The present invention relates to a releasable guidepost extension for use on the seabed together with a seabed fixed guidepost part, which parts together make up a guidepost for assistance during lowering of a component from the surface of the water to a subsea structure to obtain a focused landing of said component at a predetermined location, said guidepost part includes an upward (in the position of use) projecting end designed for engagement with a lower (in the position of use) end of the guidepost extension.
In the lowering of subsea equipment towards a structure or construction on the seabed, such as a manifold or a wellhead, guidelines are often used, usually steel ropes. Each guideline terminates in a guidepost which is fixed to and projects from the structure on the seabed. The guidepost is used to locate components on seabed bases or foundations during oil drilling or production operations, or in order to install modules on top of each other. In the drilling of a subsea well, for example, a template guiding foundation is placed around the conductor casing of a well that is drilled. The guiding foundation has guideposts and these are used to position a blowout preventer BOP on top of the wellhead. Guideposts can also be used to install and position other modules, for example to guide and position a lower riser package on a blowout preventer, or an emergency disconnect package on a well workover safety valve.
Such guideposts provide a coarse alignment between the equipment and wellhead and provide vertical stability in the system in order to be able to make up connection to the wellhead. Final alignment is performed by the connector itself. Normally four guide wires and four posts will be used during a lowering operation.
A problem with traditional guideposts of this nature is that they are very long and project higher up in the water than the equipment itself and thus is more exposed to damages from fish trawls and similar.
Guidepost extensions have therefore been developed and introduced in the later years, and such an extension is contemporary put onto and extends a shorter, fixedly mounted guidepost part. They are such designed that the bottom fixed part has a receiving end that is able to receive a pin end on the guidepost extension and the post parts can be locked to each other by mechanical locking means.
This known solution (prior art) is based on guide wire and standard upwards projecting guidepost extension. The guidepost extension is hollow and the guide wire extends there through and further on to a wire anchor with pawls that are anchored to the guidepost part which, when they are activated, lock the post parts together.
The now proposed solution is using the upwards projecting guidepost extension as kind of a tool, i.e. move the tool around between the respective guideposts, which are stationary deployed at predetermined locations on the bottom structure, on a seabed structure according to needs to have the job done and then retrieve that one/those ones (at least one short and one long) up to the surface. The guide posts project often 3.5 meters. As mentioned, the guideposts project above the bottom structure and will be a risk for fishing nets etc. and need to be removed.
To be able to move one (two) isolated guidepost(s) around from place to place by one ROV will be cost effective, contra the use of one guidepost equipped with a guide wire that need to be secured to the base of the guidepost by pawl mechanisms, and subsequently released again from these, for each place.
At the same time use of guide wire from the surface is avoided, which is no longer needed due to good and easily maneuverable ROVs. Guide wire is very time consuming to deploy, in addition to that their costs are substantial, in particular in deeper waters. For example, the Goa field offshore the African coast is 1200 meters deep.
Normally two guideposts are needed, the one longer than the other. Usually, a funnel means on the component to be lowered needs to enter the long post first. Then the component is orientated by revolving in the horizontal plane until funnel means no. two is located right above the shorter guidepost. Then the component is lowered onto the shorter guide post extension and further down the first post.
With the new solution, the total weight of the removable guidepost is made possible to reduce, i.e. that it will now weight about 44 kg. Normally a ROV will be able to lift about 50-70 kg.
According to the present invention a guidepost extension of the introductory said kind is provided, which is distinguished in that the guidepost extension is loosely connected to the seabed fixed guidepost part via a pin and socket part on respective ends, that a gap, or clearance, exists between the pin and socket part in the longitudinal direction thereof, and that at least one friction forming means is arranged in the gap on either the pin part or in the socket part, said at least one friction forming means do not get in contact, or engaged, with the other part unless the guidepost extension is subjected to a lateral force.
The theory is that by applying laterally acting forces against the guidepost extension, this extension will tilt and the socket or sleeve part thereof will pinch to the pin part and the pinching is supposed to be substantially enhanced by use of said friction forming means. The higher up the lateral forces are acting on the guidepost extension, the longer moment arm is acting and correspondingly higher pinch forces are achieved.
Contrary, the guidepost extension can only be removed in that the extension is lifted approximately vertically straight upwards (by an ROV). As soon as it tilts, it will pinch. The tendency to tilting will take place all the time during a landing operation of a component onto a bottom structure, but this does not matter. This only keeps the guidepost extension still firmer in place. If there is no tilting during lowering, this does neither matter, and then the guidepost extensions stand in place by their own gravity.
In a first embodiment the guidepost extension includes the socket part itself; while the seabed fixed guidepost part includes the pin part.
In a second embodiment, or variant, the seabed fixed guidepost part includes the socket part and the guidepost extension has the pin part.
In a practical embodiment the friction forming means can be in the form of an O-ring, that is either arranged internally within the socket part or externally to the pin part and in grooves provided in the internal/external surface of the part.
Preferably, the O-ring is made of an elastomeric material, such as a rubber mixture or similar. This solution will be particularly well suited if an existing pin or socket end is already standing on the seabed and only the guidepost extension is to be replaced with a new one, i.e. modify existing equipment.
In still another embodiment, the internal surface of the socket part is divided in an upper surface having smaller diameter and a lower surface having somewhat larger diameter and where an O-ring is arranged on each respective surface. This means that the guidepost extension is somewhat reduced in diameter relative to the socket part, which in turn has reduced diameter relative to the guidepost part. The part has such geometric configuration that abutment only takes place at one spot.
In still another embodiment at least one fluid passage is arranged through the wall of the socket part somewhere between the friction forming means.
In an alternative embodiment the friction forming means can be in the form of tongue and groove means, where the tongue is able to make a mechanical engagement with the groove. This solution will probably be preferred if a delivery of complete guideposts for an equipment takes place before deployment has been done.
In still an alternative embodiment, the friction forming means can be in the form of a layer of elastomeric material, such as rubber, arranged in the gap between the pin and socket parts.
In still an alternative embodiment the friction forming means can be in the form of a metallic ring arranged in the gap between the pin and socket parts. The metallic ring can have any suitable cross section profile that is able to pinch against a surface.
The guidepost extension can preferably be in order of magnitude 1 to 3 meters long.
At least one of the parts, the pin end or the socket end, can be coated with a slippery material, for example Teflon or similar.
The clearance existing between the pin end and the socket end will conveniently be in order of magnitude about 1 mm without this being construed as a limitation. In one embodiment, the external diameter of the pin can be about 180 mm, just as an example. As another an example, two internal O-rings can be placed approximately 300 mm apart internally of the socket or sleeve part. Ideally viewed, the O-rings do not touch the pin.
Other and further objects, features and advantages will appear from the following description of preferred embodiments of the invention, which are given for the purpose of description, and given in context with the appended drawings where:
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Number | Date | Country | Kind |
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20101624 | Nov 2010 | NO | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/NO2011/000324 | 11/18/2011 | WO | 00 | 5/17/2013 |
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WO2012/067520 | 5/24/2012 | WO | A |
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