Patent Application
20170137092
This invention relates generally to safety systems and methods used in offshore oil and gas drilling. More specifically, the invention relates to safety systems and methods used in the offshore drilling environment to prevent a suspended load from causing damage to sub-sea equipment when the lifting system fails.
Dropping a large suspended load from a rig while operating over existing installed subsea infrastructure can be catastrophic. To minimize the adverse effects of such an accident, a need exists for a system that guides the dropped or run-away load away from specific seabed locations and to a safe landing area.
A preferred embodiment of a safety system for guiding a dropped or run-away suspended load includes:
A preferred method for guiding a dropped or run-away suspended load along a predetermined guide path includes the steps of
A preferred embodiment of a safety system 10 includes a safety winch 20 located on an offshore rig “R”, a safety buoy 30, and a safety buoy anchor 40. A safety winch line or cable 25 stored on the safety winch's spool 21 is routed through a spool 31 of the safety buoy 30 and then at a downward oblique angle to a cable connection 50 of the suspended load “L” which is to be lowered by the rig's drawworks winch (or other heavy lifting system) “S” and its associated steel cable or drilling line 60. The buoy 30 helps provide a mechanical advantage to the cable 25 and its spool 31 serves as a kind of head pulley for the cable 25, changing a direction of the cable 25 toward the load L. A safety buoy line or cable 35 connects the safety buoy 30 to the safety buoy anchor 40 located on the seabed.
The safety winch's cable 25 is allowed to “pay out” when the suspended load L is being actively lowered by the rig's lifting system S. If anything in the rig's lifting system S fails, breaks, or otherwise can no longer support the load L, the safety winch 20 is arranged to lock using winch means well known in the art, or optionally set to pay-out slowly (again using winch means well known in the art), thereby utilizing the buoyancy of the safety buoy 30 to guide the run-away load L to a relatively safe landing area on the seabed. Safety buoy 30 is a water tight and submergible buoy, having a size or buoyancy force appropriate for submerging when subjected to the run-away load L (and then resurfacing).
The safety winch 20 can be synchronized to freely pay out cable 25 as the lifting system S lowers the load L, and then offer resistance when the lifting system S stops. A similar scenario could operate during a lifting operation. Or, the winch 20 could simply have its brake applied slightly all the time (comparable to the “drag” setting on a fishing reel). Once the load L is in position or properly secured at its final destination, additional cable 25 can be paid out to release tension on the line and a remote operated vehicle (not shown) can be used to detach cable 25 or the line's fastener from the load L. The cable 25 can then be retrieved and, if needed, secured to the next load L to be lowered (or lifted).
Rather than the run-away load L dropping vertically downward from the lifting system S, the load L swings away and follows an arcuate path “P”. The stopped or slowed pay-out of the rig's safety winch 20 causes the safety buoy 30 to submerge until the run-away load L comes to rest on the seabed, at which time the safety winch 20 can continue to pay-out cable 25 until the buoy 30 re-surfaces, giving an approximate location of the dropped load L on the seabed. The winch 20 can then be used to assist in retrieving the dropped load L.
To lower load L, a steel cable or drilling line 60 of the lifting system L is connected to the load L. Safety winch 20 is positioned at a predetermined horizontal distance “d1” from the line 60, indicated by a vertical centerline “C” of the lifting system S. Preferably the winch 20 is located toward the perimeter of the rig R. Safety buoy 30 is then positioned at a predetermined horizontal distance “d2” from the safety winch 20. Similarly, safety buoy anchor 40 is positioned a predetermined horizontal distance “d3” from the buoy 30. The location of the safety winch 20, safety buoy 30, and buoy anchor 40 can be tailored to guide the trajectory of the run-away load along a pre-determined path P in the safest direction away from the rig R.
While system 10 does not prevent an accident while running heavy payloads to the seabed, it avoid damaging equipment located on the seabed below the rig R and will minimize the damage such an accident causes to the dropped payload.
