Seal for a joint or juncture – Seal for well apparatus – For overpressure control device
Reexamination Certificate
1999-12-17
2002-05-28
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal for well apparatus
For overpressure control device
C277S377000, C277S324000, C277S343000
Reexamination Certificate
active
06394460
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to wireline blowout preventers (BOP's) which are utilized to prevent well blowout when wireline operations are being conducted. More specifically, the present invention concerns wireline blowout preventers which incorporate pressure responsive sealing rams each having a one-piece ram element block for sup port and positioning of an elastomer sealing element for sealing with a wireline and for preventing misalignment of seal support plates especially when the plates are machined to accommodate larger wire sizes.
2. Description of the Prior Art
After a well has been drilled such as for discovery and production of petroleum products, wireline controlled apparatus is frequently employed to conduct various downhole installation, retrieval and servicing operations. Wireline equipment is utilized to install and retrieve a wide variety of downhole tools such as packers, gas lift valves, downhole safety valves, bottom hole pressure sensors and the like. Wireline equipment is also frequently utilized to run various well servicing tools such as for cleaning and treating production tubing. The wireline for supporting and controlling movement of the downhole well tool is payed out from a large diameter spool, typically mounted to a service vehicle, and is run through an elongate lubricator body having an internal grease or lubricant chamber containing grease for maintaining a seal between the wireline and the lubricator body to prevent escape of well pressure as the wireline is moved linearly into and from the well.
At times it is desirable to establish a seal about the wireline to permit well servicing operations to be conducted within the well head and free of well pressure above the blowout preventer (BOP). More importantly, wireline BOP's are required to accommodate various emergency situations and alleviate any dangerous condition that might otherwise occur. During wireline operations the wireline BOP is typically static in an open, non-sealing position which allows the wireline to freely traverse the wellhead of the well without interference with any portion of the wellhead structure including the safety equipment of the wellhead.
At times during well servicing operations it will be necessary to quickly close and seal the wireline BOP about the wireline. For example, in the event a kick develops in the open hole or in the casing of the well, the wireline BOP is closed to develop a seal between the wireline and the BOP body to contain well pressure and prevent a blowout. Such emergency closure and sealing of a BOP can be manually accomplished or it can be automatically operated responsive to the well pressure condition. With well pressure thus contained, kill fluid can be pumped into the well below the seal established by the wireline BOP to counterbalance the well pressure condition and shut in the well. The wireline BOP may also be closed to temporarily maintain well pressure while bleeding off the lubricator of wireline equipment to replace packoff elements. In some cases it becomes necessary to remove, add or make repairs to the riser or cable of the wireline well servicing equipment. In this case the wireline BOP is typically closed and sealed about the wireline cable to thus permit bleeding of pressure from the lubricator riser, enabling cable repairs to be made above the level of the wireline seal within the BOP. Most critically, wireline BOP's are shut automatically or manually in the case of failure of the well control system above the level of the BOP.
Typically, wireline sealing elements are formed by two elastomer faced metal rams which have been contoured to fit a particular size of wireline cable. These rams are positioned in opposed relation and are actuated such that they establish sealing engagement with the wireline positioned centrally of the BOP housing. In other words, the opposed rams center the wireline within the housing and establish a seal about the wireline. The opposed rams are closed manually or hydraulically (with mechanical backup) to shut in the well. When the BOP is activated, the elastomer faces of the rams will seal around the outer surface of the cable by extruding the elastomeric material into the interstitial spaces between the armor strands of the wireline.
The ram elements each define a ram body that is linearly movable within a transversely oriented ram passage or chamber of a BOP body. The ram element include at least one external seal which establishes sealing of the ram body with respect to the internal surface of the ram passage or chamber. At the opposed sealing face of each ram body, the ram body defines at least one and preferably a pair of seal receptacles. Within each seal receptacle is located a seal body, typically comprising an elastomeric sealing body having metal support plate members providing upstream and downstream structural support for the elastomeric sealing body and providing the elastomeric sealing body with sufficient structural integrity to resist the force of pressure differential that might otherwise permit sufficient yielding of the elastomeric sealing body to allow leakage to occur. The metal support plate members also provide the elastomeric sealing body with enhanced structural integrity to resist excessive pressure induced extrusion of the elastomeric material especially in the region of its seal with the wireline. Typically the elastomeric body and the metal support plates are in molded assembly and thus form a ram seal unit than can be replaced when necessary without necessitating replacement of the ram body.
When the ram seal units are manufactured by a molding operation, the metal support members are located within a molding fixture and the elastomeric material is injected in uncured state into the molding fixture and then cured by heating to a suitable temperature range for a predetermined period of time. Since the uncured elastomeric material is quite viscous during molding, the metal support places can be slightly displaced, i.e., moved from side to side, during elastomer injection especially when the support plates are machined to allow for larger wireline size. When the support plates become misaligned during the molding operation, the misaligned wireline recesses of the plates will be misaligned and the resulting wireline channel of the ram seal unit will be improperly constructed. This manufacturing problem can cause the sealing integrity of the ram seal unit to be of less than desirable quality. Additionally, during the molding operation the support plates can become bowed, thus also adversely influencing the sealing capability of the ram seal unit. Another problem that is often encountered during the seal manufacturing process is that the upper and lower support plates can easily become improperly spaced. It is necessary the support plates be disposed in parallel relation and that the spacing of the support plates of each of the ram seals of each of the BOP rams have the same spacing to enable equal elastomer deformation in each of the ram seals in response to a particular pressure differential. It is desirable therefore to provide a ram seal unit that can be easily manufactured in a manner avoiding the above-identified problems.
Ram type BOPS are designed to seal with the wireline cable in a static position. It is necessary therefore to always stop movement of the wireline before the rams are closed about the wireline to effect sealing. Short lengths of wireline cable can be stripped through the BOP as needed to repair a stranded cable but the amount of elastomeric material that can be worn away by such stripping without resulting in leakage of the BOP is limited. Pulling an appreciable length of wireline cable through the BOP will usually induce severe wear or erosion of the elastomeric seals of the rams, resulting in leakage, and can cause damage to the ram s as well, causing a more serious failure.
Under conditions of high differential pressure the elastomeric seal is prevented from pressure indu
Douty James A.
Leggett Henry H.
Finnegan Henderson Farabow Garrett & Dunner LLP
Knight Anthony
Peavey Enoch
Tuboscope I/P
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