Coupling analysis on mechanical properties of near-well interface of methane hydrate-bearing sediments under depressurization exploitation

The methane hydrate (MH) has been attracting extensive attention as one of the most potential clean energy sources. During its exploitation, hydrate dissociation induces the weakening of mechanical properties of near-well MH bearing sediments (MHBS), which can result in series of engineering problems. Given that most current researches do not focus on the interface properties of MHBS-well structure during exploitation, the practical multi-field TOUGH+HYDRATE+PFC coupling framework is adopted, and considering different conditions of a more real MHBS-well interface, the multi-field coupling numerical simulation of depressurization is performed. Comparison and analysis are made on the mechanical properties of near-well soil and the well, and the influences of surface roughness on wellbore stability are discussed. The results show that: (1) Different well roughnesses doesn't have obvious influences on the thermal-mechanical-chemical evolution and production efficiency. (2) Appropriately increasing the surface roughness of the well can effectively reduce the settlement amplitude of the contact soil, enhance the stability of soil in the contact area with the wellbore, and reduce the risk to ensure a relatively stable long-term production. (3) The increase of well roughness will lead to greater frictional force on the well. It is necessary to control the well surface not to be too rough, in order to prevent the wellbore itself from suffering the impact of the excessive forces, destabilizing and becoming failure.