Drilling rig

Abstract

An offshore drilling rig comprising a drill floor deck having a hole defining a first well center. The drilling rig may further include a first hoisting system configured for hoisting and lowering tubular equipment through the first well center. The drilling rig may further include first pipe handling equipment for presenting 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. The drilling rig may include a mounting structure, separate from the first hoisting system 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 center; wherein the mounting structure is movable between a lower position for rigging up auxiliary equipment to the mounting structure, and an elevated position allowing lowering or hoisting of auxiliary equipment suspended from the mounting structure through the first well center.

Claims

1. An offshore drilling rig comprising: a drill floor deck having a hole defining a first well centre; a support structure including one or more guide members, displaced from and located on a first side of the first well centre; a mounting structure for suspending suspendable auxiliary equipment from an elevated position above the drill floor deck and into the first well centre; a first hoisting system configured for hoisting and lowering tubular equipment through the first well centre, wherein the first hoisting system is operable independently of the mounting structure; 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 wherein: the mounting structure is connected to the one or more guide members of the support structure such that the one or more guide members of the support structure supports the mounting structure and the suspended suspendable auxiliary equipment, and the mounting structure is movable vertically along the guide members of the support structure between at least a lower position and said elevated position; and the lower position is for rigging up the suspendable auxiliary equipment to the mounting structure at the lower position, and the elevated position is for allowing lowering or hoisting of the suspendable auxiliary equipment suspended from the mounting structure through the first well centre.

2. The offshore drilling rig according claim 1, wherein the mounting structure and the support structure combined define a perimeter at least partially surrounding the first well centre.

3. The offshore drilling rig according to claim 1, comprising a protective barrier suspendable from the mounting structure for preventing items handled above the first well centre from falling onto adjacent deck areas.

4. The offshore drilling rig according claim 1, wherein the first hoisting system is operable to lower tubular equipment through the well centre while the suspendable auxiliary equipment is suspended from the mounting structure at the elevated position.

5. The offshore drilling rig according claim 1, comprising a first mast upwardly extending relative to the drill floor deck, and configured to support the first hoisting system at least against lateral forces and wherein the first mast forms at least a part of the support structure.

6. The offshore drilling rig according to claim 5, 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 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.

7. The offshore drilling rig according to claim 6, wherein at least a part of the mounting structure extends across the access path.

8. The offshore drilling rig according to claim 5, comprising a guard structure configured to prevent tubular equipment operated above the first well centre from falling onto the drill floor deck area in a direction away from the first mast.

9. The offshore drilling rig according to claim 8, wherein the guard structure is elevated above the drill floor deck so as to provide an access path to the first well centre under the guard structure.

10. The offshore drilling rig according to claim 8, wherein the guard structure is configured to be moved between different elevations above the drill floor deck.

11. The offshore drilling rig according to claim 8, wherein the guard structure is operable to be moved between a closed position where it prevents tubular equipment operated above the first well centre from falling onto the drill floor deck area and an open position where it allows unobstructed access to the first well centre.

12. The offshore drilling rig according to claim 8, wherein the guard structure extends between support structures located on respective sides of the first well centre.

13. The offshore drilling rig according claim 1, wherein the mounting structure extends between support structures located on respective sides of the first well centre.

14. The offshore drilling rig according claim 1, wherein the first hoisting system is configured to allow tubular equipment to be moved towards the first well centre from a first side.

15. The offshore drilling rig according to claim 14, wherein the first hoisting system defines an opening through which tubular equipment is movable towards the first well centre from the first side.

16. The offshore drilling rig according claim 1, wherein the drilling rig further comprises a pipe storage structure positioned on a second side of the first well centre opposite the first side.

17. The offshore drilling rig according 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.

18. The offshore drilling rig according to claim 17, wherein the drilling rig comprises a guard structure extending between the first well centre and the second work centre.

19. The offshore drilling rig according to claim 17, comprising a first mounting structure operatively associated with the first well centre, and a second mounting structure operatively associated with the second work centre.

20. The offshore drilling rig according claim 1, wherein the mounting structure comprises one or more retaining portions operable to receive falling tubular equipment and to retain at least a part of the tubular equipment.

21. The offshore drilling rig according to claim 1, wherein the mounting structure is arranged so that preparation of the connection between the suspendable auxiliary equipment and the mounting structure is performed at a horizontal displacement from the first well centre of less than 7 meters.

22. The offshore drilling rig according to claim 1, wherein the mounting structure is a beam and one or more suspension devices at one or more suspension positions along the beam, said suspension devices selected from the group of a hook, a pulley, a banana-sheave, and a pad-eye.

23. The offshore drilling rig according claim 1, wherein the mounting structure and the support structure combined define a perimeter surrounding the first well centre.

24. The offshore drilling rig according to claim 1, wherein, at the lower position, the suspendable auxiliary equipment can be rigged to the mounting structure from the drill floor deck.

25. A method of suspending suspendable auxiliary equipment from an elevated position above a drill floor deck of a drilling rig; the drill floor deck having a hole defining a first well centre, the drilling rig comprising the drill floor deck, a first hoisting system configured for hoisting and lowering tubular equipment through the first well centre; a support structure displaced from and located on a first side of the first well centre supporting said first hoisting system; and 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; the method comprising: providing a mounting structure, separate from the first hoisting system, at a first position that is lower than the elevated position; providing auxiliary equipment comprising an on-deck auxiliary component and suspendable auxiliary component; suspending the suspendable auxiliary equipment from the mounting structure at the first position; elevating the mounting structure having the suspendable auxiliary equipment suspended from it to said elevated position above the drill floor deck along one or more guide members of the support structure; and suspending the suspendable auxiliary equipment through the first well centre via said mounting structure.

26. The method of claim 25, wherein the mounting structure is arranged so that preparation of a connection between the suspendable auxiliary equipment and the mounting structure is performed at a horizontal displacement from the first well centre of less than 7 meters.

27. The method of claim 25, wherein the mounting structure is a beam and one or more suspension devices at one or more suspension positions along the beam, said suspension devices selected from the group of a hook, a pulley, a banana-sheave, and a pad-eye.

28. The method of claim 25, wherein, at the first position, the suspendable auxiliary equipment can be rigged to the mounting structure from the drill floor deck.

29. 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, wherein the first mast is displaced from and located on a first side of the first well centre; one or more guide members supported by the first mast; a mounting structure supported by the one or more guide members so that the mounting structure is movable between a first position and a second position that is elevated above the first position; a first hoisting system supported by the first mast and configured for hoisting and lowering tubular equipment through the first well centre; and 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 mounting structure is movable vertically along the one or more guide members, independently of the first hoisting system, between the first position for rigging up suspendable auxiliary equipment to the mounting structure at the first position, and the elevated second position, thus allowing lowering or hoisting of the suspendable auxiliary equipment suspended from the mounting structure through the first well centre.

30. The offshore drilling rig according to claim 29, wherein the mounting structure extends between the support structure located on respective sides of the first well centre.

31. The offshore drilling rig according to claim 29, wherein the mounting structure is arranged so that preparation of a connection between the suspendable auxiliary equipment and the mounting structure is performed at a horizontal displacement from the first well centre of less than 7 meters.

32. The offshore drilling rig according to claim 29, wherein the mounting structure is a beam and one or more suspension devices at one or more suspension positions along the beam, said suspension devices selected from the group of a hook, a pulley, a banana-sheave, and a pad-eye.

33. The offshore drilling rig according to claim 29, wherein, at the first position, the suspendable auxiliary equipment can be rigged to the mounting structure from the drill floor deck.

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-C schematically show examples of a mast of a drilling rig.

(11) FIGS. 23 and 24 show 3D views of the offshore drilling rig of FIGS. 1-8.

(12) FIG. 25 shows an isolated 3D view of a raisable mounting structure.

(13) FIG. 26 illustrates a 3D view of a raisable guard and mounting structure.

DETAILED DESCRIPTION

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

(15) An embodiment of an off-shore drilling rig will be described with reference to FIGS. 1-8 and FIGS. 23-24.

(16) 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.

(17) 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 bending. 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.

(18) 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. 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 top drives move upwards and downwards along respective vertical rails 145 to which the top drives are connected via respective dollies 169. 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 load of the sheave(s).

(19) 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.

(20) 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 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.

(21) 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.

(22) 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.

(23) 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 and 23-24, 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.

(24) 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.

(25) 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 with reduced or even without any 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.

(26) 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.

(27) 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.

(28) As is most easily seen in FIGS. 2, 6, 23 and 24, the drilling rig further comprises a gantry beam or framework 125 or a similar mounting structure for suspending suspendable equipment from an elevated position above the drill floor deck, e.g. allowing auxiliary equipment to be lowered or hoisted through the first well centre and/or a protective barrier to be raised. 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 144 or tracks extending upwardly along the support structures to which the gantry beam is connected. To this end, gantry beam comprises suitable connecting members 198. 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.

(29) 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.

(30) 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.

(31) 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.

(32) 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.

(33) As is most easily seen in FIG. 8, 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. 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.

(34) Even though the embodiment of FIGS. 1-8 and 23-24 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.

(35) 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.

(36) 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.

(37) 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.

(38) 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.

(39) 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.

(40) 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.

(41) 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.

(42) 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.

(43) 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 and 23-24. 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. The drilling rig of FIGS. 12a-b further comprises a raisable mounting structure 1225 extending between the mast 1204 and a support structure of the vertical pipe handling equipment 1213. Hence, a protective barrier may be suspended from the mounting structure so as to block the access path to the well centre. Alternatively or additionally, the drilling rig may comprise a raisable mounting structure defining a perimeter around the well centre 1223, as will be described in more detail in connection with FIGS. 13a-b and FIGS. 22A-C.

(44) 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.

(45) 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.

(46) 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.

(47) 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.

(48) 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.

(49) The drilling rig of FIGS. 13a-b further comprises a raisable mounting structure 1325 defining a perimeter around the well centre 1223, as will be described in more detail in connection with FIGS. 22A-C. In this example, the mounting structure is connected at two lateral sides of the mast on either side of the well centre. Hence, the mast and the mounting structure define a perimeter that completely encloses the well centre.

(50) 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.

(51) 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.

(52) 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.

(53) 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.

(54) 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 pipe storage areas fore (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.

(55) The drilling rig comprises another storage area for risers 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.

(56) 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.

(57) The drilling rig further comprises a raisable mounting structure comprising a beam 1425 from which suspendable equipment may be suspended, such as auxiliary equipment to be lowered through one of the well centres (e.g. as described in connection with the embodiment of FIGS. 1-8 and 23-24) or a protective barrier or curtain for preventing items that are handled above one of the well centres to fall onto the other well centre or onto open deck areas surrounding the well centre(s). The raisable beam is attached to tracks or rails 1444 vertically extending along the mast 1404. The beam is attached to the rails via connecting arms 1449 such that the beam 1425 is not located directly above the well centre but such that the beam 1425, the connecting arms 1449 and the mast 1404 together define a perimeter around the well centres. The beam 1425 extends parallel to an direction intersecting with both well centres. The beam 1425 may be raised or lowered by means of a lifting wire 1448 connected to the beam 1425 or connecting arms 1449 and fed across respective pulleys or sheaves 1442 to a winch or tugger (not explicitly shown). Alternatively, the beam may be raised or lowered by the top drive or by another suitable lifting mechanism.

(58) FIGS. 15-21 show another embodiment of a drilling rig, in this example of a 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.

(59) 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, 23-24 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.

(60) 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.

(61) 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 2445 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.

(62) 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.

(63) 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.

(64) 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.

(65) 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.

(66) 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 elongated and point away from the axis connecting the well centres and towards the side where the setback area 2512 is positioned.

(67) 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.

(68) 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.

(69) 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 and 23-24 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.

(70) As can most easily seen in FIGS. 19 and 21, the drilling rig further comprises a raisable mounting structure comprising a beam 2125 from which suspendable equipment may be suspended. The raisable beam is attached to tracks or rails 2144 vertically extending along the mast 2404. The beam is attached to the rails via connecting arms 2149 and may be raised by lifting lines 2448, all as described in connection with FIG. 14. The beam 2125 is positioned at a distance from and extending alongside the mast so as to stay clear from the top drive. The beam may be fitted with support to downwards force when hooked up and with wireline pad-eyes and/or banana-sheaves or other suspension devices. These may be rated to 50 tons or another suitable weight such that the beam is able to support that weight hanging off from the eyes. FIG. 19 shows a protective barrier 1951, e.g. a net or Kevlar sheet, suspended from the beam 2125 and connecting arms 2149. The barrier may further be attached to the mast and/or the drill floor.

(71) 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 dilling rigs as well. Likewise, the guard structure, the mounting structure, and other features described with the embodiments of FIGS. 1-13 and 23-24 may be implemented on another on the drillrigs shown in FIGS. 14-21 as well.

(72) FIGS. 22A-C schematically show top views of examples of a mast structure of an offshore drilling rig. In particular, the structure of FIG. 22A-C comprises a dual-activity mast 2204 arranged next to two well centres 2223, e.g. as described in connection with the embodiments of FIGS. 1-21 and 23-24. The mast comprises vertical guide rails 2245 for respective top drives (not shown) operating above the respective well centres 2223. A driller's cabin 2234 is located at least partly within the footprint of the mast and between the well centres 2223. The mast further comprises vertical guides 2244, e.g. rails or tracks, for guiding one or more raisable mounting beams 2225 or frames as described herein. The beams 2225 are connected to the rails via arms 2249 such that the beams 2225 extend at a distance from the mast so as to allow the top drives to move up and down between the mast 2204 and a respective one of the beams. The beams allow suspendable equipment to be lifted to an elevated position generally above the well centres, such as auxiliary equipment to be lowered through a well centre and/or a suspendable barrier for preventing tubulars or other items handled above a well centre from falling onto the neighbouring well centre and/or onto open deck space adjacent the well centres. Such a barrier may be in the form of a Kevlar sheet/curtain or a similar foldable or otherwise collapsible material. Such a barrier may be attached to and suspended from the beam or beams 2225 and/or to the connecting arms 2249, such that the barrier at least partially surrounds one or both of the well centres, e.g. so as to allow manual work processes to take place at one well centre while other operations (such as drilling or drilling operations) occur at the other well centre. The barrier may be installed permanently e.g. by means of a roller system and rolled out when needed; alternatively, the barrier may be stowed in a suitable container which is stowed away while not needed. To this end, the beams 2225 and the connecting arms 2249 extend around the position of one or both well centres such that a barrier suspended from the beam 2225 and its arms at least partially surrounds the well centre(s).

(73) In the example of FIG. 22A, two separate beams 2225 are attached to respective sets of rails 2244, each beam being arranged above one of the well centres 2223. Moreover a work basket 2231 is mounted via an arm or crane 2250 from a base 2246 arranged above the driller's cabin 2234. The arm or crane 2250 may be extendable and/or may pivot or swing horizontally and/or may be elevated lowered to a desired height so as to allow the work basket to be selectively positioned close to both beams 2225 and/or to one of the top drives. The beams 2225 and their respective connecting arms 2249 are spaced from each other by a spacing 2243 so as to allow the beams to descend to the drill floor deck level in spite of the placement of the driller's cabin 2234. Alternatively, the driller's cabin may be positioned on the other side of the well centre, opposite the mast, in which case the spacing 2243 may be reduced or even omitted. The beams 2225 and their respective connecting arms 2249 provide support for a protective barrier separating the well centre(s) from each other.

(74) In the example of FIG. 22B, a single beam 2225 is attached to a set of rails 2244. The beam 2225 extends across both well centres 2223. A work basket 2231 is mounted via an arm or crane 2250 from a base 2246 arranged above the driller's cabin 2234, as described in connection with FIG. 22A. The beam 2225 thus allows auxiliary equipment to be easily moved between well centres while suspended from the beam, e.g. by providing a rail or track along the beam along which the suspension point from which the equipment is suspended may be moved along the beam 2225.

(75) In the example of FIG. 22C, two separate beams 2225 are attached to respective sets of rails 2244, as described in connection with FIG. 22A. However, in the example of FIG. 22C, two work baskets 2231 are provided, each mounted via a respective arm or crane 2250 within the perimeter of the corresponding beam 2225 and connecting arm 2249. When a barrier is suspended from one or both beams 2225 and/or connecting arms, the work baskets may be used while such a barrier is installed. The baskets may be installed on either side of the rails 2245 for the top-drive. The individual work basket cranes may also be installed in combination with a central (e.g. larger) crane as shown in FIGS. 22A and 22B.

(76) FIG. 25 shows an embodiment of the raisable mounting structure described in FIGS. 19 and 21 comprising a beam 2125 with connecting arms 2149 enabling the beam to be attached along the mast of a drilling rig. The raisable mounting structure in this embodiment further comprises a number of pad-eyes 2501 from which equipment may be suspended. These pad-eyes may be of such a design that they may transfer loads from equipment suspended in the pad-eyes through the raisable mounting structure onto the mast. The pad-eyes may provide flexibility and enable the possibility to suspend different pieces of equipment in various configurations from the raisable mounting structure. It will be appreciated that one or more pad-eyes and/or other suspension devices may be provided on other embodiments of raisable mounting structures as the example shown in FIG. 25.

(77) In FIG. 26 an embodiment is shown to illustrate a guard and mounting structure comprising a modified beam structure 2125 with connecting arms 2149 enabling the mounting structure to be attached along the mast of a drilling rig. Furthermore, the embodiment comprises a number of pad-eyes 2501 for suspension of e.g. equipment or a protective sheeting or curtain. The beam structure 2125 is reshaped to accommodate large falling objects such as tubulars suspended in the top drive by having an angled shape ending in a central wedge shape 2601 or similar retaining portion. The embodiment includes a method for handling dropped tubulars, for example drill pipe, in such a way that a tubular 2602 falling from above the well centre is guided by the shape of the beam 2125 into the retaining part 2601 of the beam as indicated by the arrow 2603 to a position 2604 in which the drill pipe is wedged between the beam in a fixed position. This will stop uncontrolled, unsafe movements of the tubular and allow the retrieval of the fallen object in a controlled, safe manner. The guard structure may be of a design allowing it to be separated controllably to remove e.g. the wedged tubular. Further, as also described in FIG. 25, pad-eyes 2501 or similar installation means may be located on the guard and mounting structure to accommodate suspension of equipment while retaining the safety functionality of the guard and mounting structure. In a further embodiment the guard structure may be movable in a vertical direction to be able to follow the lateral movement of the top drive above the well centre. It will be appreciated that a retaining portion operable to receive a tubular may be provided on other embodiments of raisable mounting structures as the example shown in FIG. 26. Such retaining portion may e.g. be V-shaped or U-shaped or another shape open towards the well centre and the work area surrounded by the mounting structure. The retaining portion may provide two generally opposing contact surfaces, e.g. converging contact surfaces, for retaining a tubular between the contact surfaces. The portions of the mounting structure adjacent the retaining portion 2601 may be formed so as to converge towards the wedge-shape portion so as to guide a falling tubular towards and into the retaining portion, e.g. as illustrated in FIG. 26.

(78) 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.

(79) 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. Similarly, the mounting structure disclosed herein has mainly been described in connection with a hydraulic hoisting system including a gap between groups of cylinders; it will be appreciated that a mounting structure as disclosed herein may also be used in connection with other types of hoisting systems and/or other types of drill floor layouts and/or other types of masts.

(80) 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.

(81) 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.