Internal drilling riser centralizer

Abstract

The method of centralizing a rotating string within the bore of a subsea blowout preventer stack and a drilling riser comprising providing a multiplicity of rollers having a first position and a second position, when the rollers are in the first position the rollers defining a first circle which is proximately the size of the bore of the drilling riser, when the rollers are in the second position the rollers defining a second circle which is smaller than the first circle, and when the rollers are in the second position the rollers prevent the rotating string from contacting the bore of the subsea blowout preventer stack or the drilling riser proximate the rollers.

Description

TECHNICAL FIELD

This invention relates to the general subject of centralizing the rotating pipe within a deepwater drilling riser to prevent key seating damage.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable

REFERENCE TO A “MICROFICHE APPENDIX”

Not applicable

BACKGROUND OF THE INVENTION

The field of this invention is that of offshore floating drilling systems for drilling oil and gas wells in offshore waters. These have a blowout preventer stack landed on a wellhead on the ocean floor with a drilling riser attached to the top and continuing up to a vessel floating at the ocean surface.

At the connection of the riser to the top of the blowout preventer stack there is typically a flex joint to keep the riser from being overstressed due to surface vessel movement, side forces from currents, or when the riser is allowed to be momentarily slack. An example of this type flex joint is seen in U.S. Pat. No. 5,951,061. This flex joint often represents a dog leg in the alignment of the bore of the blowout preventer stack and the bore of the drilling riser.

Within the bore of the drilling riser and the blowout preventer stack, a drill string is run in order to drill the oil or gas well. Typically the drill string is rotated during drilling, and often has hard facing on the coupling to prevent wear on them. When the drill string is rotated and is centrally located within the bore, there is no effect on the bore. However, when the riser is deflected, the drill string can be deflected to contact the bore of the drilling riser or the blowout prevent stack.

When the drill string is deflected to contact the bore of the drilling riser or blowout preventer stack, wear can be concentrated at the point of contact. Hard facing on the tool joints can make them act like a cutting tool to exacerbate the damage to the bore. In the worst case, a notch can be caused which is called a key seat.

A key seat in the bore of the drilling riser or blowout preventer stack can literally wear all the way through the metal. It will typically occur above the blowout preventer rams and so will not cause a blowout. Unfortunately a hole to the seawater will cause substantial pollution of the drilling mud into the seawater and loss of drilling mud pressure to control the pressure in the well. This loss of drill mud pressure will allow oil and gas to enter the well and require that the well be closed in or a blowout will occur.

This has been a common concern throughout the history of floating drilling since the early days in the 1960s until now, with the only solution being to closely monitor the position of the vessel to prevent this misalignment. In some cases such as drilling in the water off the coast of Alaska tidal movement of the vessels in relatively shallow water cause substantial deflection. This inflicts substantial wear on the drilling components which simply must be withstood.

BRIEF SUMMARY OF THE INVENTION

The object of this invention is to provide a method to centralize an rotating drill string within the bore of a drilling riser and blowout preventer stack to prevent wear damage or key seating to the bore of the drilling riser or blowout preventer stack.

A second object of this invention is to provide a method to centralize an oscillating drill string within the bore of a drilling riser and blowout preventer stack to prevent wear damage or key seating to the bore of the drilling riser or blowout preventer stack.

A third object of this invention is to provide a method of removing the centralizing equipment from the bore so that equipment which is nearly the diameter of the full bore are able to pass by the centralizing equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a subsea blowout preventer stack connected to a semi-submersible drilling facility at surface of the water by a drilling riser.

FIG. 2 is a cross section of the drilling riser taken along lines “2-2” of FIG. 1.

FIG. 3 is a cross section of a centralizer of the present invention having the centralizing rollers in a retracted position.

FIG. 4 is a cross section of a centralizer of the present invention having the centralizing rollers in an extended position.

FIG. 5 is a cross section of a centralizer of the present invention taken along lines “5-5” of FIG. 3 having the centralizing rollers in a retracted position.

FIG. 6 is a cross section of a centralizer of the present invention taken along lines “6-6” of FIG. 4 having the centralizing rollers in a retracted position.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a blowout preventer stack 10 is landed on a subsea wellhead system 12 on the ocean floor 14. Drilling riser 16 extends to a drilling vessel 18 at the surface 20 of the ocean 22. At the connection of the drilling riser to the top of the blowout preventer stack is a flex joint 24 which is similar to a rubber ball joint.

Referring now to FIG. 2, riser pipe 16 is shown with an internal steel pipe 30, auxiliary pipes 32 and 34, and flotation material 36. Rotating internal pipe 38 is shown wearing a notch or keyseat 40 in the internal steel pipe 30. If the keyseat 40 wears all the way through the wall of steel pipe 30, the drilling mud 42 will leak into the ocean 22.

Referring now to FIG. 3, the section of drilling riser 16 shown comprises an upper riser joint 50, a drilling riser centralizer 52 and a lower riser joint 54. There is an upper bolted connection 56 between upper riser joint 50 and drilling riser centralizer 52 and a lower bolted connection between drilling riser centralizer 52 and lower riser joint 54. One of the auxiliary lines 32 is shown. The auxiliary lines can be used to supply hydraulic fluid to the blowout preventer stack, to take high pressure flow to the surface for going through chokes (a choke line), or for pumping heavy weight mud down to kill the well (a kill line). A multiplicity of rollers 56 are mounted on appropriate yokes 58, which are in turn mounted on pistons 60. As shown in this view, the rollers, yokes, and pistons are in the position of being retracted out of the bore such that equipment close to the full diameter of the internal bore of the riser can pass down to the blowout preventer stack.

Referring now to FIG. 4, the multiplicity of rollers 56, yokes 58, and pistons 60 are moved into the bore to form a circle smaller than bore of the internal steel pipe 30. In this way, any rotating pipe 62 which is passed through the bore of the drilling riser 16 will be kept from damaging the internal bore 70 of the internal steel pipe 30.

Referring now to FIG. 5, a cross section of the drilling riser centralizer 52 is shown with the rollers 56 retracted and rotating pipe 62 is shown contacting the wall 70 of the drilling riser centralizer.

Referring now to FIG. 6, a cross section of the drilling riser centralizer 52 is shown with the rollers extended and rotating pipe 62 is shown contacting rollers 56 and not contacting the internal bore 70 of the drilling riser centralizer.

In this way the internal bore 72 of the drilling riser centralizer 52 and similarly the bore 70 of the internal steel pipe 30 are protected from damage by the rotating pipe 62.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.

Claims

1. The method of centralizing a rotating string within the bore of a subsea blowout preventer stack and a drilling riser comprising:

providing a multiplicity of guides having a first position and a second position,

when said guides are in said first position said guides defining a first boundary which is proximately the size of the bore of the drilling riser,

when said guides are in said second position said guides defining a second boundary which is smaller than said first boundary, and

when said guides are in said second position said guides prevent said rotating string from contacting the bore of said subsea blowout preventer stack or said drilling riser proximate said guides.

2. The method of claim 1 further comprising said guides are moved between said first position and said second position by hydraulic cylinders.

3. The method of claim 2 further comprising said guides are rollers.

4. The method of claim 1 further comprising said guides are rollers.

5. The method of claim 1 further comprising said second boundary is proximately a circle.

6. The method of claim 5 further comprising said guides are rollers.

7. The method of claim 6 further comprising said guides are moved between said first position and said second position by hydraulic cylinders.

8. The method of claim 1 further comprising said guides are rollers.

9. In a subsea drilling system comprising a rotating or translating drilling string of pipe, a subsea blowout preventer stack, and a drilling riser extending to a floating vessel on the surface of the sea, and a flexible joint between said subsea blowout preventer stack and said drilling riser, said subsea blowout preventer stack having a minimum bore size and said drilling riser having a minimum bore size, and said flexible joint allowing said drilling riser bore to not be angularly aligned with said blowout preventer bore such that said rotating or translating drilling string of pipe can wear or “keyseat” the internal area of said subsea blowout preventer stack, said flexible joint, or said drilling riser, the method of preventing said wear or “keyseating” comprising providing a multiplicity of guides having a first position and a second position,

when said guides are in said first position said guides defining a first boundary which is proximately the size of the bore of the drilling riser,

when said guides are in said second position said guides defining a second boundary which is smaller than said first boundary, and

when said guides are in said second position said guides prevent said rotating string from contacting the bore of said subsea blowout preventer stack or said drilling riser proximate said guides.

10. The method of claim 9 further comprising said guides are moved between said first position and said second position by hydraulic cylinders.

11. The method of claim 10 further comprising said guides are rollers.

12. The method of claim 9 further comprising said guides are rollers.

13. The method of claim 9 further comprising said second boundary is proximately a circle.

14. The method of claim 13 further comprising said guides are rollers.

15. The method of claim 14 further comprising said guides are moved between said first position and said second position by hydraulic cylinders.

16. The method of claim 9 further comprising said guides are rollers.