DEM simulation of coexistence type methane hydrate bearing sediments

The hydrate morphology in sandy methane hydrate (MH)-bearing sediment (MHBS) is commonly classified as pore-filling, cementation, grain-coating and load-bearing. This paper presents a numerical investigation into the mechanical behaviour of coexistence-type MHBS using the discrete-element method (DEM). The coexistence type is represented as a combination of pore-filling and cementation types. For MHBS with a given MH saturation (S _MH), the relative content of pore-filling and cementation is characterised by the cement ratio λ (λ = 0 means pure pore-filling and λ = 1 means pure cementation). A series of drained triaxial compression tests is simulated, and micromechanical variables such as bond breakage are examined. The results show that (a) the strength and dilatancy of the coexistence-type MHBS are higher when the cement ratio is larger. The normalised strength and secant modulus increase linearly with the cement ratio. (b) When the cement ratio increases, the critical-state line on the mineral void ratio e _cr–ln p′ projection shifts towards a higher position and the bond breakage ratio is larger. (c) The shear stress of the coexistence-type MHBS with cementation is affected by the MH generation process due to the MH bond breakages.