FIELD

[0001] The present disclosure relates to a non-metallic seal using thermally induced shape change geometry. More specifically, this disclosure relates to a non-metallic seal geometric shape useful in extreme temperatures, both high and low, general degradation and/or environmental exposure.

BACKGROUND

[0002] Typical sealing solutions often include non-metallic materials that contain viscoelastic properties allowing the seal to resist fluid flow with a contact stress on mating sealing surfaces. The contact stress, also known as the seal energization force, is created by interference between the seal and mating surface of the pressure vessel. These types of seals use various geometries and non-extrusion devices on their outer portions to prevent the natural occurrence of the material moving to relax and reduce contact stresses required for maintaining a pressure tight boundary over time.

[0003] Ideally, the seal and mating parts do not overly compress or stress the seal in a way that would cause it to catastrophically fail from compression fractures or fatigue cracks. Consequently, the seal and mating part fit may also account for seal expansion resulting from swelling due to degradation, contamination from chemicals or growth from extreme temperatures, general degradation or environmental exposure.

[0004] Provision taken to account for failure from overstress conditions resulting from swelling or growth can also prevent adequate contact stresses required for maintaining a pressure boundary during seal shrinkage or contraction resulting from general degradation, environmental exposure, or extreme temperature exposure, such as, cold environmental conditions ranging from -75 to 400 degree F or even cryogenic conditions in the -320 degree F. These conditions can also cause the material to become irreversibly harder and create leak paths at the pressure tight boundary over the life of the equipment. As a result of the limitations of non-metallic seals when exposed to harsh temperatures, metal seals are often preferred or thought of to have superior performance in applications that require extreme temperatures. [0005] That said, non-metallic seals do not function well in extreme temperature, both hot and cold. Also, metallic seals are costly in comparison to no-metallic seals, i.e., non- metallic seals can be 15-25% of the cost of non-metallic seals. However, the rigidity of metallic seal is problematic.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIGS. 1A and IB are a top perspective view and a top plan view of an annular non-metallic seal according to the teachings of the present disclosure;

[0007] FIG. 2A is a cross-sectional view of the annular non-metallic seal along lines A2- 2A in FIG. 1 according to the teachings of the present disclosure;

[0008] FIG. 2B is a cross-sectional view of the annular non-metallic seal according to the teachings of the present disclosure;

[0009] FIG. 3A-3C are illustrations depicting a sequence of seal operations using thermally induced shape change geometry according to the teachings of the present disclosure; and

[0010] FIG. 4 is a cross-sectional view of a non-metallic seal illustrating the seal operating to contain pressure according to the teachings of the present disclosure.

DETAILED DESCRIPTION

[0011] The present disclosure relates to non-metallic seals primarily used in industrial applications such as oil and gas wells that require containment or control of highly pressurized liquids and gasses in conditions that include general degradation, environmental exposure, or extreme temperatures, and chemically harsh environments. Example use cases include non- metallic seals within a wellhead or tubing head to seal off pressure from above and/or below a tubing hanger that is used to hang pipe suspended in a well. Other applications include sealing off annular pressure between the outer diameter of a tubular and the inner diameter of another tubular or housing such as a spool or head. Similar applications include providing a seal between a flanged connection or fitting used in piping or vessels used to contain and distribute pressurized fluid in oil drilling/completion or processing applications. Further examples include using non-metallic seals to restrict flow between an actuated part such as a gate or plug and mating element such as seats, housings or fitting connections. [0012] Developing non-metallic seals suitable for extreme pressures and temperatures in wellbore or tubular applications is problematic using currently available design principles. The use of technologies that comprise elastomers and other viscoelastic materials have difficulty in maintaining suitable contact stresses on mating pressure vessel walls when exposed to general degradation, environmental exposure, and/or extreme temperatures, for example 0°F and below. For example, thermal computer simulations of temperature effects can show reductions in cross-sectional areas ranging from three to five percent based on the seal material mechanical properties and geometries. These reductions would lead to reduced contact stresses on the pressure vessel walls once exposed to harsh temperatures that may ultimately lead to leaks, especially when compounded with reduced contact stress due to dimensional inconsistencies resulting from product manufacturing, chemical exposure and other adverse conditions. These problems can be alleviated by using standard anti-extrusion devices and more complex designs through the use of a combination of materials and geometries, but those solutions often require increased seal energization forces to compensate for colder temperature effects, which create potential for overstress conditions if the seal expands due to chemical exposure or elevated temperatures.

[0013] Conventional solutions are therefore complex and result in higher production costs and may still not be able to resolve the technical issues in more extreme use cases, for example, an environment at -20°F and 15,000 psi or higher. Therefore, there was a need to find a solution for non-metallic seals that dynamically couple together contact stresses required for sealing and seal interference as a function of temperature effects, general degradation or changes for environmental exposure.

[0014] The seal design described herein provides a means for using a non-metallic seal in extreme temperature (e.g., -75°F to 600°F) and pressure applications up to 20,000 psi where higher-cost metallic seals have been commonly used. Consequently, the use of the non-metallic seal described herein allows for a lower cost solution for these extreme temperature and pressure applications. Non-metallic seals can have a relative cost of fifteen to twenty-five percent of equivalent metallic like solutions.

[0015] Specifically, the present seal design provides a means for using a seal fabricated from an elastomer or viscoelastic material in harsh environments by regulating contact stresses that are sufficient for maintaining a pressure tight seal throughout the full operating temperature range of the seal. Provision is made to increase contact stresses enabled by temperature exposure but also prevent over- stress conditions that result from excessive seal interference created from high loading, swelling or degradation. As shown in FIGS. 1A, IB, 2A, and 2B, an annular non- metallic seal 10 has a cross-sectional geometry that includes a raised surface 12a in the center of the seal 10. The cross-sectional geometry is also comprised of flats 13a, tapers 14a, and channels 15a that are used in combination with the raised face 12a to produce and control a shape change of the seal cross-sectional area once it is exposed to temperatures that reduce the interference between the seal and mating surfaces. The channels are in effect internal voids or cavities within the body of the seal. The embodiment shown in FIG. 2A has a lower portion profile that is a mirror image of the upper profile, also including a raised face 12b, flat surface 13b, tapered surface 14b, and channels 15b. The seal 10 further includes contoured sealing faces 16a and 16b at the inner and outer diameters of the seal. It may be seen that the cross-sectional profile of the seal 10 is symmetrical along the X and Y center axes.

[0016] FIG. 3A-3C are illustrations depicting a sequence of seal operations that take advantage of thermally-induced shape change seal geometry according to the teachings of the present disclosure. In FIG. 3A, the seal 10 is installed between pressure vessel walls 30 and is not energized. In this state, there is a narrow gap 32 between the pressure vessel walls 30 and the seal 10. An energizing ring 34a (and 34b) is installed above and below the seal 10, and due to the raised face 12a (and 12b) of the seal 10, there is a gap 36 between the height of the raised face 12a and the flat face 13a. As the seal 10 is compressed over the raised face 12a (and 12b), the seal expands in the radial directions and builds up contact stresses on adjacent vessel walls to the seal. As the energizing ring 34a (and 34b) continues to compress the seal 10 with a constant load, it eventually meets the landing flats 13a (and 13b) that are in close proximity to the raise face 12a (and 12b). The flats 13a and 13b are geometrically stiffer than the raised face 12a (and 12b) and cause reaction forces on the energizing ring 34a (and 34b) to build and eventually stop the energizing ring 34a (and 34b) from moving. The seal 10 is in a fully energized state with a force and displacement gradient across the exterior faces of the seal where the central raised portions of the seal have a higher amount of displacement and stored energy as compared to the landing flats and features surrounding the raised faces. In FIG. 3B, the installed seal experiences load and sealing pressure on the upper and lower profiles by the energizing ring 34a (and 34b), which creates and landing profile 38 that produces pressurized cavities 40 and a pressure tight boundary 42 between the seal and the vessel walls.

[0017] In FIG. 3C, the seal 10 is energized with load, temperature, and pressure. The flat faces 13a (and 13b) becomes spaced apart from the energizing ring 34a (and 34b) and forms a path 44 from the pressurized cavities 40 to conduct pressurized liquids into the channels 15a (and 15b) due to high temperature conditions. There is thus a pressure migration from the pressurized cavities 40 along the path 44 to the channel 15a. As a result, the seal 10 exerts pressure 46 to assist seal energization with contract stresses on the vessel walls. Reference number 44 denotes the area of seal shape transformation that pressure can now be conveyed into the ridge channel.

[0018] In operation when exposed to cold temperatures, the seal’s contracted geometry 50 causes its surfaces to be spaced from the walls of the pressure vessel bodies 52 compared to its geometry 54 without exposure to temperature. Seal interference and consequent contact stresses are reduced or eliminated due to contraction in the seal geometry when it is exposed to cold temperatures. The deep channels added to the seal profile allow for the pressure 56 to engage with strategic surfaces allowing the seal to function properly in extreme cold temperature or general degradation or environmental exposure, that cause a loss of seal interference 58, while preventing pressure to penetrating beyond the pressure boundaries 42 on the inner diameter and outer diameter of the pressure vessel walls. The shape change or shrinkage of the seal resulting from conditions such as extreme cold temperature allows pressure exposure to the pre determined surfaces. The shape change may also be induced due to other conditions that create a loss of seal squeeze of the inner or outer diameter walls. The reduced seal squeeze 60 is created by contraction from temperature effects on the seal material.

[0019] Expansion or swelling of the seal profile happens during conditions such as extreme high temperatures. This prevents the pressure from going into the seal internal cavity of the channels because of the absence of pathways for pressure migration.

[0020] The improved performance of regulating contact stresses as a function of temperature is achieved by using a seal having a geometry that transforms as a function of temperature exposure or other similar conditions that leads to a loss of seal interference. The seal geometry and resulting displacement and load distribution across the seal once it is energized control or guide the changing shape of the seal profile. To increase contact stresses between the seal and the mating surfaces after the point at which interference is reduced due to, for example temperature effects, a series of geometric changes occur that are also induced by the temperature exposure.

[0021] Specifically, the change transformation exposes a ridged channel that allows pressure to communicate from the pressurized vessel to internal cavities within the seal where pressure can build and exert forces on the exterior portions of the seal outwardly to further increase contact stresses between the seal and vessel walls. Once temperature exposure causes the seal to lose interference between the seal and vessel, a series of changes occur that are also induced by the temperature exposure. The seal is initially energized by compressing it with an energizing ring in the longitudinal direction. As the seal is compressed on the raised faces 12a and 12b of the seal, the seal expands in the radial directions and builds up contact stresses on the vessel walls by the seal. As the energizing ring continues to compress the seal with a constant load, it eventually meets the landing flats 13a and 13b that are in close proximity to the raise faces 12a and 12b. The flats 13a and 13b are geometrically stiffer than the raised faces 12a and 12b and cause reaction forces on the energizing ring to build and eventually stop the energizing ring from moving as shown in FIG. 3B. The seal is now in the fully energized state with a force and displacement gradient across the exterior faces of the seal where the center faces/portions of the seal have a higher amount of displacement and stored energy as compared to the landing flats and features surrounding the raised faces.

[0022] In cases where general seal degradation or extreme temperatures, notably cold temperatures below 0°F cause molecular change resulting in material contraction, the material will shrink and begin to lose interference or contact stress required for maintaining a pressure tight boundary. Under these conditions the material contracts and contact stresses on the loaded exterior portions of the seal begin to lose contact with the energizing ring where the separation distance between the mating surfaces is a function of the amount of initial displacement on the raised faces and contours. Temperature induced seal contraction causes a controlled geometry change of the seal until the material reaches an equilibrium given the temperatures and loads acting on the seal. As the seal contracts, the load and initial displacement gradient across the seal enable a desired shape transformation that includes a loss of contact between some exterior portions of the seal and pressure vessel wall and energizing ring, but not the central portions of the seal that have the raised face profile and higher degree of initial axial displacement from the initial energization sequence. [0023] In the configuration shown in FIG. 3C, a ridged channel is formed that allows pressure to communicate from the pressurized vessel to internal cavities within the seal.

Resulting radial forces between the seal and the pressure vessel walls also energize the seal and create contact stresses that form a desired pressure tight boundary along the exterior portions of the seal. At this point the seal is in a compressed and energized state where expansion of the sealing material imposes contact stresses on the inner and outer walls of the pressure vessel to create a pressure tight boundary along the exterior portions of the seal.

[0024] Pressure forces on the walls of the internal cavities of the seal build on the seal contours and push an exterior portion of the seal against the mating pressure wall, thereby providing a sufficient energization force to maintain a pressure tight seal and compensate for a loss of interference on the seal and vessel due to temperature effects. In this manner the resulting contact stresses enabled by the temperature induced shape change offset losses of contact stress from thermal effects or seal degradation.

[0025] It should be noted that the geometry of the annular seal cross-section shown herein is an example, and other cross-sectional shapes are contemplated. The example shown herein has a cross-sectional shape that is symmetrical along both the X and Y center axes with an upper and lower faces featuring a center raised or protruding face that extends beyond the shorter extensions formed by two annular channels disposed on either sides of the center protruding face. The center raised faces may be flat or have a non-planar profile. The seal geometry may include one or more channels on the upper or lower sides if the annular seal. The flat faces on the sides of the center raised face also features tapered or sloped shoulders. It is further contemplated that the annular seal profile does not include symmetry either along the X or Y axis, or both axes. In other words, the cross-sectional profile of the seal may only include the raised face, channels, and lower sloping faces on the upper or lower portions of the seal. Similarly, the cross-sectional profile of the seal may only include only one channel and one sloped face on either the inner diameter or outer diameter of the seal, depending on where the high-pressure liquid is located.

[0026] In conventional seals, the shrinking nature of the material resulting from extreme temperatures will reduce contact stresses between the sealing element and the pressure vessel and ultimately cause the seal to lose its ability to contain pressure due to insufficient contact stresses between the seal and the mating surfaces. However, the sealing technology described herein provides a controlled seal profile change that is in part induced by temperature effects that ensures adequate contact stress to maintain a pressure-tight seal over extreme operating temperature conditions.

[0027] It is important to note that the shape change enabling increased contact stresses will occur during the event that the seal loses some of its initial interference due to temperature exposure. The self-regulation of this design is important because if the shape change enabled a build of contact stresses without a reduction in seal energization required to achieve the pressure tight boundary, then the seal could fail because of tensile or compressive overstress conditions. Therefore, the shape change regulates the contact stress on the mating walls as a function of temperature and other degradation effects such that there is sufficient force to achieve the seal and not excessive force that would cause the seal to catastrophically fail.

[0028] The seal core may be constructed from variable materials including an elastomer, such as, Neoprene, Nitrile, Ethylene-Propylene (or synthetic such as EPDM), or HNBR. Alternatively, to support more extreme temperatures, the seal core may be made out of fluoropolymers, such as, PTFE, FKM, FFKM or FEPM. The seal could also use re-enforcement components that are either embedded in the seal core or placed on the exteriors. Example materials for re-enforcement may include thermoplastics, nylon, or metals such as stainless steel or high nickel and chromium content alloys or meshed fabrics using various materials such as Kevlar or synthetic cotton.

[0029] Generally, a well for producing hydrocarbons is lined with steel pipes or casings to allow unobstructed access to the target reservoir deep in the ground. Up to four casing strings may be installed and each string is cemented in place to structurally support the wellbore and hydraulically isolate the target reservoir from ground water sources and other formations. In a well, the tubing string is the main conductor that brings reservoir fluid to the surface or injects fluid from the surface into the target formation. The tubing string is supported from the wellhead and is hung, anchored or sealed against the cemented casing string by the tubing hanger. The tubing hanger is threaded onto the top of a tubing string and is designed to sit on top of and seal in the tubing head. A fracking slurry with harsh chemicals are often injected at high pressure into the wellbore carried by these tubing. It is vital that seals employed as part of the fracking and production string maintain a pressure-tight seal in these harsh conditions.

[0030] The features of the present invention which are believed to be novel are set forth below with particularity in the appended claims. However, modifications, variations, and changes to the exemplary embodiments described above will be apparent to those skilled in the art, and the non-metallic seal described herein thus encompasses such modifications, variations, and changes and are not limited to the specific embodiments described herein.