The Acoustic Control System (ACS) for Blow Out Preventer (BOP) is one of Kongsberg Maritime's highly successful products for the drilling industry. Combined with the extremely versatile HiPAP system it provides an extremely important emergency shut-down facility for drilling rigs in critical operations. The big increase in rig activities worldwide has given Kongsberg a formidable rise in sales of these systems, and soon we will have more than 100 systems in operation.
The ACS system is a redundant receiver/transmitter for communication with the rig through acoustics. It is interfaced to the BOP control pod so that different sets of emergency functions can be executed to shut down the well and avoid a pollution. If the regular umbilical is broken and normal communication with the BOP is not possible, the ACS is the last and only means to shut down the well. If a function is executed from the ACS, signal goes to a solenoid that activates a big valve on the BOP; the valve is then energized by air pressure bottles on the BOP.
The surface equipment consists of a portable Acous¬tic Command and Control Unit, the ACC 401 -- with internal rechargeable battery giving 10 hours normal operation -- and a dunking transducer with hand operable cable winch. The dunking transducer may be lowered 70 m into the sea from a rig, a stand-by vessel, a lifeboat -- or a helicopter.
The ACC 401 is operated via an LCD display, using a cursor operated menu and dedicated push-buttons. The display has background lights for operations at night. To secure safe operation of critical subsea func¬tions, the operator has to use both hands during activation of armed functions.
The subsea equipment consists of the Subsea Control Unit (SCU), two transducers with cables and waterproof connec¬tors, and an interface cable for BOP solenoid pack connection. The SCU holds the subsea electron¬ics. It includes two transceivers with transducers, which makes it 100% redundant. The SCU is powered from internal lithium batteries -- normal operational battery lifetime up to two years.
The last few year's technology progress in drilling has brought forward the Surface BOP concept, where acoustics has also been implemented as an important tool for controls. In this type of operation the BOP is hanging in the splash zone of the rig as a virtual seabed to drill on, and a smaller riser is connected to a SIM ( Subsea Interface Module ) on the seabed. The seabed SIM then only has the acoustic system, which also in some cases can have a simplified umbilical with power and fiber communication. Kongsberg Maritime was the first company to make such a system – being used on the Sedco 601 for a SBOP drilling operation in Indonesia.
The exploration and upstream industries are taking the environment increasingly serious, and are building new rigs and drillships with a very high environmental safety factor. As an extra precaution against unwanted drift-off or disconnection from the well, almost every new rig being built now follows the strict legislations of the North Sea, Brazil and Canada, where the ACS system or similar is required for all drilling operations. The ACS system is very robust, and the communication principles are designed with reliability as the most important criteria.
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