Most gas hydrates are buried stably in the formations which locate 0–1000m below seafloor. The global climate, oceanographic and tectonic processes can affect the stability conditions of gas hydrate, resulting in highly dynamic changes of subseafloor environments. A coupled seafloor∕borehole observatory system can be used to monitor the chemical, microbiological and physical data to achieve a better understanding of these changes and the carbon cycling in gas hydrate-bearing continental margin. When the borehole instrumentations are deployed, the geomechanical stability of hydrate-bearing formation should be assessed if it can support the borehole instrumentations. Some drilling and completion methods will be taken...