Drilling rig

Abstract

Embodiments of an offshore drilling rig includinga drill floor deck having a hole defining a first well center;a first mast upwardly extending relative to the drill floor deck;a first hoisting system supported by the first mast and configured for hoisting and lowering tubular equipment through the first well center; wherein the load bearing structure of the first hoisting system is displaced from and located on a first side of the first well center;first pipe handling equipment for moving tubular equipment to the first hoisting system so as to allow the first hoisting system to hoist or lower the tubular equipment through the first well center; wherein the first pipe handling equipment is operable to move tubular equipment at least partly underneath the load bearing structure and/or through a gap formed in said load bearing structure.

Claims

1. An offshore drilling rig comprising: a drill floor deck having a hole defining a first well centre; a first hoisting system configured for hoisting and lowering tubular equipment having a weight through the first well centre via a top drive arranged to be raised over said drill floor deck up to a maximum elevation above the drill floor deck, said hoisting system comprising a load bearing structure extending upwardly from the level of the drill floor deck to a height of at least said maximum elevation and from which the top drive is suspended, said load bearing structure supporting a vertical load of said top drive and tubular equipment as it is being hoisted and lowered through the first well centre; a first mast extending upwardly from the drill floor deck, said first mast is at least one of (i) comprising a mast portion supporting at least part of said vertical load so that said mast portion forms at least part of said load bearing structure, and (ii) supporting said load bearing structure in a horizontal direction; wherein the load bearing structure of the first hoisting system is displaced from and located on a first side of the first well centre; first pipe handling equipment for moving the tubular equipment to the first hoisting system so as to allow the first hoisting system to hoist or lower the tubular equipment through the first well centre; wherein the first pipe handling equipment is operable to present said tubular equipment to the top drive in at least one of: (i) a path from the first side towards the well center and entirely underneath the load bearing structure and under the level of the drill floor deck, and (ii) a path from the first side towards the well center where at least part of the tubular equipment passes through a gap formed in said load bearing structure.

2. An offshore drilling rig according to claim 1, further comprising a storage structure comprising a setback structure wherein said path is a path from said setback structure to a presentation to said top drive.

3. An offshore drilling rig according to claim 1, comprising a driller's cabin positioned on the first side of the first well centre.

4. An offshore drilling rig according to claim 1, wherein the drill floor deck comprises at least a first open drill floor deck area located adjacent the first mast, other than any drill floor deck area on or over which the drilling rig is configured for movement of tubular equipment or subsea equipment to the first well centre during normal drilling operation; and an access path connecting the open drill floor deck area with the first well centre.

5. An offshore drilling rig according to claim 4, wherein the drilling rig is configured to perform movement of tubular equipment or subsea equipment to the first well centre along one or more pipe feeding paths during normal use which one or more pipe feeding path only crosses drill floor deck areas outside the first open drill floor deck area.

6. An offshore drilling rig according to claim 4, wherein the access path is a straight path and extends entirely outside a footprint of the first mast.

7. An offshore drilling rig according to claim 4, wherein the first open drill floor deck area is located adjacent the first well centre in a longitudinal direction defined within a plane of the drill floor deck by the first well centre and the first hoisting system.

8. An offshore drilling rig according claim 4, wherein the first open drill floor deck area is located adjacent the first well centre in a transverse direction normal to a longitudinal direction defined within a plane of the drill floor deck by the first well centre and the first hoisting system.

9. An offshore drilling rig according to claim 1, wherein the first hoisting system comprises a draw-works operable to roll up and feed a length of hoisting line.

10. An offshore drilling rig according to claim 1, wherein the first pipe handling equipment defines a first pipe feeding path along which the tubular equipment is moved towards the first well centre, wherein the first pipe feeding path extends substantially along a longitudinal direction defined within a plane of the drill floor deck by the first well centre and the first hoisting system.

11. An offshore drilling rig according to claim 1, wherein the drilling rig further comprises: a second work centre displaced from the first well centre; the positions of the first well centre and the second work centre together defining a transverse direction in the plane of the drill floor deck; a second hoisting system configured for hoisting and lowering tubular equipment through the second work centre; wherein the first and second hoisting systems are arranged side by side in the transverse direction; pipe handling equipment for feeding tubular equipment towards the first well centre; and pipe handling equipment for feeding tubular equipment towards the second work centre; and wherein the pipe handling equipment for feeding tubular equipment towards the first well centre and the pipe handling equipment for feeding tubular equipment towards the second work centre define respective pipe feeding paths each extending substantially along the longitudinal direction normal to the transverse direction.

12. An offshore drilling rig according to claim 11, wherein the second work centre is a well centre.

13. An offshore drilling rig according to claim 1 wherein at least a part of the drill floor deck is formed by a roof of an enclosure for accommodating mud mixing equipment and/or other operational equipment of the drilling rig.

14. An offshore drilling rig according to claim 1, comprising a storage area for storing the tubular equipment located below the drill floor deck level, and pipe handling equipment for feeding such tubular equipment from said storage area through an opening in the drill floor deck towards the first well centre.

15. An offshore drilling rig according to claim 1, wherein the first pipe handling equipment is operable to move the tubular equipment between the spaced apart support members from a storage structure for storing the tubular equipment, the storage structure being located at least partly behind the load bearing structure when seen from the first well centre.

16. An offshore drilling rig according to claim 1, where said load bearing structure comprises one or more sheaves from which the top drive is suspended via one or more hoisting lines.

17. An offshore drilling rig according to claim 16, wherein said support members of the load bearing structure comprises at least one substantially vertically extending linear actuator having a stationary end being fixed with respect to the drill floor deck, and a travelling end connected to said at least one of one or more sheaves.

18. An offshore drilling rig according to claim 17, comprising a plurality of cylinders extending upwardly relative to the drill floor deck, wherein the plurality of cylinders comprises at least two groups of cylinders that are spaced apart from each other so as to form a gap between the two groups of cylinders through which gap the tubular equipment is movable towards the first well centre from the first side.

19. An offshore drilling rig according to claim 18, wherein the first hoisting system is a hydraulic hoisting system where said at least one substantially vertically extending linear actuator is a hydraulic actuator.

20. An offshore drilling rig according to claim 16, wherein the first hoisting system is a draw works system wherein said one or more sheaves are carried by the first mast so loads to be hoisted are transferred to the drilling vessel via the first mast; and the load bearing structure of the first hoisting system comprises the sheaves and those mast portions that carry the sheaves and any load suspended from the sheaves.

21. An offshore drilling rig according to claim 16, wherein the load bearing structure includes at least two spaced apart support members that bear the weight of said sheaves and of the tubular equipment as it is being hoisted and lowered through the first well centre and wherein the first pipe handling equipment is operable to present said tubular equipment to the top drive in the path from the first side towards the well center where at least part of the tubular equipment passes through a gap between the spaced apart support members.

22. An offshore drilling rig according to claim 16, wherein the load bearing structure includes at least two spaced apart support members, that bear the weight of said sheaves and of the tubular equipment as it is being hoisted and lowered through the first well centre, extending from a foundation above the level of the drill floor deck and wherein the first pipe handling equipment is operable to present said tubular equipment to the top drive in the path from the first side towards the well center where at least part of the tubular equipment passes through a gap in the foundation.

23. An offshore drilling rig according to claim 1, wherein said tubular equipment is a stand of drill pipe.

24. An offshore drilling rig according to claim 1, wherein said tubular equipment is marine riser pipe.

25. An offshore drilling rig comprising: a drill floor deck having a hole defining a first well centre; a first mast extending upwardly from the drill floor deck; a first hoisting system supported by the first mast and configured for hoisting and lowering tubular equipment having a weight through the first well centre; wherein a load bearing structure of the first hoisting system is displaced from and located on a first side of the first well centre; first pipe handling equipment for moving tubular equipment to the first hoisting system so as to allow the first hoisting system to hoist or lower the tubular equipment through the first well centre; and a storage structure for storing the tubular equipment chosen from drill pipes, casings, stands of drill pipes and stands of casings, the storage structure being located on the first side of the well centre; and the storage structure being at least partly underneath the drill floor deck or entirely behind the load bearing structure when seen from the first well centre.

26. An offshore drilling rig according to claim 25, wherein the first hoisting system is a hydraulic hoisting system comprising upwardly extending cylinders for carrying the load to be hoisted or lowered via sheaves mounted on top of the cylinders so that the load bearing structure of the first hoisting system comprises the cylinders and the sheaves, wherein the cylinders comprise at least two groups of cylinders that are spaced apart from each other so as to form a gap between the two groups of cylinders through which gap the tubular equipment is movable towards the first well centre from the first side.

27. An offshore drilling rig according to claim 25, wherein the first hoisting system is a draw works system comprising one or more sheaves carried by the mast so loads to be hoisted are transferred to the drilling rig via the mast; and the load bearing structure of the first hoisting system comprises the sheaves and portions of the first mast that carry the sheaves and any load suspended from the sheaves and wherein the first pipe handling equipment is operable to move the tubular equipment between the spaced apart support members.

28. An offshore drilling rig according to claim 25, wherein the first pipe handling equipment is operable to move the tubular equipment between the spaced apart support members from a storage structure for storing the tubular equipment, the storage structure being located at least partly underneath the drill floor deck.

29. An offshore drilling rig according to claim 25, wherein the first mast includes the at least two spaced apart support members.

30. An offshore drilling rig according to claim 25, wherein the load bearing structure includes the at least two spaced apart support members.

31. An offshore drilling rig according to claim 25, wherein the first hoisting system is configured for hoisting and lowering the tubular equipment via a top drive arranged to be raised over said drill floor deck up to a maximum elevation above the drill floor deck, said hoisting system comprising a load bearing structure extending upwardly from the level of the drill floor deck to a height of at least said maximum elevation and from which the top drive is suspended, said load bearing structure supporting a vertical load of said top drive and tubular equipment as it is being hoisted and lowered through the first well centre; and said first mast is: (iii) comprising a mast portion supporting at least part of said vertical load so that said mast portion forms at least part of said load bearing structure, or (iv) supporting said load bearing structure in a horizontal direction.

32. An offshore drilling rig comprising: a drill floor deck having a hole defining a first well centre; a first mast extending upwardly from the drill floor deck; a first hoisting system supported by the first mast and configured for hoisting and lowering tubular equipment having a weight through the first well centre; wherein the first mast and a load bearing structure of the first hoisting system are displaced from and located on a first side of the first well centre; wherein one of the first mast and the load bearing structure includes at least two spaced apart support members that bear the weight of the tubular equipment as it is being hoisted and lowered through the first well centre; first pipe handling equipment for moving the tubular equipment to the first hoisting system so as to allow the first hoisting system to hoist or lower the tubular equipment through the first well centre; and a storage structure for storing the tubular equipment, the storage structure being located at least partly underneath the drill floor deck and behind the load bearing structure when seen from the first well centre; wherein the first pipe handling equipment is operable to move the tubular equipment at least partly underneath the load bearing structure or between the at least two spaced apart support members.

33. An offshore drilling rig according to claim 32, wherein the first mast includes the at least two spaced apart support members.

34. An offshore drilling rig according to claim 32, wherein the load bearing structure includes the at least two spaced apart support members.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and/or additional objects, features and advantages of embodiments and aspects of the present invention, will be further elucidated by the following illustrative and non-limiting detailed description with reference to the appended drawings, wherein:

(2) FIGS. 1-8 illustrate views of an embodiment of an offshore drilling rig wherein FIG. 1 shows a 3D view of the drilling rig, FIGS. 2-6 show 3D views of parts of the drilling rig from different viewpoints, FIG. 7 shows a cross-sectional view of the drilling rig in a longitudinal plane through the centre of the drilling rig, looking in the transverse direction, and FIG. 8 shows a top view of the drilling rig.

(3) FIG. 9 schematically illustrates further embodiments of the deck layout of the drill floor deck of a drilling rig.

(4) FIG. 10 schematically illustrates the open drill floor deck areas in an embodiment of a drilling rig.

(5) FIG. 11 schematically illustrates the footprint of the mast in an embodiment of a drilling rig.

(6) FIG. 12 schematically illustrates drill floor deck layouts of another embodiment of a drilling rig.

(7) FIG. 13 schematically illustrates drill floor deck layouts of further embodiments of a drilling rig.

(8) FIG. 14 illustrates another embodiment of an offshore drilling rig.

(9) FIGS. 15-21 illustrate another embodiment of an offshore drilling rig, wherein FIGS. 15-16 show 3D views of parts of the drilling rig from different viewpoints, FIGS. 17-18 show horizontal cross-sectional views of the drilling rig, FIGS. 19-20 show lateral cross sections of the drilling rig, and FIG. 21 shows another 3D view of the drill floor seen from the starboard side of the drillship.

(10) FIGS. 22A-22D show horizontal cross-sectional views of the drilling rigs illustrating different layouts in which tubulars can be fed to a well centre.

(11) FIGS. 23 A)-D) illustrate different configurations of gaps to accommodate tubulars being delivered to a well centre.

(12) FIG. 24 shows an embodiment where a mast structure is shown having a gap to allow tubulars to be fed to a well centre.

DETAILED DESCRIPTION

(13) In the following description, reference is made to the accompanying figures, which show by way of illustration how the invention may be practiced.

(14) An embodiment of an off-shore drilling rig will be described with reference to FIGS. 1-8.

(15) The drilling rig is a semisubmersible drilling rig, comprising pontoons 101 from which support columns 102 extend upwardly, and a topside platform 103 supported by the columns 102. During operation, the drilling rig floats at the ocean surface with the pontoons 101 typically under the water and the support columns extending out of the water such that the topside platform is elevated above the water. To this end, the pontoons may be filled with ballast water so as to cause the rig to be submersed to the desired level.

(16) The topside platform comprises a drill floor deck 107 arranged elevated from a main deck 120 and partly formed by the roof of an enclosure 121 accommodating mud mixing equipment and/or other equipment. The drill floor deck 107 comprises two holes defining well centres 123a,b located next to a dual activity mast 104. The dual activity mast 104 extends upwardly from the drill floor deck 107 and comprises two mast portions 104a,b arranged side by side in the transverse direction. The drilling rig comprises respective hydraulic hoisting systems 105a,b, each for lowering a drill string through a respective one of the well centres 123a,b towards the seabed. Each hydraulic hoisting system comprises cylinders 106a,b, respectively, that extend upwardly from the drill floor deck and support the load to be lowered or hoisted. Each mast portion is associated with one of the hoisting systems and stabilises the hoisting systems against lateral forces and/or against bending of support members carrying the weight of the sheaves and the load suspended from the hoisting system. Each well centre is located next to one of the mast portions and the corresponding hoisting system; both well centres are located on the same side relative to the mast. The position of each of the well centres relative to the corresponding hoisting system defines a longitudinal direction, in this example the longitudinal direction of the drilling rig, i.e. between bow and aft of the drilling rig. The well centres are arranged along a transverse direction, normal to the longitudinal direction, in this example the transverse direction (from port to starboard) of the drilling rig. The longitudinal and transverse directions are indicated by arrows 140 and 141, respectively, in FIG. 8.

(17) The cylinders of each hoisting system are arranged in two groups that are positioned displaced from each other in the transverse direction so as to form a gap 126a,b, respectively, between the two groups. Each gap 126a,b is thus aligned with a respective one of the well centres along the longitudinal direction. Each gap extends upwardly along the entire length of the cylinders, thus allowing tubulars to be moved through the gap towards the respective well centre and even raised into an upright position while being located at least partly in the gap between the cylinders. The well centre is longitudinally displaced from the gap. Alternatively or additionally the cylinders or other support members may be positioned on a foundation elevated above the drill floor and the gap may at least partly be formed in the foundation. A gap may also be obtained in an alternative way or in combination with a gap between cylinders, as will be illustrated in combination with FIGS. 22-24 below. The rods of the cylinders support sheaves 133a,b, respectively, of a travelling yoke over which the hoisting wires are suspended. One end of the hoisting wires is anchored to the drilling rig, while the other end is connected to top drive 137a,b or hook of the corresponding hoisting system. The sheaves 133a,b are laterally supported and guided by the respective mast portions. The axis of the sheaves extends in the transverse direction between two groups of cylinders, i.e. between support members for bearing the weight of the sheave(s).

(18) The side-by-side configuration of the dual activity mast and well centres allows efficient dual operations, easy access to both well centres, and convenient visual control of both well centres from a single driller's cabin 134 which may e.g. be positioned transversely between the well centres, e.g. within the footprint of the mast.

(19) The drilling rig comprises a setback structure 112 or similar pipe storage structure for storing stands of tubulars located on the other side (seen in longitudinal direction) of the well centres, opposite the mast. The setback structure comprises a support framework supporting fingerboards having horizontally extending fingers between which tubulars may be stored. The setback structure is arranged transversely between the transverse positions of the well centres so as to allow stands to be moved to/from both well centres from/to the setback. To this end, two column rackers 113a,b or similar vertical pipe handling equipment are arranged to move stands into and out of the setback structure 112. The column rackers are operable to move along the transverse direction along a support beam 130 spanning the transverse distance between the well centres. The support beam may be a part of the setback support framework. The setback structure 112 may extend downwards to a deck below the drill floor deck so as to allow stands assembled from multiple pipes to be stored and moved to a respective one of the well centres. The setback structure may comprise a foxhole and separate or integrated stand-building equipment, thus allowing stands of pipes to be assembled and stored without interfering with operations at the well centres. Alternatively or additionally, one of the hoisting systems and well centres, e.g. well centre 123a,b may be utilised for building stands.

(20) A pipe storage area 109 for storing pipes in horizontal orientation is located behind the setback structure, seen from the well centres. On either transverse side of the pipe storage area respective catwalk machines 108a,b, or similar horizontal pipe handling equipment, are located extending in longitudinal direction, each aligned with one of the well centres, i.e. such that the horizontal pipe handling equipment defines a longitudinal axis that intersects with one of the well centres. Each catwalk machine is operable to move pipes from the storage area 109 to the corresponding well centre and hoisting system. To this end, the pipes may be placed on the catwalk machine by a crane, e.g. one of the knuckleboom cranes 138, and the catwalk machine may be longitudinally moved to the corresponding well centre, e.g. on skid beams or tracks 139a,b defining a straight pipe feeding path to the corresponding well centre. Hence, the catwalk machines move tubular equipment along the corresponding pipe feeding paths 139a,b towards the corresponding well centre. The catwalk machines and tracks 139a,b thus define longitudinal pipe feeding paths, each intersection with one of the well centres. The pipe feeding paths 139a,b extend towards the well centres from a side of the well centres opposite the side on which the mast is located. The column rackers 113a,b may be transversely moved to a position on the pipe feeding path, i.e. in longitudinal extension of one of the catwalk machines. In this position, the column racker may thus receive a pipe from the catwalk machine and, in cooperation with the catwalk machine, bring the pipe in a vertical position.

(21) The drilling rig comprises another storage area 115 on the other side of the mast, i.e. on the side opposite the well centres. This storage area is located at a lower deck than the drill floor deck, and it is used for storing marine riser joints (also simply referred to as risers) in a vertical orientation. The risers may then be moved, e.g. by means of a gantry crane 136 and respective chutes 132a,b or other suitable pipe feeding equipment to the respective well centres. As the risers may be moved through the gaps 126a,b between the cylinders 106a,b of the hoisting systems, the risers may be moved directly from the riser storage area 115 to the well centre in a space efficient manner.

(22) In this example, as all tubulars are moved to the well centres from opposite sides of the well centres along the longitudinal direction, and since the setback structure 112 and the storage area 115 are located longitudinally displaced from the well centres, the drill floor deck 107 comprises large open drill floor deck areas 110a,b on both lateral sides of the mast and well centres. These open drill floor deck areas are not occupied by pipe handling equipment, and all pipe movements between the storage/setback areas 112, 115 and the well centres 123a,b are performed along the longitudinal direction. The pipe feeding paths along which the pipes and other tubulars are moved to/from the well centres do not cross the lateral open drill floor deck areas 110a,b. Consequently, these areas may be used as working area, e.g. for rigging up suspendable auxiliary equipment such as coiled tubing, and/or for positioning on-deck auxiliary equipment 111. In the example of FIGS. 1-8, the open drill floor deck area 110a is used for placing and/or moving on-deck auxiliary equipment and/or for handling and/or operating such auxiliary equipment while at the same time allowing efficient and safe access to the well centre. Open drill floor deck area 110b is kept free of any pipe handling equipment and any other permanently installed equipment; this area may thus be used as a working area and/or intermediate storage area. Both open drill floor deck areas 110a,b are connected with the well centres by direct, straight access paths 114a,b, respectively, thus allowing equipment to be conveniently moved between the open drill floor deck areas 110a,b and the well centres, e.g. on skid beams 116. Any work within open drill floor deck areas 110a,b does not interfere with pipe movements to/from the well centres or with other operations at the well centres.

(23) The well centres are placed outside the footprint of the mast and longitudinally displaced relative to the cylinders 106a,b, and the access paths are not blocked by any other fixedly installed structures on the drill floor deck or structures elevated at a low height above the drill floor deck. Thus, convenient access between the open drill floor deck areas 110a,b and the well centres is provided.

(24) The open drill floor deck areas even extend laterally along the catwalk machines, thus allowing equipment to be moved along the catwalk machines and/or stored on open drill floor deck areas 117a,b extending along each of the catwalk machines. In particular, as the catwalk machines are located on the drill floor deck and as the drill floor deck comprises a large floor area extending along the catwalk machines, crew members may work with or at the catwalk machines without any (or at least with reduced) danger of falling. The parts 117a,b of the open drill floor deck area extending along the catwalk machines are large enough to allow skid beams to be installed, thus allowing equipment to be moved away from the lateral open drill floor deck areas 110a,b.

(25) The lateral open drill floor deck areas 110a,b are even connected with each other by a connecting drill floor deck area 118, in this example a straight path of open drill floor deck area extending between the setback structure 112 and the pipe storage area 109. The connecting drill floor deck area 118 forms a path wide enough for skid beams to be installed or a fork lift to move along, thus allowing equipment to be conveniently moved from one of the lateral open drill floor deck areas 110a,b to the other, without having to traverse the well centres.

(26) As is most easily seen in FIGS. 2 and 4, the drilling rig comprises guard structures 119 that extend in the longitudinal direction from respective lateral sides of the mast 104 to the support framework of the setback structure 112. It will be appreciated, however, that the guard structures 119 may be supported by a separate support structure. The guard structures span across the access paths 114a,b between the well centres and the respective open drill floor deck areas 110a,b at a height high enough to allow equipment to be moved under the guard structures. For example, the access paths 114a,b may have a free height of at least 10 m, such as at least 20 m, thus allowing even tall items to be moved. The guard structures are further located at a height above the drill floor deck that is suitable for preventing tubulars run through one of the well centres from falling on the open drill floor deck areas 110a,b. Consequently, equipment stored or even crew members working in one of the open drill floor deck areas 110a,b are protected against falling tubular equipment. In some embodiments, the height at which the guard structures are arranged may be adjustable. For example, the guard structures may be mounted to rails or tracks extending upwardly along the support structures to which the guard structures are mounted. The guard structures may then be lifted by wires or cables, by a hydraulic mechanism, or by another suitable hoisting mechanism. Hence, the guard structures may be positioned at different heights in accordance with the length of the tubular equipment run. Alternatively, the guard structure may be formed as a plurality of separate structures that are arranged at different heights and/or whose height can be individually adjusted. In yet another embodiment the guard structures may be operable to be opened so as to allow unobstructed access to the well centre, even for equipment having a large height. For example, defective tubulars may need to be placed within one of the open drill floor deck areas 110a,b, so as to allow maintenance or repair of the defective equipment while the drilling operation continues. The guard structures may be opened in a number of different ways. For example, they may be hinged at one side or at both sides, or they may be slidable to a large height. The inventors have realised that such a guard structure may also be implemented in combination with other types of mast structures, such as other guard structures providing an open drill floor deck.

(27) As is most easily seen in FIGS. 2 and 6, the drilling rig further comprises a gantry beam or framework 125 or a similar mounting structure for suspending suspendable auxiliary equipment from an elevated position above the drill floor deck, allowing the auxiliary equipment to be lowered or hoisted through the first well centre. The gantry beam 125 is connected to respective support structures on both longitudinal sides of the well centres and laterally displaced from the well centre. In this particular embodiment, the gantry beam is secured to the mast 104 and to the setback structure 112 and spans the access path 114a between the open drill floor deck area 110a and the well centres. The gantry beam 125 is operable to be hoisted and lowered at least between an operational position elevated above the drill floor deck, and a lower position immediately above the drill floor deck allowing the rigging up of auxiliary equipment to the mounting structure. For example, the lower position may be no more than 2 m above the drill floor deck or another height sufficiently low for personnel to attach equipment to the gantry beam directly from the drill floor deck. The elevated position may be at least, 3 m, 5 m, or 10 m above the drill floor deck, such as at least 15 m above the drill floor deck, e.g. at least 20 m above the drill floor deck. To this end, the gantry beam may be mounted on rails or tracks extending upwardly along the support structures to which the gantry beam is connected. The gantry beam may then be lifted by wires or cables, by a hydraulic mechanism, or by another suitable hoisting mechanism. For example, the gantry beam 125 and the guard structure 119 may be mounted to the same hoisting mechanism. In some embodiments, the gantry beam may even be a part of the guard structure. It will be appreciated that a gantry beam or similar mounting structure may be arranged proximal to, and operable with, each of the well centres or proximal to, and operable with, only one of the well centres as in the example of FIGS. 1-8.

(28) When the gantry beam 125 is lowered to its lower position, the rig crew may conveniently rig up the gantry beam with suspendable equipment that is to be lowered through one of the well centres. Examples of such equipment include logging-while-drilling equipment, measuring-while-drilling equipment, coiled tubing equipment. To this end, the equipment to be lowered through the well centre may be connected to a wire, cable or coiled tubing 135 which in turn may be led via hooks, pulleys, guide arches and/or similar guide members 129 that are connected to the gantry beam 125 to reels, drums, or similar on-deck auxiliary equipment 111 positioned on one of the open drill floor deck areas 110a,b. In some embodiments, the rigging up may thus be performed without any need for members of the drill crew to climb to unsafe heights. Moreover, the rigging up is performed away from the well centre, thus not interfering with any activity performed at the same time at the well centre. Once rigged up, the gantry beam 125 is hoisted to the desired height thus allowing lowering the suspendable auxiliary equipment through the well centre 123a at a suitable angle. The reels, drums or other on-deck auxiliary equipment 111 used for lowering the suspendable auxiliary equipment through the well centre may conveniently be positioned, e.g. skidded on skid beams 116, at a desired location within the open drill floor deck area 110a.

(29) The main deck 120 is located beneath the drill floor deck and allows heavy subsea equipment 124, e.g. BOPs and Christmas trees to be moved to the moon pool 122 under the well centres so as to allow such equipment to be lowered toward the seabed. Consequently, the drill floor deck and, in particular, the part of that drill floor deck that is located in close proximity to the well centre may be stationary and does not need to be hoisted or lowered for the subsea equipment to be lowered to the seabed.

(30) One or more iron roughnecks 127 or similar pipe handling equipment may be arranged on the drill floor deck in immediate proximity of the well centres. Such equipment may be arranged such that it may serve only one of the well centres or both well centres.

(31) As may be most easily seen in FIGS. 4-6, risers may be moved directly from the riser storage area 115 through one of the gaps 126a,b to one of the well centres 123a,b. To this end, a riser may be moved by a gantry crane 136 from its position in the storage area 125 onto a chute 132a,b, respectively, or other suitable pipe feeding equipment, defining a slanted surface extending upwards and towards one of the gaps 126a,b. The riser may then be picked up by the top drive 137a,b of the corresponding hoisting system 105a,b and pulled into vertical position above the corresponding well centre 123a,b. FIG. 4 shows a riser 128 positioned on the chute 132b and extending through the gap 126b towards the well centre 123b. FIG. 5 shows the riser connected to the top drive 137b of the hoisting system 105b and in the process of being hoisted upwards and through the gap 126b towards the well centre 123b. FIG. 6 shows the riser after being hoisted into a vertical position above the well centre 123b and ready to be lowered through the well centre 123b.

(32) As is most easily seen in FIG. 8, the drilling rig comprises access to the well centre from all four sides, i.e. from both longitudinal directions and from both transverse directions. Moreover, the symmetrical arrangement of the mast, the well centres and the pipe storage and handling equipment allow tubulars from all storage areas to be efficiently moved to both well centres. In some embodiments, both mast portions and hoisting systems may be designed in a similar or even identical fashion and provide similar or even equal hoisting capacity. Consequently, full redundancy of the dual drilling system may be achieved. It will be understood, however, that the dual system may alternatively be designed with a primary and a secondary well centre/hoisting system e.g. with different hoisting capacities. In such embodiments, a certain degree of redundancy may still be achieved.

(33) Even though the embodiment of FIGS. 1-8 has been described in the context of a semi-submersible, it will be appreciated that the described features may also be implemented in the context of a drillship or other type of drilling rig. In particular, the guard structure, the mounting structure, the open drill floor areas, unobstructed access paths to the well centres, and/or the gap between the hoisting cylinders may be implemented on another type of drilling rig.

(34) FIG. 9 shows top views of another example of a drill floor deck 107. FIG. 9a shows the drill floor deck and adjacent storage area 115 for risers, while FIG. 9b only shows the drill floor deck. Furthermore, while FIG. 9a shows the skid beams 116 arranged throughout the drill floor deck, the skid beams are not shown in FIG. 9b for the purpose of a simpler illustration. This embodiment of a drill floor deck is similar to the drill floor deck that was described with reference to FIGS. 1-8 above. In particular, the embodiment of FIG. 9 comprises a large drill floor deck 107, a dual activity mast 104 and corresponding well centres 123a,b arranged side by side, a horizontal pipe storage area 109, a setback structure 112 with vertical pipe handling equipment 113a,b, all as described above.

(35) As can easily been seen in FIGS. 9a-b, the vertical pipe handling equipment 113a,b is movable along the transverse direction along a support beam 130. They may be positioned in longitudinal extension of respective ones of the catwalk machines 108a,b between the catwalk machine and the corresponding well centre 123a,b, i.e. on the pipe feeding path defined by the corresponding catwalk machine between the catwalk machine and the corresponding well centre. The catwalk machines 108a,b are movable on respective rails or skid beams 139a,b along the horizontal direction to a respective well centre. Hence, the skid beams define longitudinal pipe feeding paths to the respective well centres.

(36) Also, an iron roughneck 127 is shown positioned between the well centres 123a,b and arranged on skid beams, thus allowing the iron roughneck to be moved out of the way, and alternatingly serve both well centres.

(37) Also FIG. 9a clearly shows the cylinders 106a,b forming a gap 126a,b, respectively, so as to allow access to the well centres 123a,b directly from the riser storage area 115 by means of a gantry crane 136 and respective chutes 132a,b leading to the respective well centre.

(38) FIGS. 9a,b also show the driller's cabin 134 positioned inside the footprint of the mast 104, transversely between the well centres. Hence, the driller's cabin does not interfere with the access paths 114a,b from the open drill floor deck areas 110a,b, while allowing convenient visual control with both well centres. The open drill floor deck areas 110a,b comprise parts 117a,b that extend along the catwalk machines, and a connecting drill floor deck area 118 connecting the lateral open drill floor deck areas 110a,b with each other, also all as described above.

(39) FIG. 10 shows the drill floor deck 107 of FIGS. 9a,b clearly illustrating the open drill floor deck areas 110a,b as hatched areas. The drill floor deck area extending outside the footprint of the first mast is sized and shaped so as to allow installation of skid beams for skidding equipment and/or for a forklift or other vehicles to operate on the drill floor deck area outside the mast footprint. For example, the drill floor deck area outside the mast footprint may be at least 200 m.sup.2, such as at least 500 m.sup.2, such as at least 1000 m.sup.2, such as at least 2000 m.sup.2, e.g. at least 5000 m.sup.2. The open drill floor deck areas are not otherwise obstructed by fixed installations such as the first mast, further masts, pipe handling equipment, and/or the like. The open drill floor deck area has a free height of at least 10 m, such as at least 20 m, e.g. at least 30 m. FIG. 10 also illustrates the lateral access from the open drill floor deck areas to the well centres by arrows 1014a,b. The access paths 1014a,b are straight and they extend entirely outside the footprint of the mast. The additional path connecting the open drill floor deck areas with each other is illustrated by arrow 1018. All access and connecting paths 1014a,b and 1018 are wide enough to be equipped with skid beams and/or allowing fork lifts or similar vehicles to operate across the entire drill floor deck. For example, the access and connecting paths may each be at least 2 m wide, such as at least 3 m e.g. at least 5 m wide. FIG. 10 further illustrates the large open drill floor deck sector 1010b around the well centre 123b. The sector 1010b may have a radius of at least 5 m such as 20 m, such as 30 m, the sector having a central angle of at least 60, such as at least 90, e.g. at least 120.

(40) Generally, as illustrated by sector 1010b, each well centre defines polar coordinates (,) on the drill floor deck where the mast position resides at =0 and the mast footprint spans from .sub.mast,min (negative) to .sub.mast,max intersecting at .sub.mast,min and .sub.mast,max at these angles, respectively. In some embodiments, the open drill floor deck spans more than 1 m, such as more than 2 m, such as more than 5 m, such as more than 10 m, e.g. more than 20 m within an angle interval spanning from .sub.mast,max or below .sub.mast,min. In some embodiments, is larger than 10, such as larger than 30, such as larger than 60, such as larger than 90, e.g. larger than 30.

(41) FIG. 11 shows the drill floor deck 107 of FIGS. 9a,b clearly illustrating the footprint of the mast 104 by a dotted line 1104. The well centres 123a,b are each located outside the footprint, and they are displaced from the footprint and from the cylinders 106a,b along the longitudinal direction 1140. The longitudinal direction 1140 may be defined by the position of the well centres 123a,b and the positions 1175a,b of the corresponding hoisting systems. The position of the hoisting system may be defined by the centre of mass of the corresponding one of the sheaves 133a,b shown e.g. in FIG. 1. FIG. 11 also illustrates the pipe feeding paths along which tubulars are advanced to the respective well centres, namely the pipe feeding paths 1239a,b defined by the skid beams of the catwalk machines 1108a,b, and the pipe feeding paths 1132a,b defined by respective chutes for advancing tubulars from a rear side of the hoisting systems. In this embodiment, all pipe feeding paths extend along the longitudinal direction 1140, and they do not cross or otherwise interfere with the open drill floor deck areas 110a,b.

(42) FIG. 12 illustrates a drill floor deck layout with a single well centre 1223, but using the same principles as described in connection with the drilling rig shown in FIGS. 1-8. The drilling deck of FIG. 12 comprises a mast 1204, a well centre 1223, a pipe storage area 1209, a setback structure 1212, horizontal pipe handling equipment 1208 and vertical pipe handling equipment 1213, all as described above. Also in this embodiment, the drilling rig comprises access paths to the well centre from all four sides, i.e. from both longitudinal directions and from both transverse directions.

(43) In FIG. 12a, the vertical pipe handling equipment 1213 is positioned away from and, in particular, transversely displaced relative to the pipe feeding path defined by rails or skid beams 1239 between the horizontal pipe handling equipment 1208 and the well centre 1223. Hence, in this position the horizontal pipe handling equipment 1208 may move along skid beams 1239 all the way to the well centre 1223.

(44) FIG. 12b shows the vertical pipe handling equipment 1213 in a position on the pipe feeding path 1239 connecting the horizontal pipe handling equipment 1208 and the well centre 1223. Hence, in this configuration, the horizontal pipe handling equipment 1208 may cooperate with the vertical pipe handling equipment 1213.

(45) As in the previous embodiments, the mast comprises a hydraulic hoisting system where the cylinders 1206 are arranged so as to form a central gap 1226, through which risers from a storage area behind the mast may be moved to the well centre 1223 e.g. using a chute 1232 or other pipe handling equipment.

(46) FIG. 13 shows embodiments of a drill floor deck similar to the one of FIG. 12, comprising a mast 1204, a well centre 1223, a pipe storage area 1209, a setback structure 1212, horizontal pipe handling equipment 1208 movable on rails 1239, vertical pipe handling equipment 1213, a hoisting system comprising cylinders 1206 arranged in groups forming a gap between them, and pipe handling equipment 1232 for moving risers or other tubulars through the gap 1226, all as described above.

(47) In particular, in the example of FIG. 13a, the pipe storage area 1209, the setback structure 1212, the horizontal pipe handling equipment 1208 and the vertical pipe handling equipment 1213 are located longitudinally aligned with the mast 1204. In the example of FIG. 13b, the pipe storage area 1209, the setback structure 1212, the horizontal pipe handling equipment 1208 and the vertical pipe handling equipment 1213 are located transversely displaced from the mast. Hence, in FIG. 13a the pipe feeding path 1239 used by pipe handling equipment 1208 extends in the longitudinal direction as in the previous examples, while in the example of FIG. 13b, the pipe feeding path 1239 extends in a transverse direction. Nevertheless, in both examples, the drill floor deck comprises an open drill floor deck area 1210 shown schematically as a hatched area. In FIG. 13a, the open drill floor deck area is located adjacent the mast in the transverse direction, while the open drill floor deck area of FIG. 13b is located adjacent the first mast in the longitudinal direction.

(48) FIG. 14 illustrates another embodiment of an offshore drilling rig. The drilling rig of FIG. 14 is a drillship having a hull 1401. The drilling rig comprises a drill floor deck 1407 formed on top of a substructure 1497. The substructure comprises a platform supported by legs. The platform defines the drill floor deck and spans across a moon pool formed in the hull of the drillship. The drill floor deck 1407 comprises two holes defining well centres 1423 located next to a dual activity mast 1404. The direction intersecting with both well centres defines a transverse direction which, in this case, is parallel with a longitudinal axis of the drillship. The dual activity mast 1404 is supported by the substructure 1497 and extends upwardly from the drill floor deck 1407. The mast comprises two mast portions arranged side by side in the transverse direction such that they are both located on the same side relative to the well centres. Each mast portion accommodates a hoisting system, each for lowering a drill string through a respective one of the well centres 1423 towards the seabed. In the example of FIG. 14, the hoisting system is a draw-works system where the hoisting line is fed over stationary sheaves 1433 carried by support members. The drawworks motor/drum (not shown) may be positioned at a suitable location on the drilling rig. Alternatively, other hoisting systems such as a hydraulic hoisting system may be used, as will be illustrated below. Each well centre is located next to one of the mast portions and the corresponding hoisting system. The position of each of the well centres relative to the corresponding hoisting system defines a longitudinal direction, in this example the transverse direction of the drill ship.

(49) The side-by-side configuration of the dual activity mast and well centres allows for efficient dual operations, easy access to both well centres, and convenient visual control of both well centres from a single driller's cabin 1434 which may e.g. be positioned symmetrically relatively to the well centres but displaced from the axis connecting the well centres, e.g. within the footprint of the mast. The driller's cabin may be split up into two or more cabins.

(50) The drilling rig comprises a setback structure 1412 or similar pipe storage structure for storing stands of tubulars such that the stored tubulars are located partly or completely below the level defined by the drill floor deck, i.e. below the uppermost platform of the substructure 1497 and partly covered by the drill floor deck 1407. The setback structure comprises a support framework supporting fingerboards having horizontally extending fingers between which tubulars may be stored. The setback structure is positioned and arranged so as to allow stands to be moved to/from both well centres from/to the setback. To this end, on or more column rackers or similar vertical pipe handling equipment may be arranged to move stands into and out of the setback structure 1412. The handling of tubulars to and from the setback area 1412 will be illustrated in more detail in connection with the embodiments described below. In some embodiments, e.g. in case of stands of drill pipe or casings, the tubulars may be taller than the drill floor. Hence, when they are stored in the setback structure in an upright orientation their uppermost ends may extend above the drill floor level. When feeding them to one of the well centres they may be laid into a chute as will be described below. Alternatively, the setback structure may extend from the drill floor deck upwards. The handling of tubulars within the setback area may be performed by vertical pipe rackers or the like. The setback structure 1412 further comprises stand building equipment 1477 configured to build stands from individual pieces of pipe. An example of such stand building equipment is described in WO 02/057593. Alternatively or additionally, stands may be built on the drill floor.

(51) In some embodiments, each mast portion and hoisting system form a respective gap between the two support members that carry the sheaves 1433, through which gap tubular equipment is movable between the setback structure 1412 towards the respective well centres.

(52) Optionally, the drilling rig further comprises a pipe storage area 1409 for storing pipes in horizontal orientation located towards the bow of the drillship, i.e. transversely displaced from the well centres. One or more catwalk machines 1408 or similar horizontal pipe handling equipment are arranged to feed tubulars from the storage area 1409 or from other storage areas to the well centres. To this end, the catwalk machines are aligned with the axis defined by the two well centres. These catwalk machines 1408 and one or more stores for (e.g. 1409) or aft (not shown) may be used in combination or as an alternative to having riser 1415 stored below the drill deck. In the embodiment of FIG. 14 the catwalk machines 1408 may be used to provide additional riser joints, load the riser storage below the drill deck and/or to provide the drill floor with other tubulars. One or each of the catwalk machines may be operable to service both well centres. Moreover the drilling rig comprises one or more further catwalk machines travelling on tracks 1476 and configured to feed tubulars from the pipe storage area 1409 or from other storage areas on the opposite side of the mast (towards the aft of the ship) to the stand building equipment 1477. The catwalk machine(s) travelling on tracks 1476 is/are configured to travel along a direction parallel with the catwalk machines 1408, but on the other side of the mast. In the present embodiment, one or more catwalk machines may be operable to travel along a substantial portion of the length of the drillship. It will be appreciated that, in some embodiments, each catwalk machine may be configured to only travel to/from the stand building equipment 1477 without being configured to pass the stand building equipment. Consequently, the drilling rig may comprise two catwalk machines travelling on tracks 1476 on respective sides of the stand building equipment so as to be able to feed tubulars to the stand building equipment from both sides. The stand building equipment 1477 may thus receive pipes from the catwalk machine on tracks 1476, bring them in upright orientation, and connect them to other pipes as to form stands. The stands may then be placed in the setback structure for future use.

(53) The drilling rig comprises another storage area 1415 below the drill floor deck 1407 and configured for storing risers in a vertical orientation. The risers may then be moved, e.g. by means of a gantry crane and respective chutes or other suitable pipe feeding equipment through holes in the drill floor, as will be described in more detail in connection with the description of the further embodiments below.

(54) As the mast structure 1404 is located on one side of the well centres, and since the setback area is located on the side of the mast opposite the well centres and/or behind the driller's cabin 1434, the drill floor deck provides a large, unobstructed deck area on the side of the well centres opposite the mast. This area provides unobstructed access to both well centres and is free of pipe handling equipment. Consequently, these areas may be used as working area, e.g. for rigging up suspendable auxiliary equipment, and/or for positioning on-deck auxiliary equipment as described in connection with the example of FIGS. 1-8 above. Generally, riser joints and/or other tubulars may be tilted between an upright and a horizontal orientation by a tilting apparatus as described in co-pending Danish patent application no. PA 2013 00302, the entire contents are hereby included herein by reference.

(55) FIGS. 15-21 show another embodiment of a drilling rig, in this example of drillship having a hull 2501, similar to the drilling rig of FIG. 14 but with a different mast structure and hoisting system. In particular, FIGS. 15 and 16 show 3D views of the drill floor seen from the starboard and port sides of the drillship, respectively (a part of the hull of the ship is cut away in FIG. 16); FIGS. 17 and 18 show horizontal cross sections in a plane above the drill floor and a plane below the drill floor, respectively; FIGS. 19 and 20 show lateral cross sections of the drill ship. Finally, FIG. 21 shows another 3D view of the drill floor seen from the starboard side of the drillship.

(56) As in the example of FIG. 14, the drilling rig of the present embodiment comprises a drill floor deck 2407 formed on top of a substructure 2897. The substructure comprises a platform supported by legs. The platform defines the drill floor deck and spans across a moon pool 2722 formed in the hull of the drillship. The drill floor deck 2407 comprises two holes defining well centres 2423, one or both being equipped with a diverter housing. The mast includes two mast portions, each associated with, and adjacent to, one of the well centres. In the present example, the well centres are located outside the footprint of the mast 2404 as described in detail in connection with FIGS. 1-8 and 14. As in the previous embodiments, the direction between each well centre and the associated hoisting system defines a longitudinal direction. In this example, the direction intersecting with both well centres defines a transverse direction which, in this case, is parallel with a longitudinal axis of the drillship. The dual activity mast 2404 is supported by the substructure 2897 and extends upwardly from the drill floor deck 2407.

(57) As described in connection with the embodiment of FIGS. 1-8, each mast portion accommodates a respective hydraulic hoisting system each for lowering a drill string through a respective one of the well centres 2423 towards the seabed. Each hydraulic hoisting system comprises cylinders 2406, respectively, that extend upwardly from the drill floor deck and support the load to be lowered or hoisted. Each well centre is located next to one of the mast portions and the corresponding hoisting system; both well centres are located on the same side relative to the mast, i.e. in a side-by-side configuration.

(58) The cylinders 2406 of each hoisting system are arranged in two groups that are positioned displaced from each other in the transverse direction so as to form a gap between the two groups. Each gap is thus aligned with a respective one of the well centres along the longitudinal direction and is shaped and seized so as to allow tubulars to be moved through the gap towards the respective well centre and even raised into an upright position while being located at least partly in the gap between the cylinders. The exact shape, size and location of the gap may depend on the type of tubular to be fed through the gap, e.g. whether the gap is to be used for feeding drill pipes, casings and/or riser through the gap. The well centre is longitudinally displaced from the gap. The rods of the cylinders support respective sheaves 2533, e.g in the form of a sheave cluster, over which the hoisting wires 2484 are suspended. The cable sheaves 2533 define an axis that is parallel to the direction connecting the two groups of cylinders of one of the hoisting systems. One end of the hoisting wires 2484 is anchored to the drilling rig, while the other end is connected to top drive 2437 or hook of the corresponding hoisting system, via a travelling yoke 2187. The sheaves 2533 are laterally supported and guided by the respective mast portions. Each top drive 2437 is connected via a dolly 2569 to a vertical track arranged at the mast 2404. The fixed ends of the hoisting wires are anchored via a yoke 2482 and respective sets of deadline compensators 2483. The compensators 2483 are also arranged in two groups so as to form a gap over which the yoke 2482 extends. Hence, tubulars can pass through the gap between the compensators 2483 and below the yoke 2482.

(59) The side-by-side configuration of the dual activity mast and well centres allows efficient dual operations, easy access to both well centres, and convenient visual control of both well centres from a single driller's cabin 2434 which may e.g. be positioned transversely between the well centres, e.g. within the footprint of the mast.

(60) The drilling rig further comprises a pipe storage area 2509 for storing pipes in horizontal orientation and catwalk machines 2508 or other horizontal pipe handling equipment for transporting pipes between the storage area 2509 and the well centres 2423, also as described in connection with FIG. 14.

(61) The drilling rig comprises a setback structure 2512 or similar pipe storage structure for storing stands of tubulars below the substructure 2897 and partly covered by the drill floor deck 2407. The setback structure comprises a support framework 2590 supporting fingerboards having horizontally extending fingers between which tubulars may be stored. One or more column rackers 2491 or similar vertical pipe handling equipment may be arranged to move stands into and out of the setback structure 2512. The setback structure 2512 further comprises stand building equipment 2677 configured to build stands from individual pieces of pipe through a foxhole 2592. The setback structure 2512 is located adjacent the moon pool 2722 laterally displaced from the axis defined by the well centres.

(62) Moreover the drilling rig comprises one or more further catwalk machines (not shown) configured to feed tubulars from the pipe storage area 2509 or from other storage areas on the opposite side of the mast (towards the aft of the ship) to the stand building equipment 2677, all as described in connection with FIG. 14. The stand building equipment 2677 may thus receive the pipes from the catwalk machine, bring them in upright orientation, and connect them to other pieces so as to form stands. To this end the stand building equipment may comprise a mousehole 2589 through which the stand may be gradually lowered while it is made up until the lowermost end of the stand is at the lowermost level of the setback area 2512, while the uppermost end of the stand is below the drill floor level. The stands may then be received by pipe rackers 2491 and placed in the setback structure 2512 for future use. To this end the pipe rackers are operable to traverse across the setback area, e.g. in the direction parallel to the direction connecting the well centres.

(63) The drilling rig comprises a number of slanted chutes 2592 each for feeding pipes from the setback area 2512 to one of the well centres. Each chute 2592 receives pipes from one of the pipe rackers 2491 feeds the pipes in a slanted upward direction through a corresponding slit 2485 in the drill floor and through the gap formed by the cylinders 2406 of the corresponding hoisting system towards a respective one of the well centres 2423, where they are picked up at their uppermost end by the corresponding hoisting system and lifted through the slit 2485 until they are vertically suspended above the corresponding well centre. To this end, the drilling rig further comprises pipe handling equipment operable to guide the pipes while they are being lifted through the slit 2485. The slits 2485 are are elongated and point away from the axis connecting the well centres and towards the side where the setback area 2512 is positioned.

(64) The drilling rig comprises another storage area 2515 below the drill floor deck 2507 and configured for storing risers in a vertical orientation, as described in connection with FIG. 14. The riser storage area 2515 is located adjacent the moon pool 2722, e.g. on the side of the moon pool opposite the setback structure 2512. The risers may be moved, e.g. by means of a gantry crane and respective chutes 2794 or other suitable pipe feeding equipment through holes 2481 in the drill deck floor. The riser feeding holes 2481 may be covered by plates, hatches or similar covers. In FIG. 15, the holes are shown in the open position with the uppermost end of a riser extending through the open hole. The riser feeding holes are displaced from the axis connecting the well centres.

(65) As in the previous example, in the embodiments of FIGS. 14-21 a main deck is located beneath the drill floor deck and allows heavy subsea equipment, e.g. BOPs and Christmas trees to be moved to the moon pool under the well centres so as to allow such equipment to be lowered toward the seabed. Consequently, the drill floor deck and, in particular, the part of that drill floor deck that is located in close proximity to the well centre may be stationary and does not need to be hoisted or lowered for the subsea equipment to be lowered to the seabed.

(66) As the stands of tubulars and the risers are stored below the drill floor deck, and since the catwalk machines 2508 extend towards opposite sides from the well centres, and since the mast structure 2404 is located on one side of the well centres, the drill floor deck provides a large, unobstructed deck area on the side of the well centres opposite the mast. This area provides unobstructed access to both well centres and is free of pipe handling equipment. Consequently, these areas may be used as working area, e.g. for rigging up suspendable auxiliary equipment, and/or for positioning on-deck auxiliary equipment as described in connection with the example of FIGS. 1-8 above. In particular, when no riser operations are performed, the holes 2481 may be covered or otherwise secured. Moreover, at least parts of the setback structure 2512 may be covered by a platform so as to provide additional storage or working area.

(67) Even though the embodiments of FIGS. 14-21 have been described in the context of a drillship, it will be appreciated that the described features may also be implemented in the context of a semi-submersible or other type of drilling rig. In particular, storage of risers and/or other tubulars below the drill floor deck may be implemented on other types of drilling rigs as well. Likewise, the guard structure, the mounting structure, and other features described with the embodiments of FIGS. 1-13 may be implemented on another on the drillrigs shown in FIGS. 14-21 as well.

(68) FIGS. 22A-22D show embodiments of a drilling rig in which stands of tubulars that are built in a stand building structure 2277 and stored vertically in a setback area 2212 behind a mast structure 2204 are delivered to a number of well centres 2223 situated on a drill floor deck 2207. Tubulars are delivered from the setback area by means of slanted chutes 2292 through corresponding slits 2285 allowing access from the setback area to the drill floor deck. The operation of running tubulars to the well centres may be controlled and monitored in the driller's cabin 2234.

(69) The embodiment of FIG. 22A has separate slanted chutes 2292 and slits 2285 located perpendicular to the setback area 2212 thus linking it to the drill floor deck 2207 through a gap between the cylinders of the hoisting system 2206.

(70) FIG. 22B shows an embodiment where the chutes and slits are located between the well centres such that tubulars are fed to the well centres by means of a number of pipe handling apparatus 2201. Two adjacent sets of chutes, slits and pipe handling apparatus are shown in order to ensure redundancy in operation in such a way that drilling operations may be performed even though one set should experience failure or otherwise be out of operation.

(71) FIG. 22C illustrates an embodiment where the chutes and slits are located between the well centres and following an angled path leading to the well centres such that the chutes 2292 may feed tubulars directly to the well centres 2223. In this embodiment a gap between the cylinders 2206 of the hoisting system is not needed.

(72) FIG. 22D illustrates an embodiment where tubulars are delivered from the setback area 2212 to the well centres 2223 following a path along the outside of the mast structure 2204.

(73) FIGS. 23 A)-D) show cut outs of a portion of a drilling rig to illustrate various embodiments of layouts in which hoisting system cylinders 2206 are positioned inside a mast structure 2204 such that a gap 2301 into the side of the mast facing the well centre 2223 can be made. These gaps allow tubulars to be delivered from a setback area 2212 through a slit 2285 by means of a chute 2292 to a well centre 2223 without clashing with the mast structure or the hoisting system in any way.

(74) In FIG. 23A) a layout is shown where the cylinders 2206 of the hoisting system are arranged such that a portion of them are located further inside the footprint of the mast 2204 to allow a gap 2301 in the mast such that tubulars may be fed through a slit 2285 to a well centre 2223 without interfering with the cylinders and mast structure, rendering a large spacing between the cylinders unnecessary.

(75) FIG. 23B) shows a variation of the layout in FIG. 23A) where some of the cylinders 2206 are moved even further back inside the footprint of the mast structure 2204 to accommodate a larger gap/deeper recess compared to FIG. 23 A).

(76) In FIG. 23C) an embodiment is shown where the cylinders 2206 are laid out in two rows facing each other to create a larger gap in the mast structure 2204 enabling access around the slit 2285 and chute 2292.

(77) FIG. 23D) shows as embodiment where the cylinder hoisting system is replaced with a hoisting system utilising a different means of lifting, for instance a draw works, such that the load bearing qualities of the cylinders are transferred to a strengthened mast structure 2302 in such a way that this structure carries these loads entirely. The mast structure is strengthened while having enough space for a gap 2301 to allow access to the tubulars being fed to the well centres.

(78) FIG. 24 shows an embodiment of a drilling rig where a mast structure 2204 is shown having gaps 2301 to allow tubulars to be fed to well centres 2223 through slits 2285 in the drill floor deck 2207. The embodiment shown does not utilise a cylinder type hoisting system but is rather a variant of the embodiment shown in FIG. 23 D) where the mast structure is strengthened to accommodate the lack of load bearing cylinders. The lack of cylinders positioned in relative proximity to the well centres in the horizontal plane allows gaps 2301 to be provided in the mast structure for tubulars to pass under and through the mast structure to be delivered to the well centre.

(79) 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 utilised and structural and functional modifications may be made without departing from the scope of the present invention.

(80) For example, the described embodiments comprise two well centres, but it will be appreciated that alternative embodiments may comprise a single well centre or a well centre and additional work centres.

(81) The inventors have further realized that many of the advantages of several further aspects of the drilling rig described herein, e.g. the open drill floor deck, a guard structure and/or a mounting structure described herein or defined in the dependent claims may be obtained with a variety of different embodiments of drilling rigs, not limited to the specific embodiments described herein. For example, one or more of these aspects and/or other aspects may be embodied in combination with other embodiments of an offshore drilling rig, e.g. an offshore drilling rig comprising: a drill floor deck having a hole defining a first well centre; a first mast upwardly extending relative to the drill floor deck, and a first hoisting system supported by the first mast and configured for hoisting and lowering tubular equipment through the first well centre; wherein the first hoisting system is displaced from and located on a first side of the first well centre; first pipe handling equipment for moving tubular equipment to the first hoisting system so as to allow the first hoisting system to hoist or lower the tubular equipment through the first well centre.

(82) In device claims enumerating several features, several of these features can be embodied by one and the same item of hardware. 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. For example, even though not explicitly shown, it will be appreciated that the drilling rigs of FIGS. 9-13 may be provided with a guard structure as described herein and/or a hoistable mounting structure as described herein.

(83) It should be emphasized that the term comprises/comprising 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.