Abstract:
Embodiments of the present invention generally relate to a subsea salvage operation using a lifting magnet. In one embodiment, a method of salvaging a submerged production platform includes deploying a salvage vessel to a wreckage site of the submerged production platform; lowering a lifting magnet from the salvage vessel to the submerged production platform; and activating the lifting magnet, thereby capturing at least a portion of the submerged production platform.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention generally relate to a subsea salvage operation using a lifting magnet. 
         [0003]    2. Description of the Related Art 
         [0004]      FIG. 1A  is a cross section of a prior art sub-sea wellbore  5  drilled and completed with a land-type completion  1 . A conductor casing string  10  may be set from above sea-level  15 , through the sea  20 , and into the sea-floor or mudline  25 . The conductor casing  10  allows the wellhead (not shown) to be located on a production platform  30  above sea-level  15  rather than on the sea-floor  25 . Alternatively, the platform  30  may service a subsea-type completion or a manifold from multiple subsea-type completions. 
         [0005]    Once the conductor casing  10  has been set and cemented  35  into the wellbore  5 , the wellbore  5  may be drilled to a deeper depth. A second string of casing, known as surface casing  40 , may then be run-in and cemented  45  into place. As the wellbore  5  approaches a hydrocarbon-bearing formation  50 , i.e., crude oil and/or natural gas, a third string of casing, known as production casing  55 , may be run-into the wellbore  5  and cemented  60  into place. Thereafter, the production casing  55  may be perforated  65  to permit the fluid hydrocarbons  70  to flow into the interior of the casing. The hydrocarbons  70  may be transported from the production zone  50  of the wellbore  5  through a production tubing string  75  run into the wellbore  5 . An annulus  80  defined between the production casing  55  and the production tubing  75  may be isolated from the producing formation  50  with a packer  85 . 
         [0006]    Additionally, a stove or drive pipe may be jetted, driven, or drilled in before the conductor casing  10  and/or one or more intermediate casing strings may be run-in and cemented between the surface  40  and production  55  casing strings. The stove or drive pipe may or may not be cemented. 
         [0007]      FIG. 1B  is a cross section of the platform  30  and completion  1  damaged by a hurricane. Hurricanes in the Gulf of Mexico have recently damaged or destroyed several production platforms  30  along with the completions  1 . The production platforms and the completions  1  have sunk to the sea-floor  25 . 
         [0008]      FIG. 2  illustrates a prior art salvage operation in progress. A diver may be dispatched from a salvage vessel (not shown) to the wreckage. A remotely operated vehicle (ROV) (not shown) may be deployed instead of or in addition to the diver. The diver and/or ROV may cut the platform wreckage into manageable pieces  30   p.  The diver and/or ROV may also assist in flooding the wellbore  5  with seawater or other kill fluid and cut the casing assembly  1  at or near the mudline  25 . The diver and/or ROV may then connect a piece  30   p  of the wreckage to a line from a crane on the salvage vessel. The connected piece may then be raised to the surface  15  and loaded on a barge (not shown) or other scrap vessel. Alternatively, the piece  30   p  may be moved to a debris pile on the sea-floor  25 . The process may be repeated for the wreckage pieces  30   p  and the severed casing assembly  1 . Once the larger pieces have been loaded on the barge, a basket (not shown) may be lowered to the diver. The diver may then proceed to pick up smaller remaining debris off of the seafloor  25  and load the debris in the basket. The basket may then be raised and dumped on the barge. The prior art operation is time-consuming, cumbersome, and may expose the diver or other salvage equipment to unnecessary risk. 
       SUMMARY OF THE INVENTION 
       [0009]    Embodiments of the present invention generally relate to a subsea salvage operation using a lifting magnet. In one embodiment, a method of salvaging a submerged production platform includes deploying a salvage vessel to a wreckage site of the submerged production platform; lowering a lifting magnet from the salvage vessel to the submerged production platform; and activating the lifting magnet, thereby capturing at least a portion of the submerged production platform. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0011]      FIG. 1A  is a cross section of a prior art sub-sea wellbore  5  drilled and completed with a land-type completion  1 .  FIG. 1B  is a cross section of the platform  30  and completion  1  damaged by a hurricane. 
           [0012]      FIG. 2  illustrates a prior art salvage operation in progress. 
           [0013]      FIG. 3  illustrates a salvage vessel deploying a lifting magnet, according one another embodiment of the present invention.  FIG. 3A  is a detailed view of the lifting magnet. 
           [0014]      FIGS. 4 and 5  illustrate a salvage operation conducted with the salvage vessel of  FIG. 3 , according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 3  illustrates a salvage vessel  300  deploying a lifting magnet  350 , according one another embodiment of the present invention. The salvage vessel  300  may support a crane  305 . The crane  305  may include a swivel  307 , a mast  309 , a guy line  311 , a load line  313 , an electric cable  315 , a boom  317 , a cable reel  319 , and a lifting magnet  350 . The swivel  307  may support the mast  309  from a hull of the vessel  300  so that the mast may rotate relative to the hull. A motor (not shown), such as an electric or hydraulic motor, may rotate the mast  309 . The boom  317  may be pivoted to the mast  309  so that the boom may be hoisted relative to the mast  309  by winding or unwinding the guy line  311  to/from from a boom winch (not shown), such as an electric or hydraulic winch, mounted on the mast  309 . Alternatively, the boom may be hoisted by a piston and cylinder assembly. The load line  313  may extend from a load winch (not shown) mounted on the boom  317  or mast  309  through a sheave or pulley disposed at a distal end of the boom. The electric cable  315  may extend from a direct current (DC) power supply, such as a rectifier, wind around the reel  319  and through a sheave or pulley on the boom  317 . The load line  313  may be connected to a sling  370  of the lifting magnet  350  and the electric line  315  may be connected to a terminal of the lifting magnet. The crane  305  may also include a load sensor to provide the crane operator with an indication of a weight of the load hoisted by the magnet  350 . 
         [0016]      FIG. 3A  is a detailed view of the lifting magnet  350 . The lifting magnet  350  may include a winding  355 , a case  360 , a bottom  365 , and the sling  370 . The case  360  may be round and made from a metal or alloy, such as steel. The case  360  may have an annular cavity formed therein for receiving the winding  355 . The winding  355  may include two or more layers  358  vertically stacked. Each layer  358  may include wire or strap  357  wound into a spiral and made of conductive material, such as aluminum, copper, aluminum alloy, or copper alloy. Each turn of the spiral may be electrically isolated by electrical insulation, such as tape, or the conductive material may instead be anodized. Each layer  358  of the winding  355  may be isolated by electrical insulation and an outer surface of the winding  355  may be isolated from the case by electrical insulation  359 . The bottom  365  may be welded to the case  360 , thereby making the cavity watertight. The bottom may be round plate and made from a non-magnetic material, such as a metal or alloy, such as manganese-steel. The terminal connection to the electrical wire  315  may be watertight. Alternatively, a rectangular magnet may be used instead of the circular magnet  350 . Additionally, the lifting magnet  350  may include one or more permanent magnets. 
         [0017]    A magnet controller (not shown) may be disposed on the salvage vessel in electrical communication with the power supply. The magnet controller may include a switch for activating and deactivating the magnet and regulate electricity supplied from the power supply to ensure optimum performance of the magnet. The magnet controller may also reverse the current in the magnet  350  in order to release a scrap load. The controller may also regulate discharge of stored energy from the magnet  350 . The controller may also track the service time of the magnet  350  in order to warn the operator of potential overheating of the magnet  350 . 
         [0018]      FIGS. 4 and 5  illustrate a salvage operation conducted with the salvage vessel  300 , according to another embodiment of the present invention. The salvage vessel  300  may be deployed to the wreckage site. A diver may be dispatched from the salvage vessel  300  to the submerged platform  30 . A remotely operated vehicle (ROV) (not shown) may be deployed instead of or in addition to the diver. The diver and/or ROV may cut the platform  30  into manageable pieces  30   p.  The diver and/or ROV may also assist in flooding the wellbore  5  with seawater or other kill fluid and cut the casing assembly  1  at or near the mudline  25 . The diver and/or ROV may then return to the salvage vessel  300 . Returning the diver and/or ROV to the vessel  300  before deployment of the magnet  350  into the water to capture the pieces  30   p  reduces risk to the diver and/or ROV of the pieces  30   p  shifting during hoisting of the pieces  30   p.    
         [0019]    Alternatively, the diver and/or ROV may remain in the water and in communication with the crane operator while the magnet  350  is hoisting the pieces  30   p.  Alternatively, an acoustic transponder, such as a beacon, may be disposed on the the load line  313 , the magnet  350 , or the cable  315  and the salvage vessel may include a hydrophone for receiving an acoustic signal from the beacon, thereby tracking the location of the magnet relative to the submerged platform  30 . Alternatively, a subsea camera may be deployed from the salvage vessel to provide the crane operator visual guidance for positioning the magnet  350 . 
         [0020]    The lifting magnet  350  may then be deployed to the submerged platform  30  from the salvage vessel  300  using the crane  305 . The magnet  350  may be activated and swept across the wreckage site until the magnet has captured a load of one or more pieces  30   p,  the casing assembly  1 , and/or other debris. The magnet  350  may then be raised to the surface  15  and the load  30   p  may be positioned over a barge  500 . The load  30   p  may then be released on to the barge  500  or other scrap vessel by deactivating the magnet  350 . The process may be repeated until no more pieces  30   p,  casing assembly  1 , and/or debris are collected by the magnet  350 . The barge  500  may then be towed to a salvage yard for recycling and/or disposal of the pieces  30   p,  casing assembly  1 , and/or debris. Additional barges may be used if needed. The diver/ROV may be redeployed to check for and recover any non-magnetic debris. 
         [0021]    The downtime of the magnet  350  from releasing the load  30   p  on to the barge  500  to re-deployment of the magnet to the wreckage may be used as cooling time for the magnet 
         [0022]    Using the magnet  350  to hoist the pieces  30   p  eliminates the cumbersome process of the diver and/or ROV having to secure the load line  315  to each piece  30   p.  Further, the magnet  350  may also capture smaller debris that would otherwise require the diver and/or ROV to find, pick up, and place in the basket, require recovery by a subsequent trawling operation, or be left behind. 
         [0023]    Alternatively, the salvage operation may be conducted on a platform servicing a subsea-type completion or a manifold from multiple subsea-type completions. 
         [0024]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.