomb criterion was then established and validated against experimental results, with prediction errors of only 0.06–0.77% for failure strength (qf). The validated model was subsequently used to investigate the effects of layered heterogeneity on stress evolution and failure mechanisms during shearing. The results show that after inserting a clay interlayer into the middle layer, under σ3’ = 1 MPa, the peak deviatoric stress qf of HBShet-M and HBShet-I decreases by 3.65 and 4.05 MPa, respectively, compared with HBShom. Under high confining pressure, they decrease by 2.48 and 1.19 MPa, respectively. By contrast, HBShet-Sh reduces the strength of HBS by impairing hydrate cementation, with strength reductions of 5.14 and 5.03 MPa under low and high confining pressures, respectively. Preferential deformation of the weak layer governs failure in all heterogeneous HBS and induces pronounced stress concentration. The minimum and maximum principal stresses within the weak layer are 4.7–6.7 and 1.2–1.8 times those in the strong layer, respectively. These findings provide new insights into the failure mechanisms of layered heterogeneous HBS and offer theoretical guidance for safe marine gas hydrate production.