DK201300303A1 - An offshore drilling rig and a method of operating the same. - Google Patents

Abstract

An offshore drilling rig comprising a drill deck, at least one primary well center and a diverter system arranged below the primary well center, a drilling sup- port structure extending upwardly from the drill deck and above the primary well center and the other work center and a first and a second hoisting sys- tem supported by the drilling support structure and being adapted for raising or lowering a first and a second load carrier, respectively, and where the off shore drilling rig comprises a positioning system adapted for selectively positioning at least the first load carrier or the primary well center in at least a first or a second horizontal position different from the first horizontal position, where the first load carrier in the first horizontal position is positioned above the primary well center, and in the second horizontal position is positioned above the other work center.

Description

title:

An offshore drilling rig and a method of operating the same.

The prior art:

The present invention relates to an offshore drilling rig comprising a drill deck and to a drilling support structure extending upwardly from the drill deck, and where at least one or two work centers are arranged in the drill deck, at least one of the work centers being a primary well center meaning that it is equipped for drilling operations using a diverter that can be connected to a mud return system, such as a marine riser or a mud return conductor being capable of conducting drilling mud from the sea floor to the offshore drilling rig .

Offshore drilling rigs of this kind are expensive to build and operate, and the continued development of this kind of rigs is therefore focused on providing a rig that will reduce the time of production, meaning that the time for drilling and installing the necessary equipment for e.g. oil production should be as short as possible without significantly increasing the costs of building and operating the rig.

For this purpose many different embodiments of offshore drilling rigs have been proposed during time.

Against this background, it is in some embodiments the purpose of the present invention to provide an offshore drilling facility that will increase the possibility of operating the rig, even when essential equipment is out of order, e.g. due to maintenance or breakdown.

summary:

In some embodiments of the present invention this is achieved by the rig mentioned in the introduction further having two hoisting systems (a first and a second hoist system) supported by the drilling support structure and each being adapted for raising or lowering a load carrier ( a first and a second load carrier, respectively), and by comprising a positioning system adapted for selectively positioning at least a first load carrier or the primary work center in at least a first or a second position different from the first position, where the first load carrier in the first position is positioned above the primary well center, and in the second position is positioned above the other work center.

Additionally, the two hoisting systems may operate over the same work center simultaneously or individually, so that when both hoisting systems are operational it will be possible to use both over the same work center or to use one over a work center and to operate at the same time. the other hoisting system over the primary well center, or another work center.

For the purpose of the present description, the term drilling support structure means any construction extending upwardly from the drill deck and being equipped to support a hoisting system for hoisting and lowering tubulars (such as drill strings, casings and / or risers towards the seabed) so that drilling into the seabed can be performed. The drilling support structure may extend from the drill deck or from a deck different to the drill deck. The hoisting system is in this relation any system that provides a lifting capacity above one or more of the work centers arranged in the drill deck. This may in one embodiment of the invention be in the form of a hydraulic hoisting system comprising upwardly extending cylinders for supporting the load to be hoisted or lowered typically via cable sheaves mounted on top of the cylinders or alternatively it may be in the form of a conventional draw works system. Examples of a drilling support structure include a derrick structure which are typically applied to support a draw works hoisting system and a mast structure which are typically applied to support a cylinder hoisting system.

The term work center refers to a hole in the drill deck through which the drilling rig is configured to lower tubulars towards the seabed and, in particular, through which tubulars may be lowered all the way to the seabed. In this respect, the term work center covers e.g. a well center, a mousehole, a rathole or a standbuilding foxhole, with or without different tools inserted or supported from it, such as powerlips or other equipment. A well center is sometimes also referred to as a drilling center. It will be appreciated that the drill deck may comprise additional holes such as foxholes and mouse holes which may e.g. be used for building stands of tubulars but through which the drilling rig cannot lower tubulars to the seabed and / or through which the drilling rig cannot perform drilling into the seabed e.g. by lacking a system arranged to rotate a drill string with sufficient force such as a Top drive or a turntable. In some embodiments such additional holes is simply a hole in the drill deck through which the drilling rig cannot progress a drill string through a riser system or a mud return conductor. A primary well center is in this relation a well center being adapted for drilling operations comprising a mud return system using e.g. a marine riser or a mud return conduit extending from the seabed to the offshore drilling rig. In this relation, a primary well center is therefore differentiated from other work centers by having a diverter and / or a diverter housing arranged below so that drill string passed through the primary well center extends through said diverter or diverter housing arranged for diverting e.g. blow outs to one side of the offshore drilling rig.

The offshore drilling rig may be a semi-submersible drilling rig, i.e. it may comprise one or more buoyancy pontoons located below the ocean surface and wave action, and an operation platform elevated above the ocean surface and supported by one or more column structures extending from the buoyancy pontoon to the operation platform. Alternatively, the offshore rig may be of a different type, such as a jack-up drilling rig or a drill ship.

The term tubular equipment is intended to refer to tubular equipment that is advanced through the well center towards the sea floor during one or more stages of the drilling operation. The tubular equipment may be selected from drill pipes and / or other tubular elements of the drill string, risers, liners and casings. Examples of tubular elements of the drill string include drill pipes, drill collars, etc.

For the purpose of this description, the term drill deck is intended to refer to the deck of an operating platform of an offshore drilling rig immediately above which joints of tubulars are assembled to form the drill string which is advanced through the well center towards the seabed . Hence the drill deck is the primary work location for the rig crew and / or machines performing similar functions, such as iron roughnecks. The drill deck normally includes at least one rotary table to support the rotating drill string during drilling operations. For the purpose of the present description, the term drill deck includes the drill floor located directly below / next to the mast and surrounding the well center as well as deck areas on the same level as and connected to the drill floor area by uninterrupted floor area on the same level, ie the floor area where human operators and movable equipment such as forklifts, equipment moved on skidbeams, etc. can move around and to / from the well center; in some embodiments without having to climb / descend stairs or other elevations. The drill deck is typically the floor of a platform, e.g. the lowest platform, above the diverter system.

At least parts of the drill deck may be formed by the roof of a housing or enclosure accommodating mud mixing equipment and / or other operational equipment of the drilling rig, thus allowing for a compact and space-saving arrangement of equipment on the drilling rig. For example, the drill deck may comprise a storage area for storage pipes, e.g. a storage area for storage pipes in horizontal orientation. The storage area may be located next to the two horizontal pipe handling devices or, if this is movable, next to the path along which the horizontal pipe handling device may travel. In some embodiments, the pipe storage area and / or horizontal pipe handling equipment may be partially or completely surrounded by open drill deck area, e.g. drill deck area shaped and sized to allow vehicles or skiddable items to be moved around the pipe storage area.

While the invention is applicable to rigs with two or more work centers any embodiments described herein may also be applicable where only one work hole is available (or used) with the lifting yokes, hoisting systems, load carriers or lifting yokes. In such embodiments, the other work center from the primary well center is replaced by the absence of a work center e.g. and blank.

In some embodiments, the present invention relates to an offshore drilling rig, therefore, comprising two hoist systems each comprising a lifting cable hanging over at least one cable crown being supported by the drilling support structure and each being adapted for raising or lowering a load carrier, and further comprising a positioning system adapted for selectively positioning each load carrier in a number of different horizontal positions comprising at least a first horizontal position above the primary well center, and a second horizontal position different from the first horizontal position, wherein the positioning system is adapted for positioning each cable crown above said first horizontal position above the primary well center, or said second horizontal position.

In some embodiments the present invention relates to an offshore drilling rig comprising at least one top drive and a positioning system adapted for selectively positioning the top drive in at least a first or a second horizontal position different from the first position, where the top drive in the first position is positioned above the primary well center, and where the offshore drilling rig further comprises a connecting yoke having two opposite ends, each being adapted for being directly or indirectly connected to one of the load carriers, and where the connecting yoke has an intermediate load carrier arranged between said two opposite ends and being adapted for carrying a load.

Additionally, the two hoisting systems may be used simultaneously to provide the combined lifting capacity of each hoisting system in order to lift a load otherwise too heavy for one hoisting system e.g. out of the primary well center.

The hoisting systems may in this connection be any suitable hoisting system such as based on a draw works or a hydraulic cylinder configuration. In this relation, the term cable crown covers any device supported by the drilling support structure and being adapted to support one or more lifting cables hanging below the drilling support structure below the cable crown. This may be in the form of a single cable sheave adapted to support one or more cables, or a cluster of cable sheaves being independently rotatable so as to constitute a crown block or a cable sheave cluster e.g. supporting a traveling block beneath the crown block. Furthermore, the term load carrier in this relation means any device adapted for being carried by the hoisting system, and allowing a load to be connected to the load carrier. Examples of load carriers may be a load carrying hook, yoke, shackle or a traveling block, but in one embodiment the load carrier may even comprise a top drive adapted for simultaneously rotating and carrying the load of a drilling string.

In one embodiment of the present invention, each of the load carriers is connected to a lifting cable hanging from a cable crown (such as a cable sheave cluster or a crown block) supported by the drilling support structure, and the positioning system is adapted for shifting at least one or each of the cable crowns to and from a first and a second horizontal position relative to that cable crown where the load carrier is positioned directly above a selected one of the work centers. The position of the cable crown is measured by the position of the load carrier. Also, with each cable crown having at least two positions several configurations are possible including but not limited to the configurations where the rig having two working holes or three holes discussed below where the cable crowns have a common position in the middle and each a second position to the side. In a configuration with two holes one or both cable crowns may be arranged to be positioned over both holes so that one can replace the other for redundancy and / or the load carriers may be arranged to lift together in one of the work holes.

The drilling rig may further comprise a connecting yoke having two opposite ends each adapted for directly or indirectly connecting it to one of the load carriers, so that the connecting yoke can be carried by two different load carriers, and where the connecting yoke has an intermediate load carrier being arranged between said two opposite ends and being adapted for carrying a load. In this way, it is possible to mount the connecting yoke so that it is suspended below and between two load carriers, and thereby it is possible to provide a lifting power being higher than the lifting power of each of the hoisting systems by using both hoisting systems to lift the same load via the connecting yoke.

In this regard, the positioning system may advantageously be further adapted for shifting each of the two cable crowns to a position right next to the first position, and so that the two load carriers are positioned on opposite sides of the first position.

Furthermore, the positioning system may advantageously comprise a retractable dolly arranged for each load carrier, and the retractable dolly being adapted to connect the load carrier to a vertically extending track mounted on the drilling support structure, and to position the load carrier in the first and the second horizontal position above eg two different work centers and being adapted for positioning the load carrier at a distance from the track, so that it is positioned right above one of the work centers. In order to enable this feature in practice it will be recognized that the retractable dolly may be adapted to reach a load carrier at a substantially horizontal distance from the vertically extending track, even where such a distance exceeds 4 or even 5 meters, such as exceeds 6 or even 7 meters, such as exceeds 8 or even 9 meters, such as exceeds 10 or even 11 meters, such as exceeds 12 or even 13 meters.

In order to reduce the horizontally induced load on the retractable dolly it is preferred in this relation that the cable crown carrying a load carrier, and the retractable dolly connecting the same load carrier to said vertically extending track be adapted to keep the lifting cable between the cable crown and the load carrier substantially vertical.

It is understood that variations of the present invention may be made by applying a retractable dolly. First, in some embodiments, the retractable dolly comprises a load carrier for carrying loads extending into the work hole and the load carrier of the cable connected to the hoisting system is connected to the retractable dolly for providing vertical lifting power to the dolly. In combination of alternatively, the retractable dolly may be provided to offset the load carrier connecting the cable from the position it would have based on the position of the cable crown and no retractable dolly. Typically, it is advantageous if these two positions are substantially aligned so that the lift provided by the hoisting system via the cable is substantially vertical. Flowever, by providing such offset via the dolly less movement may be necessary of the cable crown which may be a faster and / or simpler way of changing position of the load carrier. Accordingly, in some embodiments the position of the cable crown refers to the position of the load carrier as provided by the cable crown and the dolly in combination. In some embodiments the position of the cable crown refers to the position of the load carrier as it would have been without a retractable dolly influencing the horizontal position.

In another preferred embodiment, the two work centers are mounted in a substantially horizontal track in the drill deck, and the drill deck comprises a work center positioning system adapted to selectively move at least one or each of the work centers in the horizontal track to the first or second position in the drill deck.

In this relation, the horizontal track may preferably be linear at least along a portion of it, and the diverter system may comprise at least one diverter over board tube having a first end being connected to the primary well center and the other end being supported and fixed. With respect to the drill deck and having at least one telescopic section between the first and the second end, the telescopic section extends parallel to the linear portion of the horizontal track in the drill deck. Additionally, the diverter over board tube, which may be directing well fluids under high pressure from the diverter and over board, is relatively easy to keep tight during drilling operations e.g. by using a hydraulic, pneumatic or mechanical packer to tighten and seal the telescopic section during drilling operations.

The drilling rig may advantageously further comprise at least one riser tensioning arrangement below the drill deck, and where the riser tensioners are mounted on linear tracks for repositioning, and in parallel to the horizontal track in the drill deck, so that the riser tensioners can be positioned below either the work centers and / or below either the first or second positions.

In some embodiments each load carrier is lifting a top drive, which in some embodiments is considered a load carrier itself.

In a further preferred embodiment, two work centers may be both primary well centers comprising a rotary table and a diverter system arranged in the drill deck.

In yet another preferred embodiment, the shifting means is adapted for shifting each of the cable crowns along a line being parallel to the linear portion of the horizontal track in the drill deck.

In the context of this description, the terms of moving, positioning, skidding shifting and so on are meant to include the process of displacing a component or part from one position to another, but also the necessary means for holding or fixing the component or part at a selected position during operation of the drilling rig.

The drawing:

The following one or more embodiments of the invention will be described in more detail and with reference to the drawing, wherein:

FIG. 1a and 1b: Are concept drawings showing two different operation situations of a dual activity drilling facility seen from one side, incorporating full redundancy for the intended drilling operation by incorporating skidding well centers / work centers in the drill deck.

FIG. 2a and 2b: Are concept drawings showing two different operation situations of a cyclic operating hoisting system within the same drilling facility seen from one side, enabling both hoisting systems to work over the same work center individually or in turn to provide fast tripping of drill pipe , casing running or riser and BOP running / retrieval operation. FIG. 3: Is a concept drawing showing an alternative embodiment of the invention, where each hoisting system comprises a cable winch.

FIG. 4: Is a concept drawing showing an operation mode where the two hoisting systems are operated synchronously within the same drilling facility seen from one side, enabling both hoisting systems to work over the same work center in sync to provide a combined lifting capacity in the one work center. NY Fig 5: Is a concept drawing showing an operation mode where the two hoisting systems are operated synchronously within the same drilling facility seen from one side, enabling both hoisting systems to work over the same work center in sync to provide a double lifting capacity in the one work center, but with only one hoisting system carrying a topdrive, and with a single work center.

FIG. 6: Is a concept drawing showing a transferable diverter housing and mud return tubing system with telescoping diverter overboard lines according to the invention, seen from below.

FIG. 7: Is a sectional drawing showing a cross section through the center of a primary well center in the form of a rotary table supported on a transferable skidbase on tracks arranged in the drill deck, with a diverter housing suspended from underneath the said transferable skidbase and with a riser supported by in-line hydraulic riser tensioners mounted on a separate track below the drill deck.

Description of exemplary embodiments:

FIG. 1 a, 1 b, 2a, 2b and 4 all show a drilling support structure 1 arranged above a drill deck 2 and three work centers 3a, 3b and 3c, where one is in the form of a primary well center 3a being equipped with a diverter housing 13. The three work centers 3a, 3b and 3c are supported on individual skid-bases on tracks 4 arranged in the drill deck 2, and the drilling support structure 1 carries two cable crowns 5a and 5b on fig. 1a, 1b, 2a, 2b and 4 in the form of a crown sheave cluster, and on fig. 3 in the form of a crown block, being skidably arranged on the top of the drilling support structure 1 on separate tracks.

From each of the crown sheave clusters 5a and 5b lifting cables 7a and 7b are run down and connected to a load carrier 8a and 8b each carrying a top drive 9a and 9b at the end of the lifting cables 7a and 7b. Each of the top drives is connected via a retractable dolly 10a and 10b to a vertical track 11 a and 11 b arranged on the drilling support structure 1. The retractable dollies 10a and 10b are each adapted so that they can position and keep the top drives in different positions above the work centers 3a, 3b, 3c in the drilling deck 2.

In the embodiment shown in fig. 1a, 1b, 2a, 2b, and 4 each hoisting system has a linear actuator in the form of a hydraulic cylinder 28a, 28b, having its lowermost end 29a, 29b fixed with respect to the drill deck 2 and an upper traveling end 30a, 30b with a cable sheave 31a, 31b. At least one lifting cable 7a, 7b has one end extending from another hydraulic cylinder 32a, 32b arranged for compensating heave during eg drilling operation, and over the traveling cable sheave 31 a, 31 b and further below a second cable sheave 33a, 33b being fixed with respect to the drilling support structure 1, and thereafter over the crown sheave cluster 5a, 5b. skidably mounted on the drilling support structure 1 on a track 26. In these figures only a single lifting cable is shown for each hoisting system, but in practice it is necessary in order to provide significant lifting capacity, as well as redundancy in case that one cable breaks, to have multiple mutually parallel lifting cables extending along with the lifting cables 7a, 7b.

Alternatively the drilling support structure 1 shown on fig. 3 has a hoisting system with two cable crowns 5a, 5b each in the form of a crown block being connected to a traveling block 34a, 34b via multiple cable loops hanging down from the crown block 5a, 5b, In this embodiment each traveling block is carrying a topdrive 9a, 9b. In this embodiment, a single lifting cable 7a, 7b provides the multiple cable loops, and thereby the necessary cable lifting capacity of the hoisting system, and therefore, in order to provide the necessary traveling length of the traveling block, a cable winch 27a, 27b is arranged for each hoisting system.

However, the skilled person will appreciate that the more combination of the skidable crown sheave clusters 5a, 5b shown on Figures 1a, 1b, 2a, 2b and 4 and the linear actuators 28, disregarding other features of the present invention, mutatis mutandis, provides both efficient and safe lifting capacity, because each hoisting system may comprise multiple lifting cables 7a, 7b extending parallel to each other in order to carry the same load carrier 8a, 8b or the same topdrive 9a, 9b.

In Figures 4 and 5 a connecting yoke 12 is connecting the load carriers 8a and 8b via the top drives 9a and 9b in fig. 4 and a single top drive 9a in FIG. 5. In addition, it is possible to connect a load to the connecting yoke 12, so that it is possible to provide a lifting force by combining the lifting force of both hoisting systems lifting the two load carriers 8a and 8b.

Figure 6 shows the conceptual layout of a preferred embodiment of a diverter system attached to the primary well center 3a as shown in fig. 7th

This diverter system comprises a diverter housing 13 suspended from the skidbase 25 and supporting the rotary table 14 of the primary well center 3a.

The diverter housing 13 has at least two outlet ports 17a and 17b each being connected to telescopic overboard lines 18a and 18b. This allows the diverter housing 13 to be positioned at different positions along a line defined by the track 4 being parallel to the overboard lines. One such position is shown in fig. 6 in full line, and another is shown with dotted lines.

The diverter housing 13 also comprises a mud return outlet port 19 adapted for leading drilling mud from the diverter housing back to the mud process systems via the main mud return line system 20. The mud return line comprises a number of telescopic connectors 21 a 21 b and 21 c arranged at selected positions in order to connect the mud return line to the mud return outlet port 19 on the diverter housing 13.

In Figure 7 a primary well center 3a is shown in more detail including the components and parts mentioned above, and in this figure a riser tensioner system is also shown comprising skidding carriages 22 and hydraulic in-line tensioning cylinders 23 being skidably supported by a separate riser tensioner track 24 arranged parallel to and below the track 4 supporting the rotary table skidbase 25. In addition, the riser tensioners 23 may be moved along with the rotary table and diverter housing 13 or independently of the rotary table 14 and diverter housing 13.

The following different modes of operating the drilling rig shown in the figures are disclosed in more detail with reference to the relevant figures. 1. Full redundancy:

With reference to FIG. 1 a and 1 b especially, but not only, a fully redundant dual activity hoisting and drilling facility is provided.

Full redundancy is achieved by having a transferable, riser-capable primary well center 3a, which may be positioned under either one of the top drives (eg 9a or 9b) and load carriers (8a and 8b) of the two fully rated main hoisting and drilling systems comprising the facility. In this regard, the primary well center may be transferred and positioned as mentioned above, with or without one tubular or a string of tubulars 35, such as riser tubes, casings, drilling pipes or the like being supported and / or hanging down from the primary well center, and these tubulars may either hang freely down from the primary well center, or they may extend all the way to the sea floor and further extend into the well or be connected to the well at the sea floor. In the latter case a diverter system and a tensioning system as shown on figures 6 and 7 respectively may be employed along with other well control equipment.

The riser-capable primary well center 3a shall consist of a rotary table 14 supported by a horizontally transferable skid / trolley 25 which is sunk into a slot in the drill deck 2, so that the rotary table 14 top cover is substantially flush with the drill deck 2 level.

The transferable skid / trolley 25 shall rest on horizontal skid beams forming a track 4 spanning the width between the two fully rated main hoisting and drilling systems 9a and 9b. A diverter housing 13 with telescoping overboard lines (overboard tubing 18a and 18b) and a detachable main flowline (mud return tubing 20) shall be suspended from underneath the said transferable skid / trolley 25. A transferable / skidding riser tensioning system shall be arranged on horizontal skid beams suspended from underneath the drill deck structure, while spanning the full width between the two fully rated main hoisting and drilling systems.

Following examples are provided for the intended operation to ensure full redundancy e.g. in the case that the one (active) fully rated main hoisting and drilling system suffers a main equipment breakdown: 1. While drilling, tripping drill pipe or running casing during the riserless top-hole sections of the well. 1.1 the drillpipe or casing string is hung off in the power slips / casing spider 1.2 the drillpipe or casing string, while being suspended from the pow er er slips / casing spider inside the rotary table, will be transferred to the opposite fully rated main hoisting and drilling system 1.3 drilling, tripping drill pipe or casing running operation may resume on the opposite fully rated main hoisting and drilling system

2. While running or retrieving riser and BOP 2.1 the riser string and BOP is lowered and hung-off in the riser spider and gimbal, which is resting on top of the rotary table. 2.2 the riser string and BOP, while being suspended from the riser spider and gimbal, will be transferred to the opposite fully rated main hoisting and drilling system 2.3 running of the riser may resume on the opposite fully rated main hoisting and drilling system 3 while drilling, tripping drill pipe or running casing through the riser and BOP after this has been connected to the well and the riser has been put in tension 3.1 the drill pipe or casing string is hung off in the power slips / casing spider 3.2 the well is secured 3.3 the drillpipe or casing string, while being suspended from the pow er-slips / casing spider inside the rotary table, will be transferred to the opposite fully rated main hoisting and drilling system 3.4 the diverter housing with telescoping overboard lines and detachable main flowline, suspended from below the transferable skid / trolley supporting the rotary table, will be transferred to the opposite fully rated main hoisting and drilling system 3.5 in full synchronous motion, the riser string, while being suspended from the riser tensioners will be transferred to the opposite fully rated main hoisting and drilling system 3.6 drilling, tripping drill pipe or casing running operation may resume on the opposite fully rated main hoisting and drilling system

The fully redundant dual activity hoisting and drilling facility illustrated in Figures 1a and 1b will allow for continued operation on either port or starboard side hoisting and drilling system (by repositioning the primary well center), while the opposite side is decommissioned for any extended period of time, eg for Class required Special Periodic Survey, breakdown or other reason. 2. Cyclic Dual Hoisting:

With reference to FIG. 2a and 2b especially, but not only, a cyclic dual hoisting facility is provided especially for Fast Tripping, Casing or Riser Running:

Fast tripping, casing or riser running operation is ensured by having two independent and fully redundant hoisting and drilling systems (top drives 9a and 9b) working in cyclic operation over a common primary well center 3a.

Each hoisting and drilling system shall consist of a main hoisting system with a horizontally transferable cable crown in the form of a crown sheave cluster arrangement 5a, 5b, allowing the crown sheave cluster 5a, 5b to be horizontally transferred, aligned and locked into position over at least two independent positions / well centers 3a, 3b, 3c on the drill deck 2 below.

Each hoisting system supports a vertically traveling load carrier 8a, 8b arrangement, from which a topdrive 9a, 9b is suspended below on a horizontally extendable / retractable dolly 10a, 10b system for guiding the topdrive 9a, 9b.

The extend / retractable dolly 10a, 10b shall have a horizontal travel corresponding to the horizontal travel of the crown sheave cluster 5a, 5b arrangement above, while extending / retracting horizontally in synchronous motion with the skidding crown sheave cluster 5a, 5b arrangement above, ensuring that the hoisting system is kept in true vertical alignment with the cable sheave cluster / load carrier / yoke / hook arrangement and the topdrive 9a, 9b suspended underneath it.

The following typical examples are given for the intended cyclic operation of the dual hoisting and drilling facility to provide fast tripping, casing or riser running operation: 1. Tripping / running in the hole: low setback and pipe racking system off-drill deck. 2. Tripping / running in the hole: setback and pipe racking system on-drill deck.

Fast running or retrieval of the riser and BOP may be performed in a similar cyclic operation, while employing suitable arrangements for facilitating handling of the riser joints to / from the primary well center 3a with this being in the center position

An added benefit of the invention is the full redundancy provided within this facility in that each hoisting and drilling system will offer full redundancy for the other system in the center operating position, without repositioning of the primary well center 3a. 3. Synchronous Dual Hoisting:

With reference to FIG. 4 especially, but not only, a synchronous dual hoisting facility is provided for heavy duty well construction.

The synchronous hoisting facility is realized by utilizing the two independent and fully redundant hoisting and drilling systems in a combined synchronous mode of lifting operation above the common primary well center 3a, by using a connecting yoke 12.

In FIG. 4 the synchronously hoisting facility comprises two top drives, but as shown in fig. It is possible to operate the hoisting systems synchronously even when only one topdrive 9a is used. In this situation the connecting yoke 12 is carried by the topdrive 9a on one side, but is directly connected to the hoisting cable via the load carrier 8b on the other side.

This principle allows for extra heavy duty lifting operation without necessitating any of the two hoisting and drilling systems to be rated beyond the current design loads of such equipment, where especially the load capacity of the top drives 9a, 9b are limiting the load capacity of the hoisting systems.

Recurring requests for rigs capable of running extended sections of heavy wall casing strings through deep formations in ultra-deep water may require lifting facilities of 1500 metric tons SWL or beyond.

Current designs of hoisting and drilling systems are limited to approx. 1200 metric tons only, with systems and equipment currently under design and development for up to 1500 metric tons.

Consequently, the next generation of DW drilling rigs may only provide incrementally larger hoisting capacity compared to the current generation of rigs and will therefore restrict well designs to within the 1500 metric ton limit of the next generation of top drives.

However, this invention will allow for hoisting and lowering loads exceeding 2000 metric tons, limited only by the structural integrity and load carrying capacity of the casing and landing string tubulars, running and handling tools. A generic ultra-deep subsalt and / or HPHT well development program in ultra-deep water might utilize all aspects of the invention to their full potential through the following steps and transitions between modes of operation: 1. Dual activity operation for concurrently drilling tophole sections, while running and cementing casing down to and including the 18 "casing section. 2. Dual activity operation for concurrently running riser and BOP, while cementing the 18" casing section, incorporating full redundancy. 3. Transferring the primary well center 3a with riser and BOP suspended to the center position with subsequent landing of the BOP. 4. Drilling, tripping and running casing in cyclic operation through riser with primary well center 3a in center position 5. Running and landing extra-long heavy casing sections in synchronous dual hoisting mode

Although some embodiments have been described and shown in detail, the invention is not restricted to them, but may also be embodied in other ways within the scope of the subject matter defined in the following claims. In particular, it is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention.

The mere fact that certain measures are recited in mutually different dependent claims or described in different embodiments does not indicate that a combination of these measures cannot be used to advantage.

It should be emphasized that the term "comprises / includes" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps , components or groups thereof.

Claims (22)

1. An offshore drilling rig comprising; - a drill deck; - at least two work centers arranged in the drill deck next to each other, and where at least one of the work centers is a primary well center; - a diverter system arranged below the primary well center; - a drilling support structure extending upwardly from the drill deck and above the primary well center and the other work center; - a first and a second hoisting system supported by the drilling support structure and each being adapted for raising or lowering a first and a second load carrier, respectively, and where the offshore drilling rig comprises a positioning system adapted for selectively positioning at least the first load carrier or the primary well center in at least a first or a second horizontal position different from the first horizontal position, where the first load carrier in the first horizontal position is positioned above the primary well center, and in the second horizontal position is positioned above the other work center.

2. An offshore drilling rig comprising; - a drill deck; - at least one primary well center - a diverter system arranged below the primary well center; - a drilling support structure extending upwardly from the drill deck and above the primary well center; - two hoist systems each comprising a lifting cable hanging over at least one cable crown being supported by the drilling support structure and each being adapted for raising or lowering a lifting load carrier, - a positioning system adapted for selectively positioning each load carrier in a number of different horizontal positions comprising at least a first horizontal position above the primary well center, and a second horizontal position different from the first horizontal position, wherein the positioning system is adapted for positioning each cable crown above said first horizontal position above the primary well center, or said second horizontal position.

3. An offshore drilling rig comprising; - a drill deck; - at least one primary well center; - a diverter system arranged below the primary well center; - a drilling support structure extending upwardly from the drill deck and above the primary well center; - two hoist systems supported by the drilling support structure, each being adapted for raising or lowering a load carrier, and at least one of the load carriers being a top drive; - a positioning system adapted for selectively positioning the top drive in at least a first or a second horizontal position different from the first position, where the top drive in the first position is positioned above the primary well center; - a connecting yoke having two opposite ends, each being adapted for being directly or indirectly connected to one of the load carriers, and where the connecting yoke has an intermediate load carrier arranged between said two opposite ends and being adapted for carrying a load.

4. An offshore drilling rig according to claim 1 or 2, further comprising a connecting yoke having two opposite ends each being adapted for directly or indirectly connecting it to one of the load carriers, so that the connecting yoke can be carried by two load carriers, and where the connecting yoke has an intermediate load carrier arranged between said two opposite ends and being adapted for carrying a load.

5. An offshore drilling rig according to claim 3 or 4, wherein the positioning system is adapted for shifting both said first and second load carriers, being at said first horizontal position or second horizontal positions, to a position right next to the first horizontal position, so that the two load carriers are positioned on opposite sides of the first horizontal position to allow both load carriers to operate simultaneously above the first horizontal position.

6. An offshore drilling rig according to claim 1 or 3, wherein each of the load carriers are connected to a lifting cable hanging from a cable crown supported in by the drilling support structure, and where the positioning system is adapted for shifting at least one of or each of the cable crowns to and from the first and the second horizontal position relative to that cable crown where the load carrier is positioned above one of the work centers.

7. An offshore drilling rig according to claim 6, wherein the hoisting systems comprises at least one substantially vertically extending linear actuator, such as hydraulic cylinder, having a stationary end being fixed with respect to the drill deck, and a travelling end comprising at least one cable sheave.

8. An offshore drilling rig according to one or more of the preceding claims, wherein the positioning system comprises a retractable dolly for each load carrier, the retractable dolly being adapted to connect the load carrier to a vertically extending track mounted on the drilling support structure, and to position the load carrier in the first and the second position above the work centers and being adapted for posi tioning the load carrier at a distance from the track, so that it is vertically aligned above one of the work centers.

9. An offshore drilling rig according to claim 8, wherein the positioning system is adapted for positioning each cable crown carrying a load carrier, and where the retractable dolly connecting the same load carrier to said vertically extending track are adapted to keep the lifting cable between the cable crown and the load carrier substantially vertical.

10. An offshore drilling rig according to one or more of the preceding claims, wherein each work center is mounted in a substantially horizontal track in the drill deck, and where the drill deck comprises a work center positioning system adapted for selectively moving and positioning each of the work centers in the horizontal track to a first or a second or a third position in the drill deck.

11. An offshore drilling rig according to claim 10, wherein the horizontal track is linear at least along a part of it, and where the diverter system is connected to the primary well center and comprises at least one diverter over board tube having a first end being connected to the primary well center and the other end being supported and fixed with respect to the drill deck and having at least one telescopic section between the first and the second end, the telescopic section extending parallel to linear part of the horizontal track in the drill deck.

12. An offshore drilling rig according to claim 10 or 11, and comprising at least one riser tensioning system arranged below the drill deck, and where the riser tensioners are mounted on a linear riser tensioner track being arranged below, and in parallel to the horizontal track in the drill deck, so that the riser tensioner selectively can be positioned below a selected work center.

13. An offshore drilling rig according to one or more of the preceding claims, wherein each load carrier is a top drive.

14. An offshore drilling rig according to claim 1 or 3 and/or any of claims 4 to 13, wherein the two work centers are both primary well centers each comprising a diverter system arranged below the primary well center.

15. An offshore drilling rig according to any one of claims 10 to 14, wherein the horizontal track is linear at least along a part of it, and where the positioning system is adapted for shifting each of the cable crowns along a line being parallel to the linear part of the horizontal track in the drill deck.

16. An offshore drilling rig according to one or more of claims 1 and 4 to 15, wherein one of said work centers is a mousehole, or a standbuilding foxhole.

17. A method of performing drilling operations by using an offshore drilling rig comprising: - a drill deck; - at least one work center arranged in the drill deck, the work center being a primary well center; - a diverter system arranged below the primary well center; - a drilling support structure extending upwardly from the drill deck and above the primary well center and the other work center; - a first and a second hoisting system supported by the drilling support structure and each being adapted for raising or lowering a lifting a first and second load carrier, respectively, and where one or more of the load carriers and/or the primary well center is moved during or between the drilling operations from one position where the primary well center is positioned below a first one of the load carriers to another position where the primary well center is positioned below a second one of the load carriers or where both load carriers are positioned above the primary well center.

18. A method according to claim 17, wherein the primary well center is moved from said one position to said second position.

19. A method according to claim 18, wherein a tubular or a string of tubulars is placed in and at least partly supported by or hanging down from the primary well center during movement of the primary well center.

20. A method according to claim 19, wherein the string of tubulars are connected to, or extending into the well at the sea floor before the primary well center is moved from said one position to said second position.

21. A method according to claim 17, wherein the first and the second load carrier are alternately moved from said one position to said second position.

22. A method according to one or more of claims 17, 18, 19 or 20, wherein the two load carriers are connected by a connecting yoke, and where the two load carriers are raised or lowered synchronously when carrying a load via the connecting yoke.