Abstract:
A protective covering for subsea well apparatus is provided. The covering is generally a pyramidal structure and includes blades at the corners extending below the base of the structure. The blades are sized to prevent snaring of objects dragged over the covering. The covering may be assembled from sections after transport over a public highway. Methods for transporting and installing the covering and achieving penetration of the blades into the seafloor are also provided.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to subsea drilling and production operations. More particularly, the invention relates to apparatus for mechanically isolating equipment on the seafloor and methods for placing the apparatus on the seafloor and over the equipment to be isolated.  
           [0003]    2. Description of Related Art  
           [0004]    Fish harvesting operations and production of oil and gas co-exist in many offshore areas of the world. If a well is temporarily abandoned in a water-covered area and the depth of the water is such that commercial fishing gear may be affected by the presence of a well apparatus extending above the seafloor, a subsea covering over the well is needed. In the U.S. Gulf of Mexico Outer Continental Shelf Region, according to 30 C.F.R. 250.703(b), when a subsea covering is used to protect a casing stub or other equipment, the subsea covering must allow commercial fishing gear to pass over the covering without causing damage to the covering, the casing stub or other equipment, or the fishing gear. Approval may be required from a government agency to install a subsea protective covering over a well.  
           [0005]    To ensure that a subsea protective covering is effective and does not pose a hazard or conflict with other uses of the outer continental shelf of the United States, operators are required to perform a “trawling test.” In this test a trawling boat pulls a net across the subsea protective covering. The net is dragged over the device a sufficient number of times and in a sufficient number of directions to ensure 100 per cent coverage of all potential device impediments. Impediments may include edges and corners, anchoring equipment, eyelets or other attachments to the subsea protective covering. A description of the trawling operation and the nets that were used is then reported to a government agency within thirty (30) days after completing the trawling test.  
           [0006]    To confirm that the subsea protective covering remains properly installed, a visual inspection or trawl test must be performed at least annually. The test may be waived if the proposed design and installation method for the protective covering have proven to be successful in the past and government agency approval is requested and granted.  
           [0007]    U.S. Pat. No. 5,259,458 discloses a subsea abandoned wellhead protection structure that can be installed by lowering and centering the structure over a wellhead while the structure is attached to drill pipe. Downward-directed jets around the periphery of the base area of the structure allow the seafloor to be excavated around the base by pumping fluid through the structure and out the jets. This arrangement is designed to cause the structure to be embedded in the seafloor. If it is evenly embedded so that none of the base is exposed above the seafloor, then nets or other fishing equipment would not become snared by the structure.  
           [0008]    Although an embedded subsea protective covering should pose no problems, events can prevent proper placement and maintenance of the position of the covering. The seafloor may be uneven. Water currents may cause erosion of the seafloor around the base. If a jetting process is used to place the protective covering, the jetting may produce non-uniform penetration, leaving exposed areas of the base of the structure. What is needed is a subsea protective covering that will not be snared by nets or other commercial equipment passing over the structure even if the covering is not completely or uniformly embedded in the seafloor. There is also a need for a protective covering that may be transported to a well site in sections, so that it can be transported at minimum cost over public highways. 
       
    
    
     DESCRIPTION OF THE FIGURES  
       [0009]    [0009]FIG. 1 shows a partial cutaway side view of a preferred embodiment of the subsea protective covering.  
         [0010]    [0010]FIG. 2 shows a partial cutaway top view of the embodiment shown in FIG. 1.  
         [0011]    [0011]FIG. 3( a ) shows a detail top view of the cap of the protective covering of FIG. 1.  
         [0012]    [0012]FIG. 3( b ) shows a detail side view of the cap of the protective covering of FIG. 1.  
         [0013]    FIGS.  4 ( a ),  4 ( b ) and  4 ( c ) show side, end and top views, respectively, of the protective blade of this invention.  
         [0014]    [0014]FIG. 5 illustrates installation of the subsea protective covering over a subsea wellhead. 
     
    
     SUMMARY OF THE INVENTION  
       [0015]    A protective covering for subsea apparatus is provided that includes blades that extend below the corner support members of the covering. The blades prevent snaring of fishing or other equipment on the corners of the protective covering. The covering may be installed by drill pipe, and a television camera deployed by wireline through the drill pipe may be used to guide the covering to a selected location. A bumper sub in the drill pipe may be used to drive the blades into the seafloor. The covering may also be installed by cable.  
       DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0016]    Referring to FIG. 1, a partial cut-away side view of subsea protective covering  10  is shown. Covering  10  includes skin  12 , which is preferably steel plate. The thickness of the plate is preferably in the range from about {fraction (3/16)}-inch to about ½ inch. Skin  12  is preferably welded to all slanted support members, which include lateral slanted support members  13  and  15  and corner slanted support members  14 . Bottom horizontal members  16  form a base, while intermediate horizontal members  19  may be used to add strength to covering  10 . Lateral slanted support member  15 , positioned where covering  10  may be divided into sections, consists of parts,  15 A and  15 B, which may be flanged together. Skin  12  and bottom horizontal members  16  may also be flanged where they intersect a lateral slanted support member that is flanged and skin  12  may be attached at each flange, such that protective covering  10  can be assembled in a plurality of sections. Cap  18  is preferably attached to all slanted support members. Cap  18  may include an attachment point for placing protective covering  10  on the seafloor. Blade assembly  20  is preferably attached to base  16  and corner slanted support members  14  at each corner. Blade assembly  20  and cap  18  will be described in more detail below.  
         [0017]    The overall height of covering  10  is selected to cover a casing stub or mudline suspension or any other equipment that is to be mechanically protected. The dimensions of covering  10  may be in the range of about 14 to 20 feet square at the base with a height usually in the range from about 7 feet to 10 feet. A height in the lower part of this range may be needed for covering a stub of 30-inch casing extending above the seafloor, for example. An anode for corrosion protection may be attached if the covering is to be left subsea for an extended time.  
         [0018]    [0018]FIG. 2 illustrates a partial cutaway top view of subsea protective covering  10 . Lateral slanted support members  15 A and  15 B are bolted together and may be separated for transport of covering  10 . This is a great advantage when covering  10  is to be transported by highway to a dock for deployment subsea. The maximum width without escort along a public highway can sometimes be achieved by separating the covering. The maximum width with escort can be used to allow a greater spread distance of a covering by separating it and re-assembling it at the dock.  
         [0019]    Although four corners are shown in the drawings herein, each corner forming a 90-degree angle in a horizontal plane, it should be understood that any structure having a polygonal base and sides which form the bases of triangular surfaces meeting at a common vertex may be used. The number of base corners may vary from three to ten or more. Lateral slanted support members may or may not be used, but a corner slanted support member will normally be present at each corner.  
         [0020]    [0020]FIG. 3( a ) illustrates a top view and FIG. 3( b ) illustrates a cross-section view of cap  18 . Drill pipe connector  30  is joined to top plate  34  by cap support members  32  and  36 . Lateral slanted support members  15  are welded to top plate  34 . Connector  30  is preferably adapted to receive drill pipe or other pipe to be used for deploying covering  10  on the seafloor. Alternatively, connector  30  is a hook or other means for lowering covering  10  to the seafloor by cable.  
         [0021]    FIGS.  4 ( a ),  4 ( b ) and  4 ( c ) illustrate details of blade assembly  20 . Blade  40  is attached to blade support  42 . Support  42  is adapted to attach to bottom horizontal support members  16  and corner slanted support members  14  (FIG. 1) as an extension in the direction of support members  14 . Blade  40  may be directly attached to corner slanted member  14  or bottom horizontal member  16  at the corners of covering  10  by welding or may be attached through support  42  and bolts (not shown) placed through bolt holes  48 . The extension of skin  12  and corner slanted support members  14  by blade  40  prevents snaring of a net or other object that is dragged over covering  10 . Alternatively, blade  40  may be at a slope angle different from the slope angle of corner support  14  and still achieve the purpose of preventing snaring on the covering. For example, blade  40  may be at a slope angle that is about 30 degrees less than the slope angle of corner support  14 . (Vertical is zero slope angle.) Also, blade  40  may be at a greater slope angle than corner support  14 . Blade  40  may have sloping surfaces  50  positioned at the bottom to allow easier penetration of the blade into the seafloor. Blade  40  may be formed from steel plate and may have a thickness in the range of about 0.5 inch to about 1 inch and a length along the top edge in the range from about 1 foot to about 3 feet, for example. Blade  40  should have enough length to insure that an object will not snare under a corner of the covering even if the seafloor is uneven or there are variations in hardness of the seafloor at different areas under bottom horizontal members  16  of covering  10  that cause blades at different corners to penetrate different distances into the seafloor. Blade  40  is preferably rounded such that a net would be less likely to hang if contacting the end of the blade.  
         [0022]    [0022]FIG. 5 illustrates a method for installing protective covering  10  on seafloor  62  over protrusion  64  of a subsea well. Protrusion  64  may be casing, a wellhead, mudline suspension or any other equipment. Normally, protrusion  64  will be a stub of 30-inch diameter casing. Preferably, the casing will contain corrosion cap  65 , which has previously been set in the casing by well known techniques. Corrosion cap  65  may have stripes or other pattern painted on the upper surface so that it can be more easily seen with television camera  68 . Drill pipe  60 , deployed from rig  55 , may be used to lower covering  10  to the seafloor. Bumper sub  66  may be present in drill pipe  60  to assist in driving blades of blade assemblies  20  into seafloor  62 . Covering  10  may be located over protrusion  64  by television camera  68  that may be run through drill pipe  60  on wireline  70 . Wireline  70  is deployed from a reel located on rig  55 . After covering  10  is positioned and lowered over protrusion  64  to seafloor  62 , bumper sub  66  may be operated to drive blade  40  of blade assembly  20  into the seafloor. Drill pipe  60  is then released from covering  10  and retrieved.  
         [0023]    While particular preferred embodiments of the present invention have been described, it is not intended that these details should be regarded as limitations upon the present invention, except as and to the extent they are included in the following claims.