The present invention relates to seal assemblies suitable for sealing between a wellhead and a hanger, thereby sealing the casing within the wellhead. More particularly, the seal assembly disclosed herein is well suited for high temperature and high pressure applications to reliably seal the casing annulus.
Various types of seal assemblies have been devised of the past fifty years for sealing between a casing hanger and a wellhead. Some seal assemblies are suitable for either high temperature or high pressure application, but not both high temperature and high pressure applications. Other seal assemblies are only suitable for modest temperature and pressure applications. Other seal assemblies initially form a seal, but over time lose their sealing effectiveness.
U.S. Pat. No. 6,705,615 discloses a seal assembly for sealing between a cylindrical surface and a tapered surface. Another type of seal assembly suitable for sealing between a cylindrical surface and tapered surface is disclosed in U.S. Pat. No. 6,666,276. A split carrier seal assembly for sealing between a sub-sea wellhead housing and a casing hanger is disclosed in U.S. Pat. No. 6,969,070. U.S. Pat. Nos. 4,757,860 and 5,076,356 and discloses another form of seal assembly for sealing between a cylindrical surface and a tapered surface.
U.S. Pat. No. 7,096,956 discloses a downhole tool for activating a seal assembly. U.S. Pat. No. 6,202,745 discloses a casing hanger positioned within a wellhead.
Most downhole wellhead-hanger seal assemblies are manufactured from two or more components which make up the seal body which supports one or more seals that seal with the wellhead and the hanger. In many cases, these components are interconnected by threads, which inherently allow axial travel between components. This axial travel between seal body components allows travel and thus wear on both the seals and the sealing surfaces. High seal setting forces are also conventionally difficult to transmit through a seal body with threaded components.
Another significant problem with prior art sealing assemblies is that when fluid pressure is applied from below the set seal assembly, the interior wellhead wall expands radially outward, and the exterior hanger wall contracts radially inward, thereby creating a significant increase in the radial gap, which inherently detracts from sealing effectiveness. The disadvantages of this created gap are particularly significant when high downhole pressure is applied from below the seal assembly.
The disadvantages of the prior art are overcome by the present invention, and an improved seal assembly and method are hereinafter disclosed.
In one embodiment, a seal assembly is provided for sealing between an interior surface on a wellhead and an exterior surface on a hanger positioned within the wellhead. In this embodiment, the seal assembly comprises a unitary body including an upper portion for engagement with a force tool to set the seal assembly, and a lower portion with one or more radially internal seals for sealing with the exterior hanger surface and one or more radially exterior seals for sealing with the wellhead surface. A first C-shaped locking member supported on the unitary body is radially movable inward for securing the seal assembly to the hanger, and a second C-shaped locking member supported on the unitary body is radially movable outward for securing the seal assembly to the wellhead. An actuation member axially movable downward through a portion of the unitary body forces the second locking ring radially outward for engagement with the wellhead and forces the first locking ring radially inward for engagement with the hanger.
In another embodiment, a seal assembly is provided for sealing between the interior surface on a wellhead and the exterior surface on a hanger positioned within the wellhead. The seal assembly when in use withstands a rated high fluid pressure from below the seal assembly which forces a portion of the interior surface of the wellhead radially outward by an expansion amount and forces a portion of the exterior surface of the hanger radially inward by a compression amount. The seal assembly includes a seal body with an upper portion for engagement with the force tool, a lower portion with one or more radially internal seals for sealing with the exterior hanger surface and one or more radially external seals for sealing with the interior wellhead surface. During installation of the seal assembly, a lower portion of the seal body forces a portion of the interior surface of the wellhead engaged by the lower portion of the seal body radially outward by at least substantially the expansion amount, and forces a portion of the exterior surface of the hanger radially inward by at least substantially the compression amount, thereby effectively preloading both the wellhead and the hanger at substantially the equipment rated fluid pressure to fluid pressure from below.
These and further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.
Referring to
Referring still to
The lower portion 34 of the seal body includes a base 56 and a radially outward projecting member 36, which has annular bumps 38 and 40 at its upper and lower ends for sealing engagement with the interior surface 14 on the wellhead 12. A gap 42 between a portion of the projecting member 36 and the base 56 provides for limited outward deflection of the bump 38 at the upper end of member 36 when pressure is applied to the seal assembly from above, while a similar gap 44 allows limited outward deflection of annular bump 40 when fluid pressure is applied to the seal assembly from below.
In the
To set the seal assembly, the running and force tool 90 may first be rotated by the work string to release the running tool from the hanger. A sleeve rotates with the tool mandrel such that threads cause the sleeve to move axially upward during this rotation, which allows a C-ring to radially collapse. The C-ring thus moves radially inward and out of engagement with the internal locking grooves on the casing hanger to release the hanger from the tool 90.
The running tool may be further rotated to move the sleeve further upward, thereby releasing the seal assembly 10 from the tool 90 to drop to a preset position. The seal assembly 10 and the running tool mandrel 92 move independently down, with the seal assembly in the annulus between the upper enlarged OD of the hanger and the ID of the wellhead. At this stage, the BOP conventionally positioned on top of the wellhead may be closed, and fluid pressure exerted on the force tool 90 through the running string to drive the seal assembly 10 further downward from its preset position to its final sealing position.
Referring now to
During assembly of the locking ring 24 within the seal body 20, the split C-ring 24 may first be installed in the radially outward position, and the split retaining ring 54 then supported on the unitary body 20. Ring 54 includes an annular retainer 30 for engaging an upper portion of the locking ring 24 to limit radially inward movement of the locking ring. Ring 54 may be installed on stop member 68 formed as part of the seal body 20, so that the retainer ring 54 is axially affixed to the seal body by the stop member and does not exert a downward force on the C-ring 22. Once the C-ring 54 is installed, a spacer member may be secured by a bolt to the body 20, and fills the space between the ends of the C-ring to prevent the ring 54 from collapsing inward, thereby retaining the C-ring 24 into position on the seal body.
The seal body 20 includes circumferentially spaced upper slots 94 and aligned lower slots 96. Slots 94 are formed radially outward from the inner surface of body 20, while slots 96 are formed radially inward from the outer surface of the body 20. A slight radial overlap of these slots allows a respective finger 66 to axially slide through the body, with each finger passing through a portion of an upper slot and a portion of a lower slot, while still maintaining the desired strength of the body 20 to withstand the forces driving the seal body downward. Projecting member 36 and protective member 46 are also shown at the lower end of the seal body 20.
Referring now to
A first outer metal member 148 on the seal body 20 projects radially outwardly and upwardly from the seal body base 256 and forms a first gap 1156 exposed to fluid pressure above and radially outward of the seal assembly. The first gap is radially between the seal body base and the upwardly projected member. A second outer metal member 150 projects radially outwardly and downwardly from the seal body base 256 and forms a second gap 154 open to fluid pressure below and radially outward of the seal assembly. The second gap is radially between the seal body base and the downwardly projecting member. Each of the metal members 148 and 150 has an exterior surface 156, 158, respectively, which is substantially parallel to an interior surface of the wellhead. This exterior surface preferably extends along an axial length greater than a maximum radial width of the respective metal member.
The running and force tool 90 moves the seal body downward from its released and preset position to its set position, i.e., its final axial position wherein the seal body exerts the desired force to move a portion of the wellhead inner surface radially outward, and to move a portion of the hanger outer surface radially inward, thereby preloading both the wellhead and the hanger at the axial location of the engaging surfaces on the seal body. The seal body remains in this axial position while sealing the casing annulus, although the upwardly and downwardly projecting members 38 and 40, or the modified fingers as shown in
Radial deflection of the wellhead inner surface and the hanger outer surface due to the action of the force tool acting on the seal assembly preferably causes radial deflection of the wellhead and hanger which is substantially equal to or greater than the radial deflection which otherwise occurs on these surfaces in response to fluid pressure at the rated pressure from below the seal assembly. To obtain the significant benefits of a preloading, the preloading force on the wellhead inner surface and the hanger outer surface is at least 70% of the fluid pressure deformation of these surfaces caused by fluid pressure at the rated pressure for the seal assembly. In many applications, preload deformation of these surfaces through the force tool and seal assembly will be at least 80% of the deformation caused by fluid pressure at the rated pressure level.
The seal body 20 is used to perform the preloading function, and this objective is accomplished by providing an outer seal body surface which engages the wellhead inner surface and an inner seal body surface which engages the hanger outer surface. The substantial forces exerted on the seal body thus brings the inner surface of the seal body into engagement with the hanger, even though seals 51 and 52 may initially extend outward from the inner surface of the seal body. A solid portion 98 of the seal body thus extends in a pure radial direction from an outer surface which engages the wellhead to an inner surface which engages the hanger, since a solid mass between these surfaces allows the seal body to withstand the high forces generated by the force tool and the force multiplier due to the taper of the exterior surface of the hanger.
The seal assembly as disclosed herein is particularly well suited for sealing between an interior surface of a wellhead and an exterior surface of a hanger positioned within the wellhead. The seal assembly is particularly well suited for subsurface applications, although the seal assembly may also be used to seal between a surface wellhead and a hanger positioned within the surface wellhead. In this latter application, a running string may be a relatively short tubular for positioning the seal assembly within the surface wellhead. Various types of actuation members may be used for activating the seal assembly.
Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.
This application is a U.S. national stage application of PCT Appln. No. PCT/US11/43296 filed on Jul. 8, 2011, which claims the priority of U.S. Provisional Application No. 61/389,435 filed on Oct. 4, 2010, the disclosure of which is incorporated herein by reference for all purposes.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2011/043296 | 7/8/2011 | WO | 00 | 3/21/2013 |
Publishing Document | Publishing Date | Country | Kind |
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WO2012/047351 | 4/12/2012 | WO | A |
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