This invention relates in general to subsea oil and gas well production, and in particular to a tieback connector extending from the subsea well to a platform at the surface.
Subsea wells typically have a subsea wellhead assembly at the seafloor. In some installations, a subsea production tree is mounted on the wellhead assembly. The tree has valves connected to flow lines for controlling flow from the well. In another type of installation, a string of tieback conduit extends from the subsea wellhead assembly to a platform at the surface. A surface tree is mounted on the upper end of the tieback conduit. Some riser systems have inner and outer tieback conduits, each of which is run separately and connected by a tieback connector. The inner and outer tieback conduits make up the tieback riser in that type of system.
The inner tieback conduit is installed by connecting a tieback connector to the lower end of the conduit and lowering it into the bore of the subsea wellhead housing assembly. The tieback connector has a locking member that locks to the subsea wellhead housing or to the tapered stress joint at the bottom of the outer tieback conduit. The inner tieback connector also has a seal that seals to an internal component of the subsea wellhead housing assembly. Typical outer tieback connectors are locked to the exterior of the subsea wellhead housing assembly. Other outer tieback connectors are locked to the interior. An internal tieback connector typically has a mandrel with a sleeve on the exterior. The mandrel is connected to the inner tieback conduit and is capable of moving between an upper running-in position and a lower landed position in the subsea wellhead housing. An actuator holds the mandrel in the upper position until the actuator lands on structure in the wellhead housing. Then, downward movement of the inner tieback conduit causes the locking member to engage an internal profile in the subsea wellhead housing assembly.
One example embodiment is an apparatus for tying back a subsea well assembly to a surface platform, the subsea well assembly having an outer tieback conduit mounted on top of a wellhead housing. The apparatus includes a mandrel having an axis, external threads, and adapted to be lowered through the outer tieback conduit, an upward facing lip on an external lower end portion of the mandrel, a backup ring having internal threads engaged with the external threads of the mandrel, a sleeve carried on an outside diameter of the backup ring, the sleeve having a downward facing load bearing surface located above the upward facing lip on the mandrel, a first locking member carried by the sleeve, the first locking member having a plurality of teeth biased in a radially outward direction and adapted to engage with a corresponding profile located on an inner diameter of the outer tieback conduit as the mandrel is lowered into the outer tieback conduit, an annular seal assembly carried between the load bearing surface of the sleeve and the upward facing lip of the mandrel, the seal assembly adapted to be located within a bore of the wellhead housing when the teeth have engaged the profile in the tieback conduit, and an anti-rotation member that allows the mandrel to rotate relative to the backup ring, the sleeve, and the first locking member once the teeth have engaged the profile in the tieback conduit. When the mandrel is rotated relative to the backup ring, the sleeve, and the first locking member, a portion of the backup ring advances axially relative to the first locking member to a backup position between the mandrel and the first locking member and in engagement with an inner diameter of the first locking member, thereby locking the first locking member in a radially outward position. The rotation of the mandrel causes the mandrel to move axially upward relative to the sleeve, deforming the annular seal assembly between the upward facing lip of the mandrel and the load bearing surface of the sleeve, thereby creating a seal between the apparatus and the wellhead housing.
Another example embodiment is a subsea well apparatus for communicating with a surface platform. The apparatus includes a wellhead assembly including a wellhead housing, an outer tieback conduit mounted on top of the wellhead housing, and an internal tieback connector including a mandrel having an axis, external threads, and adapted to be lowered through the outer tieback conduit, an upward facing lip on an external lower end portion of the mandrel, a locking ring having internal threads engaged with the external threads of the mandrel, a sleeve carried on an outside diameter of the locking ring, the sleeve having a downward facing load bearing surface located above the upward facing lip on the mandrel, a plurality of first dogs carried by the sleeve, the plurality of first dogs having a plurality of teeth biased in a radially outward direction and adapted to engage with a corresponding profile located on an inner diameter of the outer tieback conduit as the mandrel is lowered into the outer tieback conduit, an annular seal assembly carried between the load bearing surface of the sleeve and the upward facing lip of the mandrel, the seal assembly adapted to be located within a bore of the wellhead housing when the teeth have engaged the profile in the outer tieback conduit, and an anti-rotation member that allows the mandrel to rotate relative to the locking ring, the sleeve, and the plurality of first dogs once the teeth have engaged the profile in the outer tieback conduit. When the mandrel is rotated relative to the locking ring, the sleeve, and the plurality of first dogs, a portion of the locking ring advances axially relative to the first dogs to a backup position between the mandrel and the first dogs and in engagement with an inner diameter of the first dogs, thereby locking the first dogs in a radially outward position. The rotation of the mandrel causes the mandrel to move axially upward relative to the sleeve, deforming the annular seal assembly between the upward facing lip of the mandrel and the load bearing surface of the sleeve, thereby creating a seal between the internal tieback connector and the wellhead housing.
Another example embodiment is a method for tying back a subsea well assembly to a surface platform. The method includes lowering an internal tieback connector into an outer tieback conduit mounted on a wellhead housing of the subsea well assembly. The internal tieback connector includes a mandrel having an axis, external threads, and adapted to be lowered through the outer tieback conduit, an upward facing lip on an external lower end portion of the mandrel, a locking ring having internal threads engaged with the external threads of the mandrel, a sleeve carried on an outside diameter of the locking ring, the sleeve having a downward facing load bearing surface located above the upward facing lip on the mandrel, a plurality of first dogs carried by the sleeve, the plurality of first dogs having a plurality of teeth biased in a radially outward direction and adapted to engage with a corresponding profile located on an inner diameter of the outer tieback conduit as the mandrel is lowered into the outer tieback conduit, an annular seal assembly carried between the load bearing surface of the sleeve and the upward facing lip of the mandrel, the seal assembly adapted to be located within a bore of the wellhead housing when the teeth have engaged the profile in the outer tieback conduit, and an anti-rotation member that allows the mandrel to rotate relative to the locking ring, the sleeve, and the plurality of first dogs once the teeth have engaged the profile in the outer tieback conduit. The method also includes engaging the plurality of first dogs with the corresponding profile located on the inner diameter of the outer tieback conduit of the subsea well assembly, and rotating the mandrel relative to the locking ring, the sleeve, and the plurality of first dogs, such that a portion of the locking ring advances axially relative to the first dogs to a backup position between the mandrel and the first dogs and in engagement with an inner diameter of the first dogs, thereby locking the first dogs in a radially outward position, and the rotation of the mandrel causes the mandrel to move axially upward relative to the sleeve, deforming the annular seal assembly between the upward facing lip of the mandrel and the load bearing surface of the sleeve, thereby creating a seal between the internal tieback connector and the wellhead housing.
So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only example embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.
The methods and systems of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The methods and systems of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout.
It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.
Turning now to the figures,
A sleeve 104 circumscribes at least a portion of the mandrel 102. The sleeve 104 carries a plurality of first locking members or upper dogs 110 that are spaced around a circumference of the sleeve 104. Each of the upper dogs 110 has a dog body with a series of teeth 148 extending radially outward through an opening, which may be a window, in the sidewall of the sleeve 110. The dogs 110 are secured within an inner diameter of the sleeve 104 and are biased in a radially outward direction. In one example embodiment, the series of teeth 148 extending radially outward is pointing downward so as to restrict upward movement of the external riser (not shown) that the internal tieback connector 100 engages with.
A backup ring or locking ring 120 having internal threads 128 is threaded using threads 106 on to the mandrel 102 and located between the mandrel 102 and the sleeve 104. The locking ring 120 has a portion with an increased outer diameter 156 and portion with a reduced diameter 160. The increased outer diameter 156 can engage an inner diameter of the dog body of the upper dogs 110, locking the upper dogs 110 in a radially outward position so that the upper dogs 110 cannot retract radially inward. Locking ring retainers 158, which may be bolted or screwed into the body of the locking ring 120, are spaced around an outer diameter of the locking ring 120 and extend into axially oriented slots 108 through the sidewall of the sleeve 104. The locking ring retainers 158 are axially shorter than the axial height of the slots 108. This prevents relative rotational movement between the locking ring 120 and the sleeve 104, but will allow for relative axial movement between the locking ring 120 and the sleeve 104.
Internal tieback connector 100 includes a plurality of anti-rotation keys 116 that may be spaced circumferentially around and extend through openings within sleeve 104. Each key 116 is biased outward by a coil spring (not shown) and keys 116 are able to fully retract so that they are flush within the exterior surface of sleeve 104.
The sleeve 104 also carries a plurality of second locking members or lower dogs 112 that are spaced around a circumference of the sleeve 104 and are axially spaced from the upper dogs 110. In the example of
Turning now to
In an example of operation, the internal tieback connector 100 is lowered through the outer tieback conduit 166 so that the end 150 of the internal tieback connector 100 is located within the subsea wellhead housing 134 assembly. The upper dogs 110 are biased in the outward direction and will be pushed inward while passing through the inner diameter 124 of the outer tieback conduit 166 so that they are sliding against the inner diameter 124 of the outer tieback conduit 166. As illustrated in
Moving now to
As the mandrel 102 moves upward relative to the sleeve 104, the lower dogs 112 move axially past the upper shoulder 138 towards the lower shoulder 142, causing the lower dogs 112 to move radially outward and to be locked in the radially outward position due to the increase in outer diameter of the mandrel 102 between the two shoulders 138,142. In the radially outward position, the teeth 152 of the lower dogs 112 engage the lower profile 132 located on the inner diameter 124 of the outer tieback conduit 166. This will provide additional capacity for compressive loading in the connector 100. Because an increased diameter of the mandrel 102 is positioned adjacent the lower dogs 112, the lower dogs 112 cannot be retracted radially inward and instead they will remain in engagement with the outer tieback conduit 166.
The rotation additionally causes the locking ring 120 to rotate along the threads 106 of the mandrel 102 and move axially downward along the threads 106 of the mandrel 102. This will cause the larger diameter portion 156 of the locking ring 120 to be located axially adjacent to the dog body of the upper dogs 110 so that the lower dogs 112 are locked in place and cannot be retracted radially inward but will instead remain in engagement with the outer tieback conduit 166. As the rotation is completed a torque build up is achieved through the series of locking dogs 110, 112 driving the metal to metal seal 122 and preloading the connector 100.
One example embodiment is a method for unlocking and retrieving the internal tieback connector 100. In order to unlock and retrieve the internal tieback connector 100, the mandrel 102 of the internal tieback connector 100 is rotated in the opposite direction. This opposite rotation will move the mandrel 102 downward relative to the sleeve 104, un-energize the seal assembly 122, and unlock the upper and lower dogs 110, 112. The internal tieback connector 100 can be rotated until torque is released and then the inner tieback conduit can be pulled back to the surface.
Therefore, example embodiments of this disclosure allow a dual barrier to be installed at almost any time, regardless of casing hanger program. In addition, the inner tieback connector can pass through the outer tieback conduit, and then seal with the inner diameter of a wellhead housing or other wellhead assembly member that has a larger inner diameter than the inner diameter of the outer tieback conduit through which the internal tieback connector is passed.
The terms “inner”, “outer”, “upward”, “downward”, “above”, and “below” and similar spatial relation terminology are used herein only for convenience because elements of the current disclosure may be installed in various relative positions.
The system and method described herein, therefore, are well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While example embodiments of the system and method have been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the system and method disclosed herein and the scope of the appended claims.
While the invention has been shown in only some 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.
This application claims priority to U.S. Provisional Patent Application No. 62/055,238 filed on Sep. 25, 2014, the entire contents of which are incorporated herein by reference.
Number | Date | Country | |
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62055238 | Sep 2014 | US |