DEM investigation on dissociation characteristics of methane hydrate bearing sediments by chemical injection method

Abstract

Methane hydrate (MH) is regarded as a potential future clean energy source, which has attracted lots of attention in recent decades. The sediment containing MH is called as Methane Hydrates Bearing Sediment (MHBS). The evolutions of mechanical behaviors of MHBS from macro and micro scales are needed in detail for safe MH exploitation (e.g., chemical injection method). For this purpose, a novel 3D thermo-hydro-mechanical-chemical (THMC) bond contact model was proposed and implemented into a DEM commercial software to capture the mechanical behavior of MHBS under exploitation stress path. Firstly, MHBS samples were compressed to different deviator stress levels, which represents the different initial stress state. Then the chemical injection process was simulated by increasing the salinity from 3wt% to 14wt% to allow MH dissociate while the deviator stress remained constant. After which, the recovery stage was simulated by decreasing the salinity from 14wt% to 3wt%. The results show that the salinity can affect the mechanical behavior of MHBS by changing the properties of inter-particle methane hydrate. During chemical injection process, the axial strain increases with the increase of salinity. The chemical injection method will result in soil collapse when initial deviator stress is larger than the strength of pure sand at exploitation stage but slight deformation at recover stage.