1. Field of the Invention
This invention relates in general to hydro/pneumatic tensioners for applying tension to a riser supported from a floating platform.
2. Background of the Invention
An offshore facility includes a riser extending to a subsea facility such as a subsea well or subsea manifold located at the sea floor. Offshore facilities that float, such as a tension leg platform, move up and down and horizontally relative to the subsea well with the oscillations of the waves and currents. It is often desirous to maintain a desired tension on the riser during these oscillating movements. Tensioners are often utilized in order to react to the movements of offshore facilities moving with the wave oscillations and currents.
Previous tensioner assemblies, like those on tension leg platforms, include a plurality of piston assemblies suspended from a deck that connect to a tension ring surrounding the riser. One type relied upon gas positioned in a chamber surrounding the piston rod to create tension. These piston assemblies are pull-type piston assemblies because they react when the piston is being pulled through the piston chamber and the fluid surrounding the piston rod is compressed. These assemblies require large piston assemblies to accommodate the necessary fluid for creating tension in reaction to the movements of the platform.
Other previous tensioner assemblies include ram style or push-type piston assemblies that have the reactive fluid on the side of the piston opposite from the piston rod. Ram style piston assemblies react when the piston is being pushed through the piston chamber. This arrangement allows for smaller piston assemblies because there is no piston rod in the chamber containing the fluid. Moreover, in previous assemblies, the piston rod extends downward to the piston housed with the piston chamber. Therefore, drippings and debris from above often fall onto the piston rods which can damage the seals of the piston assembly. Failure and less reactive tensioning can occur when the seals are damaged.
In other ram style or push-type piston assemblies, the piston rod extends upward to the piston housed with the piston chamber. In these assemblies, drippings and debris fall from above onto the rods. Such an arrangement typically required expensive coatings to be applied to the outer surface of the piston rods that were exposed to the elements.
A surface assembly that communicates with subsea structures includes a working deck on a floating structure. The working deck has an aperture extending axially therethrough. A riser extends from a subsea location to the working deck. The riser extends through the aperture. The surface assembly includes a frame extending circumferentially around the riser. The frame is connected to the riser so that the frame moves axially with the riser. The assembly also includes a tensioner assembly connected between the working deck and the frame. The tensioner assembly comprises a piston, a piston chamber, a sealing portion between the piston and the piston chamber, a piston rod extending from the piston and away from the piston chamber, and a shroud enclosing the piston rod and at least the sealing portion of the piston assembly.
In another configuration, the sealing portion is between the piston and an interior surface of the shroud. A piston chamber is defined by the sealing portion, the piston, and the shroud. The tensioner assembly can also include a cylinder. The sealing portion can then be located between the piston and the cylinder. The piston chamber is then defined by the sealing portion, the piston, and the cylinder. The shroud typically has a closed upper end, and an open lower end that exposes a portion of its interior surface to atmospheric pressure.
In yet another configuration, a surface assembly for subsea wells includes a working deck on a floating structure. The working deck has an aperture extending axially therethrough. A riser extends from a subsea location to the working deck and through the aperture. A frame extends circumferentially around the riser. The frame is connected to the riser so that the frame moves axially with the riser. A tensioner assembly is connected between the working deck and the frame. The tensioner assembly includes a piston slidably carried in a piston chamber, a piston rod extending from the piston and away from the piston chamber, and a shroud enclosing the piston rod. The shroud has a plurality of segments with at least one of the shroud segments being movable in unison with the piston rod.
The plurality of segments can include an inner shroud segment being stationary relative to the piston rod. The plurality of segments can have an inner shroud segment and an outer shroud segment, with the outer shroud segment telescoping over the inner shroud segment when the tensioner assembly is in a contracted position. A substantial portion of the inner shroud segment can be uncovered when the tensioner assembly is in an extended position. Either the outer shroud segment or the inner shroud segment that is fixedly connected to an end portion of the piston chamber that receives the piston rod.
The plurality of segments can also include an intermediate shroud segment. The intermediate shroud segment telescoping over the inner shroud segment when the tensioner assembly is in a contracted position, and the outer shroud segment telescoping over the intermediate and inner shroud segments when the tensioner assembly is in a contracted position.
In another configuration a riser tensioner assembly for maintaining tension in a riser extending from a subsea well through an aperture in a working deck of a floating structure includes a piston slidably carried in a piston chamber. A piston rod extends from the piston chamber. The piston rod and piston are movable between a contracted position and an extended position of the tensioner assembly. A shroud surrounds at least part of the piston rod while in the contracted and extended positions. The shroud has a plurality of shroud segments with at least one of the shroud segments being movable in unison with the piston rod and at least one of the shroud segments being fixedly connected to an end portion of the piston chamber that receives the piston rod.
In the tensioner assembly, the plurality of shroud segments can include an inner shroud segment and an outer shroud segment. The inner shroud segment can have a flange end connected to either the piston chamber or the piston rod and a telescoping end having an outer lip. The outer shroud can also have a flange end connected to the other of the piston chamber or the piston rod and a telescoping end having an inner lip. When the tensioner assembly is in the extended position, the outer lip of the inner shroud engaging another shroud segment telescoping over the inner shroud and the inner lip of the outer shroud engaging another shroud segment telescoping within the outer shroud.
The plurality of shroud segments can also include an intermediate shroud segment. The intermediate shroud segment telescopes over the inner shroud segment when the tensioner assembly is in a contracted position. The outer shroud segment telescopes over the intermediate and inner shroud segments when the tensioner assembly is in a contracted position.
Each intermediate shroud segment can have an extension end and a contraction end. The extension end has an outer lip and the contraction end has an inner lip. When the tensioner assembly is in the extended position the outer lip of the intermediate shroud segment engages an interior lip of either another intermediate shroud segment or the outer shroud segment, and the inner lip of the intermediate shroud segment engages an outer lip of either another intermediate shroud segment or the inner shroud segment.
Referring to
Riser 15 is connected on its lower end to a subsea well. In this embodiment, riser 15 is a production riser. Typically, a production tree (not shown) is mounted to the upper end of riser 15. Well fluids flow from the subsea wellhead of production riser 15 to the tree. Typically, the floating platform will support a number of risers 15.
A tensioner assembly comprising a plurality of hydro/pneumatic cylinder assemblies 17 supplies tension to each riser 15 as deck 11 moves upward and downward. Two cylinder assemblies 17 are shown in
In the preferred embodiment, a plurality of seals 22 surround the circumference of piston 21. In the embodiment shown in
Cylinder 19 is connected on its lower end to a brace 27 by a pin 25. In the preferred embodiment, pin 25 is spherical so as to allow pivotal rotation not only in the plane containing the drawing, but also in a Z-plane perpendicular to the plane containing the drawing. Brace 27 in this embodiment is secured to deck 11, and the lower ends of cylinders 19 are located approximately at the same level as deck 11.
Each cylinder assembly 17 inclines relative to riser 15 and deck 11 in the embodiment shown in
A shroud 35 encloses the exposed portion of rod 23 of each cylinder assembly 17. Shroud 35 is a cylindrical member having a closed upper end 37 and an open lower end 39. Each rod 23 extends through a hole in closed end 37 that is preferably sealed to prevent corrosive fluids from contacting rod 23. Shroud 35 protects rod 23 and seals 26 from any debris falling onto cylinder assemblies 17 from above. The length of shroud 35 is selected so that lower end 39 will be close to the lower ends of cylinders 19 while cylinder assembly 17 is fully retracted as shown in
Sets of guide rollers 41 are employed to engage riser 15 and maintain riser 15 generally centralized in opening 13 but allow for angular offset of the riser relative to the platform. Although only two guide rollers 41 are shown, preferably more would be employed for each riser 15. Each guide roller 15 is mounted to an arm 43 that is fixed in length in the preferred embodiment. Arm 43 has an outer end that is secured by a pin 45 to a lug 47. Lug 47 mounts to deck 11 in this embodiment. Pivot pins 45 allow rods 43 to be pivoted and rotated away from deck opening 13 for other operations, such as when a larger diameter drilling riser is employed in a preliminary operation. In this embodiment, arms 43 are spaced above deck 11 only a short distance, thus provide centralizing to riser 15 at opening 13.
An upper deck 51 is located below tensioning ring 33 and above deck 11 in this embodiment. Mounting guide rollers to deck 51 reduces any moment arm on guide rollers 41 due to the failure of a cylinder assembly 17. Preventing angular movements are desirable during many workover and intervention operations. Preferably, pivot pins 45 allow rods 43 to be pivoted and rotated so that rollers 41 connected to upper deck 51 may be disengaged and pivoted away from riser 15. This may be desirable during operations where angular movements are allowable, or when a larger diameter drilling riser is employed.
The embodiment of
The embodiment shown in
Referring to the embodiment shown in
Referring to another alternative embodiment shown in
In operation of the embodiments in
In each of the embodiments, seals 22 are protected from drippings and debris from above while in both the contracted and retracted positions. Moreover, in the embodiments shown in
In the alternative embodiment of cylinder assembly 17′ shown in
Referring to
As is perhaps shown best in
In the preferred embodiment, each intermediate segment 35b′ includes both upper and lower lips 61b, 63b because each intermediate shroud segment receives a shroud segment, and is received by a larger shroud segment. In the preferred embodiment, large shroud segment 31a′ includes only lower lip 63a, but has a flange 62 at its upper end for connecting to a piston rod connector flange 67 located on a piston rod connector 65 (
In the embodiments shown in
In each of the alternative embodiments illustrated in
While the invention has been shown in only three of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention. For example, the number of intermediate shrouds 35b′ can be increased or decreased, even such that large shroud 35a′ registers with small shroud 35b′. Furthermore, the telescoping shroud segments could also be utilized with the tensioner assemblies having the piston rod extending radially inward from the working deck to the tension ring.
Number | Date | Country | |
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60534831 | Jan 2004 | US |
Number | Date | Country | |
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Parent | 11020857 | Dec 2004 | US |
Child | 11507865 | Aug 2006 | US |