BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to wellhead assemblies and, in particular, to an improved system, method, and apparatus for forming a metal seal between inner and outer wellhead members.
2. Description of the Related Art
As shown in FIG. 1, seals 11 are used between inner and outer wellhead tubular members 13, 15 to contain internal well pressure. The inner wellhead member may be a tubing hanger that supports a string of tubing extending into the well for the flow of production fluid. The tubing hanger lands in an outer wellhead member, which may be a wellhead housing, a Christmas tree, or tubing head. A packoff or seal seals between the tubing hanger and the outer wellhead member. Alternately, the inner wellhead member might be a casing hanger located in a wellhead housing and secured to a string of casing extending into the well. A seal or packoff seals in the annular space between the casing hanger and the wellhead housing.
A variety of seals of this nature have been employed in the prior art. Prior art seals include elastomeric seals 17 (see, e.g., FIG. 2) and partially metal anti-extrusion rings backing up elastomeric seal rings. Prior art seal rings made entirely of metal for forming metal-to-metal seals are also employed. The seals may be set by a running tool, or they may be set in response to the weight of the string of casing or tubing. One type of prior art metal-to-metal seal 19 (see, e.g., FIG. 3) has a U-shaped cross-sectional shape with inner and outer walls separated by a conical slot. An energizing ring 21 is pushed into the slot to deform the inner and outer walls apart into sealing engagement with the inner and outer wellhead members 13, 15. The energizing ring is a solid wedge-shaped member. The deformation of the inner and outer walls exceeds the yield strength of the material of the seal ring, making the deformation permanent.
Thermal growth between the casing or tubing and the wellhead may occur, particularly with wellheads located at the surface, rather than subsea. The well fluid flowing upward through the tubing heats the string of tubing, and to a lesser degree the surrounding casing. The temperature increase may cause the tubing hanger and/or casing hanger to move axially a slight amount relative to the outer wellhead member. During the heat up transient, the tubing hanger and/or casing hanger can also move radially due to temperature differences between components and the different rates of thermal expansion from which the component materials are constructed. If the seal has been set as a result of a wedging action where an axial displacement of energizing rings induces a radial movement of the seal against its mating surfaces, then sealing forces may be reduced if there is movement in the axial direction due to pressure or thermal effects. A reduction in axial force on the energizing ring results in a reduction in the radial inward and outward forces on the inner and outer walls of the seal ring, which may cause the seal to leak. A loss of radial loading between the seal and its mating surfaces due to thermal transients may also cause the seal to leak.
SUMMARY OF THE INVENTION
One embodiment of a system, method, and apparatus for sealing between inner and outer well members utilizes a bi-directional metal seal that is energized and un-energized by a rolling action that takes place between radiused seal lips. The seal forms an assembly with upper and lower energizing rings. The energizing rings have opposing grooves on the o.d. and i.d. for engaging hook ends on the inner surfaces of the seal lips in a nesting arrangement when the seal is in the un-energized position. When the upper ring is pulled upward, the seal is un-energized and does not contact the adjacent conductors or wellhead members. When the upper ring is forced downward, the hooks ends in the seal's inner cavity are forced out of the grooves of the energizing ring (i.e., moving from the thinnest section of the energizing ring, out to the thickest section), causing the seal lips to spread apart and roll around in a radial outward direction, rather than stretch. This process increases the seal's outer diameter and decreases the seal's inner diameter, causing the seal to form a pressure-assist, metal-to-metal seal between the adjacent conductors.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the features and advantages of the present invention, which will become apparent, are attained and can be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings which form a part of this specification. It is to be noted, however, that the drawings illustrate only some 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.
FIG. 1 is a sectional side view of a conventional surface wellhead assembly;
FIG. 2 is an enlarged sectional side view of one type of prior art seal assembly for the wellhead assembly of FIG. 1;
FIG. 3 is an enlarged sectional side view of another type of prior art seal assembly for the wellhead assembly of FIG. 1;
FIG. 4 is an enlarged sectional side view of one embodiment of a seal assembly for a wellhead assembly shown in an un-energized position and is constructed in accordance with the invention;
FIG. 5 is a further enlarged sectional side view of the seal assembly of FIG. 4 in the un-energized position and is constructed in accordance with the invention;
FIG. 6 is an enlarged sectional side view of the seal assembly of FIG. 4 shown in an energized position and is constructed in accordance with the invention;
FIG. 7 is a further enlarged sectional side view of the seal assembly of FIG. 6 in the energized position and is constructed in accordance with the invention; and
FIG. 8 is an enlarged sectional side view of an alternate embodiment for actuating the seal assembly, shown in the un-energized position, and is constructed in accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIGS. 4-7, one embodiment of system, method, and apparatus for forming a metal wellhead seal assembly between inner and outer wellhead members is disclosed. The wellhead seal assembly 31 is located in an annular space or annulus 32 (FIG. 4) that is radially between a set of co-axial wellhead members 33, 35. A radially-movable member 37 is located in and extends through outer wellhead member 35 for actuating the wellhead seal assembly 31 between an engaged or energized position (FIGS. 6 and 7), and unengaged or un-energized position (FIGS. 4 and 5).
The wellhead seal assembly 31 comprises at least one seal ring 41 (e.g., one shown in FIGS. 5 and 7) that are formed from metal. In FIGS. 4 and 6, two seal rings 41 are shown and are axially spaced apart from each other in annulus 32 relative to wellhead members 33, 35. As best shown in FIG. 5, the seal ring 41 has inner and outer walls 43, 45 curving toward each other on the open end and spaced apart to form a slot 47 between walls 43, 45. In the embodiment shown, each seal ring 41 comprises a first or upper set of inner and outer walls 43, 45, a second or lower set of inner and outer walls 43, 45 located axially opposite the upper set, and both sets of the inner and outer walls 43, 45 are separated by respective slots 47. The slots 47 are formed on a radius and have an arcuate cross-sectional profile. In one embodiment, both sets of the inner and outer walls 43, 45 of the seal ring 41 have exterior surfaces 49 that are radiused to define a seal ring cross-sectional shape having inner and outer profiles that are both arcuate in shape.
In one embodiment, the seal ring 41 has an axial length 51 (FIG. 5) and a radial width 53 in the un-energized position. However, in the energized position (FIG. 7), the seal ring 41 shortens in axial length 55 and expands in radial width 57 (i.e., to the width of the annulus 32) relative to length 51 and width 53 of the un-energized position. As shown in FIGS. 5 and 7, optional elastomeric members 81 may be located between axially central portions of seal rings 41 and the surfaces of the wellhead members 33, 35.
The wellhead seal assembly 31 further comprises one or more solid energizing rings 61 that are formed from metal. Each energizing ring 61 is associated with one of the sets of inner and outer walls 43, 45. For example, in FIGS. 5 and 7 a pair of energizing rings 61 is shown, but in FIGS. 4 and 6, two single-ended energizing rings 63, 64 and one double-ended energizing ring 65 are shown. In the embodiment shown, upper energizing ring 63 has a chamfer 67 for sliding engagement with radially-movable member 37, and lower energizing ring 64 is located on an orthogonal shoulder 69 formed on the outer surface of inner wellhead member 33.
As best shown in FIG. 7, each set of the inner and outer walls 43, 45 of the seal ring 41 terminates in seal lips having recessed edges 44, forming hooks that extend along interior surfaces thereof. Each energizing ring 61 has inner and outer surfaces that are generally concave in cross-sectional shape. In one embodiment, each inner and outer surface comprises external grooves 71 that engage and mate with respective ones of the recessed edges 44 in a nesting configuration in the un-energized position. Located axially on either side of grooves 71 are a neck 73 on a proximal end thereof, a hooked feature 75 on a distal end thereof, with the groove 71 forming the concave cross-sectional shape between the proximal and distal ends. In the energized position, the distal ends of the seal rings engage the necks 73 and the distal ends of the energizing rings 61 abut axially interior portions of the slots 47 to elastically deform the inner and outer walls 43, 45 of the seal rings 41. In the un-energized position, the distal ends of the seal rings 41 seat in the grooves 71 and the hooked features interlock with features 44 inside the inner and outer walls 43, 45 of the seal rings 41 to retain the energizing rings 61 in the internal slots 47.
The inner and outer surfaces of energizing rings 61 slidingly engage the inner and outer walls 43, 45 of the slots 47 in the seal rings 41 between the energized position wherein the inner and outer walls 43, 45 elastically deform into bi-directional sealing engagement with the inner and outer wellhead members 33, 35. In the un-energized position, the inner and outer walls 43, 45 of seal ring 41 do not form a seal between the inner and outer wellhead members 33, 35. In the energized position, the seal lips of seal rings 41 are forced out of the external grooves 71 causing the seal lips to roll around in a radial outward direction, rather than stretch, and expand both sets of walls 43, 45 against the inner and outer wellhead members 33, 35.
Referring now to FIG. 8, an alternate embodiment for actuating the seal assembly is depicted with the seal in the un-energized position. The upper energizing ring 81 is provided with a circumferential, radially internal flange 83 that is mechanically coupled to an axially movable ring 85. In one embodiment, ring 85 is threaded to and reacts in response to inner wellhead member 33 as shown. Ring 85 is used to axially stroke (i.e., push and retract) energizing ring 81 and, thereby, the other energizing rings 87, 89 to manipulate seal rings 91, 93, respectively, between the energized and un-energized positions as described herein.
While the invention has been shown or described 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.
Patent Grant
7614447
