BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates generally to systems and methods for closing off sub sea wells. 
         [0003]    2. Description of the Related Art 
         [0004]    There are many instances when a sub sea wellbore must be closed in or sealed off to both protect the well and prevent chemicals and production fluids within the well from being dispersed into the sea. In some instances, the well reaches the end of its productive life and must be closed off. In other instances, the well must be closed down on a temporary basis. In addition, hurricanes and other storms can damage sea-based platforms, even removing them from their moorings. Sub sea risers can be destroyed during such storms. Storm-damaged sub sea wells must be capped off to limit harm to the environment. Currently, divers are used to submerge and cap off the wellbore manually. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention provides methods and devices for closing off sub sea wells. In a preferred embodiment, a remotely operated submersible vehicle (ROV) is used to carry a bridge plug down to a sub sea well. Preferably, the ROV is operated from a surface vessel or platform and is outfitted with a submersible hydraulic pump and a manipulator arm. Additionally, the ROV is provided with a carrying rack which can support a well closure assembly made up of an inflatable bridge plug and an affixed hydraulic running tool. The bridge plug and running tool are placed into the carrying rack and operably interconnected with the hydraulic pump so that the plug element can be selectively inflated by the pump. 
         [0006]    In operation, the ROV is deployed into the sea from the surface vessel or platform. The ROV descends to the depth of the wellbore and deploys the well closure assembly into the open wellbore using one or more manipulator arms. The pump is actuated to inflate the plug element of the bridge plug and thereby close off the wellbore. The running tool releases from the bridge plug upon receipt of a predetermined amount of fluid pressure from the pump. Thereafter, the running tool is removed from the wellbore, and the ROV returns to the surface vessel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The advantages and further aspects of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing and wherein: 
           [0008]      FIG. 1  is an external side view of an exemplary surface vessel, ROV and wellbore to be closed off in accordance with the present invention. 
           [0009]      FIG. 2  is an external isometric view of the ROV in greater detail. 
           [0010]      FIG. 3  is a side view of an exemplary fluid pump used in conjunction with the present invention. 
           [0011]      FIG. 4  is an end view of the exemplary fluid pump shown in  FIG. 3 . 
           [0012]      FIG. 5  is an external side view of the surface vessel, ROV and wellbore, now with the well closure assembly being inserted into the wellbore by the ROV. 
           [0013]      FIG. 6  is an external side view of the surface vessel, ROV and wellbore now with the packer device set within the wellbore. 
           [0014]      FIG. 7  is an external side view of the surface vessel, ROV and wellbore, now with the hydraulic disconnect device having been released from the bridge plug. 
           [0015]      FIG. 8  is side, cross-sectional view of well closure assembly. 
           [0016]      FIG. 9  is a side, cross-sectional view of upper portions of the well closure assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]      FIG. 1  illustrates an exemplary sub sea wellhead  10  on the sea floor  12 . The wellhead  10  is shown in a greatly simplified and schematic manner, but includes a wellbore  14  which extends downwardly through the sea floor  12  and which it is desired to close off. A vessel  16  floats at the surface  18  of the sea  20  in the area generally above the wellhead  10 . The surface vessel  16 , which in this case is shown to be a ship, is provided with standard equipment needed for operation of a remotely operated vehicle (ROV). 
         [0018]    A submersible ROV  22  is shown deployed within the sea  20 . The ROV  22  is preferably a work class ROV. Suitable ROVs for this application include the TRITON® XLX ROV manufactured by Perry Slingsby Systems of 10642 West Little York, #100, Houston, Tex. 77041. The ROV  22  is interconnected with the surface vessel  16  by a control tether  24 , of a type known in the art. 
         [0019]    As best shown in  FIG. 2 , the ROV  22  includes an upper flotation pack  26 , as is known in the art. A metal support frame  28  depends from the flotation pack  26  and includes a tool sled  30 . Sled extensions  32  are affixed to the tool sled  30 . The tool sled  30  supports a submersible fluid pump  34 . The fluid pump  34  is preferably operably interconnected with the control cable  24  to permit the pump  34  to be selectively actuated from the surface vessel  16 . The fluid pump  34  is preferably fitted with sea water filters, as is known in the art. An exemplary fluid pump  34  is shown in greater detail in  FIGS. 3 and 4 . The pump  34  has a fluid inlet  36  and a fluid outlet  38 . The fluid outlet  38  of the pump  34  is interconnected with a well closure assembly  40  via a fluid conduit  42 , which, in turn, is interconnected with the fluid outlet  38  of the pump  34 . The ROV  22  also includes propulsion thrusters  44  and manipulator arms  46 ,  48 , as are known in the art. 
         [0020]    The well closure assembly  40  includes an inflatable bridge plug  50  and a hydraulic disconnect running tool  52 . The bridge plug  50  is of the type which includes an elastomeric sealing element  54  that is inflatable between and unset, radially reduced condition and a set, radially-enlarged condition via selective injection of fluid. A suitable bridge plug for use in this application is the Thru-Tubing Inflatable Retrievable Bridge Plug, which is available commercially from Baker Oil Tools of Houston, Tex. The running tool  52  is preferably a hydraulically-operated running tool, such as the “hydraulic disconnect” tool, which is also available commercially from Baker Oil Tools. The hydraulic disconnect running tool  52  will automatically release from the bridge plug  50  upon the application of a predetermined level of fluid pressure from the fluid conduit  42 .  FIG. 8  depicts the exemplary well closure tool  40  in side cross-section, and  FIG. 9  illustrates the upper portions of an exemplary well closure assembly  40  to illustrate the manner in which the running tool  52  is releasably interconnected with the fluid conduit  42 . A fitting  53  is used to operably interconnect the fluid conduit  42  with the running tool  52 . The fitting  53  encloses the upper end of the central flowbore  56  within the running tool  52  to permit the flowbore  56  to be filled with fluid. 
         [0021]    The running tool  52  is affixed by a releasable latching assembly, generally shown at  58 , to a reduced diameter neck  60  of the bridge plug  50 . The latching assembly  58  includes an annular piston  62  which is disposed within a piston chamber  64  within the housing  66  of the running tool  52 . The piston  62  is initially affixed by a frangible shear pin  68  to an inner sleeve  70  of the running tool  52 . The latching assembly  58  also includes a plurality of latching collet fingers  72 , of a type known in the art, which extend axially downwardly from the inner sleeve  70  and present inwardly directed latching flanges  74  at their lower ends. The flanges  74  underlie a radially outwardly extending lip  76  on the neck  60  of the bridge plug  50 . This engagement of the flanges  74  and lip  76  secures the running tool  52  to the bridge plug  50 . 
         [0022]    It is noted that a radial fluid passage  78  is formed within the inner sleeve  70  to permit fluid communication between the central flowbore  56  and the piston chamber  64 . As a result, pressurized fluid within the flowbore  56  is communicated into the piston chamber  64  via the passage  78  and brought to bear upon the piston  62 . The running tool  52  may be released from the bridge plug  50  by increasing fluid pressure within the flowbore  56  to a predetermined level that is sufficient to shear the shear pin  68  and shift the piston  62  axially downwardly within the chamber  64 . When the piston  62  is shifted downwardly within the chamber  64 , the collet fingers are freed to deflect radially outwardly and out of overlapping engagement with the lip  76 . 
         [0023]    In operation the ROV  22  is deployed into the sea  20  from the surface vessel  16 . The ROV  22  is guided to the wellhead  10 . Thereafter, the ROV uses manipulator arms  46 ,  48  to remove the well closure assembly  40  from the sled extensions  32 . The well closure assembly  40  is then disposed into the wellbore  14  using the manipulator arms  46 ,  48 , as illustrated in  FIG. 5 . The pump  34  is actuated to flow fluid through the fluid outlet  38  and into conduit  42 . The fluid will pass through the fitting  53 , the hydraulic disconnect tool  52  and into the packer device  50  to inflate the packer element  54 . As the packer element  34  is inflated, a fluid seal is formed between the packer device  50  and the wellbore  14 , thereby closing it off ( FIG. 6 ). As noted, the hydraulic disconnect running tool  52  will automatically release from the bridge plug  50  upon the injection of a predetermined amount of fluid pressure from the pump  34  via fluid conduit  42 . Thereafter, the tool  52  is removed from the wellbore  14  ( FIG. 7 ). The ROV  22  may then be guided back to the surface vessel  16 . 
         [0024]    The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention.
A remotely operated submersible vehicle (ROV) is used to carry a bridge plug down to a sub sea well. The ROV is operated from a surface vessel or platform and is outfitted with a submersible hydraulic pump and a manipulator arm. Additionally, the ROV is provided with a carrying rack which can support a well closure assembly made up of an inflatable bridge plug and an affixed hydraulic running tool. The bridge plug and running tool are placed into the carrying rack and operably interconnected with the hydraulic pump so that the plug element can be selectively inflated by the pump.