Subsea protective covering

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] FIG. 1 shows a partial cutaway side view of a preferred embodiment of the subsea protective covering.

[0010] FIG. 2 shows a partial cutaway top view of the embodiment shown in FIG. 1.

[0011] FIG. 3(a) shows a detail top view of the cap of the protective covering of FIG. 1.

[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] 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, 15A and 15B, 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] FIG. 2 illustrates a partial cutaway top view of subsea protective covering 10. Lateral slanted support members 15A and 15B 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] 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] 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.

Claims

1. A protective covering for equipment protruding from a subsea location, comprising:

a skin, the skin being attached to a plurality of slanted support members, the slanted support members including a plurality of lateral slanted support members and a plurality of corner slanted support members, the corner slanted support members being disposed at a selected angle of slope and being attached to a plurality of bottom horizontal support members;

a cap, the cap being attached to a selected number of the plurality of slanted support members and having an attachment point for lowering the protective covering to a selected seafloor location; and

a plurality of blades, the blades being affixed to the corner slanted support members and being disposed at a selected angle of slope.

2. The protective covering of claim 1 wherein the number of corner slanted support members is four.

3. The protective covering of claim 1 wherein the attachment point of the cap is adapted to attach to a drill pipe.

4. The protective covering of claim 1 wherein the selected angle of slope of the blades is approximately the angle of slope of the corner slanted support members.

5. The protective covering of claim 1 wherein the blades include sloping surfaces disposed so as to improve penetration of the blades into a seafloor.

6. The protective covering of claim 1 wherein a selected number of the plurality of lateral support members and bottom horizontal support members are joined such that they may be divided and re-joined by a joining apparatus.

7. The protective covering of claim 6 wherein the joining apparatus is a flange.

8. A method for installing a protective covering having a plurality of corner slanted support members over equipment protruding from a seafloor location, comprising:

attaching a plurality of blades to the protective covering, the blades extending below the plurality of corner slanted support members;

attaching the protective covering to a drill pipe operated from a rig;

lowering the drill pipe and protective covering; and

guiding the protective covering over the equipment protruding from the seafloor location and landing the protective covering on the seafloor location.

9. The method of claim 8 wherein the step of guiding the protective covering over the equipment protruding from the seafloor location includes placing a television camera through the drill pipe and observing the equipment protruding from the seafloor location while the drill pipe and protective covering are lowered.

10. The method of claim 9 further comprising the step of placing a pattern on the equipment protruding from the seafloor location for observation with the television camera before the step of guiding the protective covering over the equipment protruding from the seafloor location.

11. The method of claim 8 further comprising the step of operating a bumper sub after the after the step of landing the protective covering on the seafloor location.

12. A method for installing a protective covering having a plurality of corner slanted support members over equipment protruding from a seafloor location, comprising:

attaching a plurality of blades to the protective covering, the blades extending below the plurality of corner slanted support members;

attaching the protective covering to a cable operated above the seafloor location;

lowering the cable and protective covering; and guiding the protective covering over the equipment protruding from the seafloor location and landing the protective covering on the seafloor location.

13. A method for transporting a protective covering for equipment protruding from a seafloor location, the protective covering comprising a skin, a plurality of slanted support members including a plurality of lateral slanted support members and a plurality of corner slanted support members, at least two contiguous lateral slanted support members being joined such that they may be divided at a plane and re-joined by a joining apparatus, the corner slanted support members being disposed at a selected angle of slope and being attached to a plurality of bottom horizontal support members, at least two contiguous bottom horizontal support members being joined such that they may be divided at the plane and re-joined by a joining apparatus, a cap and a plurality of blades, comprising:

dividing at least two contiguous lateral slanted support members and two bottom horizontal support members at the plane and transporting the protective covering to a selected location;

re-joining the contiguous lateral slanted support members and the contiguous bottom horizontal support members at the plane;

attaching the skin and the cap to a plurality of slanted support members; and

attaching the blades.