Pressure energized seal

A seal for use in sealing on a wellhead assembly, where the seal is pressure energized and comprises an annular element having an inverted portion on its outer portion along its length. The seal may further include upper and lower ring members sandwiching the element between the ring members. The seal is formable by adjoining the open surfaces of two “W” shaped annular seals along their edges thereby forming an element responsive to pressure.

BACKGROUND

1. Field of Invention

The device described herein relates generally to wellhead assemblies, and in particular to provide a pressure seal for use with a wellhead assembly.

2. Description of Related Art

Wellheads used in the production of hydrocarbons extracted from subterranean formations typically comprise a wellhead assembly. Wellhead assemblies are attached at the opening of wellbores that intersect hydrocarbon producing formations. Wellhead assemblies also provide support for casing inserted into the wellbore. The casing lines the wellbore, thereby isolating the wellbore from the surrounding formation. Tubing typically lies concentric within the casing and provides a conduit for producing the hydrocarbons entrained within the formation. Wellhead assemblies also typically include production trees that connect to the upper end of the tubing and distribute the produced fluids. The tubing may be supported by a tubing hanger in the wellhead housing or in the production tree.

Hardware within the wellheads for suspending the tubing and casing is arranged in a concentric arrangement. If the hanger is in the wellhead housing an isolation sub extends between the tubing hanger and a production bore in the production tree. Various seals are employed between the sub and its mating parts.

SUMMARY OF INVENTION

The present disclosure includes a wellhead assembly comprising, a housing, a tubular within the housing, a support shoulder, and a seal assembly disposed between the tubular and the housing where the seal assembly is configured to engage the shoulder. The seal assembly comprises an annular seal having a lower portion, an upper portion an inner side wall and an outer side wall, wherein a portion of the outer surface of the seal is inverted. One of the lower portion or upper portion may be inverted. The wellhead assembly may further comprise a lower support ring formed for mating engagement with the lower portion and an upper support ring for mating engagement with the upper portion. The support rings may include raised portions for engagement with the inverted contours of the portions. Optionally, a vent may be formed through a wall of the annular seal and solid particles may be included in the annular seal. The annular seal is energized into sealing engagement between the tubular and housing in response to pressure applied to its outer surface. The annular seal may be a metal face seal.

Also disclosed herein is a pressure energized seal assembly for sealing between a tubular and a corresponding member. In this embodiment the seal comprises an annular element configured to circumscribe the tubular member, the annular element having an upper portion, a lower inverted portion, and side walls, wherein the lower inverted portion is formed for pressure communication with a pressure source, and wherein pressure applied to the lower inverted portion urges the side walls into sealing engagement with the tubular and the corresponding member, and a supporting shoulder formed for compressive engagement with the upper portion.

A method of sealing between a tubular and a housing in a wellhead assembly is further included herein, the method comprising, forming a shoulder within the wellhead assembly, wherein the shoulder circumscribes the tubular, disposing a seal assembly adjacent the shoulder, wherein the seal assembly comprises an annular sealing element circumscribing the tubular having an axis, an upper portion, an inner side wall, an outer side wall, a lower portion wherein the lower portion is inverted towards the axis, and putting a pressure source in pressure communication with the lower portion thereby imparting a compressive force onto the annular sealing element that outwardly urges the inner side wall into sealing engagement with the tubular and the outer side wall into sealing engagement with the housing.

DETAILED DESCRIPTION OF INVENTION

Referring now toFIG. 1, one embodiment of a wellhead assembly having a pressure activated sealing element is provided.FIG. 1shows a cross sectional view of a wellhead assembly5comprising a production tree7mounted atop a wellhead housing9. A production bore11is formed within the production tree7that provides fluid communication with a production flow outlet15extending from the production tree7. In the embodiment shown, a portion of the production bore11extends laterally within the production tree7to the production flowline15. Control valves13are provided in the primary portion of the production bore11and also on the production outlet15. Selectively opening and closing the control valves13selectively allows wellbore fluid flow through the production outlet15.

The wellhead housing9is attached to the production tree7by an external connector17. Included within the housing9are production tubing22, a tubing hanger21, and a casing hanger23. In the embodiment shown, the casing hanger23, which is a generally annular member, is coaxially secured within a portion of the housing9and supports a string of casing cemented in the well. Packoffs19(also referred to as casing hanger seals) are disposed between the outer circumference of the casing hanger23in a portion of the inner circumference of the housing9. An inner groove is shown formed within the casing hanger23formed to receive the annular tubing hanger21. Production tubing22extends downward from the tubing hanger21into the wellbore3from within the housing9.

An annular isolation sleeve27coaxially resides within a portion of the production tree7on its upper end and extends downward terminating within the upper portion of the tubing hanger21. Wellbore flow from the production tubing22reaches the production bore11through the isolation sleeve27. Examples of seal assemblies30are shown circumscribing the isolation sleeve27on the sleeve27upper end and sleeve27lower end. For the purposes of reference and clarity, the term “upper” generally refers to a position closer to the top of the production tree7, and the term “lower” generally refers to a position closer to the bottom of the wellbore5.

The seal assembly30on the sleeve27upper end resides in an upper pocket26formed in the sleeve27. The seal assembly30on the sleeve27lower end is in a lower pocket28formed in the sleeve27. In the embodiment ofFIG. 1, seal assembly30provides a sealing function between the outer circumference of the isolation sleeve27and surrounding concentric hardware. Optionally the seal assembly30can be positioned in other concentric members of the wellhead assembly5or multiple seal assemblies30may be included within the wellhead assembly5.

FIG. 2illustrates one cross-sectional view of an embodiment of a seal assembly30for use within a wellhead assembly5. In this embodiment, the seal element34is in a pocket26formed by an upward facing shoulder31formed on the isolation sleeve27and a downward facing shoulder36on a threaded retainer ring29. Optionally and as noted above, the pocket26may be formed in any one of a number of the concentric members making up the wellhead assembly5. The seal assembly30ofFIG. 2comprises a seal element34in the annular space between a pair of concentric wellhead assembly elements. In the embodiment shown, the seal element34is an annular member comprising a metal, elastically deformable outer wall39circumscribing an inner hollow space41. The hollow space41does not have to be sealed. The wall39forms a pressure harrier around the hollow space41whereby applying a force at a first location on the outer surface of the wall39causes an outward bulge on the wall39at a second location. The wall39may be formed from a pliable and elastic metal allowing it to deform under applied force and in some situations return to its original un-deformed shape. Optionally the seal element34may be a metal faced seal.

With reference to the specific embodiment illustrated inFIG. 2, the seal element34comprises an upper portion40, a lower portion42, an outer sidewall46, and an inner sidewall44. The outer sidewall46is shown in contacting engagement with a wall of the tree production bore11. The inner wall of the pocket26in this embodiment is the isolation sleeve27, thus, the inner sidewall44is illustrated in contact with a cylindrical exterior surface of the isolation sleeve27. The upper and lower portions40,42of the seal element34ofFIG. 2are inverted wherein the mid section of these portions40,42bows inward toward the axis of the seal element34. Inverting each of the upper and lower portions40,42creates a “W” shaped cross section of these respective portions40,42. Inverting the upper and lower portions40,42fashions an inwardly protruding space on the outside of the wall39at the upper and lower portions40,42.

Thus in one example of use applying a distributed force, such as pressure, at the outer wall39where the lower portion42is inverted, the upward force on the inverted portion flexes the sidewalls40,46radially inward and outward into contacting and sealing engagement with the respective walls of the pocket26between the wall of the tree production bore11and the wall of the isolation sleeve27. In use, normally the upper portion40of the seal34will be exposed to internal pressure in the tubing22via the clearance existing between the end of the isolation sleeve27and the tree production bore11. Since wellbore pressure normally exceeds ambient pressure existing below the seal assembly30, a pressure differential will form between the lower portion42and the upper portion40. The resulting pressure differential results in a force distribution that energizes the seal assembly30into sealing engagement between the isolation sleeve27and the tree production bore11. If a higher pressure occurred on the exterior of the isolation sleeve27, the reverse would occur with pressure being exerted in the lower seal portion42.

Optionally the seal assembly30may further comprise annular rigid conformed members32on top.FIGS. 2 and 3provide a cross sectional view of the conformed members32. The conformed members comprise a base33, wherein the base is shown roughly perpendicular to the axis of the wellhead assembly5. Perpendicularly extending from roughly the middle of the base33is a cylindrical vertical member35giving each member32a “T” shape in cross section. The members32include a cylindrical portion that inserts into one of the inverted portions and a cap that contacts one of the shoulders31or36. Conforming members32prevent the inverted portion from deflecting excessively when under pressure.

In one optional embodiment, individual solid particles38may be included within the inner annulus of the seal34. These particles38provide a structural support to the seal element34without hindering the distribution of or transfer of pressure forces throughout the seal element34, thereby energizing the seal element34. The diameter of the particles38can vary or be substantially homogenous. In one embodiment, the particles38comprise a multitude of glass beads. Optionally the particles may comprise fine particles such as talc. The particles38would not completely fill all void space within the seal element34, rather room is left between the particles to allow inward and outward flexing of the seal element34.

Another optional embodiment of the seal assembly30ais provided in cross sectional view inFIG. 3. In this embodiment, a pressure vent37is shown formed through the wall39a. The pressure vent allows equalization of the pressure within the seal element34aand the surrounding area. This may be useful in situations when the area surrounding the seal element34amay experience a pressure increase during use. If the pressure in the seal element34ais substantially lower than its surrounding environment, the unequal pressure distribution may prevent it from expanding into sealing engagement as needed.

The seal element34may be formed by combining together two metal W seals, the W seals may be seam welded along their edges at a line of symmetry. Additionally, the apex of the corresponding upper and lower portions40,42may include added support for accommodating the presence of the ring members32.

The member32may comprise other embodiments. For example, the cross section may resemble that of a triangle having rounded edges as well as a semi-circular member, where the apex of the semi-circle protrudes into the inverted portion of the seal34. In order to ensure proper sealing engagement of the seal member34, the design of the seal34should maintain an axial clearance between the apex of the inverted portions, even under related conditions.

It is to be understood that the invention 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. For example, the seal element34may have a single side that is inverted and not both sides. Additionally, the inverted space may comprise a generally rectangular cross section and be positioned at any radial location on the outer surface of the wall39. The seal may be used in many other applications other than on an isolation sleeve of a wellhead assembly. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.