NO347831B1 - Slick joint and method for assembling a slick joint - Google Patents

Description

The invention relates to a slick joint for subsea operations, comprising a central pipe and an outer pipe defining therebetween an annular space, and a number of small-bore pipes disposed within the annular space and extending along the central pipe.

It also relates to a method for assembling the slick joint of the invention.

When developing a subsea hydrocarbon reserve, it is necessary to use a blowout preventer (BOP) to keep control of the well during drilling and workover operations. The BOP sits on top of the wellhead or, depending on the operations, a Christmas tree. It has a number of shear rams and pipe rams designed to shear and close around a pipe that runs through the BOP. BOP’s can exist in many different configurations with various number of rams (pipe rams and shear rams) depending upon functionality and the type of operations.

During workover or completion operations a special pipe called a slick joint or shear joint is used. This joint is designed to sit in the BOP during operations and is specially made to enable shearing off the pipe and isolating the well. Depending upon the type of BOP this joint may be up to ten meters long.

At present, the slick joint has to be custom made of several parts. The main reason is that hydraulic lines have to be incorporated into the slick joint to supply hydraulic fluid to a tool below the slick joint. For this, longitudinal holes are drilled in the wall of the pipe. However, since the length of such holes are limited due to the practical issue of drilling long smallbore holes, each part cannot be longer than about two meters. Because each part of the joint is connected up using flanges, the slick joint also needs to fit the type of BOP it is designed to work with. Therefore, each part must be designed to sit in a specific segment of the BOP to ensure safe operations. For example, a part of the slick joint may have to be designed to be more easily cut off and located in the slick joint such that this part sits where the shear ram is located.

This has a number of disadvantages, not the least the cost of having to custom make each slick joint to fit the various manufacturers BOP. When doing operations, the service provider has to find out the type of BOP and design the slick joint to fit this particular BOP.

During completion of the well, a tubing hanger running tool is run on a drill pipe through a marine riser to the well. To provide hydraulic power for the operation of the running tool an umbilical containing hydraulic conduits and electric cables is attached to the drillpipe with clamps. The umbilical hydraulic lines are then extended through the BOP through the longitudinal bores in the slick joint (as described above) to the tubing hanger installation tool.

The invention aims to solve these problems by creating a universal landing string that can be sheared and sealed over the full length without the need to add interconnecting flanges along without any length limitation making the shear/slick joint independent of the BOP space out dimensions. This enables BOP flexibility and reduces the need for custom space out joint landing strings. This will reduce cost and delivery time for each operation.

To achieve these aims, the invention proposes a multi-pipe arrangement consisting of inner and outer pipes with hydraulic tubing and electrical cables arranged in the annular space between them.

Such multi-pipe arrangements are generally known. In for example AU 3173471 there is described a flexible underwater line that has a central pipe surrounded by a plurality of smaller conduits laid in a helical configuration about the central pipe. The line includes a group of spokes disposed at spaced intervals along its length to prevent the conduits rubbing each other. A suitable cover, for example a plastic sheet, is placed around the conduits. The annular space between the central pipe and the lining can be filled with a polymer resin. The flexible underwater line includes buoys and is especially designed to be used as a riser or underwater flowline.

WO 0006933 describes a tubular system made up of a tubular with members disposed in grooves in the tubular. The members may be used for maintaining the structural strength of the liner or for carrying electrical current or signals, fiberoptic signals, or data communications; for heating the liner; and/or for detecting faults.

GB 2368861 describes a ported slick joint. This includes a tubular section having a central passageway that may be used to communicate well fluids. The wall of the tubular section includes longitudinal ports that establishes fluid communication between the top and bottom of the slick joint.

US 8869903 describes a slick joint for subsurface operations that has a central pipe and an outer pipe defining an annular space between them. A control line

can be disposed within the annular space, extending along the central pipe.

None of these multi-pipe solutions address the problems that can arise when forces act on the pipe. Such forces may result because of different expansions of the inner and outer pipes due to different temperature or forces. For example, in a slick joint weight caused by raising and lowering the installation tools may result in elongation of the inner pipe with up to 10 mm. This will put a strain on the outer pipe since they are bonded together. They are therefore not suitable for use as a slick joint.

The invention proposes to remedy these deficiencies by providing a multi-pipe slick joint for use with a tubing hanger running tool. This is achieved by providing a first flange arranged at one end, said flange having bores providing a seal-through passage of the small-bore pipes, a second flange connected to the first flange, and that a first end of the outer pipe is attached to the second flange, the outer pipe extending only a part of the length of the slick joint and is unattached at its second end.

In one aspect of the invention the small bore-pipes carries hydraulic fluid.

In another aspect of the invention the small bore-pipes include electrical cables.

In the method for assembling a slick joint according to the invention, it comprises the steps of

Providing a central pipe,

- Welding a first end to the central pipe, said first end comprising a flange having through-bores,

- Placing a number of small-bore pipes around the central pipe, where each smallbore pipe terminates in the bore of the flange,

- Providing an outer pipe having a second flange at one end,

- Sliding the outer pipe onto the central pipe,

- Securing the second flange to the first flange, and

- Welding a second end to the central pipe.

The invention will now be described in more detail with reference to the enclosed drawings where

Fig.1 shows the operation of a tubing hanger running tool,

Fig.2 shows the pipe according to the invention,

Fig.3 is a section through the pipe in Fig.2,

Fig.4 is a drawing of a detail in Fig.2,

Fig.5 is a section drawing similar to Fig.3, showing an alternative embodiment, and

Fig.6 is a drawing of a detail of Fig.5.

In Fig.1 there is shown a tubing hanger operation with the use of the pipe in the present invention. A marine riser 1 is suspended from a drilling rig and at its end have a flex joint 2 connected to a BOP 5. The BOP sits on top of the wellhead 11. The BOP includes a number of rams as is well known in the art. A tubing hanger running tool is shown having been lowered from the drilling rig suspended on a drill pipe 4. The running tool includes a tubing hanger 10 attached to a tubing hanger running tool 9 and a tubing hanger orientation joint 8. An umbilical 7 clamped to the drillpipe includes a number of hydraulic and electric lines for the supply of hydraulic fluid and for communications for operation of the installation tool.

A slick joint 10 is located between the tubing hanger running tool 8, 9 and the drillpipe 4 and is designed to be connected to the drill pipe at its upper end and the tubing hanger installation tool at its lower end so that it is located within the BOP during the installation operation.

The slick joint 10 according to the invention is further shown in Fig.2. The slick joint consists of a central thick-walled pipe 20. It has an upper part 12 welded (at 16) to the central part and has a connector 15 for connecting to the drillpipe. It has a lower part 13 welded (at 44) to the central pipe 20 and has a connector 14 for connecting to the running tool. The lower part 13 includes a flange 22. The flange comprises a number of through bores 23. The bores can be fitted with seals that seals around the pipes when the joint is assembled.

A second flange 30 is attached to the flange 22 by bolts 24. Between the flange and the central pipe there is formed a space 38 that can be filled with a resin or similar filler. The resin is introduced into the space through a port 39.

The central pipe 20 is surrounded at least partway along its length by an outer sleeve 21. The outer sleeve 21 is preferably an extruded pipe with a very slick surface that can be easily sealed by the pipe ram in the BOP. The space between the pipes 20 and 21 is preferably sealed with a filler. The sleeve is at one end welded (at 44) to the second flange 30 but is at its other end unattached. In this way the sleeve is free to move in relation to the inner pipe. When a force is applied to the joint, as for example during lifting or lowering of the joint, the inner pipe can be stretched more than the sleeve. Such force can result in breaking of the sleeve because it is much thinner than the inner pipe. It is therefore important that the sleeve is able to move in relation to the inner pipe.

A number of pipes 42 are arranged along the length of the slick joint between the central pipe and the outer sleeve. The pipes are at one end designed to connect with a corresponding hydraulic line in the running tool and at the other end to lines in the umbilical.

In a preferred embodiment shown in Fig.3, grooves 41 are milled in the outer surface of the inner pipe 20. The pipes 42 are located in the grooves. After installation the grooves can be filled with a polymer.

In an alternative embodiment shown in Fig.5 and 6 pipes 52 are arranged in the annular space between the central pipe 20 and the outer sleeve 21. The annular space is preferably filled with a polymer resin 53. At intervals there is placed a number of structural spacers 54 to keep the pipes in position.

It should also be noted that in addition to the use for conveying hydraulic fluid the ipes can also accommodate cables for electric power and for communication.

In the manufacturing of the slick joint there is first provided a thick-walled pipe that will be the inner pipe 20. The lower part 13 with the flange 22 is then welded to the central pipe 20. Longitudinal groves 41 are milled on the outer surface of the pipe and then small-bore hydraulic piping 42 is placed in the grooves. The pipes are made to enter the bores 23 and secured. Next, the outer sleeve 21 is welded or otherwise attached to the second flange 30. This assembly is slid onto the central pipe. The two flanges can now be bolted together.

The filling port 39 is used to vacuum the air from the space 38 as well as to inject polymer resin filling the space. The annular space between the central pipe and the sleeve is also preferably filled with a resin.

There can now be performed a pressure test to ensure that the seal between the pipes 42 and the bores 23 is tight.

At last, the drill pipe thread connector 12 is welded to the central pipe 20.

This method enables a slick joint to be built without length limitation.

The manufacture of the joint according to the second embodiment is largely similar, the main difference being that spacers 54 must be put around the central pipe to hold the smaller pipes before the outer sleeve is installed.

The slick joint has been shown with a traditional umbilical attached to the drillpipe.

However, it will be more useful in combination with the applicants tubing hanger control system as disclosed in a co-pending application no. This eliminates the need for an umbilical from the surface, resulting in a large saving of costs.

Claims (10)

1. A slick joint for subsea operations, comprising a central pipe (20) and an outer pipe (21) defining therebetween an annular space, and a number of small-bore pipes (42; 52) disposed within the annular space and extending along the central pipe, characterized in that it comprises a first flange (22) arranged at one end, said flange having bores (23) providing a seal-through passage of the small-bore pipes (42; 52), a second flange (30) connected to the first flange, and that a first end of the outer pipe (21) is attached to the second flange (30), the outer pipe (21) extending only a part of the length of the slick joint and is unattached at its second end.

2. A slick joint according to claim 1, characterized in that the small-bore pipes (42) are disposed in grooves (41) milled in the surface of the central pipe (20).

3. A slick joint according to claim 1 , characterized in that the small-bore pipes carry hydraulic fluid.

4. A slick joint according to claim 1 , characterized in that the small-bore pipes carry electrical and communication cables.

5. A slick joint according to claim 1, characterized in that the annular space is filled with a polymer resin.

6. A slick joint according to claim 1, characterized in that the second flange (30) comprises a port (39).

7. A method for assembling a slick joint according to claims 1 – 6, characterized by the following steps:

- Providing a central pipe (20),

- Welding a first end (13) to the central pipe, said first end comprising a flange (22) having through-bores (23),

- Placing a number of small-bore pipes (42; 52) around the central pipe, where each small-bore pipe terminates in the bore (23) of the flange,

- Providing an outer pipe (21) having a second flange (30) at one end,

- Sliding the outer pipe (21) onto the central pipe (20),

- Securing the second flange (30) to the first flange (22), and

- Welding a second end (12) to the central pipe.

8. Method according to claim 7 where the small-bore pipes carry hydraulic fluid.

9. Method according to claim 8 where the small.bore pipes supply hydraulic fluid to a function in a tubing hanger installation tool.

10. Method according to claim 7 where the small-bore pipes carry electrical and communication cables.