Proposition of Operational Maps As Tools for Evaluating Safety During the Emergency Disconnection of Risers

The construction of subsea wells under deep water depths brought the necessity to understand the behavior of columns on such conditions. These columns can be risers, drill strings or casing strings, which are either being installed by lowering them until they reach the sea bottom and/or inside the well, or they are already connected and fully operational. Since these columns are exposed to the open sea, environmental loads such as waves and currents will affect them. Depending on how harsh these environmental conditions are, drilling operations may be suspended. Therefore, understanding how such loads interact with such columns are of the utmost importance if one wants to ensure operational safety. In this paper, we discuss about the problem of emergency disconnections of risers. The concern of doing an emergency disconnection is fundamental for ensuring operational safety because the well will lose a safety barrier, as the level of the drilling fluid inside the well can no longer be controlled after the riser is disconnected, and thus the fluid cannot maintain its downhole pressure anymore. This work focuses on a finite elements modeling of riser dynamics, with the appropriate applied loads, to verify under which sea conditions the riser must be disconnected. The result of such analysis is called an “operational map”, which displays the maximum values of stress along the riser as a function of different sea conditions. Using the riser material properties, this map can then be divided in two regions — failure and admissible — and thus one can see for which sea conditions the riser must be disconnected to avoid its failure. The contribution of the present study is proposing a methodology to elaborate an operational map for a given riser scenario, from which both failure and admissible regions can be seen for emergency disconnection operations.