Wells – Expansible anchor or casing – Liner hanger
Reexamination Certificate
2000-11-06
2003-01-28
Tsay, Frank S. (Department: 3672)
Wells
Expansible anchor or casing
Liner hanger
C166S217000, C277S328000, C285S348000
Reexamination Certificate
active
06510895
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to sealing mechanisms for sealing between tubular elements such as between a rough casing and the wellhead seal bore of a wellhead assembly. More particularly, the present invention concerns a mechanically energized seal cartridge for metal-to-metal sealing and elastomer sealing between substantially concentrically arranged tubular element for sealing the annulus therebetween.
2. Description of the Prior Art
In the oil and gas industry, and especially in subsea or other underwater well drilling procedures, it is well established practice to employ an annular seal assembly, referred to as a packoff, between adjacent concentric wellhead elements such as the wellhead seal bore and rough well casing or between a wellhead housing and casing hangers that support the casing strings in the well, to pressure seal the annuli between these elements. For many years these packoffs have included elastomeric or other non-metallic annular seal elements that, when energized into tight contact with the opposed wellhead and hanger surfaces, provided the requisite pressure barrier. However, the increasing trend towards drilling deep wells into relatively high pressure strata, and the frequency of encountering hydrogen sulfide or other dangerous or corrosive gases in these wells, has led to development of packoffs with all metal seal elements to establish a metal-to-metal pressure barrier. Although some of the known packoffs with metal-to-metal seals function satisfactorily under certain conditions, there is a growing industry need for such packoffs that can be installed from a remote location without difficulty, that will withstand higher operating pressure and higher corrosive environments than heretofore experienced, and that will maintain the seal throughout wide fluctuations in pressure.
It is often the case that it is desirable to accomplish annulus sealing between the inner, typically smooth wellhead seal bore of a wellhead and the typically rough outer peripheral surface of a section of well casing. Moreover, at times the well casing will be slightly out of round, thus present the requirement that sufficiently high mechanical force be applied during setting of the metal-to-metal annulus seal that the casing is deflected to a cylindrical external configuration in the immediate region of the seal. This is not a practical consideration when elastomer seals are employed or when metal sealing elements lack sufficiently high setting force to accommodate the geometric non-conformity of the well casing. Even further, when the outer peripheral surface of the well casing is rough, which is often the case, metal-to-metal annulus sealing between the tubular elements can be exceedingly difficult due to the lack of sufficiently high setting force of the metal seals for adequate sealing with the rough surface of the casing. Another difficulty of metal-to-metal sealing under these conditions is that the metal sealing elements are typically formed of hard metal, and thus are incapable of deforming into and establishing efficient sealing with the surface pits, fissures and other surface irregularities of the outer peripheral well casing surface. Of course, the well casing can be machined to form a relatively smooth outer peripheral surface to facilitate effective sealing, but the difficulty and expense of machining a portion of a well casing cause machining of the well casing to be a commercially impractical solution to the problem. It is desirable, therefore, to provide a packoff sealing cartridge having the capability for development of efficient sealing force and the provision of efficient sealing materials in a packoff sealing mechanism for development of metal-to-metal sealing of the annuli between the wellhead and well casing, without necessitating machining of the casing.
SUMMARY OF THE INVENTION
It is a principal feature of the present invention to provide a novel mechanically energized annulus sealing cartridge having the capability of accomplishing efficient metal-to-metal sealing between concentric tubular components even when one of the tubular components has a rough peripheral surface in the region where annulus sealing is desired and without necessitating surface preparation of the rough surface to permit metal-to-metal sealing.
Broadly considered, the present invention contemplates the provision of an annulus seal cartridge which is interposed within the annulus between tubular well elements, such as a tubular wellhead having a seal bore and a section of well casing or a casing hanger element and which is activated to establish a metal-to-metal annulus seal even under circumstances where an annular surface to be sealed is quite rough, such as in the case of the outer peripheral surface of a well casing. Additionally, the annulus packoff seal cartridge is provided with an elastomeric sealing system as well as pressure energized metal-to-metal sealing capability to provide for effective control of the sealing capability of the seal cartridge, especially when elevated well pressures are expected to be encountered.
A tubular energizing mandrel for the annulus sealing cartridge is provided with pair of oppositely tapered or double tapered circular internal and external frusto-conical cam surfaces. A pair of circular metal sealing elements or rings composed of a relatively soft and preferably corrosion resistant metal, such as 316 stainless steel or the like, or any other metal material being softer than the metal material of the concentric tubular elements, define circular frusto-conical cam surfaces that are operatively positioned with respect to the double tapered internal and external cam surfaces of the energizing mandrel. Additionally, the energizing mandrel carries metal spring reinforced and enhanced annular elastomeric sealing elements disposed for sealing respectively with the smooth internal sealing surface of the seal bore of the wellhead and with the rough outer peripheral surface of the well casing to thus provide an elastomer annulus bridging seal so that the seal cartridge can be pressure energized to effectuate sealing.
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patent: 4842061 (1989-06-01), Nobileau
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Cain David E.
Hunt Michael
Koleilat Bashir M.
Zheng Qiu Shi
Andrews & Kurth LLP
FMC Technologies
Jackson James L.
Tsay Frank S.
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