Theoretical Analysis of Macroscopic Mechanical Properties of Coexistence Type Methane Hydrate-Bearing Sediments by Micromechanics-Based Model

Abstract

The impacts of different types of methane hydrates (e.g., pore-filling, load-bearing, grain-coating, and cementing types) on the mechanical properties of methane hydrate-bearing sediments (MHBS) exhibit significant variations. However, the quantitative distinctions remain largely unexplored. Following the framework of the classical micromechanics-based model, a simplified physical model of regularly arranged particle assembly is proposed for the coexistent-type MHBS (the MHBS containing two or more types of hydrates) to derive the macroscopic constitutive relations, strength criteria, and corresponding macro–micro quantitative correlation of elastic and strength parameters. The obtained theoretical solutions are verified by comparison with indoor test results, and the influence of environmental factors and hydrate saturation, especially different types of hydrates, on the macroscopic mechanical properties of MHBS under various initial planar void ratios of sediments is investigated in detail. The results show that there are significant differences in the micromechanisms that affect the macroscopic mechanical properties of different hydrate types. Specifically, the load-bearing hydrate has almost no contribution to the improvement of the elastic modulus and peak strength, while the cementing type plays a dominant role in the macroscopic mechanical properties of MHBS, and the influence of the hydrate with the grain-coating type is between the load-bearing and cementing types.