Shrinkage compensated seal assembly and related methods

Abstract

Shrinkage compensated seal assemblies and methods of compensating for shrinkage of a seal due to temperature variations, are provided. According to an exemplary shrinkage compensated seal assembly, the assembly includes a seal, a first compression member for engaging the upper surface of the seal, a second compression member for engaging the lower surface of the seal, and a plurality of pin members each having an elongate body and a head portion. The elongate body of each separate one of the plurality of pin members slidably extends through a different one of a plurality of sets of apertures in the first compression member, the seal, and the second compression member to provide for maintaining a substantially constant pressure on the seal at given pressure under varying temperature conditions that result in variations in the volume size of the seal.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention relates to seal assemblies, in general, and to seal assemblies having seal material that undergoes a substantial volume change resulting from varying temperatures at given pressures, in particular, and methods of compensating for seal shrinkage due to varying temperatures at given pressures.[0003]2. Description of the Related Art[0004]Casing hanger seal assemblies, often referred to as slab packing, pack-off, etc., are provided to prevent well fluid from escaping through the casing head. The force necessary to energize the seal packing is equivalent to the pressure to be contained multiplied by the exposed surface area of packing of the seal in compression. The exposed surface is the portion facing downwards towards the casing hanger slip bowl and / or the opposite upward facing surface. As the exposed surface area is reduced, the force required to energize the seal packing to contain a certain pressure is ...

AI Technical Summary

Benefits of technology

[0010]Recognized by the inventors, therefore, is the need for an apparatus / assembly and methods of compensating for shrinkage that does not require an excessively high energizing source and / or requirement for specially made seals or custom seal material. Also recognized by the inventors, with respect to an interference seal application, is the need for an apparatus / assembly and methods of compensating for shrinkage that does not require the reduction in radial clearance, and thus, does not require reduced tolerances and higher costs.

[0011]In view of the foregoing, various embodiments of the present invention provide a shrinkage compensated seal assembly and methods of compensating for shrinkage of a seal, which provide a plurality of floating pin members slidably positioned through an otherwise conventional seal assembly portion. Advantageously, when used, for example, in a high temperature pack off, the floating pin members can reduce the surface area of the exposed portion of the seal, which results in a requirement of less force to energize the packing, especially when the annular area of the packing is large. The floating pin members also advantageously improve the ability of the packing to maintain a seal with a well casing and / or casing head when the temperature cycles from hot to cold. As the volume decreases due to shrinkage, a constant force can still be applied by the pin members to compensate for the reduced compression in the seal material due to the shrinkage.

[0012]Advantageously, when used, for example, in interference elastomer seal applications, the floating pin members can reduce the volume fill, and thus, reduce the amount of force required to energize the packing. Additionally, the floating pin members can provide a constant force, allowing the packing to maintain a seal at a reduced packing volume and / or volume-dependent compressive force caused by shrinkage of the seal material due to low temperatures. Further, when employed bidirectionally, the floating pin members can compensate for pressure located both above and below the seal assembly.

[0013]More specifically, an example of an embodiment of a shrinkage compensated seal assembly includes a seal, a first compression member having a first surface for engaging a first surface of the seal and a second surface opposite the first surface, a second compression member having a first surface for engaging a second surface of the seal and a second surface opposite the first surface, and a plurality of pin members each having an elongate body including a first end, a second end opposite the first end, and a head portion connected to the first end of the elongate body. The elongate body of each separate one of the plurality of pin members slidably extends through a different one of a plurality of sets of apertures in the first compression member, the seal, and the second compression member to provide for maintaining a substantially constant pressure on the seal at given pressure under varying temperature conditions that result in variations in volume size of the seal. In an exemplary configuration, the head of each pin member on the lower side of the seal assembly engages the second compression member in response to in situ pressure. Also or alternatively, some of pin members are oriented opposite with other of the members to provide a bi-directional capability.

[0014]According to another aspect, the head of each pin member is positioned within a recess of a casing hanger slip bowl. According to another aspect, each pin member also includes a fastener connected to the second end of the elongate body. The fastener includes an engagement surface positioned (oriented) to engage the second surface of the second compression member when the shrinkage compensated seal assembly is operationally employed and when a sum of force applied to a surface opposite the engagement surface of the respective fastener and the force applied to the surface of the second end of the elongate body of the respective pin member exceeds the force applied to the surface of the head portion of the respective pin member opposite the engagement surface thereof to provide the bi-directional capability. According to another aspect, the first compression member is a compression plate and the second compression member is a bottom plate landed upon the slip bowl.

[0015]According to another aspect, the first compression member is a first split ring, the second compression member is a second split ring, and the seal assembly is positioned within a recess in the casing head. The recess forms a confined space to restrict movement of the pin members to both allow free-floating of the pin members and to prevent an inadvertent departure of the pin members from within the split rings and / or seal.

Problems solved by technology

Advantageously, when used, for example, in a high temperature pack off, the floating pin members can reduce the surface area of the exposed portion of the seal, which results in a requirement of less force to energize the packing, especially when the annular area of the packing is large.

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