Patent ID: 8511388

Claim:
An offshore drilling assembly, comprising: a drilling riser containing a fluid column and having an upper end configured for support by a drilling vessel; a subsea blowout preventer assembly having a blowout preventer (BOP) stack for securing to a subsea wellhead and a lower marine riser package (LMRP) detachably attached to an upper end of the BOP stack, the LMRP being connected to a lower end of the drilling riser; a subsea controller mounted to the blowout preventer assembly and hydraulically connected with the BOP stack for controlling various functions of the BOP stack, including blocking upward flow through the drilling riser; an electrical line extending from the subsea controller for connection to the drilling vessel for providing signals to the subsea controller; a backup system to block upward flow through the drilling riser in the event signals to the subsea controller via the electrical line are interrupted, comprising: a pressure pulse generator located within the drilling riser close to an upper surface of the fluid column and configured to generate a predetermined pressure variation pattern corresponding to an emergency disconnect signal (EDS) and including at least one of positive and negative pressure pulses, the signal being propagated downwards in the fluid column; a pressure pulse receptor mounted to the blowout preventer assembly and configured to sense pressure variations in the fluid column at the blowout preventer assembly; a subsea data processor electrically connected with the receptor for determining whether pressure variations sensed by the pressure pulse receptor comprise the pressure variation pattern propagated by the pulse generator corresponding to the EDS; an wherein the data processor is electrically connected with the subsea controller to cause the subsea controller to block upward flow through the riser upon determining the pressure variation pattern corresponding to the EDS was detected by the pulse receptor.