Patent Application
20140131954
1. Field of the Invention
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.
2. Description of the Related Art
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 also reduced.
Bolting that is employed to hold the packing to the casing hanger bowl necessarily covers part of the exposed surface area, and thus, acts as a built in surface area reducer. The bolting is normally tightened sufficiently to cause a substantial level of stress in the seal. When shrinkage occurs in the seal due to cold temperature, however, some of the stress that is stored in the seal material is relieved, causing the seal to leak. This phenomenon occurs because the bolt head top junk ring and casing hanger bowl remain in a fixed location relative to the complementing nut. In an extreme case, if enough shrinkage were to occur, the amount of stress applied to the seal by bolting would be reduced to zero.
This problem has been previously addressed by compressing the seal sufficiently to attempt to compensate for the varying compression at the varying temperatures resulting from the temperature driven volume changes. This methodology, however, requires application of a higher energizing force during the complete cycle, which can in turn drive a requirement for the seal to be made of special material that is strong enough to withstand the compression forces under both stable conditions and at the varying temperatures. Additionally, since these bolts are used to hold the assembly together, the compression of the seal can only stay constant as long as the bolts can resist elongation (bolt stretch) at the varying temperatures.
A similar problem has been found in interference elastomer seal applications. In such applications, volume fill and squeeze can play a major role in the design of the seal. When the seal is exposed to a wide range of temperature variations, shrinkage becomes an issue to the amount of squeeze in the seal. The larger the volume of the seal material, the more that shrinkage plays a major role in the seal's design.
This shrinkage factor problem has been previously addressed in the pump field by changing seal compounds and/or by reducing radial clearance between housing and piston. This makes the assembly process more difficult and can result in damage to the seal during assembly.
Another attempt at solving the problem in a subsea well field application involved intensifying pressure on the seal through use of a metal ‘T-Ring’ with rubber molded on the outside and inside of the ring. Implementation, however, has been deemed to be excessively complicated and cost-prohibitive. Further, such a configuration does not provide an ability to compress the seal bi-directionally.
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.
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.
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.
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.
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.
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.
According to another embodiment of the present invention, a method of compensating for shrinkage of a seal for a casing head member due to temperature variations at given pressures, is provided. The method includes the step of providing a seal assembly comprising an 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 providing a plurality of pin members. Each pin member has 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 method also includes the steps of slidably extending the elongate body of each separate one of the plurality of pin members through a corresponding different one of a plurality of sets of apertures in the first compression member, the seal, and the second compression member, and 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.
According to another aspect, the method can also or alternatively include the step of providing a second 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 head portion of each pin member has a diameter along a radial axis thereof substantially larger than a diameter along the radial axis of the elongate body. Further, each head portion of each pin member of the second plurality of pin members has an engagement surface positioned to engage the second surface of the first compression member. According to this aspect, the method also includes the step of slidably extending the elongate body of each separate pin member of the second plurality of pin members through a corresponding different one of a second plurality of sets of apertures in the first compression member, the seal, and the second compression member, a direction opposite that of the first plurality of pin numbers. The method also includes the step of 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 by each of the second plurality of pin members when in situ force applied to a surface opposite the engagement surface of the head portion of the respective pin member exceeds force applied to an end surface of the second end of the elongate body of the respective pin member.
So that the manner in which the features and advantages of the invention, as well as others which will become apparent, may be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it may include other effective embodiments as well.
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, which illustrate embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. Prime notation, if used, indicates similar elements in alternative embodiments.
As production of oil and gas occurs at greater water and surface depths the temperature variation becomes wider and more critical to the effectiveness of elastomer seals. Accordingly, a constant effectiveness of the seal 43, especially at higher pressures, has become more desirable. Various embodiments of the present invention provide compensation for the behavior of the seals at these varying temperatures. Specifically, various embodiments of the present invention feature seal assemblies, which employ a plurality of floating pins, bolts, or other similar structures, that can function as both a seal surface area reducer and a constant effectiveness shrinkage compensator. The various embodiments can be used in a plethora of seal applications including, but not limited to, casing hanger seal arrangements and interference seal arrangements.
Referring to
Referring primarily to
Referring primarily to
The body 63 of each pin member 61 is sufficiently long so that the nut 75 can be connected spaced apart at a sufficient distance from the head 71 of the pin members 61 to allow substantial bidirectional movement of the pin member 61. Each pin member 61 moves upward when the annulus pressure between the casing head 37 and the outer surface 31 of the casing 33 provides net forces on the head 71 of the pin member 61 which exceed those provided on the upper surfaces of the nut 75 and pin member body 63. This results in the head 71 of the pin member 61 engaging the lower surface of the bottom plate 53, and correspondingly, the seal 43 being compressed against the compression plate 51 and lower surface of upper fastener 59. Similarly, the pin member 61 moves downward when the forces acting upon the upper surfaces of the nut 75 and pin member body 63 exceed those acting upon the lower facing surface of the head 71 of the pin member 61. This results in the nut 75 engaging the upper surface of the compression plate 51, and correspondingly, the seal 43 being compressed against the bottom plate 53 and the slip bowl 41 that is sitting on a shoulder 76 in the casing head 37.
Whether or not the pin members 61 engage the bottom plate 51 or compression plate 51 is dependent upon the in situ pressure acting upon the head 71 or tail of the pin members 61.
Note, according to an alternative configuration, the pin members 61 may not include the nut 75. In such configuration, it is assumed that the forces applied to the head 71 of the pin member 61 will always control. If the pressure associated with the tail of the pin member 61 instead exerts a greater force on the tail surface than that exerted on the head 71, the associated recess 73 in the slip bowl 41 will prevent the respective pin member 61 from being blown out of the seal assembly 30. Non-extrusion rings 77, 79, are located in the plates 51, 53, or alternatively, in the upper and lower surfaces of the seal 43 coaxial with aperture 67.
In operation, the floating pin members 61 are extended through the compression plate 51, seal 43, and bottom plate 53 (i.e., slab packing) prior to installing the seal assembly 30 on the casing hanger slip bowl 41. The pin members 61 are retained from both ends of the packing and are allowed to float in either direction. As pressure is applied from either direction of the packing a net force is exerted by the pin members 61 that is equivalent to the pressure applied times the sealed area of each pin member 61. That force will act against the connectors of the clamping members 55 which is retaining the seal assembly 30 to the slip bowl 41, while the casing tube weight holds the slip bowl 41 in place. This force will remain substantially constant if the pressure remains substantially constant. This constant force is proportional to the number of pin members 61 installed and the pressure applied, irrespective of the temperature. Hence that force can provide constant stress in the seal material independent to what happens to the volume of the seal material as the temperature changes. Note, as the outer diameter of head 71 is not sealed to the sidewalls of the recess 73 in slip bowl 41 as in the embodiment shown in
Referring to
According to the illustrated configuration, similar to the embodiment of the pin member 61 including a nut 75 or other connector, each pin member 61′ moves upward when the pressure between the casing head 37 and the outer surface 31 of the casing tube 33 provides net forces on the head 71′ of the pin member 61′, which exceed those provided on the upper surfaces of the pin body 63′. This results in the seal 43′ being compressed between the plates 51, 53. If, however, the forces acting upon the upper surfaces of the pin member body 63′ exceed those acting upon the lower facing surface of the head 71′ of the pin member 61′, the pin member 61′ will move downward until hitting the bottom of the recess 73 in the slip bowl 41.
In operation, the floating pin members 61′ are extended through the compression plate 51, seal 43′, and bottom plate 53 (slab packing) and are assembled into the wire mesh 101, 105, prior to installing the seal assembly 30′ on the casing hanger slip bowl 41. With respect to conditions where the pressure is higher on the underside of the pin members 61′, the function remains the same as that described with respect to pin members 61 (
Referring to
According to a configuration, a first non-extrusion ring recess 121 having a camber angle (beveled cut) extends between the inner diameter surface and lower facing surface of the compression plate 51′ to receive a first non-extrusion ring 123. Similarly, a second recess 125 having an oppositely oriented camber angle (beveled cut) extends between the inner diameter surface and upper facing surface of the bottom plate 53′ to receive a second non-extrusion ring 127 to prevent extrusion of the seal 43″, or seal 43, 43′, depending upon the respective application of the non-extrusion rings. Note, in an exemplary configuration, extrusion rings 123, 127, are “PEEK” or other hard ATL non-extrusion rings. Note also, one of ordinary skill in the art would recognize that various combinations of compression plate 51, 51′, seal 43, 43′, 43″, and bottom plate 53, 53′, and non-extrusion rings 123, 127, to form various configurations of the present invention are within the scope of the present invention. Further, recesses 118, 119 can receive a set of oppositely oriented non-extrusion rings 128, 129.
Referring primarily to
In the embodiment shown in
In the embodiment shown in
Each pin member 161 has an elongate body 163 positioned to slidably extend through a set of coaxially aligned apertures/recesses 201, 202, 203, in the upper segmented ring 187, the seal 143, and the lower segmented ring 188, respectively. Each pin member 161 also includes a head 171, typically round, which has a larger diameter than the elongate body 163 and larger than at least the coaxial aperture extending through the upper or lower segmented ring, respectively, depending upon the orientation of the pin members 161. The head 171 is located within a recess 211 extending into the upper or lower segmented ring 187, 188, depending upon whether the pin member 161 is oriented facing upward or facing down. In the exemplary configuration, the depth of the recess 211 is substantially the same as the thickness of the head 171.
According to the exemplary configuration, the longitudinal length L1 of the seal assembly 130 is less than the longitudinal length L2, e.g., typically approximately 1.5″ in this application, and the combined length of the pin 161 and head 171 is typically slightly smaller than that of L1, to allow the pin member 161 to slide up and down within the set of coaxial apertures/recesses 201, 202, 203, and to allow for a certain amount of compression of the seal 143. The difference between the lengths L1 and L2 are sufficiently small to prevent the pin members 161 from extracting through either of the apertures/recesses 201, 203, in the upper or lower segmented rings 87, 88, respectively. This results in a set of pin members 161 capable of floating within a confined space. The pin members 161 function to compensate for shrinkage of the seal 143, preventing leaking of the seal 143 as a result of a temperature-induced volume reduction. Also, the volume of the pin member 161 that penetrates the, e.g., elastomer seal material, as a result of the apertures in the seal 143, will reduce the volume of material needed to construct the seal 143, and thus, will further reduce the amount of expected shrinkage.
Note, although the pin members 161 are shown in
In operation, when pressure is applied on the face of the seal 143 at low temperature, the floating pin members 161 will push the seal 143 towards the opposite wall of the recess 148 in the casing spool 137, thereby compensating for the lost squeeze in the seal 143 due to temperature-induced shrinkage. Depending upon whether the effective pressure is greater at the upper or lower end of the seal 143, the segmented rings 187, 188, located at the respective upper and lower ends of the seal 143 are engaged by the head 171 of the associated pin members 161. The segmented rings 187, 188 act as hard surfaces for the pin members 161 to act on the seal 143 and to distribute the compressive force evenly. The upper and lower segmented rings, along with the respective pair of tapered rings 189, 190, each surrounding the pin members 161, also can act as non-extrusion devices. In the embodiments having the pin members 161 alternating in opposite directions, the pin members 161 compensate for shrinkage when pressure is applied in either direction.
Various embodiments of the present invention provide several advantages. For example, in a casing hanger seal-type implementation, various embodiments reduce the surface area of the packing, and thus, reduce the amount of force necessary to energize the packing, especially when the annular area of the packing is large. Various embodiments provide improved packing ability to seal between the casing head and the casing tube when the temperature cycles from hot to cold. As the volume decreases due to shrinkage, a constant force is still being applied by the pin members 161 to compensate for the reduced compression in the seal material (e.g., rubber) due to shrinkage. In an interference seal-type implementation, for example, various embodiments reduce the volume fill due to the floating pin members 161, which requires less force to energize the packing. Various embodiments also provide a dependable seal function at low temperatures due to the application of a substantially constant force applied by the pin members 161 to compensate for the shrinkage factor resulting from the low temperatures. Advantageously, the various embodiments satisfy a need for elastomer seals of different configurations capable of sealing oil and gas components subject to substantial temperature variations at greater water and surface depths, by providing a more stable/constant effectiveness, a factor which can be more critical at such depths, especially at higher pressures.
In the drawings and specification, there have been disclosed at set of typical preferred embodiments of the invention, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The invention has been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the invention as described in the foregoing specification. For example, the seal assemblies were described as circumscribing an outer surface of a casing tube. The various embodiments can work equally as well around smaller components such as, for example, shafts or other components.
