Wells – Submerged well – Connection or disconnection of submerged members remotely...
Reexamination Certificate
2002-02-04
2003-12-23
Will, Thomas B. (Department: 3671)
Wells
Submerged well
Connection or disconnection of submerged members remotely...
C348S359000, C348S125000
Reexamination Certificate
active
06666272
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to subsea wellhead and pipe connectors, and more particularly to axially locking connectors for tying back to subsea wellheads with well conductor or riser pipe. Even more specifically, the present invention concerns a passive wellhead tieback connector having an internal lock mechanism which is externally mechanically actuated such as by a remote operated vehicle (ROV) controlled tieback actuator tool. Even further, the present invention is provided with an adjustment mechanism which can be adjusted on the working deck of the drilling and production vessel or spar or adjusted in the subsea environment to develop a high pre-load force of the lock mechanism during connector installation, enabling the releasable connector to withstand loads generated by spars, tension leg platforms (TLP's) and any other floating riser support structures.
2. Description of the Prior Art
The development of offshore petroleum oil and gas deposits from undersea wells involves drilling production wells in the sea bed from a drilling platform, and then capping the wellhead at the ocean floor until a production platform, either stationary of floating, is put into place on the surface of the ocean. To commence production from a subsea well, large diameter marine riser pipe is run downward from the production platform and connected to the subsea wellhead, a procedure known as tying back to the wellhead.
Several types of tieback connectors are available to connect or tie back production risers to wellheads. Certain of these connectors require rotation of a riser string to lock them to, and release them from, the wellhead housing. However, when rotating to the left to unlock the connector, the joints in the riser string tend to unthread and loosen. Reconnecting these loosened joints can be a serious and costly problem to the operator.
To solve this problem, tieback connectors that are actuated by axial movement have been developed to provide a connection to, and disconnection from a wellhead without rotary motion. In certain of such connectors, a pre-load force can be imposed through the connector's lock ring and onto the wellhead housing. Prior devices also include adjustment of the pre-load force through cumbersome changes between the relative positions of the inner body and outer body forming such connectors. However, such connectors are not constructed to provide an adequate pre-load force between a lock ring on the connector and the wellhead, and may not be adequate to maintain the locking force when extreme production fluid pressures are encountered which tend to separate the riser from the wellhead.
One approach is disclosed in U.S. Pat. No. 5,259,459 to Valka titled “Subsea Wellhead Tieback Connector,” which is directed to a wellhead tieback connector actuated solely by axial motion to achieve connection and disconnection from the subsea wellhead using a type of expanding lockdown ring and a type of adjustment assembly. After the connection is made between the tieback connector and the wellhead, the apparatus taught by this patent is used to effectuate a rigid lockdown, thereby eliminating any slippage that exists in the manufacturing or installation tolerances in the riser pipe being connected.
The advent of spar-type floating production facilities has increased the need for a premium, high force-resistant, tieback connection system for affixing a riser pipe conduit from pre-drilled subsea wellheads to completion trees at the surface within the spar's structure. One unique problem that a spar presents is the limited space from which to lower and install a riser pipe conduit and tieback connector since the inside diameter of the pipe will only permit passage of equipment 26 inches in diameter or smaller.
In addition to the small profile requirements, the subsea tieback connection system must be resistant to extreme external bending and axial loads in addition to the pressures generated from the well. A tieback connection system is required which can generate sufficient locking force to resist separation forces in excess of 800,000 pounds, which is often referred to as a connector's pre-load force.
SUMMARY OF THE INVENTION
To generate this force in a tieback connector, the present invention provides a structure wherein the relative location between a recessed groove in the wellhead and a lock ring forming part of the tieback connector can be readily adjusted to provide maximum pre-load. The lock ring is actuated to expand into the wellhead groove, and beveled engagement surfaces on the lock ring and wellhead groove interact in cam-like fashion to develop the necessary pre-load force.
The tieback connector of the present invention is considered “passive” in that it does not incorporate an internal hydraulic or otherwise powered mechanism for accomplishing locking and unlocking thereof with respect to a subsea wellhead. In accordance with the present invention, there is provided a tieback connector that has a tubular outer connector body that is adapted to rest axially upon an upper surface of the wellhead. The tieback connector has an inner body that is adapted to extend partially into an inner diameter of the wellhead. A lock ring, being a split ring having spring-like characteristics, extends circumferentially around a portion of the inner body and is adapted for expansion into locking engagement with internal locking geometry of a wellhead component for establishing locking connection of the tieback connector to the wellhead. An energizing mandrel is in linearly moveable assembly with the tieback connector and has an elongate tubular extension that extends axially between the wellhead and the inner body, with a lower end of the tubular extension oriented for expansion of the lock ring. The energizing mandrel is moved linearly for expanding the lock ring into the internal locking geometry of the wellhead and thus lock the tieback connector to the wellhead. An elongate tubular adjustment element or ring extends around and is operatively connected to the inner body, the adjustment ring positioned beneath and in positioning and supporting contact with a lower annular surface of the lock ring. The tubular adjustment element is capable of axial movement relative to the inner tubular body of the tieback connector to alter the axial position of the lock ring relative to the inner body to establish an adjustable tensile pre-load force on the tieback connector as the lock ring is forced into fully engaged locking engagement with the internal locking geometry of the wellhead. One or more tubular elements, including a tubular lock positioning element are subjected to axially compressive force, developed by the cam-like activity of the lock ring with the internal locking geometry of the wellhead, and thus then to yield or buckle to provide a cushioning activity or compressive spring pre-load force.
The structure of the present invention provides a significant mechanical advantage between a linearly moveable lock actuator assembly and the lock ring which compresses the lock ring into the internal wellhead locking groove. Further, the tieback connector of the present invention is specifically constructed whereby mating locking parts under compressive force in the tieback connector bend and/or buckle to create a tensile pre-load force acting on the inner tubular body of the tieback connector.
To accomplish a high force-resistant tieback connection pursuant to the above objectives, the expanding lock ring of the connector is positioned a short distance above the internal recessed locking groove within the wellhead such that upon contact, the tapered shoulders between the lock ring and wellhead groove stretch the inner connector body down until the lock ring fully enters the internal locking groove, thus developing sufficient tensile force to generate a desired pre-load. The relative position of the lock ring to the internal wellhead locking groove is adjusted by a threaded tubular adjustment member or ring havi
Baten Robert B.
McBeth Russell E.
Singeetham Shiva P.
Andrews & Kurth LLP
Beach Thomas A.
Bush Gary L.
FMC Technologies Inc.
Will Thomas B.
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