Seal assembly with accumulator ring

A seal assembly with an accumulator ring for protecting a seal from explosive decompression is disclosed. The accumulator ring and the seal are contained within a seal gland. The seal is made of a material that is susceptible to damage from explosive decompression. When exposed to a high-pressure fluid environment, the accumulator ring fills with a quantity of high-pressure fluid, either by permeation if it is solid or by permeation and/or vents and/or channels leading to a void if it is hollow. During an explosive decompression event, the accumulator ring expands to fill the remaining volume of the seal gland. Then, the accumulator ring exerts an axial compressive or supporting force on the seal for a sufficient amount of time to allow the seal to expel fluid contained in it and minimize the effects of explosive decompression thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a seal assembly and method of sealing for use in high pressure application, for example, drilling and production applications. More particularly, the invention involves a seal assembly and method of sealing the junction between the male and female members or face seal members, wherein the seals are susceptible to explosive decompression effects.

2. Related Art

Ring seals are used in a variety of environments. Of particular interest are ring seals used in high-pressure environments. These include applications such as oil field drilling and production operations, hydraulic couplings, blowout preventer packings, etc.

Typical ring seals are often made from semi-permeable elastomeric materials. The sealing rings are intended to seal against a particular medium; if the pressure brought against the sealing rings by the medium becomes too great, the medium begins to penetrate the elastomeric material that constitutes the sealing rings. If a sudden pressure drop occurs in the surroundings of the sealing ring after such a penetration has occurred, the medium that has penetrated into the sealing rings abruptly expands. As a consequence of this expansion, the sealing rings are damaged or even destroyed. This kind of event is called an “explosive decompression.” This is a particular problem when the fluid is a gas at high temperature and pressure. In order to reduce the risk of an explosive decompression occurring, it is known to use seals, for example, o-rings, having a reduced cross-section and, as a result, a reduced exposed surface area. The likelihood of explosive decompression is also decreased by using seals made of materials having very low or very high permeability rates, such as costly and weaker silicone materials. Low permeability rates minimizes the incorporation of fluid in such materials, typically having a high durometer, thereby minimizing the effects of explosive decompression thereto. High permeability rates allows any fluid within such a material to be quickly released, thereby minimizes such effects thereto. Additionally, seal designers attempt to achieve a maximum volume fill of the seal gland partly to try to minimize such effects, but are constrained from doing so due to the thermal coefficient of expansion of the materials placed within the seal gland. Thus, a 100% volume fill cannot be accomplished. At best, about a 90% volume fill is attainable at room temperature.

There is a need to protect ring seals and provide a degree of resistance to explosive decompression regardless of the material that constitutes the ring seals.

SUMMARY OF THE INVENTION

In a broad aspect, there is provided a seal assembly for high pressure applications, said assembly comprising:

a first member having a first surface;

a second member having a second surface, wherein the first surface and second surface oppose and are spaced from each other when the first and second members are joined;

a third surface and a fourth surface, wherein each of the third and fourth surfaces is integral to, attached to or supported by one of the first and second surfaces and wherein the third surface and fourth surface oppose and are spaced from each other,

wherein the first, second, third and fourth surfaces define a seal gland therewithin;

a ring seal positioned within the seal gland, wherein the ring seal being axially compressible to sealingly engage the first surface and the second surface and the ring seal is susceptible to explosive decompression effects; and

an accumulator ring positioned within the seal gland on the side of the ring seal to be exposed to a high pressure fluid, wherein said accumulator ring has an exterior and an interior, wherein the interior has a void fraction defining an accumulator volume and said accumulator ring has at least one channel providing communication between the exterior of the accumulator ring and the accumulator volume, wherein in an installed position exposed to high pressure fluids, the accumulator volume fills with fluid and during an explosive decompression event, the at least one channel allows the fluid in the accumulator ring to escape at a rate sufficient to allow the exterior to compress the ring seal for a sufficient amount of time to minimize the explosive decompression effects on the ring seal.

In one embodiment, the first member is a female member and the second member is a male member. In this embodiment, the seal assembly comprises:

a female member having a longitudinal bore and an annular shoulder in the bore;

a male member insertable into the female member bore, having an annular shoulder on the outer surface thereof,

wherein the male and female members are joined and define a seal gland between the shoulders thereof;

a ring seal positioned within the seal gland, wherein the ring seal is axially compressible to sealingly engage the male member and the female member bore and the ring seal is susceptible to explosive decompression effects; and

an accumulator ring positioned within the seal gland on the side of the ring seal to be exposed to a high pressure fluid, wherein said accumulator ring has an exterior and an interior, wherein the interior has a void fraction defining an accumulator volume and the accumulator ring has at least one channel providing communication between the exterior of the accumulator ring and the accumulator volume, wherein in an installed position exposed to high pressure fluids, the accumulator volume fills with fluid and during an explosive decompression event, the at least one channel allows the fluid in the accumulator ring to escape at a rate sufficient to allow the exterior of the accumulator ring to compress the ring seal for a sufficient amount of time to minimize the explosive decompression effects on the ring seal. This active support of the seal during pressure venting provided by the accumulator ring simulates a 100% volume fill design (or zero void fraction) of the seal gland.

In one embodiment, the accumulator ring and the ring seal fill the seal gland in an installed position.

In an alternate embodiment, a seal retainer is placed in the seal gland. The seal retainer has a first end and a second end. The first end is configured to contact the annular shoulder of the male member and the second end configured to contact the ring seal to compress the ring seal axially. A locking means may be added to limit axial movement of the seal retainer. The locking means may, for example, be a clip engageable with the female member bore to hold the retainer in the bore.

In one embodiment, the accumulator ring is an o-ring made of a flexible but relatively strong and preferably semi-resilient material, for example, metal and plastics (such as Kevlar), where the o-ring is provided with at least one vent hole between the exterior and interior of the o-ring. The o-ring is pressure-energized to engage the ring seal and the shoulder abutting accumulator ring in response to an explosive decompression event in the seal assembly, thereby supporting the seal. After the pressure venting process has terminated or during any application of pressure that has equalized, the accumulator ring, being made of a strong yet resilient material, eventually restores itself to its original shape.

In another embodiment, the accumulator ring is made of a material permeable by the high-pressure fluid. In this case, the extent of permeation of the high-pressure fluid is the void fraction. The material releases the permeated fluid therefrom during an explosive decompression event at a slower rate than the ring seal. This allows the accumulator ring to expand and place an axial compressive load the ring seal within the seal gland to minimize the explosive decompression effects on the ring seal. The accumulator ring may also be partly hollow providing an additional volume for containing the high-pressure fluid that has permeated through the material and thus increases the void fraction. In either configuration, when the rate of pressure change is near zero, the accumulator ring will eventually restore itself to its original shape.

In another embodiment, the accumulator ring has at least a first toroidal ring and a second toroidal ring. Each of the first and second toroidal rings has an axial cross section that defines a planar figure. The planar figure partially encloses an area having an open side and a closed side. The open side of the first toroidal ring is placed within the open side of the second toroidal ring with the closed sides of the first and second toroidal rings opposing each other. The thus positioned first and second toroidal rings define an enclosed volume therewithin and an exterior surface.

The planar figure formed by the axial cross section of the first and second toroidal rings is preferably U-shaped. Therefore, the first and second toroidal rings are each a U-shaped toroidal ring having an open side and a closed side.

Preferably, at least one of the first and second toroidal rings has at least one vent to allow high-pressure fluid to enter or exit the enclosed volume. During an explosive decompression event, the fluid in the enclosed volume expands and exits through the at least one vent. The number and size of the vent(s) controls the exit flow rate of the fluid and allows the expanding fluid remaining within the enclosed volume to urge the first and second toroidal rings to expand radially against each other and the male member. The first and second toroidal rings are also urged apart axially against the ring seal and the shoulder abutting the accumulator ring to axially compress or support the ring seal for a sufficient amount of time during an explosive decompression event to minimize the explosive decompression effects on the ring seal.

Alternatively or in addition, the material of at least one of the first and second toroidal rings may be permeable to the high-pressure fluid. If the rate of permeation is sufficient, vent(s) may not be necessary.

Each sealing element of the present invention is fabricated in the shape of a toroidal ring, which is defined herein as the body formed by the rotation of a planar figure about a line or axis of rotation which lies in the same plane as the planar figure but does not intersect it. The axis of rotation is the axis of the toroidal ring. The axial cross section of a toroidal ring therefore is defined by the intersection of the ring with a plane, wherein the axis of the toroidal ring lies entirely in the plane. As an illustration, the rotation of a disc about an axis of rotation which lies in the same plane as the disc forms a toroidal ring typically known as an o-ring, and the axial cross section of the o-ring forms a disc.

Each sealing element has an axial cross section forming any planar shape or figure that defines an area having an open side and a closed side. The open side of the figure formed by the cross section is oriented in a generally axial direction relative to the toroidal ring, and the closed side is oriented in a generally opposite direction from the open side. Likewise, the toroidal ring defines a general circumferential volume enclosed or defined by an open side and a closed side. Typically, the open side of the toroidal ring is oriented in a generally axial direction and the closed side is oriented in a generally opposite axial direction from the open side. The circumferential volume typically is oriented in a generally axial direction.

As an example, one of the preferred sealing elements of the invention has an axial cross section defining a U-shaped body in which the open end of the U is oriented in the axial direction and the closed end of the U is oriented in the opposite axial direction. When used in a seal assembly as described below, two U-shaped rings are used with the open side of the inner U inserted into the open side of the outer U-shaped ring. This defines an enclosed volume within this double U assembly. Vents in one or both of the inner and outer U-shaped rings and gaps between the inner and outer U-shaped rings allows fluid to enter the enclosed volume. The inner and outer U-shaped rings are each a toroidal ring defined by the rotation of the U-shaped body about the axis.

As another example, one of the preferred sealing elements of the invention has an axial cross section defining an E-shaped body in which the open end of the E is oriented in the axial direction and the closed end of the E is oriented in the opposite axial direction. When used in a seal assembly as described below, the E-shaped ring is placed with the open side in contact with the ring seal. This defines an enclosed or internal volume within the E-shaped body, since the open end is now closed by the ring seal. Vents in E-shaped ring or the permeability of the material the E-shaped ring is made of, together with gaps between the open end thereof and the ring seal, allows fluid to enter the enclosed volume. The E-shaped ring is a toroidal ring defined by the rotation of the E-shaped body about the axis with the open end oriented in the axial direction.

Other axial cross sections of the sealing element or toroidal ring are possible which form planar figures having other general shapes, some of which can be described schematically by the letters C, E, H, V, W, X, and Y. Other more complex shapes can be envisioned which have similar mechanical properties. The common characteristic of these planar figures is that the toroidal ring defined by each figure has a circumferential volume which is oriented in a generally axial direction and allows one to be placed within another in a similar fashion as the double U assembly to in turn define an internal volume.

During pressure venting, including an explosive decompression event, the pressurized fluid in the internal volume expands and urges the compliant arms or members of the ring to expand against both each other (as in the double U-shaped ring embodiments) and axial surfaces of a seal gland (as in both the double U-shaped ring embodiments and the E-shaped ring embodiment) to temporarily retain and controllably release or vent the pressurized fluid contained in the internal volume. Also, as the pressurized fluid in the internal volume expands, the inner and outer toroidal rings in the double U-shaped ring embodiments are urged axially apart, thereby exerting a compressive force against the seal being protected due to such fluid expansion. In the E-shaped ring embodiment, the expanding pressurized fluid within the internal volume exerts the compressive force against the seal being protected. This allows any fluid that may have permeated therein to escape at a rate that prevents or at least minimizes the deleterious effects of such an event. The fluid within the internal volume is allowed to escape at a controlled rate via permeation or a suitable number and sized vents in one or both of the toroidal rings to allow a sufficient amount of time for fluid to escape from the protected seal.

There is also provided well sealing assembly for sealing between the interior surface of a housing and the exterior of a tubular body. The tubular body having a first exterior surface, a second exterior surface that has a larger diameter than the first exterior surface and a tapered surface between said first and second surfaces. The well sealing assembly comprises a seal ring assembly, an accumulator ring, and means for moving said seal ring assembly axially from its position surrounding said first surface of said tubular member, over said tapered surface and into its set position surrounding said second surface.

The seal ring assembly has a resilient ring with upper and lower flat surfaces, an interior convex surface and an exterior flat surface and annular metal end caps. The metal end caps have flat portions bonded on the upper and lower flat surfaces of the resilient ring, inner legs tapering with the convex interior surface of the resilient ring and outer legs on the flat exterior surface of the resilient ring. The interior surface of the resilient ring is in close spaced relationship to the first surface of the tubular member when said seal ring assembly surrounds the first surface.

The accumulator ring axially positioned adjacent to the seal ring assembly on the side of the seal ring assembly to be exposed to a high-pressure fluid. The accumulator ring has an exterior and an interior. The interior has a void fraction defining an accumulator volume. The accumulator ring has at least one channel providing communication between the exterior of the accumulator ring and the accumulator volume. The channel may be a vent or present in the material due to molecular spacing allowing permeation of a fluid therethrough. In an installed position exposed to high-pressure fluids, the accumulator volume fills with fluid. During pressure venting, for example, an explosive decompression event, the at least one channel allows the fluid in the accumulator ring to escape at a rate sufficient to allow the exterior to compress or support the seal ring assembly for a sufficient amount of time to minimize the explosive decompression effects on the material of the resilient ring of the seal ring assembly.

The resilient ring has sufficient resiliency and volume to expand outward when moved to the set position to seal against the interior housing surface and to move the exterior legs of the end caps into metal-to-metal sealing engagement with the interior housing surface and to seal against the second surface with the interior legs in metal-to-metal sealing engagement with the second surface.

DETAILED DESCRIPTION

FIG. 1is a section view of a first member10and second member12. The first member10has a first surface13and a shoulder14, which in this embodiment is the third surface. The second member12has a second surface15and a shoulder16, which in this embodiment is the fourth surface. A space or void known as a seal gland18is defined by the first surface13, second surface15, and shoulders14and16, the third and fourth surfaces respectively.

FIG. 1Ais a section view of a first member10aand second member12a. The first member10ahas a first surface13aand a shoulder14aand shoulder16a, which in this embodiment are the third and fourth surfaces. The second member12ahas a second surface15a. A space or void known as a seal gland18ais defined by the first surface13a, second surface15a, and shoulders14aand16a, the third and fourth surfaces respectively.

FIG. 1Bis a section view of a first member10band second member12b. The first member10bhas a first surface13b, a threaded portion17and a shoulder14b, which in this embodiment is the third surface. The first surface13bis located between the threaded portion17and the shoulder14b. The second member12bhas a second surface15b. A threaded member19has a bottom surface16b, which in this embodiment is the fourth surface. The threaded member19in an installed position threadedly engages the threaded portion17. A space or void known as a seal gland18bis defined by the first surface13b, second surface15b, bottom surface16band shoulder14b, the latter two being the third and fourth surfaces respectively.

Other seal gland embodiments are shown in FIG.3and FIG.9.

In a first embodiment of the present invention shown inFIGS. 2 and 2A, the seal gland18of seal assembly1contains a metal end cap seal20in the set position and a hollow o-ring24. Though seal gland18is depicted herein, any other seal gland may be used which is defined by four surfaces, for example, those shown inFIGS. 1A,1B,3and9. The hollow o-ring24has vents26. In the set position, the metal end cap seal20seals against surfaces13and15. The hollow o-ring24is made of a material that substantially retains its shape during the setting of the metal end cap seal20. The o-ring24may be a hollow metal o-ring or of an elastomeric material. In another embodiment of the o-ring24, a spring33, for example, a helical or wave spring, as shown inFIG. 2Bcan be contained within the hollow o-ring in this embodiment referred to a24ato aid in retaining the shape of the o-ring24aduring the setting operation.

During high-pressure operations, the fluid follows path F through gap28. The seal made by the metal end cap seal20against surfaces13and15prevents the fluid from getting passed this point. The high-pressure fluid, typically a gas, enters the interior of the o-ring24through vents26.

During pressure venting, including an explosive decompression event, some of the gas may have permeated the non-metal portions of the metal end cap seal20behind metal end cap22on the high-pressure side. The rapid decompression causes the gas that has permeated into the metal end cap seal20to expand rapidly. To prevent or at least minimize the deleterious effects of rapid pressure venting or explosive decompression on the non-metallic portions of the metal end cap seal20, the vents26and the interior of the o-ring24are sized to gradually release the rapidly expanding gas contained therein. This causes the o-ring to exert a compressive force against the metal end cap seal20. This compressive force allows the gas trapped within the metal end cap seal20to be released at a rate that prevents or minimizes these deleterious effects on the seal20. The compressive load applied to the metal end caps seal20by the accumulator ring during the venting process simply supports the elastomer of the metal end cap seal20and therefore prevents its elastomeric material from axially elongating too far and rupturing.

If a spring33is contained within the o-ring24a, it can also provide continuous compressive loading against the seal20. In this case, the compressive loading provided by the spring33is a backup for the compressive or support force provided by the expanding gases. Further, with the spring, the sizing of the interior of the o-ring24aand the vents26is less critical. If desired, the spring33can be sized to provide the required compressive load without relying on the compressive force generated by the expanding gas within the o-ring24a. However, since it is believed that the axial compressive forces developed by the o-ring on the seal at high pressures is so much greater than could be provided with the spring, the spring's role would in many cases be an expander or restorer for the o-ring24a.

In a second embodiment of the present invention shown inFIG. 3, seal assembly2is similar to seal assembly1shown inFIG. 2, with the exception that the seal gland18of seal assembly2further contains a seal retainer30.

In a third embodiment of the present invention shown inFIG. 4, seal assembly3is similar to seal assembly1shown inFIG. 2, with the exception that the hollow o-ring24has been replaced by a solid o-ring32. O-ring32is made of a material that is permeable by the high-pressure gas. The o-ring32is sized to allow a sufficient amount of gas to permeate and accumulate within it; and, during pressure venting including an explosive decompression event, o-ring32expands as a result of the gas rapidly expanding therein trying to escape. This expansion exerts a compressive force against seal20to prevent or at least minimize the explosive decompression effects on seal20. The rate of gas escape from the o-ring32is less than that of the non-metallic material of the seal20.

In a fourth embodiment of the present invention shown inFIG. 5, seal assembly4is similar to seal assembly1shown inFIGS. 2 and 2A, with the exception that the hollow o-ring24has been replaced by a hollow o-ring34. O-ring34is made of a material that is permeable by the high-pressure gas. The interior void36of o-ring34is sized to allow a sufficient amount of gas to permeate and accumulate within it and during an explosive decompression event expands as a result of the gas rapidly expanding therein trying to escape. This expansion exerts a compressive force against seal20to prevent or at least minimize the explosive decompression effects on seal20. The rate of gas escape from the o-ring34is less than that of the non-metallic material of the seal20.

In a fifth embodiment of the present invention shown inFIGS. 6 and 6A, seal assembly5is similar to seal assembly1shown inFIG. 2, with the exception that the hollow o-ring24has been replaced by a slip double U assembly38. The slip double U assembly has an inner U-shaped ring40and an outer U-shaped ring54. The inner U-shaped ring40has a back42, a vent or vents52in the back42, legs44and46axially extending substantially perpendicular from the back42, and outer U leg stops48and50radially extending from the back42in opposite directions. The outer U-shaped ring54has a back56, a vent or vents62, and legs58and60axially extending substantially perpendicular from the back56. The radial spacing between the outside surfaces of legs44and46is less than the radial spacing of the inner surfaces of legs58and60. The inner U-shaped ring40is inserted into the outer U-shaped ring54with the legs58and60placed adjacent to the outer U leg stops48and50, respectively. This placement of the inner and outer U-shaped rings40and54, respectively, defines an internal volume or void64. The interior volume64of the slip double U assembly38is sized to allow a sufficient amount of gas to accumulate within it to allow the assembly38to exert a compressive force against the seal20during an explosive decompression event for a sufficient amount of time to prevent or at least minimize the deleterious effects of the explosive decompression event to seal20.

During pressure venting, including an explosive decompression event, the fluid within the volume64rapidly expands. The fluid may initially be a liquid that converts to a gas or a pressurized gas that rapidly expands during such an event. The vents52and62are of a size and number that allows the rapidly expanding gas in volume64to exert an outward force against the interior surfaces of the double U assembly38. This gas expansion causes legs44and46to radially diverge and place an outward load against legs58and60creating a seal to prevent gas escape therebetween. Therefore, the only gas escape route is via vents52and62. The gas expansion also causes the inner and outer U-shaped rings to axially diverge from each other with legs44and46and legs58and60, respectively, slipping over each other as the gas continues to expand. This gas expansion places a compressive load against the seal20to prevent or at least minimize the explosive decompression effects on seal20. The rate of gas escape from the slip double U assembly38is controlled by the size and number of vents52and62in the inner and outer U-shaped rings40and54, respectively.

In a sixth embodiment of the present invention shown inFIGS. 6B and 6C, seal assembly7is similar to seal assembly5shown inFIGS. 6 and 6A, with the exception that the slip double U assembly38has been replaced by an interlocking double U assembly138. The interlocking double U assembly has an inner U-shaped ring140and an outer U-shaped ring154. The inner U-shaped ring140has a back142, a vent or vents152in the back142, legs144and146axially extending substantially perpendicular from the back142, outer U leg stops148and150radially extending from the back142in opposite directions, and grooves149and151, for example, adjacent the outer U leg stops148and150. The outer U-shaped ring154has a back156, a vent or vents162, legs158and160axially extending substantially perpendicular from the back156, and ridges159and161. Ridges159and161are adapted to matingly engage grooves149and151, preferably with the grooves149and151sized to be axially wider than the corresponding ridges159and161. As seen inFIG. 6C, this difference in axial width shown as gaps163and165allows the respective U-shaped rings140and154to expand and contract in the axial direction. The radial spacing between the outside surfaces of legs144and146is less than the radial spacing of the inner surfaces of legs158and160. The inner U-shaped ring140is inserted into the outer U-shaped ring154with the legs158and160placed adjacent to the outer U leg stops148and150, respectively. This placement of the inner and outer U-shaped rings140and154, respectively, defines an internal volume or void164. The interior volume164of the interlocking double U assembly138is sized to allow a sufficient amount of gas to accumulate within it to allow the assembly138to exert a compressive or supporting force against the seal20due to gas expansion within the internal volume164during an explosive decompression event for a sufficient amount of time to prevent or at least minimize the deleterious effects of the rapid pressure venting or explosive decompression event to seal20. InFIGS. 6B and 6C, a seal gland18bis used as depicted inFIG. 1B, though any of the other seal glands can be used.

During pressure venting, including an explosive decompression event, the fluid within the volume164rapidly expands. The fluid may initially be a liquid that converts to a gas or a pressurized gas that rapidly expands during such an event. During such an event, the fluid within the interior volume164expands faster than it can escape therefrom. Specifically, in this embodiment, the vents152and162are of a size and number that allows the rapidly expanding gas in volume164to exert an outward force against the interior surfaces of the double U assembly138(see black arrows in FIG.6C). This expansion causes legs144and146to radially diverge and place an outward load against legs158and160creating a seal to prevent gas escape therebetween. Therefore, the only escape route for the gas contained in the internal volume164is via vents152and162. The expansion also causes the inner and outer U-shaped rings140and154to axially diverge from each other. This axial divergence is initially limited by the difference in width between the width of the grooves149and151and the width of the ridges159and161with legs144and146and legs158and160, respectively, slipping over each other as the gas continues to expand producing the gaps163and165shown in FIG.6C. If the differential pressure is sufficiently great between the interior and exterior of the volume164, the ridges159and161will ride up on the grooves149and151. The U-shaped rings140and154will try to disengage from each other as the U-shaped rings140and154continue to axially move apart until there is no additional room left in the seal gland to do so. This expansion places a compressive load against the seal20to prevent or at least minimize the explosive decompression effects on seal20(see white arrows showing direction of force exerted on back156acting on seal20). The rate of gas escape from the interlocking double U assembly138is controlled by the size and number of vents152and162in the inner and outer U-shaped rings140and154, respectively.

The slip double U assembly38and the interlocking double U assembly138are made of materials that have the properties and capabilities described above. One example of such materials are high performance engineering plastics. One such plastic is polyether ether ketone, also known as PEEK, which is a strong polymer that would flex slightly during venting, withstand the stresses placed on it in operation, but would still provide an adequate seal between the legs of the inner and outer U-shaped rings during venting to minimize fluid escape therebetween. This would force the expanding fluid to exit the respective assembly by flowing through the vent holes provided.

In a seventh embodiment of the present invention shown inFIG. 6D, seal assembly5A is similar to seal assembly5shown inFIGS. 6 and 6A. However, rather than having vent holes extend through one or both of the U-shaped rings, seal assembly5A has the vent holes formed by having axial grooves21and23provided on at least one pair of legs corresponding to one of the U-shaped rings. When the two U-shaped rings are engaged, the grooves21and23on one pair of legs together with the adjacent legs of the other U-shaped ring define the venting holes.

In an eighth embodiment of the present invention shown inFIGS. 6E,6F and6G, seal assembly8shown inFIGS. 6E and 6Fis similar to seal assembly5shown inFIGS. 6 and 6A, with the exception that the slip double U assembly38has been replaced by a single E-shaped toroidal ring254. The seal gland is like that shown inFIGS. 6B and 6C. Ring254depending on perspective can also be described as M-shaped or W-shaped.

As shown more clearly inFIG. 6G, the cross-section of ring254reveals that it has a back256, a vent or vents262, a lateral channel257intersecting the vent262, outer legs258and260having ends270and271, respectively, a central leg261having end272, an equilibration vent263, ribs or ridges273and274, and internal volumes or voids264and265. Though optional, the central leg261is preferably present to provide ring254with increased load support capability. Ribs273and274are also optional, but preferred so as to provide a better seal of leg258and260against the adjacent surfaces275and276of members10band12b, respectively, during pressure venting. Vent or vents262are also optional if ring254is made of a permeable material that has a suitable permeability rate.

In an installed position, the ends270,271and272contact the metal cap22. The cooperation of the ring254and the metal cap22closes the open end of ring254allowing pressurized fluid to fill the internal volumes264and265. During pressure venting, such as an explosive decompression event, the pressurized fluid in the internal volumes264and265exerts forces in the directions of the arrows shown in FIG.6F. In one aspect, such forces push outward in a radial direction on legs258and260forcing ribs273and274into sealing engagement with surfaces275and276, respectively. In another aspect, the back256is pushed against surface278, thereby filling the seal gland volume. Further, as the pressurized fluid contained within the internal volumes264and265expands, this expanding fluid also exerts a supporting force on the metal cap22of ring seal20. Vent256and channel263with gap280cooperate to controllably release the pressurized fluid temporarily retained in the internal volumes264and265at a rate sufficient to allow any fluid contained within ring seal20to escape at a rate that will minimize the effects of rapid pressure venting thereto.

The o-rings24,32, and34may be made of any suitable semi-permeable elastomeric material that have the properties and capabilities described above that would flex during venting, withstand the stresses placed on it in operation, and return to its original pre-venting shape after the venting event has stabilized or a represurization has occurred and re-stabilized. One example of such materials are materials having a durometer of at most that of the elastomeric portion of the seal20. One example of such a material is nitrile rubber, preferably having a durometer of at least 70. Note unless otherwise specified, a durometer value specified herein is based on the Shore A scale, which is determined pursuant to ASTM D-1415.

The accumulator ring, in any of the foregoing embodiments, preferably provides at least 30 minutes of protection to the seal20during an explosive decompression or venting event to avoid or minimize the adverse effects of such an event on the seal20.

One particular application for the embodiments of the present invention is in the drilling and production area, for example, in the seal assembly disclosed in U.S. Pat. No. 4,496,162, which is hereby incorporated by reference. The seal assembly thereof is modified to include an accumulator ring66of the present invention. Accumulator ring66may be any of those disclosed previously in the first through fifth embodiments as the hollow, vented o-ring24(FIGS. 2,2A and3), solid o-ring32(FIG.4), hollow permeable o-ring34(FIG.5), slip double U assembly38(FIGS.6and6A), interlocking double U assembly138(FIGS.6B and6C), and E-shaped ring254(FIGS. 6E,6F and6G). Reference is now made toFIGS. 7 through 10.

Improved sealing assembly6of the present invention is deployed to, for example, a subsea well housing72on running tool74. Sealing assembly6is landed on and connected to hanger76supported in housing72in a known manner. Tubular body78of sealing assembly6engages hanger76through the ratchet (spring loaded, threaded segments) connection R and has its external downwardly facing shoulder80engaged on upper surface82of hanger76.

Sealing assembly6includes tubular body78, having upwardly facing external shoulder84, outer surface86, inwardly and upwardly tapering surface88, and upper surface90which is smaller in diameter than surface86, back-up ring92surrounding and releasably connected to surface86by shear pin94, seal ring assembly96and accumulator ring66above ring92and setting sleeve98above seal ring assembly96. In the unset or running position as shown schematically inFIG. 8, running tool74being removed for clarity, back-up ring92is positioned around surface86and extends upward to the bottom of tapered surface88into abutting relationship with seal ring assembly96, which in turn is in abutting relationship with the accumulator ring66. Setting sleeve98engages the upper end of seal ring assembly and surrounds surface90. Tapered split ring100is positioned in groove102in sleeve98and in groove104in body78. Split ring100and shear pin94retains sleeve98, sealing assembly96, accumulator ring66and back-up ring92in position during running. If desired, a pin or pins in back-up ring sliding in a slot in the exterior of body78can be used to assist to maintain the elements in position on body78during running. Sleeve98has internal groove106above groove102for the purposes hereinafter set forth.

Seal ring assembly96includes resilient ring108having metal end caps110and112on its upper and lower ends as shown and preferably bonded thereto. End caps110and112have a central portion114with legs116(including inner legs116band outer legs116a) extending upwardly and downwardly, respectively, in a direction toward the mid-point of resilient ring108. The inner central portion118of resilient ring108is convex and extends inward into light engagement or close spaced relationship with surface90in its unset position. It is preferred that resilient ring108be made of an elastomeric material, such as a nitrile rubber as sold by B. F. Goodrich Company under the trademark HYCAR, and metal end caps are a thin type316stainless steel. The metal end caps and the elastomeric portion of the seal ring assembly96can be coated with Teflon material, for example, to prevent the sticking of the seal ring assembly96to the first and second surfaces of the seal gland.

During running, sealing assembly6is supported on running tool74by pins120and122. Upon landing of assembly6running tool74is rotated to tighten connection R and then it is lowered to cause pin124to engage sleeve98and move it downward to the position shown in FIG.9. This downward movement shears pin94and moves seal ring assembly96and accumulator ring66downward onto outer surface86. This downward movement of seal ring assembly96moves it radially outward on tapered surface88and onto larger diameter surface86. Thus, this downward movement provides the radial energization of seal ring assembly96to move it to its sealing position between surface86and the inner surface of housing72. In this position there is metal-to-metal seals of the legs116aof end caps110and112with the sealing surfaces of housing72and body78because the inner central portion118of ring108is compressed radially outward which creates an internal force on the outer legs of the end caps outward, toward their related sealing surface. This force ensures that the inner legs116balso are held in sealing engagement with surface86. While this seal is energized by axial movement, which can be a weight set as shown, a screw set or other actuation, it creates the radial energizing of resilient ring108which ensures sealing and requires no axial load to maintain sealing after having been energized. During this setting movement of setting sleeve98the taper on groove102moves split ring100into groove104until sleeve98moves down to cause groove106to align with groove104at which position snap ring100moves into groove106and locks sleeve98against upward movement to thereby retain sealing assembly6in its set position. In this set position, resilient ring96is free to expand axially but is restricted from radial movement by surface86and the inner surface of housing78.

The improved sealing assembly provides a long life well annulus seal which is suitable for use in high pressure and high temperature environments and is radially energized so that a thread or weight setting load are not necessary to maintain the seal. Further, this assembly does not require the application and maintenance of a fluid under pressure to maintain the seal. There is no extrusion of the resilient ring by well pressure as it is completely encased at its ends by the end caps which provide the metal-to-metal annulus seal. Further, if it becomes necessary to retrieve the seal assembly from the well bore, this can be easily done by lifting the assembly upward in which case the metal end caps ensure that subsequent upward travel through the well bore does not pull off a section of the seal and possibly hang the seal assembly or drop a segment of the seal into the well.

Additionally, the accumulator ring protects the seal ring assembly from explosive decompression by placing the seal ring assembly under compression in such an event thereby avoiding or minimizing the deleterious effects of such an event on the seal ring assembly, which is also a ring seal.

In a ninth embodiment of the present invention as shown inFIG. 11, the seal gland18bas shown inFIG. 1Bis depicted with seal assembly1dwhich contains a metal end cap seal20in the set position and two hollow o-rings24and25with one on each side of the seal20. Though seal gland18bis depicted herein, any other seal gland may be used which is defined by four surfaces, for example, those shown inFIGS. 1A,1B,3and9. Further, though the accumulator rings shown herein are hollow o-rings24and25, the accumulator rings may be any of those disclosed previously in the first through seventh embodiments as the hollow, vented o-ring24(FIGS. 2,2A and3; used in FIG.11), solid o-ring32(FIG.4), hollow permeable o-ring34(FIG.5), slip double U assembly38(FIGS. 6 and 6Aand FIG.6D), interlocking double U assembly138(FIGS.6B and6C), and an E-shaped ring254(FIGS. 6E,6F and6G). Additionally, the two accumulator rings can be the same or different.

A variation of the present invention is the attachment of at least a portion of the accumulator ring to at least a portion of the ring seal. In one aspect, this will facilitate installation. For example, vented o-ring24(FIGS. 2,2A and3), solid o-ring32(FIG.4), and hollow o-ring34(FIG. 5) can be attached to the ring seal, for example, at the point of contact thereof with the metal end cap22of ring seal20. Similarly, the ends270,271and optionally272of legs258,260and263of E-shaped ring254(FIGS. 6E,6F and6G) can be attached to the ring seal, for example, at the point of contact thereof with the metal end cap22of the ring seal20. Relative to the double U-shaped rings38(FIGS. 6,6A and6D) and138(FIGS.6B and6C), the back42of ring40and the back156of ring158can be attached or even integral to, for example, the metal end cap22of ring seal20.

Although variations in the embodiment of the present invention may not each realize all the advantages of the invention, certain features may become more important than others in various applications of the device. Therefore, the invention should be understood to be limited only by the scope of the appended claims.