Patent Application
20160115665
This invention relates to access support, and in particular, but without limitation, to access support suitable for use in conjunction with both existing and new offshore installations.
An offshore installation (otherwise known as a platform) can either be manned or unmanned but, in both instances, routine maintenance needs to be carried out from time to time. In order to achieve this, it is necessary to man the platform and lift equipment & supplies onto the platform and this can be accomplished, in most cases, by a crane that is already mounted on the platform. However, in the case where the platform is unmanned, crane usage is infrequent, it becomes degraded over time, due to corrosion, fatigue and exposure to the elements and obsolescence issues cause failures. As such, before any maintenance and/or repair work can take place on the platform, it is often necessary to re-commission the crane prior to work commencing.
In order to achieve this, it is therefore necessary to air-lift crewmembers onto the platform using a helicopter, which is a hazardous activity. In addition, flying a crew onto the platform is very expensive.
In situations where the crew are required to maintain and/or upgrade a normally unmanned platform, it is also necessary to provide life-support on the platform in case of an emergency. For example, if the weather and/or the conditions are such that the crew cannot be evacuated by sea or air, it is necessary for them to be able to live safely on-board the platform, even if only for a short period of time. Whilst the platform may be supported whilst the crew are on the platform by a standby support vessel and/or a lifeboat system, it is generally not possible to leave crewmembers on an otherwise unmanned platform for extended periods of time.
With the passage of time, the platform degrades further, eventually leading to a situation where the required maintenance and remedial work exceeds the capabilities of helicopter intervention.
One known solution to this problem is to lift onto the platform temporary living accommodation units, which comprises sleeping quarters, messing facilities, first aid, and office space, etc., but this requires the use of an operational crane and if the crane is not serviceable, then alternative solutions need to be found. In addition, locating these temporary living accommodation units on a producing platform can result in unacceptable risks to personnel. These risks can only be mitigated by shutting down production and this will result in a major loss of revenue. This invention aims to locate the temporary living accommodation away from any hydrocarbon production areas and can incorporate blast and fire protection, which can significantly reduce the risk to personnel.
It is known, in such circumstances, to use a so-called “jack up”, which is a rig that can be floated out to the platform and located close by, whereupon legs can be extended downwardly from the jack-up until they rest on the seabed. Further jacking thereby raises the jack-up above the water level providing a temporary structure adjacent the main platform, which can be used for providing the necessary life-support services, equipment and storage space that, is needed for the operators on-board the platform. However, a jack-up is extremely expensive to use and therefore a need exists for an alternative type of support structure, in particular for an offshore platform.
It is also known to provide an accommodation support vessel (ASV) adjacent the main platform with a bridge connector, which can be anchored to the platform. However, these ASVs also involve the use of a jack-up for crane installation (albeit for a shorter period of time than if the jack-up were to be used, itself, as the support structure) and this, of course, introduces additional cost and complexity to the procedure.
A further consideration is that all of the above solutions rely on helicopter access and this significantly increases the risk to personnel when compared with marine access solutions. However, to date, these marine access solutions have been unable to provide a method of safely docking and remaining on station.
The invention therefore aims to provide a solution to one or more of the above problems and/or to provide an improved and/or alternative support structure for use when working on, or servicing, an offshore platform.
The invention may also provide a solution, which reduces the risk to personnel whilst addressing one or more of the above problems: the combination of remote temporary living accommodation and marine access may result in a major reduction in the risk to personnel and may facilitate further safety improvements.
Various aspects of the invention are set forth in the appendent claims.
According to a first aspect of the invention, there is provided a support structure suitable for use as an extension structure to an offshore platform (new or existing), the extension structure comprising a main support strut having a lower end and anchorable, in use, to the seabed or platform and an upper portion arranged, in use, to extend above sea level to a height substantially equal to, or greater than, that of the platform, the support strut comprising a guide rail extending upwardly from a level above the sea level to the top of the support strut for cooperating with a framework mountable to the guide rail, and further comprising drive means cooperating between the framework and the guide rail for elevating the framework relative to the support rail.
A second aspect of the invention provides a support structure suitable for use as a support structure to an offshore platform, the support structure comprising a main support strut having a lower end and anchorable, in use, to the seabed and an upper portion arranged, in use, to extend above sea level to a height substantially equal to, or greater than, that of the platform, the support strut (30) comprising a guide rail extending upwardly from a level above the sea level to the top of the support strut for cooperating with a raising framework slideably mountable to the guide rail, and further comprising drive means cooperating between the raising framework and the guide rail for elevating the raising framework relative to the support rail, the support structure being characterised by: the support strut and raising framework each comprising tracks arranged to substantially align end-to-end when the raising framework is elevated to the top of the support strut, the tracks, when so aligned, forming a substantially continuous track for laterally transferring a payload from the raising framework to the top of the strut.
Suitably, the framework can be used to elevate items relative to, or to the top of, the support strut. Suitably, the invention provides a system whereby the support strut can be anchored to the seabed adjacent to a platform and maintained in a fixed relationship thereto, and which enables equipment to be hoisted onto the support strut after installation. Advantageously, this means that the support strut itself, in one embodiment, can be floated to the site of the platform and anchored in position separately from any associated equipment, which can later be affixed to the support strut. Such a configuration may greatly facilitate the initial installation procedure.
Thereafter, the invention enables various items of equipment to be hoisted up, and optionally, mounted to the support strut after the support strut has been installed. This conveniently provides a solution to the problem having to use a jack-up to install and/or commission the support structure prior to work commencing.
Suitably, the main support strut floats so that it can be floated and/or towed out to the platform by a barge or other support vessel. One or more flotation collars may initially be provided on the support strut to enable it to be up-ended during the installation process. By suitably locating the flotation collar relative to the support strut, the combined centre of buoyancy of the collar(s) and strut can be aligned with the centre of gravity of the strut to enable the strut to be floated in a controlled manner. When the strut is in position, the position of the flotation collar(s) can be adjusted to tilt the support strut into a vertical orientation to allow it to sink vertically to engage the seabed.
The support strut suitably comprises an anchorage at its lower end, such as a suction pile or screw pile that enables the lower end of the support strut to be positively engaged with the sea bed. Additionally or alternatively, anchorages may be provided, connected to the support strut by guy wires that serve to stabilise the attitude and/or position of the support strut.
Once in position, the support strut can be affixed permanently, temporarily or semi-permanently to the platform, for example, using a connecting frame that can be welded, bolted, riveted etc. to the platform and the support strut. Thereafter, any guy wires can be kept in position, or discarded, as required.
Suitably, the sliding framework is adapted to receive a crane, which can be mountable thereto in one embodiment, for example, on tracks. By such a configuration, it may be possible to hoist a crane to the top of the support strut using the framework and guide rail assembly such that when the support frame reaches the top of the support strut, it is then possible to transfer the crane laterally from the framework to the top of the support strut. By such a configuration, it may be possible to install the support strut in the first instance and then to offer-up a framework-mounted crane to support strut via a support vessel, such as a barge boat.
The drive means cooperating between the framework and the guide rail for elevating the framework relative to the support rail can be provided in any number of ways. In a first embodiment of the invention, the drive means comprises a pulley system, which is suitably motor-driven, which enables items of equipment to be hoisted up the support strut by pulling on a pulley cable connected at one end to the framework and at the other end to a driving motor. In alternative embodiments of the invention, the guide rail comprises a toothed section forming a rack and the drive assembly comprises a gear adapted to engage the rack of the guide rail such that the framework can be driven directly up the guide rail by the cooperation of the motor-driven drive gear cooperating with the rack of the guide rail.
Suitably, means is provided for preventing the inadvertent and/or unintentional lowering of the framework relative to the guide rail. This can be provided in any one of a number of ways including the provision of a fall-arrest device associated with a hoisting cable (in the case of a pulley hoist system), or, in a preferred embodiment, by the use of a pawl cooperating between the framework and the rack of the guide rail, which is able to ratchet freely up the guide rail, but which engages with the rack when the motor drive assembly is stopped and/or disengaged. In a yet further possible embodiment of the invention, the fall-arrest device comprises a plurality of catches located on the guide rail that sequentially engage with the framework as it is elevated and which are arranged to inhibit and/or prevent inadvertent downward movement of the framework relative to the guide rail.
An embodiment of the invention shall now be described, by way of example only, with reference to the accompanying drawings, in which:
In
The support structure 10 is located next to the platform 12 and comprises a main support strut 30 that is anchored to the seabed 16 using a suitable attachment, which, in the illustrated embodiment, is a suction pile 32, although other anchorages may be used depending on the type of seabed (rock, sand, silt, gravel, etc.). An upper part of the support strut 30 is connected to the platform 12 by connecting steelwork (not visible in
The support structure 10 is thus comprised of a number of components, these being: interface steelwork (for connecting the support structure to the platform); a main support strut and suction pile; a crane pedestal; a crane, accommodation and installation system; and a power system for independently powering the support structure, for example, a diesel generator.
The interface steelwork 50 comprises a part-circular profile 52 that seats against, and which can be welded to the support strut 30, along with at least two splayed connectors 54 that extend between the part-circular profile 52 and the spider deck framework 24. Additional bracing may be provided to add rigidity to the connecting steelwork, where necessary.
The interface steelwork 50 fulfils four functions: as installation aid for the support strut 30 and suction pile 32; support for the crane installation system (described below); support for the support strut 30 and suction pile 32; and support for the access walkways to and from the platform.
Suitably, the interface steelwork 50 will be pre-fabricated and installed on the platform using bolted connectors, which require a minimum of preparation work on the platform 12. The interface steelwork 50 also incorporates a locating device and clamps to fix the support strut 30 before it is rotated to a vertical orientation. As such, the interface steelwork provides a pivot point and securement for the support strut 30 as it is tilted to a vertical orientation. Once the pile 32 is set at the correct depth, the clamps (not shown) can be closed and secured.
The support strut 30 and suction pile 32 are designed in accordance with the site-specific requirements: the main considerations being the locations of the access and egress levels; the crane requirement; platform support and environmental considerations. In addition, the support strut 30 is designed to float so that it can be towed to site, which can reduce installation costs significantly.
In situations where a crane 42 is specified, the support strut 30 and suction pile 32 design needs to be modified to accommodate both the crane installation loads and the crane operating loads.
Because most crane pedestals are typically of a larger diameter than what is required for the support strut, a pedestal is provided at the top of the support strut, as shown in
The support structure 10 additionally comprises a pair of guide rails 62 that extend from a point level with the upper edge 64 of the pedestal 40 to a point above sea level 18. The guide rails 62 are rigidly connected to the support strut 30, at intervals, by connectors 66, which, in practice, would comprise triangulation elements (not shown for clarity) to form a rigid connection between the two.
The upper surface 68 of the pedestal comprises a pair of parallel tracks 70 that project beyond the edge 64 of the pedestal and overlie the upper ends of the guide rails.
The guide rails 62 are shown in greater detail in
In
As can also be seen in
The installation of the support structure proceeds as shown in the sequence of
In
In
Now that the crane 42 has been installed, it is possible to use the crane 42 to transfer other items from the support vessel 104, such as a deck 106 and to install it on the support strut 30. The deck 106 would have to be installed piecewise. Thereafter, living accommodation units 36 and the like can be hoisted, using the crane 42, onto the deck 106 of the support structure 10 to complete the installation.
At this point, as shown in
The fast intervention vessel 124 can be hoisted using a set of under-hull slings or by attachment of crane hooks to hard eyes on the deck of the vessel 124. Once hoisted into position relative to the raising framework, linkages can be used to free the crane for other uses. Alternatively, on a low tide, the vessel 124 can be located below the raising framework 90 and connect thereto by slings or wires, and the raising framework driven up the support strut 30 in the previously described manner to hoist the vessel 124 out of the water. Such an arrangement is shown in
The crane 42 can be powered by an internal combustion engine, and fuel tanks therefor can be conveniently located within the interior of the strut 30 or pedestal 40.
A fall-arrest device is also provided for the raising framework 90 to prevent inadvertent falls, for example, in the event of an engine 98 failure. The fall-arrest device can comprise a pawl arrangement that ratchets against the toothed racks 82 of the guide rails 62, or a supplementary set of catches can be provided, as shown in
From
The raising framework 90 comprises a pair of arms 92 that extend behind the guide rails 202 at a relatively elevated position to support a set of rollers 80 that bear against the rear rolling surface 76 of the guide rails 202. The raising framework 90 additionally comprises another set of rollers (not visible) which are arranged to bear against front rolling surface of the guide rails 62. The toothed portions 82 of the guide rails 62 project sideward from the guide rails 62 and are engaged by motor-driven gears 96 to raise or lower the raising framework 90.
The raising framework 90 thus cooperates with the guide rails 62 to enable a payload, such as a support vessel, or crane, to be hoisted up the support strut 30 using set of motors 204 for driving the gears 96.
In
The support vessel 104 can thus be located within the boat hoist 210, and raised out of the water by the raising framework 90, as previously described (in particular, with reference to
In certain embodiments (not shown), a flexible and/or reticulated support sheet is affixed to the upper edges of the side walls 212 and hangs between them above the base 214 wall of the boat hoist 210. The provision of a flexible sheet or net enables the support vessel 108 to be retained securely by the boat hoist 210, i.e. by the sheet conforming to the shape of the underside of the hull. Such a configuration additionally reduces the likelihood of point-loading the hull of the support vessel 108 (for example, where the keel would otherwise engage the base wall struts).
Given that the boat hoist 210 is likely to be used in heavy seas, wave suppression means and/or fendering may be provided on the boat hoist 210, although not shown in the drawings. For example, inflatable tubes may be affixed to the upper edges of the side walls 212 of the boat hoist 210, thereby cushioning the support vessel 108 from impacts with the side walls 212, as well as providing shelter from the waves. Further, the inflatable tubes, or booms/pontoons may extend axially away from the boat hoist 210, and may provide a relatively protected entrance and exit to the boat hoist 210.
As can be seen in
The raising framework 90 is connected to the support strut 300, as previously described. The raising framework can likewise be used to hoist a support vessel (not shown) out of the water, a crane (not shown) to the top of the support strut 300, or other equipment and components, as previously described.
Notably, because the raising framework 90 of the embodiment shown in
It will be appreciated from the foregoing that although the invention is particularly suited to servicing operations for existing platforms, e.g. crane replacement etc., it is equally applicable to new installations, and an example of a new build offshore platform 400 and support structure 10 is shown in
A pair of additional support struts are provided: a first access strut 300, as described herein, which comprises a raising framework 90, crane 42, deck area 38 for temporary living accommodation etc.; and a second strut 410, which supports an additional deck 406. The additional deck 406 usefully provides an alternative location for certain items, e.g. equipment to support drilling operations etc., and also enables the support structure 10 of the invention to be truly “independent” of the main platform. The struts 300, 410, 402 comprise foundations 424 at their lower ends, enabling them to be driven into a sea bed with relative ease. Further, because the struts 300, 410, 402 are interconnected by cross-struts 408, a tripod-type structure is formed, which is inherently more stable than a mono-pile, and can be driven vertically into the sea bed by differentially varying the pressure in the foundations 424 during the driving process (as described in greater detail in UK Patent Application No: GB 12407991.7).
Referring now to
The cradle 248 additionally comprises, extending outwardly at an angle, from each of its corners, a retractable boom 256. Each boom 256 comprises a pair of spaced-apart, horizontal metal tubes that terminate at their free ends, with a float 258. The floats 258 serve to stabilise the cradle 248 when floating in the water, or when lightly supported by the suspension lines (not shown). The angling of the booms 256 provides a tapered entrance and exit for the cradle 248 facilitating the entry and exit of a support vessel (not shown).
A flexible skin (e.g. of sheet plastics, or canvas), or a sheet metal skin 254, is provided on the exterior of the side walls 212 and booms 256, and optionally, below the base wall 214 of the cradle 248, to buffet the waves and to create a relatively calm “harbour” within the confines of the cradle 248.
Attached to the cradle 248, spanning the side walls, are a set of flexible slings 260, which engage with the contoured underside of the support vessel (not shown) as it is raised out of the water. As previously discussed, the slings could be replaced by a net or a flexible sheet to more evenly distribute the transference of the weight of the support vessel (not shown) to the cradle 248, thereby stabilising it and reducing the likelihood of hull punctures.
The invention is not restricted to the details of the foregoing embodiments, which are merely an example of an embodiment of the invention. For example, the foregoing description has focussed on the use of the support structure an alternative to an accommodation type jack-up. However, there are other types of jack-up, such as a drilling jack-up, to which the concept of the invention may offer an alternative solution. Specifically, the crane of the invention could be used to lift a drilling rig onto a platform that was designed to support such weight. This could be a particularly attractive concept to those energy companies looking to drill for shale gas offshore and utilise, where possible, their existing infrastructure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1310272.8 | Jun 2013 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2014/051765 | 6/9/2014 | WO | 00 |
