CN1119498C - Device related to resers - Google Patents

Abstract

A riser (2) for conveying liquid between a member (7) on the seabed and a second member at or near the sea surface, comprising: a vertically extending upper part (2a), the upper part of which the upper end is connected to the member located on the sea surface; the middle part (2b) of a riser (2) is connected to one or more buoyancy elements on at least a part of its length direction; and a lower part (2c) has a connecting To the lower end on the subsea structure (1), one or more counterweight elements (3) are mounted on the lower part (2c) of the riser (2).

Description

Riser

technical field

The invention relates to a riser for conveying liquid between a first member on the seabed and a second member on the sea surface, comprising an upper portion extending approximately vertically and connected at its upper end to the surface member, a An intermediate portion of the riser connecting at least a portion of one or more buoyancy elements, and a lower portion the lower end of which is connected to the subsea structure.

Background technique

Many different types of risers are known for conveying liquids from the seabed to the surface. Common configurations are types such as "Lazy S" and "Steep S", both of which have risers extending to the seafloor through an intermediate region. In the middle portion, the riser is connected to one or more buoyancy elements which lift the corresponding portion of the riser and form a downwardly concave curved surface.

From the above-mentioned intermediate region, in the "Lazy S" configuration, the riser extends in a gentle curve to the seafloor, and in the "Steep S" configuration, the riser extends in a straighter line to an anchor on the seafloor, which also includes A coupler for use on a pipeline extending between the anchor and the subsea structure.

A disadvantage about the "Lazy S" construction is that it requires more space, making it a danger of the risers coming close to each other and being damaged. This makes it difficult to use in larger constructions with many risers and great depths.

The solution of anchoring "Steep S" provides good control of the vertical and horizontal movement of the riser, however, in the way of anchoring to the seabed, the coupling connection is more complicated and special equipment is required in order to complete the connection . Also, if the anchors are broken, the riser will float to the surface, making it fundamentally unstable.

A solution between these two options is shown in US4906137. In this case, anchors are fixed to the lower part of the riser in order to obtain a stretchable section between the buoyancy elements coupled to the middle part and the sea bottom, so that the riser obtains a fairly clear as in the "Steep S" scheme And compact improvements. The anchors are connected to the riser so that the riser has a smooth curved transition channel from vertical to horizontal with a predetermined curvature. The riser can extend further towards the subsea structure or be connected in a conventional manner to a pipeline on the subsea. Due to the anchors, this technical solution is also susceptible to damage if something goes wrong with the subsea component or the anchor. Also the coupling points between the anchors on the riser are susceptible to tensile and bending stresses and can be damaged due to large movements at the top of the riser caused by the vessel or platform.

The disadvantage of the above-mentioned US patent is that it has little flexibility with respect to large movements on the riser. And it requires a relatively complicated operation to connect the anchor to the riser on the seabed.

Contents of the invention

The invention relates to a simple solution to obtain a riser similar to the "Steep S" configuration, since during the riser installation the counterweight elements fixed to the riser can be installed in the assembly vessel at sea , so no complicated operations are required to connect the riser to the seabed.

Attaching the weight element to a suitably preloaded anchor is also simpler than the prior art described in the above US patent, since the anchor chain can be installed in a slack condition, thus simplifying the attachment operation.

The present invention provides a riser for conveying fluid between a member on the seafloor and a second member at or near the surface, the riser comprising a vertically extending upper part, the upper end of which is connected to On a structure located on the surface of the sea, an intermediate portion of a riser to which one or more buoyancy elements are connected over at least a portion of its length, a lower part having a lower end connected to the seabed structure, characterized in that there is also a One or more counterweight elements are mounted on the lower part of the riser.

The result is a technical solution that is as flexible as the "Lazy S" construction and at the same time almost as compact as the "Steep S".

Description of drawings

The invention will be described in more detail below with reference to the accompanying drawings, which show possible embodiments of the invention.

Figure 1a shows the complete riser configuration.

Figure 1b shows another configuration relevant to the present invention.

Figures 2a and 2b show details of the construction shown in Figure 1b above.

Figure 3 shows a detail of the lower part of the riser with counterweight elements.

Figure 4 is a cross-sectional view showing two weight elements mounted on the riser.

Detailed ways

In Fig. 1a, a floating platform 1 is shown. A riser 2 is connected to the platform by means of a coupling mounted to a mounting deck. The platform itself is not essential to the invention, but the upper part of the riser may of course be coupled to other components, such as a vessel, in particular a submersible turret loading vessel or extraction vessel.

In the figure, the upper part 2a of the riser hangs substantially vertically. The middle part 2b has, in a known manner, a number of buoyancy elements 8 provided on the middle part for bending the riser on this part.

The riser also includes a lower portion 2c below the buoyancy elements. The lower part 2c extends at least down to the sea bottom, preferably along the sea bottom. A number of counterweight elements 3 are arranged on the lower part in order to balance the buoyancy forces generated by the buoyancy elements, which at the same time act to limit the vertical movement of the riser. Preferably at least one of the counterweight elements is located on the seabed, which has the effect of limiting horizontal movement normal to the risers, whereby the risk of collisions between the risers is reduced. As the rise of the riser lifts the counterweight element from the sea floor, this increases the weight of the floating portion of the riser, which in turn pulls the riser down, which also acts to stabilize the vertical position of the riser in the water .

A particular embodiment of the present invention is shown in Figure 1b, wherein one or more weight elements 3b lifted from the seabed are connected to a buoy 12 by first anchor chains or the like, which is further passed by a second An anchor chain or similar 13 is connected to an anchor 14 to be anchored to the seabed. This gives an additional anchoring of the upper part of the weight element, which resists horizontal movement of the riser and at the same time reduces the possibility of changes in the curvature of the lower part 2c of the riser. When the upper part of the riser is pulled in the same direction as the bending of the lower part 2c, eg due to drifting of the platform 1, then said radius of curvature is generally reduced. Said anchoring generally inhibits the above-mentioned reduction in the radius of curvature, since the anchor chain laid on the seabed is pulled upwards from the seafloor, and the anchor chain is fixed on the counterweight element, which helps to gradually increase the vertical resistance in the horizontal direction. The force to move the tube. This, together with the stiffness of the weight elements, helps to avoid reducing the radius of curvature of the lower portion of the riser below a critical limit.

The additional anchoring 11 , 12 , 13 , 14 is particularly advantageous when the surface component is arranged directly above the subsea component, such as where a drilling pipe 15 extends from the platform 1 to the wellhead 7 , as shown in FIG. 1 b . If no anchors are attached, a surge in the direction inwards or outwards on the drawing bends the riser in either an inward or outward direction on the paper. The above-mentioned bending may damage the riser as a result of bending of the riser beyond the critical limit of the riser and collision of the risers arranged in the same area. The aforementioned anchoring systems 11 , 12 , 13 , 14 provided on the protruding side of the lower portion of the standpipe 2c can reduce the aforementioned buckling to an acceptable level.

In order to maintain the balance of the construction of the buoyancy elements and the counterweight elements 3 , 8 , the buoyancy of the buoyant body 12 is adapted so that the first anchor chain 11 acts only on a horizontal force on the counterweight element 3 . In this way the buoyant body 12 and its corresponding anchor chains 11, 13, 14 etc. can be arranged separately on the seabed and connected thereto without affecting the balancing effect while improving the external equilibrium state characteristics. The buoy can be anchored at a selected location and the first anchor chain can then be connected to one of the counterweight elements with an ROV (Remotely Operated Vehicle). If the anchor fails, the riser will also maintain substantially the same vertical position. In the same manner as corresponding to known anchoring systems for surface vessels, the buoyant body provides a softer anchor than direct anchoring to the sea bottom, thus allowing more flotsam to be assembled on the surface before the riser is damaged, And when the first anchor chain 11 is connected to the counterweight element 3, the weight lifted by the ROV is simultaneously limited.

Figures 2a and 2b show the anchoring components shown in Figure 1b above, where Figure 2a shows the use of the buoy 12 connected to the riser 2, while Figure 2b correspondingly shows the connection via the connected anchor chains 11, 13 How to use the two floats to riser 2. The technical solution shown in Fig. 2 improves the stability of horizontal movement.

The detailed illustration in FIG. 3 illustrates the lower part of the riser with weight elements 3 , one of which 3 b comprises fixings for connecting the anchors 11 , 12 , 13 , 14 . In addition to the anchored weight element 3b, the figures also show a weight element 3a of decreasing size that provides the transition between the riser and the weight element. The weight elements can be arranged identically for the weight elements laying on the sea bottom at the bottom.

Figure 3 shows how the weight elements are mounted on the riser to maintain flexibility, since the weight elements are placed along the riser with a spacer 10 between the weight elements to give them some spacing.

Preferably there is only one weight element, and preferably the lowermost one is fixed to the riser, while the others are only fixed to each other, so as to allow relatively free movement of the weight element in the longitudinal direction. This way the riser is not subject to any additional pull when the curvature changes.

To avoid large curvatures on the riser due to bending, the weight elements and intermediate spacer parts have a smooth stiffness. This stiffness decreases towards its ends so as to gradually transition to the stiffness of the riser.

To avoid the curvature exceeding a certain limit, the radial extension of the weight elements 3 can be greater than the distance between the weight elements 3 . The relationship between the radii of the weight elements and the spacing between them is chosen such that the weight elements contact each other when the riser is at a certain curvature, which prevents further bending of the riser 2 .

As an alternative, a spacer 10 can be placed between the weight elements, which adjusts the bending stiffness so that the operating stiffness does not fall below the critical bending radius of the riser 2 . If the riser with the weight elements is bent enough that the weight elements contact each other, the spacer can take up the tension generated on the outside of the bend.

In addition to the above-mentioned advantages obtained by the use of the counterweight element according to the invention, it will also give the riser a certain protection against wear when subjected to movements relative to the seabed.

FIG. 4 shows a cross-sectional view of the structure of a weight element 3 of an embodiment. The counterweight element 3 can form a ring, such as a lead ring, and is fixed to the standpipe 2 at a distance from each other. In this way the flexibility of the riser is maintained.

In an alternative embodiment, the weight element may have a high specific gravity fluid, such as drilling fluid. If the weight elements are filled with fluid, they may also be relatively flexible, thus providing a damping increase in the bending stiffness as the weight elements are gradually pressed against each other as the riser bends. Liquid can be poured into the counterweight unit after it has been mounted, which simplifies handling.

Preferably the weight elements 3 are semicircular parts screwed together on the outside of the riser. The ring 3 shown in Figure 4 is assembled by means of an inner ring 4 having a flexible polymer of rubber like material. The inner ring 4 is glued or vulcanized to the outer ring 5, which is made of a heavy weight material, preferably lead, or contains a heavy liquid. On the outside, an O-ring 6 gives an external protection.

The stiffness of the weight elements and the connections between them can be provided in other ways, such as by using different rubber compounds in the production of the weight elements and possibly spacers, perhaps in combination with the use of heavy liquids in the weight elements, so that Give them some flexibility.

Claims (18)

1. one kind is used for being in or near the standpipe (2) of carrying fluid between second member on sea, comprising the member (7) in seabed and one:

A vertically extending upper member (2a), the upper end of described upper member are connected on the member that is positioned at the sea,

The mid portion (2b) of a standpipe (2) is connecting one or more buoyancy elements at least a portion of its length direction,

A lower member (2c) has a lower end that is connected on the seabed member (1),

It is characterized in that also having one or more counterweight elements (3) to be installed on the lower member (2c) of standpipe (2).

2. standpipe as claimed in claim 1 is characterized in that each counterweight element (3) comprises parts of being made by heavy material.

3. standpipe as claimed in claim 1 is characterized in that each counterweight element (3) comprises a kind of high specific gravity liquid.

4. standpipe as claimed in claim 1 is characterized in that counterweight element (3) comprises the annulus that is fixed on standpipe (2) periphery.

5. standpipe as claimed in claim 4 is characterized in that each counterweight element (3) comprises two semicircular ring components, and they are suitable for being fixed together with the circumference of screw around standpipe.

6. standpipe as claimed in claim 4 is characterized in that each counterweight element (3) comprises ring (4) in, and described interior ring is fixed on the outer shroud of being made by the high specific gravity solid material (5).

7. standpipe as claimed in claim 6 is characterized in that each counterweight element (3) comprises an O type outer shroud (6), and it hides the interior ring (4) and the outer shroud (5) of counterweight element (3) get up.

8. standpipe as claimed in claim 1 is characterized in that the lower member (2c) of standpipe (2) comprises two or more counterweight elements (3), and described counterweight element (3) axially has certain distance each other.

9. standpipe as claimed in claim 8 is characterized in that also comprising with the isolated distance pieces of two or more counterweight elements (3) (10).

10. standpipe as claimed in claim 1, it is characterized in that counterweight element (3) distributes along the bottom part (2c) of standpipe (2), and the bottom part (2c) of standpipe just had a bending that carries out the transition to the part (2b) of extending to one side from vertical extent part (2c) thus.

11. standpipe as claimed in claim 10 is characterized in that at least one counterweight element (3) is laid on the seabed.

12. standpipe as claimed in claim 8, it is characterized in that the lower member (2c) of standpipe (2) has the radius of curvature of a minimum, described minimum profile curvature radius is limited by the radially extension of interval between counterweight element (3) and counterweight element (3), described radially the extension greater than the spacing distance between the counterweight element (3).

13. standpipe as claimed in claim 1 is characterized in that comprising many interconnective counterweight elements (3), they standpipe vertically on have a continuous bending rigidity.

14. standpipe as claimed in claim 13 is characterized in that bending rigidity reduces towards the end of interconnective counterweight element (3).

15. standpipe as claimed in claim 1, it is characterized in that at least one counterweight element (3) is connected on the anchoring system, anchoring system comprises that at least one is connected to first anchor chain (11) on the buoyancy aid (12), and buoyancy aid (12) is anchored into the seabed by one second anchor chain (13)

Anchoring system is set at the side that standpipe (2) bottom part is protruded,

The weight of the buoyancy of buoyancy aid (12) and anchor chain (11,13) and the relation of length are suitable for the power of a level of effect on the bottom part of standpipe (2).

16. standpipe as claimed in claim 15 is characterized in that also comprising two mutual buoyancy aids (12) with an angle grappling.

17. standpipe as claimed in claim 6 is characterized in that each counterweight element (3) made by elastomeric material.

18., it is characterized in that described high specific gravity material is plumbous as claim 2 or 6 described standpipes.

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