Wells – Submerged well – Connection or disconnection of submerged members remotely...
Patent
1991-04-02
1992-09-15
Bui, Thuy M.
Wells
Submerged well
Connection or disconnection of submerged members remotely...
E21B 3302
Patent
active
051469898
DESCRIPTION:
BRIEF SUMMARY
The invention relates to apparatus for recovering a wellhead.
In the offshore oil industry when a site is to be abandoned and the rig moved to a different location, the wellhead and at least nine feet (three meters) of the casing lying below the sea-bed must be removed.
Conventionally, apparatus for recovering wellheads has been designed to be inserted in&o the wellhead and casing and to lock on to internal threads on the inside of the wellhead. After the casing has been cut by a cutting mechanism located below the apparatus, the apparatus is used to retrieve the wellhead by pulling on the wellhead where the apparatus engages the wellhead internally.
One of the main disadvantages of this prior art apparatus is that it is believed to cause internal damage to the wellhead.
In accordance with the present invention, apparatus for recovering a wellhead comprises a housing; a latch device; and a latch device actuator, the apparatus being such that when a force is applied to the apparatus to separate the apparatus from the wellhead the actuator causes the latch device to engage an external profile of the wellhead so that the apparatus remains in engagement with the wellhead.
Preferably, the apparatus also comprises a shaft which extends through the housing and which is rotatable relative to the housing, the shaft being capable of carrying a cutting mechanism.
The invention avoids the problems and disadvantages of the prior art apparatus by enabling the apparatus to engage an external profile of a wellhead as opposed to engaging the wellhead internally.
Preferably the latch device comprises an engagement arm which is pivotable between a disengaged position in which the engagement arm is disengaged from the external profile of the wellhead and an engaged position in which the engagement arm engages the external profile of the wellhead. Typically, the latch device also comprises biassing means to bias the engagement arm to the disengaged position.
In the preferred embodiment, the actuator comprises a square shoulder which co-operates with the engagement arm when actuated to pivot the arm, against the action of the biassing means, to the engaged position. Alternatively, the actuator could comprise a slip mandrel instead of a square shoulder.
Preferably, the cutting mechanism attached to the shaft is a conventional radially acting cutter. In one example of the invention the cutter is operated while force is being applied to the apparatus to pull the wellhead away from the well, i.e. the wellhead is cut in "tension". However, in a second example the cutter is operated while a force is applied to the apparatus to push the apparatus on to the wellhead, i.e. the wellhead is cut in "compression".
In the preferred embodiment, the apparatus also comprises a disengagement device to prevent actuation of the latch device actuator and to enable the apparatus to be pulled off the wellhead if the pulling force applied to the apparatus is not sufficient to remove the wellhead. In one example, the disengagement device comprises a "J" lock which may be engaged to prevent actuation of the actuator in order to enable a force to be applied to the apparatus in a direction away from the wellhead which does not activate the actuator. In a second example the disengagement device comprises a latch and a co-operating recess which may be misaligned to prevent actuation of the actuator.
In one example, the cutting mechanism is used in conjunction with a conventional marine swivel attached to the shaft to enable the shaft to rotate within the housing while the latch device remains stationary with respect to the wellhead. In a second example the apparatus comprises bearings to enable the shaft to be rotated within the housing while the latch device remains stationary with respect to the wellhead.
Two examples of apparatus for recovering a wellhead in accordance with the invention will now be described with reference to the accompanying drawings, in which:
FIG. 1 is a partial cross-sectional view of a first example of apparatus to remove a wellhea
REFERENCES:
patent: 3325190 (1967-06-01), Eckert et al.
patent: 3513911 (1970-05-01), Peterson
patent: 3589441 (1971-06-01), Brown
patent: 4181196 (1980-01-01), Darby et al.
Brochure of TAM International, published on Composite Catalogue, 1980/81, p. 6740.
Bui Thuy M.
Homco International Inc.
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