BUDDY CANTILEVER SYSTEM FOR JACK UP RIGS
FOR USE WITH SELF ELEVATING DRILLING RIGS
(OIL & GAS INDUSTRY)
Field of the Invention
This invention relates to the design of an apparatus and a method called Buddy Cantilever System for increasing the carrying capacity at extended positions of the cantilever of a self elevating drilling rig (Unit), or otherwise termed as jack-up rig, and therefore maximizing the hook load to its rated capacity or thereabout in the drill area.
Fundamentally, it is a different and innovative design and method enabling the stress in the cantilever beam to be within its structural strength limit in bending or buckling when fully extended out with increased load. Not only is the design unique and innovative, the system as a whole is made very simple and pragmatic, a concept never used before and it provides equivalent or better loading results than the relatively newer invention systems such as the "X- Y Cantilever" or "Rotating cantilever" (see Figure 2b and 2d) and does away certain disadvantages of these newer inventions in system complexity and deck space utilization, not to mention reducing capital expenditure. Working deck space is always a valuable concern of self-elevating drilling rigs.
This invention, apart from performing its intended function for the Unit, is shareable among Units. Because its application is essentially different and more pragmatic and is used only when the operating conditions require it. It is an enhancement rather than a replacement of the
conventional cantilever system design either in existing rigs or new build rigs. In addition, the manner it is used in application, the term "Buddy" is appropriately used to describe the partnering, assistance or help it provides in enabling the existing cantilever to work stronger.
A typical load or carrying capacity of conventional cantilever is depicted in figure lb. The drill floor carrying capacity diminishes as the drill centre extends out and away from the rig transom and moves to the extreme port or starboard side of the cantilever. Such is the design limit phenomena of an extending or hanging cantilever when the load is applied at the hanging end and to the extreme corner from the centre line. For the same hanging distance, this unique and innovative invention makes the conventional cantilever stronger in all aspects.
The following terminologies (in alphabetical order) commonly used in relation to a cantilevered self elevating or jack-up rig are defined below to assist in understanding the novel application of the Buddy Cantilever System ("BCS").
of down-hole services (see Figure 2c and figure
Cantilever beam A structural member to withstand bending or buckling caused by the drill floor sitting at the cantilever's aft end. Typically, there are two beams to make cantilever (see figure la)
Cantilever Load Chart A chart to indicate the safe working load the cantilever can carry when the drill floor moves within the drill area (see figure lb). The load tonnages shown are estimates and indicative of typical cantilever load chart trends.
Load charts shown in figures 6.0 and 7.0 reflect how BCS can effect positive changes and load carrying improvements.
Drill Floor movement and Drill Area The Drill Floor (complete with floor structure, derrick and drilling equipment etc.) is located at the aft end of both conventional and non-conventional cantilevers. In conventional cantilever, the drill floor is designed to move transversely while the cantilever longitudinally. This enables a drill area limit (see figure 3.0) to be created as described by the combination of cantilever and drill floor movements. In non-conventional cantilever, the drill floor structure is fixed and integral with the cantilever. To create a drill area, the whole cantilever is designed to move both longitudinally and transversely for the X-Y system. The Rotating system utilizes an arc movement for the cantilever to create the drill area, (see figure 2a)
Drill Floor strong back The structural beam to support the drill floor is sometimes called the "strong-back". Two such
strong-backs are commonly used to support the drill floor weight and load (see figure lb)
Hold Down structure As the cantilever moves aft-ward and its centre of gravity passes the transom, it will hang and tip over the aft. Hold Down structure is to hold it against tipping over (see figure 6.0).
Load Curve The load capacities, at different positions of the cantilever and drill floor, plotted against the travel of cantilever or drill floor provide two separate sets of load curves (see figures 5a, 5b and 8.0)
Non-Conventional cantilever New inventions to carry and move the drill floor for drilling away from rig stern or transom. Two inventions are mentioned. One is the X-Y Cantilever and the other is the Rotating cantilever (see figure 2b and 2a).
Disclaimer : any descriptions made with regard to these two inventions are purely the writer's own interpretation to the best of his knowledge and may not be absolutely true or correct.
Overturning stability When the Unit is elevated, the final CG of the rig affects the overturning stability. The cantilever carries a sizable variable load of the rig, therefore the position of the cantilever during storm condition can affect the rig stability.
Pedestal Pedestal is meant to be additional support structure to distribute the weight with applied load of the cantilever when it sits on the main deck of the Unit.
Push Up structure A structure to specifically provide the weight/load
reaction at stern to hold up the cantilever. It works in conjunction with Hold Down structure.
Transom The stern vertical surface of the Unit over which the cantilever hangs (see figure 9.0)
Variable deck load (VDL) A rig is designed and has a limit VDL so as not to exceed the stress limits of the structure particularly the legs during worst weather conditions and also stability when fully elevated in the ocean.
Background of the Invention
To appreciate the novelty of the invention, it is important to know the conventional cantilever installed and used on the Unit moves longitudinally aft-ward away from the rig transom when it is required to perform drilling operation at a distance. Its purpose is to bring the drill floor with the drilling derrick and drilling equipment to a point to begin drilling down into the seabed. The distance and the load it can carry when it overhangs at the aft end of the rig is important when the rig is working over a production platform (commonly known as work-over activities). This is one primary reason why cantilever is fitted on a drilling rig.
The drill floor sits above and at the end of the cantilever and is designed to be able to move transversely so drilling at various points is possible within the space envelope described by the combination of movements of the cantilever and the drill floor (see Figure 3.0). This is known as the drill area.
Such apparatus described above and other variations of such design achieve their objective in increasing the capacity of the cantilever thereby the drilling load or hook load can be maximized at all positions of the drill area. It is used when the overall load expectation in the corners of drill area prevents the conventional cantilever to perform safely. In other words, the
apparatus is not required to be applied most times. This means it can be "not a permanent fixture" on the Unit if it is so desired to be. This uniquely presents itself as portable and shareable asset with other Units.
The background of the Invention is to provide an alternative and novel design to enable the conventional cantilever to perform better, stronger and achieve higher capacity drill area in a simple manner while having several advantages. The manner this novel system works is to utilize the "buddy" cantilever in conjunction with existing conventional cantilever system (see Figure 4a and 4b). Essentially, the "buddy" cantilever acts as the second beam in support of the drill floor as the drill floor load is shifted to either to the port side or the starboard side. Figure 4a shows one single "buddy" beam is installed should the starboard drill load expectation is to be higher. Figure 4b shows both sides are installed with "buddy" beams to support higher drill load expectations throughout the drill area. Alternatively, "buddy" beam can be shifted from one side to the other depending on extreme drill point load expectations. Such is the flexibility and cost effectiveness of this novel design.
First significant difference and substantial advantage of the present invention is that the application of the invention need not be a fixed asset of the rig and can be installed when the need arises. Yet it can do the job better than conventional cantilever in a higher load requirement environment that the conventional cantilever cannot. In comparison with non- conventional cantilevers like "rotational" or "X-Y" systems, it can even outperform them with higher load carrying capability (see figure 5a and 5b). Regarding these non-conventional systems (see figure 2a and 2b), immediately, one can see that it involves taking up much deck space which is highly valuable in a drilling situation.. They both involve making the whole cantilever rotate on the deck or move X-Y direction therefore occupying much deck space for such movements.
Second significant difference and substantial advantage of the present invention is that the simplicity in design and operation of the Buddy Cantilever System ("BCS") can allow the novel system to be implemented on existing cantilevers to achieve better performance capabilities without having the whole cantilever replaced by Rotating or X-Y system for the same reason of performance betterment. BCS is significantly an enhancement novel design concept. BCS maximizes and even increases load capacity of the cantilever to above what is currently known and achieved in the industry of self elevating Rigs (see figure 5a, 5b and 8.0). It presents itself as a possible enhancement to all existing conventional cantilever designs.
Third significant difference and substantial advantage of the present invention is that when BCS is employed, it is only when the drill load demand for a particular drilling operation requires that the cantilever, as a whole, must carry more load. That means that when different drilling rigs of similar rig design perform at different locations, conditions and different times, the occasion that requires BCS to be used by any one of the rig fleet makes the novel BCS a sharing asset or sharing structural equipment. In order that BCS is installed and made operational, certain adaptation is to be made on the rig. The adaptation to install BCS is relatively simple and cost effective. Comparatively, such adaptation to allow BCS to enhance a cantilever capability is minimal and negligible vis-a-vis a complete replacement installation to a X-Y or Rotational cantilever system - or for that matter a stronger conventional cantilever - not to mention the high cost impact (see Figure 6.0). Such a replacement is extremely expensive and difficult to effect without bringing the rig back to a shipyard for major refurbishment, and may not even be feasible due to existing deck space and congestion limitations. In conclusion, the distinct advantage in BCS is the sharing ability among similar design rigs and at low cost of expenditure to effect similar or better performance results.
Fourth significant difference and substantial advantage of the present invention is that BCS is purely a structural "add-on" and inherently does not require complicated mechanism to make it move or work. No need for high pressure hydraulic moving system or rack-pinion travelling mechanism. It can be made up in one structural piece or broken up to several pieces for joining
at location all of which to allow easy handling and mobilization. Offshore support vessel or other transport means can easily bring BCS component to the rig at location for a particular usage. Such flexibility and portability cannot be found in current conventional or non- conventional cantilever systems (see figure 6.0). It can be tied to existing cantilever so that it moves as one integrated structural component. Alternatively, it can have its own portable winching machine, make use of rig crane as winching device and wire rope rigged to bring the BCS beam to any extended position to enhance the cantilever operating capabilities on the spot (see figure 6.0 and 7.0). All such adaptations of rigging and appurtenances to install and enable BCS to function as intended form part of the system invention.
Fifth significant difference and substantial advantage of the present invention is that BCS is able to allow an existing cantilever designed for only limited outreach (the limit amount of longitudinal travel aft-ward away from rig transom) to be altered to perform stronger at better outreach. This involves making extension to existing cantilever beams and together with BCS, the rig can be brought to a higher cantilever category performing level.
Needless to say a BCS design and invention optimizes apparatus utilization. As a result, cost savings in major cantilever refurbishment or correction costs, capital machinery expenditure and others to bring the cantilever to a higher performance level is obvious
The differences between BCS and non-conventional cantilever systems can be clearly observed by referring to tabulated points or comments under 'Results and Discussions'. Conventional system disadvantages and how BCS can assist to improve is also commented. BCS itself is an enhancement component of the conventional system and it is not meant to operate on its own except to support and enhance existing or new conventional cantilever system. This is BCS's novel, unique and inventive contribution.
The Objective of the Invention
The objective of the invention is to provide an improved, alternative and innovative design to enhance and improve existing or new conventional cantilevers such that the cantilever can meet the harsher demands of drilling in the industry. It also reduces the cost of fixed installation of a strong cantilever system on a Unit.
The Buddy Cantilever System ("BCS") design will obviate or mitigate the aforementioned situation of high costs, construction/installation/operation complexity and lack of usage optimization in the case of a Unit with non-conventional cantilever system. BCS at least provides the public with a useful alternative and cost effective choice with several advantages and can be adapted to existing conventional cantilever systems quite easily.
Statement of the Invention.
The BCS works to enhance the load bearing or carrying capacity of conventional cantilever design by being a "Buddy" as a second supporting beam (see figure 4a and 4b).
The application of BCS allows the conventional to perform better thus matching and even surpassing some advantages that the non-conventional cantilevers like the rotating or the X-Y cantilever are claiming. Because it acts as an "add-on" to conventional cantilever system, it is applicable for use with existing conventional cantilevers on rigs built in the past and those in the future.
It is not intended for BCS to specifically compete, in design, with non-conventional inventions of "Rotating" or "X-Y" cantilever systems, but to present itself as a practical solution to meet a particular drilling demand or situation the current rig fleet and those in the future may have to
deal with. Functionally, it is competitive and helps provides a wider choice of system to the public.
One should note that the application of BCS when used on jack up rig can be in the manner as a retrofit or refurbishment to existing rigs, or as part of new rigs currently being built and those in future. This is an enhancement concept that is new, novel and unique and the appurtenances and outfits to realize the function and completion of BCS all fall within this invention.
Whether as a retrofit or new installation, the ultimate objective is to achieve a stronger and better performing cantilever system. In simple technical term, BCS provides a duplicate or secondary beam of support when the drill floor load shifts to one side of the cantilever structure. BCS simply acts to provide the two beam support as if the load is still equally (or near enough) shared by the two beams of the cantilever before being enhanced by BCS.
Each BCS set to be incorporated into the Unit is basically made of the following components :- A main "buddy" beam (or two or more buddy beams) structurally similar to a new or existing conventional cantilever. It is not an additional support to any overhanging beam of the conventional cantilever but a secondary structure to increase the sectional modulus of the cantilever structure (see figure 4a and 4b and figure 8.0)
A "Push Up" structure to support the "buddy" beam (see figure 6.0)
A "Hold Down" structure to support or hold down the "buddy" beam (see figure
Other pedestals as required for stowing the "buddy" beam when fully retracted and stowed, (see figure 7.0)
Tie-in outfits to utilize the cantilever skidding system to move or a set of rigging equipment to enable the same effect (see figure 7.0)
To have full effect of BCS, the "Buddy" beam must effectively be connected to existing beam such that structurally they become one. This will require detail
engineering of the attachment fixtures such the Buddy beam is sharing the load with existing beam, all of which fall within this invention.
Results and Discussions
The following table highlights and compares the BCS advantages over conventional system and also other systems such as Rotating or X-Y design. The table is in no way meant to be an exhaustive exploration of all of the features of the invention, and many of those not discussed will become readily apparent to a skilled reader once the full scope of the invention is understood.
Units. This brings out its
competitiveness in usage
of the Unit.
Deck space" take-up" BCS incorporation takes The deck space saved The constant load curve is is negligible up a relatively small does not improve its achieved at the expense of amount of deck space yet application at higher load deck space. One has to always it provides a solution to demand in extreme drill allow the deck space to be kept higher load carrying positions. clear when the drill position demand of the cantilever shifts. This results in much (see figure 4a and 4b) deck handing of any temporary stowage of items in the way (see figure 2a and 2b)
Incorporation into BCS can be incorporated Replacing a conventional To replace a conventional existing operating into existing rigs with cantilever with another system with a non- Units to bring up conventional cantilever stronger conventional conventional system requires Units' performance so that the Units can cantilever does not make much alteration and systems ability perform at higher load much sense if BCS is corrections (hydraulic, all demands at all drill there to be a better services via drag-chains etc.) positions of the cantilever solution. and deck space availability (see figure 4a and 4b) may not even allow it, not to mention the high capital expenditure
Maintaining air gap BCS does not require the If an auxiliary frame is No difference in air gap issue
Unit to raise higher to used to extend the push
reach over platform in up structure so that the
work-over activities and hang-off of cantilever is
it allows the Unit to keep extended further aft-ward
the air gap as originally to improve load capacity,
designed for (see figure it can become an
9.0) obstruction when kept
close to a platform (see
Modifications of the Preferred Embodiments
While the invention has been described with particular reference to certain embodiments thereof, it will be understood that various modifications can be made to the above-mentioned embodiment without departing from the spirit and scope of the present invention. The examples and the particular proportions set forth are intended to be illustrative only.
The skilled reader will instantly realize that, although the examples have been described for the 'Buddy Cantilever System' in support of conventional cantilever system of a self elevating Unit, these aforementioned descriptions are merely illustrative and will vary depending on the application and the requirements of the Unit. An example of such variation of BCS to the Unit's cantilever is done with the Buddy beam located on the inside (inboard) and supporting the cantilever at some point before the end and not as a full duplicate of a whole beam (figure 10.0).
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