A practical multi-field coupling distinct element method for methane hydrate bearing sediments

The methane hydrate (MH) has been attracting extensive attention as a promising green energy source because of the abundant reserve and more environmental friendliness. However, large-scale exploitation induces the weakening of MH bearing sediments (MHBS) structure, which can result in engineering problems such as sand jamming, and environmental disasters such as landslide, and this will constrain efficient and safe exploitation of MH. Given that several multi-field coupling simulators fail to accurately describe large deformation of soils such as particle migration, a practical multi-field method T+H+PFC for MH exploitation analysis is established based on the commercial distinct element method (DEM), software particle flow code (PFC) and numerical code TOUGH+HYDRATE (T+H) for the multiphase flow analysis of hydrate-bearing geologic systems. The coupling computation can be achieved by exchanging the information between the porosity obtained by DEM and the temperature, pressure and salinity obtained by T+H. Then, the method is validated by conducting numerical modeling of one-dimensional (1D) consolidation and 1D heat conduction tests. Finally, focus is on the dynamic responses of MHBS and weakening of MH under the conditions of 1D dissociation tests with depressurization and heat stimulating methods. The numerical results are found to be in good agreement with the experimental data available, which demonstrates that the T+H+PFC method has a great promise in the MH decomposition-induced multi-field coupling analysis, such as deformation of seabed, sand production and submarine landslide.