WO2011022332A1

WO2011022332A1 - Vortex induced vibration suppression systems and methods

Info

Publication number: WO2011022332A1
Application number: PCT/US2010/045619
Authority: WO
Inventors: Donald Wayne Allen; Stephen Paul Armstrong; Julie Ann Dehne; Li Lee; Damon Michael Mcmillan; Christopher Steven West
Original assignee: Shell Oil Company; Shell Internationale Research Maatschappij B.V.
Priority date: 2009-08-17
Filing date: 2010-08-16
Publication date: 2011-02-24

Abstract

A system including a subsea structure defining an interior of the system, the structure subject to a water current within a body of water; at least two collars exterior to the subsea structure, the collars having a density less than the body of water; and a vortex induced vibration suppression device exterior to the subsea structure and located between the at least two collars.

Description

VORTEX INDUCED VIBRATION SUPPRESSION SYSTEMS AND METHODS

Field of the Invention

This invention is related to vortex induced vibration suppression devices that can be attached to offshore structures to reduce drag and/or vortex induced vibration (VIV).

Background of the Invention

Whenever a bluff body in a fluid environment, such as a cylinder, is subjected to a current in the fluid, it is possible for the body to experience vortex-induced vibrations (VIV). These vibrations may be caused by oscillating hydrodynamic forces on the surface which can cause substantial vibrations of the structure, especially if the forcing frequency is at or near a structural natural frequency.

Drilling for and/or producing hydrocarbons or the like from subterranean deposits which exist under a body of water exposes underwater drilling and production equipment to water currents and the possibility of VIV. Equipment exposed to VIV may include structures ranging from the smaller tubes of a riser system, anchoring tendons, or lateral pipelines to the larger underwater cylinders of the hull of a minispar or spar floating production system (a "spar").

Risers as used herein are defined to be a non-exclusive example of a marine element subject to VIV. Generally a riser system is used for establishing fluid communication between the surface and the bottom of a water body. The principal purpose of the riser is to provide a fluid flow path between a drilling vessel and a well bore and to guide a drill string to the well bore.

A typical riser system may include one or more fluid-conducting conduits that extend from the surface to a structure (e.g., wellhead) on the bottom of a water body. For example, in the drilling of a submerged well, a drilling riser usually consists of a main conduit through which the drill string is lowered and through which the drilling mud is circulated from the lower end of the drill string back to the surface. In addition to the main conduit, there may be provided auxiliary conduits such as, for example, choke and kill lines, pressurized fluid lines, hard pipes, and electrical lines, which extend relatively parallel to the main conduit. These auxiliary conduits and lines are commonly referred to as umbilical elements and/or umbilicals.

As the depth of water increases, the mass of a riser generally increases. To lower the burden on the floating structure to which the riser is attached, many risers are provided with buoyancy. Some risers have a foam covering attached to the riser's outer circumference. Alternatively, buoyancy cans or other buoyancy means can be attached to the riser to provide a suitable level of buoyancy to overcome the weight of the riser.

There are generally two kinds of water current induced stresses to which elements of a riser system may be exposed. The first kind of stress as mentioned above is caused by vortex-induced alternating forces that vibrate the underwater structure in a direction perpendicular to the direction of the current. These are referred to as vortex-induced vibrations (VIV). When water flows past the structure, vortices are alternately shed from each side of the structure. This produces a fluctuating force on the structure transverse to the current. These vibrations can, depending on the stiffness and the strength of the structure and any welds, lead to unacceptably short fatigue lives. In fact, stresses caused by high current conditions have been known to cause structures such as risers to break apart and fall to the ocean floor. The second type of stress is caused by drag forces which push the structure in the direction of the current due to the structure's resistance to fluid flow. The drag forces may be amplified by vortex induced vibrations of the structure. For instance, a riser pipe that is vibrating due to vortex shedding will disrupt the flow of water around it more so than a stationary riser. This results in greater energy transfer from the current to the riser, and hence more drag.

Many methods have been developed to reduce vibrations of sub sea structures. Some of these methods to reduce vibrations caused by vortex shedding from subsea structures operate by stabilization of the wake. These methods include streamlined fairings, wake splitters and flags. Streamlined or teardrop shaped, fairings that swivel around a structure have been developed that almost eliminate the shedding or vortexes. Other conventional methods to reduce vibrations caused by vortex shedding from sub sea structures operate by modifying the boundary layer of the flow around the structure to prevent the correlation of vortex shedding along the length of the structure. Examples of such methods include the use of helical strakes around a structure, or axial rod shrouds and perforated shrouds.

Copending PCT Patent Application published as WO 2007/149770, filed June 19, 2006, having attorney docket number TH 1500, discloses a system for producing oil and/or gas, including a subsea structure defining an interior of the system, the structure subject to a water current; a covering exterior to the subsea structure, covering at least a portion of an outside surface of the subsea structure; a vortex induced vibration suppression device exterior to the covering; the covering including a first mechanism and the vortex induced vibration suppression device including a second mechanism, wherein the first mechanism and the second mechanism are adapted to maintain the vortex induced vibration suppression device in a location along a length of the subsea structure. Patent Application WO 2007/149770 is herein incorporated by reference in its entirety.

Copending PCT Patent Application published as WO 2008/064102, having attorney docket number TH3190, discloses a long fairing with a dampening mechanism adapted to dampen a rotation of the fairing about a subsea structure. The dampening mechanism is selected from a group consisting of perforations in a tail section of the fairing, a mass in a nose section of the fairing, a buoyancy module in the tail section of the fairing and perforations and balls and/or rods in the tail section of the fairing. Patent Application WO 2008/064102 is herein incorporated by reference in its entirety.

There is a need in the art for improved apparatus and methods for suppressing VIV.

There is a need in the art for apparatus and methods for suppressing VIV that do not suffer from the disadvantages of the prior art.

There is a need in the art for apparatus and methods for providing buoyancy to subsea structures that do not suffer from the disadvantages of the prior art.

There is a need in the art for apparatus and methods for providing VIV suppression to a subsea structure. There is a need in the art for apparatus and methods for providing buoyancy to a subsea structure.

There is a need for systems and methods of installing VIV suppression devices to a subsea structure.

These and other needs will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.

Summary of the Invention

In one aspect, the invention provides a system including a subsea structure defining an interior of the system, the structure subject to a water current within a body of water; at least two collars exterior to the subsea structure, the collars having a density less than the body of water; and a vortex induced vibration suppression device exterior to the subsea structure and located between the at least two collars.

In another aspect, the invention provides a method of reducing drag and/or vortex induced vibration of a subsea structure, comprising installing the subsea structure in a body of water, wherein the subsea structure is subject to one or more water currents; installing a sleeve exterior to the subsea structure, the sleeve comprising at least one flange surface, and wherein the sleeve has a density less than the body of water; installing a vortex induced vibration suppression device exterior to the subsea structure and the sleeve.

Advantages of the invention may include one or more of the following:

improved apparatus and methods for suppressing VIV;

apparatus and methods for suppressing VIV that do not suffer from the disadvantages of the prior art;

apparatus and methods for providing VIV suppression to a subsea structure; and/or

systems and methods of installing VIV suppression devices to a subsea structure;

improved apparatus and methods for providing buoyancy to a subsea structure; apparatus and methods for providing buoyancy to a subsea structure that do not suffer from the disadvantages of the prior art;

apparatus and methods for providing buoyancy to a subsea structure; and/or systems and methods of providing buoyancy to a subsea structure.

Brief Description of the Figures

Figure 1 illustrates a subsea structure system.

Figure 2a illustrates a subsea structure system.

Figure 2b illustrates a side view of a sleeve installed around a subsea structure.

Figure 2c illustrates a side view of a sleeve installed around a subsea structure.

Figure 3 illustrates a side view of collars installed around a subsea structure.

Figure 4 illustrates a cross-sectional view of a riser with a fairing installed around it.

Detailed Description

Figure 1 :

Referring now to Figure 1 there is illustrated offshore system 100. System 100 includes surface structure 102 near the water surface, which is connected to riser 104, which riser 104 is connected to subsurface structure 106, which is adjacent to seafloor 108. The water has current 110, which may cause vortex-induced vibration of riser 104. To counter VIV, fairings 114 may be installed along the length of riser 104. Collars 112 are used to keep fairings from moving along the length of riser 104.

Figure 2a:

Referring now to Figure 2a, system 200 is illustrated. System 200 includes surface structure 202 near the surface of the water, which is connected to riser 204. Riser 204 is also connected to subsurface structure 202 near the seafloor 208.

Exterior to riser 204 are installed sleeves 215, which may serve to provide buoyancy to riser 204 and/or to keep fairings 214 on station with flanges 216. Current 210 is in the water, which may cause VIV on riser 204.

Fairings 214 are installed exterior to sleeves 215. Sleeves 215 are shown inside fairings 214, and serve to keep fairings 214 at a desired location along subsurface structure 203 and/or allow fairings 214 to rotate about sleeves 215 and structure 204. One or more sleeves 215 may be used for each fairing 214.

Figure 2b:

Referring now to Figure 2b, structure 204 is shown with sleeve 215 exterior to the riser. Sleeve 215 has one or more flanges 216 adapted to maintain a VIV suppression device at a desired location along structure 204. Sleeve 215 may be used to provide buoyancy to structure 204. Sleeve 215 is shown with water 224 and low density material 226. Low density material 226 may be a foam, a gas such as air, nitrogen, carbon dioxide, or other gases or gas mixtures, low density balls, cubes, or other shapes, or other materials or substances having a density less than water. In one embodiment, low density material 226 has a density less than about 0.5 gram per cubic centimeter, or less than about 0.25 g/cc, or less than about 0.1 g/cc.

In one embodiment, sleeve has a density less than about 0.75 gram per cubic centimeter, or less than about 0.5 g/cc, or less than about 0.25 g/cc.

Sleeve 215 has a first valve 220 adapted to receive low density material 226 into an interior of sleeve 215, and second valve 222 adapted to expel water 224 from sleeve 215.

In operation, sleeve 215 may be installed around structure 204 while full of water and neutrally buoyant. Once sleeve 215 is secured to structure 204 to keep sleeve 215 from moving along the length of structure 204, low density material 226 is injected into an interior of sleeve 215 with first valve 220. The injection of low density material 226 forces water 224 from sleeve 215 by second valve 222. After low density material 226 has displaced water 224, sleeve 215 has a density less than water and provides a buoyancy force to structure 204. Figure 2c:

Referring now to Figure 2c, structure 204 is shown with an alternative design of sleeve 215 exterior to the riser. Sleeve 215 has multiple flanges 216 adapted to maintain a VIV suppression device at a desired location along structure 204 between each set of flanges 216, such that two or more VIV suppression devices may be installed per sleeve 215. Sleeve 215 may be used to provide buoyancy to structure 204. Figure 3:

Referring now to Figure 3, riser 304 is shown with collar 315 exterior to the riser. Collar 315 has one or more flanges 316 adapted to maintain a VIV suppression device at a desired location along structure 304. Collar 315 may be used to provide buoyancy to riser 304. Collar 315 is shown with water 324 and low density material 326. Low density material 326 may be a foam, a gas such as air, nitrogen, carbon dioxide, or other gases or gas mixtures, low density balls, cubes, or other shapes, or other materials or substances having a density less than water. In one embodiment, low density material 326 has a density less than about 0.5 gram per cubic centimeter, or less than about 0.25 g/cc, or less than about 0.1 g/cc.

In one embodiment, collar has a density less than about 0.75 gram per cubic centimeter, or less than about 0.5 g/cc, or less than about 0.25 g/cc.

Collar 315 has a first valve 320 adapted to receive low density material 326 into an interior of collar 315, and second valve 322 adapted to expel water 324 from collar 315.

In operation, collar 315 may be installed around structure 304 while full of water and neutrally buoyant. Once collar 315 is secured to structure 304 to keep collar 315 from moving along the length of structure 304, low density material 326 is injected into an interior of collar 315 with first valve 320. The injection of low density material 326 forces water 324 from collar 315 by second valve 322. After low density material 326 has displaced water 324, collar 315 has a density less than water and provides a buoyancy force to structure 304. Figure 4:

Referring now to Figure 4, a cross-sectional view of riser 404 and fairing 414 is shown. Low density materials or containers 430 and 434 are secured to the interior of fairing 414 with screws 432. Suitable low density materials include foams, such as syntactic foam, or other light weight materials such as polymers that have a density less than water. Suitable low density containers include buoyancy cans which can filled with a gas, a foam, or other materials having a density less than water.

Low density materials or containers 430 and 434 are designed to occupy the annular space between riser 404 and fairing 414. With the addition of low density materials and/or containers 430 and 434, fairing 414 has a density less than the water surrounding riser 404, such that fairing 414 is buoyant in the fluid and pushes up against a sleeve or collar (see above) to provide a buoyancy force to riser 404.

To attach fairing 414 about riser 404, fairing 414 may be held open and pulled around riser 404. Fairing is then closed around riser 404. When fairing halves are aligned, screws, rivets, or other mechanical fasteners may be used to hold the two halves of fairing 414 together.

While a fairing 414 has been illustrated, fairings may be replaced with strakes, shrouds, wake splitters, tail fairings, buoyancy modules, or other devices as are known in the art.

Alternative Embodiments:

Sleeves 215 and collars 315 may be constructed in a clam shell configuration to allow easy installation by an ROV to an existing subsea structure. Suitable sleeves, suitable collars, and suitable devices to install exterior to structures, and methods of their installation are disclosed in U.S. Patent Application Number

10/839,781 , having attorney docket number TH1433; U.S. Patent Application Number 11/400,365, having attorney docket number TH0541 ; U.S. Patent Application Number 11/419,964, having attorney docket number TH2508; U.S. Patent Application Number 11/420,838, having attorney docket number TH2876; U.S. Patent Application Number 60/781 ,846 having attorney docket number TH2969; U.S. Patent Application Number 60/805,136, having attorney docket number TH1500; U.S. Patent Application Number 60/866,968, having attorney docket number TH3112; U.S. Patent Application Number 60/866,972, having attorney docket number TH3190; U.S. Patent Number 5,410,979; U.S. Patent Number 5,410,979; U.S. Patent Number 5,421 ,413; U.S. Patent

Number 6,179,524; U.S. Patent Number 6,223,672; U.S. Patent Number 6,561 ,734; U.S. Patent Number 6,565,287; U.S. Patent Number 6,571 ,878; U.S. Patent

Number 6,685,394; U.S. Patent Number 6,702,026; U.S. Patent Number 7,017,666; and U.S. Patent Number 7,070,361 , which are herein incorporated by reference in their entirety.

Suitable methods for installing fairings, collars, sleeves, and other devices to install exterior to structures, are disclosed in U.S. Patent Application Number

10/784,536, having attorney docket number TH1853.04; U.S. Patent Application Number 10/848,547, having attorney docket number TH2463; U.S. Patent Application Number 11/596,437, having attorney docket number TH2900; U.S. Patent Application Number 11/468,690, having attorney docket number TH2926; U.S. Patent Application Number 11/612,203, having attorney docket number TH2875; U.S. Patent Application Number 60/806,882, having attorney docket number TH2879; U.S. Patent Application Number 60/826,553, having attorney docket number TH2842; U.S. Patent Number 6,695,539; U.S. Patent Number 6,928,709; and U.S. Patent Number 6,994,492; which are herein incorporated by reference in their entirety.

The sleeves, collars and/or fairings may be installed on the riser before or after the riser is placed in a body of water.

The sleeves, collars, fairings and/or other devices exterior to the structure may have a clamshell configuration, and may be hinged with a closing mechanism opposite the hinge, for example a mechanism that can be operated with an ROV.

The sleeves, fairings, or collars may be a copper ring, or have a copper ring that is part of its structure.

Fairings may be provided with copper plates on their ends to allow them to weathervane with adjacent fairings or collars.

Fairings may be partially manufactured from copper. A biodegradable spacer may be placed between adjacent fairings to keep them from binding and allow them to weathervane after the spacer has degraded.

Illustrative Embodiments

In one embodiment, there is disclosed a system including a subsea structure defining an interior of the system, the structure subject to a water current within a body of water; at least two collars exterior to the subsea structure, the collars having a density less than the body of water; and a vortex induced vibration suppression device exterior to the subsea structure and located between the at least two collars. In some embodiments, the subsea structure is selected from an umbilical, a riser, and a tendon. In some embodiments, the collar is filled with a foam adapted to provide buoyancy to the collar. In some embodiments, the vortex induced vibration suppression device comprises a fairing or a helical strake. In some embodiments, the collar comprises a first valve adapted to receive a low density material within the collar. In some embodiments, the vortex induced vibration suppression device has a density less than the body of water.

In one embodiment, there is disclosed a method of reducing drag and/or vortex induced vibration of a subsea structure, comprising installing the subsea structure in a body of water, wherein the subsea structure is subject to one or more water currents; installing a sleeve exterior to the subsea structure, the sleeve comprising at least one flange surface, and wherein the sleeve has a density less than the body of water; installing a vortex induced vibration suppression device exterior to the subsea structure and the sleeve. In some embodiments, installing the vortex induced vibration suppression device comprises installing at least two vortex induced vibration suppression devices per sleeve. In some embodiments, the vortex induced vibration suppression device comprises a fairing. In some embodiments, the vortex induced vibration suppression device is adapted to rotate about the subsea structure in response to the one or more water currents. In some embodiments, the sleeve is fixed in relation to the subsea structure, and maintains the vortex induced vibration suppression device at a desired location along a length of the subsea structure. In one embodiment, there is disclosed a system comprising a subsea structure defining an interior of the system, the structure subject to a water current in a body of water; at least one collar exterior to the structure and attached to the structure to maintain the collar at a desired location along a length of the structure; and a vortex induced vibration suppression device exterior to the structure and adjacent the collar; wherein the collar provides a buoyancy force to the structure when submerged in the body of water. In some embodiments, the vortex induced vibration suppression device provides a buoyancy force to the structure when submerged in the body of water.

Those of skill in the art will appreciate that many modifications and variations are possible in terms of the disclosed embodiments, configurations, materials and methods without departing from their spirit and scope. Accordingly, the scope of the claims appended hereafter and their functional equivalents should not be limited by particular embodiments described and illustrated herein, as these are merely exemplary in nature.

Claims

C L A IM S

1. A system comprising:

a subsea structure defining an interior of the system, the structure subject to a water current within a body of water;

at least two collars exterior to the subsea structure, the collars having a density less than the body of water; and

a vortex induced vibration suppression device exterior to the subsea structure and located between the at least two collars.

2. The system of claim 1 , wherein the subsea structure is selected from an umbilical, a riser, and a tendon.

3. The system of one or more of claims 1 -2, wherein the collar is filled with a foam adapted to provide buoyancy to the collar.

4. The system of one or more of claims 1 -2, wherein the collar is filled with air adapted to provide buoyancy to the collar.

5. The system of one or more of claims 1 -4, wherein the collar comprises a first valve adapted to receive a low density material within the collar.

6. The system of one or more of claims 1 -5, wherein the vortex induced vibration suppression device has a density less than the body of water.

7. The system of one or more of claims 1 -6, wherein the vortex induced vibration suppression device comprises a fairing, a helical strake, a henning device, or a smooth sleeve.

8. A method of reducing drag and/or vortex induced vibration of a subsea structure, comprising:

installing the subsea structure in a body of water, wherein the subsea structure is subject to one or more water currents;

installing a sleeve exterior to the subsea structure, wherein the sleeve has a density less than the body of water;

installing a vortex induced vibration suppression device exterior to the subsea structure and the sleeve.

9. The method of claim 8, wherein installing the vortex induced vibration suppression device comprises installing at least two vortex induced vibration suppression devices per sleeve.

10. The method of one or more of claims 8-9, wherein the vortex induced vibration suppression device comprises a fairing.

11. The method of one or more of claims 8-10, wherein the vortex induced vibration suppression device is adapted to rotate about the subsea structure in response to the one or more water currents.

12. The method of one or more of claims 8-11 , wherein the sleeve is fixed in relation to the subsea structure, and maintains the vortex induced vibration suppression device at a desired location along a length of the subsea structure.

13. The method of one or more of claims 8-12, wherein the sleeve further comprises at least one flange surface.

14. The method of one or more of claims 8-13, wherein the subsea structure comprises a connection between adjacent sections, the connection further comprises at least one flange surface.

15. A system comprising:

a subsea structure defining an interior of the system, the structure subject to a water current in a body of water;

at least one collar exterior to the structure and attached to the structure to maintain the collar at a desired location along a length of the structure; and

a vortex induced vibration suppression device exterior to the structure and adjacent the collar;

wherein the collar provides a buoyancy force to the structure when submerged in the body of water.

16. The system of claim 15, wherein the vortex induced vibration suppression device provides a buoyancy force to the structure when submerged in the body of water.