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NTNU Norwegian University of Science and Technology Department of Marine Technology of the vessel. Every emergency system needs to be redundant and generally there are three different ways to initiate the disconnection: Manually from the bridge or control room, automatic mode function (AMF) and through ROV intervention locally at the BOP. Activating the EDS will lead to a sequence of events. One example was found in [Bernard et al. 2004]. a) b) c) d) Close all side outlet valves, shutdown mud pumps; Pick pipe up off bottom for preparation to hang off; Close pipe rams; Hang off pipe, balance pipe load for neutral weight shear to avoid main block recoil; Lock pipe rams; Close shearing rams (may also be sealing shear/blind rams); Pick up pipe; Close blind rams, if different from shear rams; Lock blind rams; Vent all pod to stack pressure connections; Vent LMRP annular preventer(s); Unlatch LMRP connections, main connector, mini connectors, if fitted; Activate riser recoil system. e) f) g) h) i) j) k) l) m) More generally it can be said that the EDS will cut the drill pipe, seal the well, open annular for mud release (if closed) and disconnect the LMRP connector. Activation of anti recoil system can happen manually or automatically depending on system. Time from EDS activation to disconnection of the riser can be around 60 seconds. 3.2.1 Automatic mode function (AMF) The EDS is designed to activate automatic if the communication between the bridge and BOP is lost. This is called the automatic mode function. The surface vessel has both hydraulic and electric communication with the BOP. If these two lines are damaged and the connection with the BOP is lost it activates. The BOP is equipped with battery and hydraulic power to function without power from the bridge. This system activated the disconnection for the Deepwater Horizon platform, but it was unsuccessful to seal the well and disconnect due to other circumstances. The AMF has also led to cases of unplanned emergency disconnections [West Engineering services Inc. 2003]. 3.2.2 Drift-‐off For drift-‐off normally 2 alert circles define the EDS activation. A yellow alert circle includes a procedure for discontinuing drilling and hanging the drill pipe off in the BOP stack. The red alert circle signals the captain or driller to “activate the red button” to start the automatic sequence. These circles will be defined by the drift-‐off speed of the vessel, the time disconnection takes and the exceedance of limits in the riser. The 17
