DEM modelling of methane hydrate bearing sand

Methane gas hydrates are crystalline compounds formed from water and methane under certain pressure and temperature. They are mostly found in marine continental margin sediments and beneath the permafrost and considered as the future non-conventional energy resource. In order to develop innovative techniques for the safe extraction of methane gas from Methane Hydrate (MH) it is important to understand the shear behaviour of methane hydrate bearing sand. It has been reported that the pore scale habits of MH have a significant influence on the shear behaviour of methane hydrate bearing sand. In this paper, an attempt has been made to capture the effect of pore scale habits on the shear behaviour of methane hydrate bearing sand using the Discrete Element Method. Two modelling approaches (i) pore filling, leading to load bearing, and (ii) cementation, bonding of the interparticle contact, have been simulated using PFC3D. A series of triaxial monotonic tests were carried on an assembly of particles for different methane hydrate saturations. Both the approaches have captured, qualitatively, the stress ratio- axial strain behaviour similar to the laboratory experiments. The DEM simulation results highlight that MH saturation has a profound influence on the shear behaviour of hydrate bearing sand. It was shown that the cementation habit closely captures the variation of peak deviator stress with MH saturation similar to the laboratory experiments. Moreover, the evolution of micro-mechanical parameter (e.g. contact force and bond breakage) during shear loading has been presented and discussed.