System, method, and apparatus for energizable metal seals in well heads

A bi-directional metal seal 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 rings have external grooves 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 of the seal are forced out of the grooves causing the seal lips to roll around in a radial outward direction, rather than stretch, and expand against the seal's outer diameter. This energizing process also causes the seal to become smaller on the seal's inner diameter, and thus forms a pressure-assist, metal-to-metal seal with the adjacent conductors.

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 inFIG. 1, seals11are used between inner and outer wellhead tubular members13,15to 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 seals17(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 seal19(see, e.g.,FIG. 3) has a U-shaped cross-sectional shape with inner and outer walls separated by a conical slot. An energizing ring21is pushed into the slot to deform the inner and outer walls apart into sealing engagement with the inner and outer wellhead members13,15. 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.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS. 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 assembly31is located in an annular space or annulus32(FIG. 4) that is radially between a set of co-axial wellhead members33,35. A radially-movable member37is located in and extends through outer wellhead member35for actuating the wellhead seal assembly31between an engaged or energized position (FIGS. 6 and 7), and unengaged or un-energized position (FIGS. 4 and 5).

The wellhead seal assembly31comprises at least one seal ring41(e.g., one shown inFIGS. 5 and 7) that are formed from metal. InFIGS. 4 and 6, two seal rings41are shown and are axially spaced apart from each other in annulus32relative to wellhead members33,35. As best shown inFIG. 5, the seal ring41has inner and outer walls43,45curving toward each other on the open end and spaced apart to form a slot47between walls43,45. In the embodiment shown, each seal ring41comprises a first or upper set of inner and outer walls43,45, a second or lower set of inner and outer walls43,45located axially opposite the upper set, and both sets of the inner and outer walls43,45are separated by respective slots47. The slots47are formed on a radius and have an arcuate cross-sectional profile. In one embodiment, both sets of the inner and outer walls43,45of the seal ring41have exterior surfaces49that 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 ring41has an axial length51(FIG. 5) and a radial width53in the un-energized position. However, in the energized position (FIG. 7), the seal ring41shortens in axial length55and expands in radial width57(i.e., to the width of the annulus32) relative to length51and width53of the un-energized position. As shown inFIGS. 5 and 7, optional elastomeric members81may be located between axially central portions of seal rings41and the surfaces of the wellhead members33,35.

The wellhead seal assembly31further comprises one or more solid energizing rings61that are formed from metal. Each energizing ring61is associated with one of the sets of inner and outer walls43,45. For example, inFIGS. 5 and 7a pair of energizing rings61is shown, but inFIGS. 4 and 6, two single-ended energizing rings63,64and one double-ended energizing ring65are shown. In the embodiment shown, upper energizing ring63has a chamfer67for sliding engagement with radially-movable member37, and lower energizing ring64is located on an orthogonal shoulder69formed on the outer surface of inner wellhead member33.

As best shown inFIG. 7, each set of the inner and outer walls43,45of the seal ring41terminates in seal lips having recessed edges44, forming hooks that extend along interior surfaces thereof. Each energizing ring61has inner and outer surfaces that are generally concave in cross-sectional shape. In one embodiment, each inner and outer surface comprises external grooves71that engage and mate with respective ones of the recessed edges44in a nesting configuration in the un-energized position. Located axially on either side of grooves71are a neck73on a proximal end thereof, a hooked feature75on a distal end thereof, with the groove71forming the concave cross-sectional shape between the proximal and distal ends. In the energized position, the distal ends of the seal rings engage the necks73and the distal ends of the energizing rings61abut axially interior portions of the slots47to elastically deform the inner and outer walls43,45of the seal rings41. In the un-energized position, the distal ends of the seal rings41seat in the grooves71and the hooked features interlock with features44inside the inner and outer walls43,45of the seal rings41to retain the energizing rings61in the internal slots47.

The inner and outer surfaces of energizing rings61slidingly engage the inner and outer walls43,45of the slots47in the seal rings41between the energized position wherein the inner and outer walls43,45elastically deform into bi-directional sealing engagement with the inner and outer wellhead members33,35. In the un-energized position, the inner and outer walls43,45of seal ring41do not form a seal between the inner and outer wellhead members33,35. In the energized position, the seal lips of seal rings41are forced out of the external grooves71causing the seal lips to roll around in a radial outward direction, rather than stretch, and expand both sets of walls43,45against the inner and outer wellhead members33,35.

Referring now toFIG. 8, an alternate embodiment for actuating the seal assembly is depicted with the seal in the un-energized position. The upper energizing ring81is provided with a circumferential, radially internal flange83that is mechanically coupled to an axially movable ring85. In one embodiment, ring85is threaded to and reacts in response to inner wellhead member33as shown. Ring85is used to axially stroke (i.e., push and retract) energizing ring81and, thereby, the other energizing rings87,89to manipulate seal rings91,93, respectively, between the energized and un-energized positions as described herein.