Patent Application
20140151024
1. Field of the Invention
This technology relates to oil and gas wells, and in particular to sealing mechanisms in packoff assemblies for use in oil and gas wells.
2. Brief Description of Related Art
Typical oil and gas wells have a wellhead. Strings of casing, each supported by a casing hanger, are lowered into the wellhead. Typically, the casing hanger is threaded, and is attached to a threaded upper end of the casing string. The casing hanger lands on a landing shoulder in the wellhead, or alternatively, may land on a previously installed casing hanger having a larger diameter. With the casing string in place, cement may be pumped down the casing until it comes back up the annulus around the casing. After the cement is pumped, a packoff assembly may be positioned between the wellhead and an upper portion of the casing hanger to seal the casing hanger annulus.
Some older wellheads include packoff seals that are elastomeric, and that don't include any form of anti-extrusion device. Furthermore, many older oil wells are now being extended past the original design life of such packoff seals, and some are experiencing long term gas migration out to the larger diameter annuli, such as those where the packoff seals are located. In addition, this older equipment has often been in use for long periods of time, and drilling operation damage to surfaces of the wellhead and/or the casing hanger is possible. The packoff seals originally installed in the wells are often not suitable for overcoming these problems. For example, elastomeric seals are susceptible to degradation in their mechanical properties over time. Thus, as the life of the well becomes extended, the packoff seal may not be reliable.
Attempts have been made to fix the problems associated with such older, inadequate packoff seals. In some instances, such seals have been replaced with newer flouroelastomer or elastomeric seal elements incorporating anti-extrusion devices. However, replacement and reinstallation of the packoff seals can be complicated, requiring the use of complex running tools and procedures. Furthermore, elastomeric seals are still subject to degradation when exposed to high pressure and temperature in the well. In addition, because surfaces of the well components may be damaged, achieving an adequate seal with a replacement packoff sealing assembly can be difficult.
Disclosed herein is a packoff assembly for sealing the space between an inner well member and an outer well member when the packoff assembly is inserted therebetween. In some embodiments, the inner and outer well members may be a casing hanger and a wellhead, respectively. The packoff assembly includes a packoff body and a sealing mechanism. The sealing mechanism has an annular shape with a U-shaped cross-section that has a packoff body leg and a well component leg extending downward from a connecting section.
The well component leg has a sealing surface that can seal against surfaces of the well members. In addition, the well component leg is elastically bendable so that it resists inward deflection toward the packoff body, and so that the sealing mechanism can be set without the use of an energizing ring. The packoff body leg may be configured for engagement with the packoff body. Alternatively, the packoff body leg may be integral to the packoff body.
If the sealing mechanism is positioned on the inside of the packoff body, the sealing surface seals against the inner well member, which may be a casing hanger. Conversely, if the sealing mechanism is positioned outside the packoff body, the sealing surface seals against the outer well member, which may be a wellhead. In some embodiments, a sealing mechanism may be located on both the inside and the outside of the packoff body. The sealing mechanism may further include an inlay positioned on an outer surface of the well component leg, and configured to engage and seal against the well member when the sealing mechanism is positioned between the packoff body and the well member. One purpose of the inlay is to conform to imperfect or damaged surfaces of well components so that the sealing mechanism can form a tight seal with such surfaces.
Also disclosed herein are additional features of the packoff assembly. For example, wiper rings may be attached to the packoff body below the sealing mechanisms to wipe the surfaces of the inner and outer well members as the packoff assembly is installed, thereby preparing the surfaces for sealing engagement with the sealing mechanisms. In addition, upper seals may be installed on the packoff body above the sealing mechanisms to shield the sealing mechanisms from pressures above the packoff assembly. Furthermore, a retainer plate may be connected to the bottom of the packoff body to retain the sealing mechanisms and wiper rings in place relative to the packoff body.
The present technology will be better understood on reading the following detailed description of nonlimiting embodiments thereof, and on examining the accompanying drawings, in which:
The foregoing aspects, features, and advantages of the present technology will be further appreciated when considered with reference to the following description of preferred embodiments and accompanying drawings, wherein like reference numerals represent like elements. In describing the preferred embodiments of the technology illustrated in the appended drawings, specific terminology will be used for the sake of clarity. However, the technology is not intended to be limited to the specific terms used, and it is to be understood that each specific term includes equivalents that operate in a similar manner to accomplish a similar purpose.
Referring now to
In addition to the sealing mechanisms 10, the packoff assembly 19 includes wiper rings 28, upper and lower retainer spacers 30, 32, upper packoff seals 34, and a retainer plate 36. The purpose of the wiper rings 28 is to wipe and clean the surfaces of the well components during installation of the packoff body 20, as described in further detail below. The wiper rings 28 may be made of any suitable material. For example, in some embodiments, the wiper rings may be made of polytetraflouroethylene. The purpose of the upper and lower retainer spacers 30, 32 is to maintain the position of the sealing mechanisms 10 and the wiper rings 28 relative to the packoff body 20 and each other. The purpose of the upper packoff seals 34 is to provide an upstream seal between the packoff body 20 and adjacent well components above the sealing mechanisms 10. Such an upstream seal may be beneficial, for example, to isolate the sealing mechanisms 10 from connection void test pressure or other upstream pressure.
Retainer plate 36 may be positioned below the sealing mechanisms 10, upper and lower retainer spacers 30, 32, and wiper rings 28, and maintains these elements in place relative to the packoff body 20. To accomplish this, the retainer plate 36 protrudes radially beyond the lower end 38 of the packoff body 20 a distance sufficient to restrict downward movement of the sealing mechanisms 10, upper and lower retainer spacers 30, 32, and wiper rings 28 relative to the packoff body 20. The retainer plate 36 may be releasably attached to the packoff body 20 by, for example, a fastener 40. Fastener 40 may optionally be a bolt that threads into a corresponding recess 42 in the lower end 38 of the packoff body 20. The ability to release the retainer plate 36 from the packoff body 20 is advantageous because it allows the removal and replacement of the sealing mechanisms 10, upper and lower retainer spacers 30, 32, and wiper rings 28.
The packoff assembly 19 shown in
With the packoff assembly 19 thus assembled, it is ready for installation between well components, such as the casing hanger 22 and the wellhead 24. To accomplish this, the packoff assembly 19 is run through a pressure management device (not shown), such as a blowout preventer, attached to the top of the well. From the pressure management device, the packoff assembly 19 is inserted into the space between the well components. During insertion, the wiper rings 28, which are positioned below the sealing mechanisms 10, wipe the surfaces of the well components, in order to remove debris and otherwise clean the surfaces. This is beneficial to provide better sealing between the surfaces of the well components and the sealing surfaces 18 of the sealing mechanisms 10 when the packoff assembly 19 is in place.
In the embodiment shown, after insertion, the packoff assembly 19 is locked axially in place by a lock down screw 48. The lock down screw 48 may pass through the wellhead 24 and engage a groove 50 in the packoff body 20, thereby restricting axial movement of the packoff assembly 19 relative to the wellhead 24. Alternate embodiments may provide different means of locking the packoff assembly 19 axially in place, and use of a lock down screw 48 is not required. For example, another embodiment might include an internal lock down ring (not shown) inserted above the packoff assembly 19 to prevent upward axial movement.
As best shown in
In one embodiment, the magnitude of the stiffness of the well component legs 16 allows deflection of the well component leg 16 and setting of the seal 10 with a relatively low set weight. For example, the set weight may be 25,000 pounds or less. Such a low set weight allows use of the seals in surface wellhead applications, and, in particular, large diameter casing annuli. In addition, because the sealing mechanism 10 is weight set, only a simple running tool is required for installation.
Because the well component legs 16 are stiff, the inward deflection of the well component legs 16 is resisted by a resistive force F. The resistive force F is constantly maintained as long as the packoff assembly 20 is in place and the well component leg 16 of the sealing mechanism 10 is deflected inward toward the packoff body 20. In addition, the resistive force F pushes the sealing surfaces 18 against the well components. Thus, a seal is formed between the sealing surfaces 18 and the well components. Because the sealing surfaces 18 of the sealing mechanism 10 are metal, and the surfaces of the well components are metal, the seal formed therebetween is a metal-to-metal seal. Thus, the seal is capable of withstanding higher pressures and temperatures than elastomeric or other types of seals.
Referring to
Thereafter, upon insertion of the packoff assembly 19 between the well components, as described above, the inlay 52 is compressed between the sealing surface 18 of the sealing mechanism 10 and the surface of a well component. Because the inlay 52 is made of a metal that is softer than the metal of the well component, the resistive force F (shown in
While the technology has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. Furthermore, it is to be understood that the above disclosed embodiments are merely illustrative of the principles and applications of the present invention. Accordingly, numerous modifications may be made to the illustrative embodiments and other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.
