AND METHOD

Technical Field The present disclosure generally relates to an arrangement for a drilling system. In particular, an arrangement for a drilling system, a drilling system comprising an arrangement, and a method of operating an arrangement for a drilling system, are provided.

Background On a conventional drilling rig, there is typically provided only one large derrick equipped with machinery for all operations through the well center required by the drilling rig. All or some preparations of a subsequent operation therefore cannot be performed until a first operation has been completed. As a consequence, the preparation times of the different operations prolong the overall time to access an oil or gas reservoir, e.g. the "flat periods", during which drilling is not progressing, are increased. Furthermore, a conventional derrick equipped with machinery for all operations is large.

WO 2018031624 Ai discloses a derrick structure including a plurality of drilling rotating/hoisting/circulation (RHC) traveling block/top drive like systems that can move between and are fully functional on multiple well centers. With such a configuration, one RHC can be disconnected from the drill lines and suspended in the drilling derrick allowing two hoisting systems with separate motors to function simultaneously on a single well center. Summary

One object of the present disclosure is to provide an arrangement for a drilling system, which arrangement enables a reduction of a time for completing drilling. A further object of the present disclosure is to provide an arrangement for a drilling system, which arrangement is cost effective.

A further object of the present disclosure is to provide an arrangement for a drilling system, which arrangement improves safety.

A still further object of the present disclosure is to provide an arrangement for a drilling system, which arrangement has a simple design.

A still further object of the present disclosure is to provide an arrangement for a drilling system, which arrangement has a compact design.

A still further object of the present disclosure is to provide an arrangement for a drilling system, which arrangement has low weight. A still further object of the present disclosure is to provide an arrangement for a drilling system, which arrangement solves several or all of the foregoing objects in combination.

A still further object of the present disclosure is to provide a drilling system comprising an arrangement, which drilling system solves one, several or all of the foregoing objects.

A still further object of the present disclosure is to provide a method of operating a drilling system, which method solves one, several or all of the foregoing objects.

According to one aspect, there is provided an arrangement for a drilling system, such as an offshore drilling rig, the arrangement comprising a suspension structure for suspending a string of tubulars, the suspension structure comprising a support table for holding a string of tubulars through a well center in the support table; at least two rig units, each rig unit having at least one lifting device configured to lift and lower a load along a vertical axis; and a drive mechanism arranged to move the suspension structure relative to the at least two rig units such that the well center moves between the vertical axes of the at least two rig units.

Instead of providing several well centers, the arrangement enables the use of only one well center that can be moved between different rig units. A first rig unit can thereby be provided with equipment dedicated for a particular first operation or first group of operations, while a second rig unit can be provided with equipment dedicated for a different second operation or second group of operations. Thus, at least two of the rig units may be configured to carry out different tasks. When the first rig unit performs the first operation or first group of operations, the second rig unit can be prepared for the second operation or second group of operation. In this way, the "flat periods" can be reduced, which in turn reduces the overall drilling period. Thereby, the operator can save time and money and the environmental footprint can be reduced. By means of the arrangement, each rig unit can access and operate in the well center during the whole drilling period. Furthermore, one rig unit can always be ready for next operation. Furthermore, when a first rig unit carries out an operation through the well center and preparations are made on a second rig unit, the personnel involved in the preparations of the second rig unit are distanced from the operational first rig unit. Thereby, the safety is increased.

Furthermore, due to the provision of several rig units according to the present disclosure, the size of the rig units can be lower than a conventional rig unit or derrick equipped with machinery for all required operations through the well center. For example, a conventional derrick may have a height of about 50 m and may have a footprint of about 12 m by 12 m while each rig unit according to the present disclosure may have a height of less than 20 m from the deck and may have a footprint of about 4 m by 4 m. The support table may be arranged to hold a string of tubulars inside a riser (which may be an additional string of tubulars). By means of the lifting device, the string can be raised or lowered, e.g. relative to a riser inside the riser. However, the arrangement may also be configured to hold a string of tubulars without a riser, i.e. for riserless drilling. Throughout the present disclosure, a string of tubulars may be a riser, a drill string and/or a casing string.

The support table may be arranged to hold the weight of the well equipment while the active rig unit adds/removes tubular from the string. The well center may be said to constitute the interface between the equipment of the active rig unit and the well equipment. That is, the well center constitutes the entrance towards the reservoir.

Throughout the present disclosure, the support table may be a rotary table or a false rotary table. That is, the support table may or may not comprise a function for rotating a string of tubulars. In case the rotating function is provided, this function may be as backup for a top drive. The support table may comprise slips for holding a string of tubulars. Thus, the support table may be a slips table.

Each rig unit may be a mast or derrick. Optionally, one or more of the rig units may be modular. As an alternative to an offshore drilling rig, the arrangement may be provided on a jackup rig or on a ship. A jackup rig typically has a blow-out preventer (BOP) onboard with the riser provided between the BOP and a subsea template or Christmas tree.

The at least two rig units may be stationary, e.g. stationary on an offshore drilling rig, and the suspension structure may be moved relative to the stationary rig units. As a possible alternative, the suspension structure may be stationary, e.g. stationary on an offshore drilling rig, and the at least two rig units may be moved relative to the stationary suspension structure. To this end, each rig unit may be moved independently relative to the suspension structure. The drive mechanism may be arranged to align the suspension structure with each of the at least two rig units. According to one example, the arrangement comprises three, four, or five rig units.

The drive mechanism may be arranged to move the suspension structure in a substantially horizontal direction, or horizontal direction. The support table together with the well center may be skidded between two or more of the at least two rig units.

The lifting device may be a top drive in some or all of the rig units. By means of a top drive, tubulars can also be rotated. One or several lifting devices may be provided in each rig unit. The vertical axis of each rig unit may be substantially centered, or centered, with the respective rig unit. The vertical axis of each rig unit may extend through a moon pool.

The drive mechanism may be arranged to move the suspension structure by driving the support table. The drive mechanism may be arranged to move the suspension structure relative to the at least two rig units substantially linearly between the vertical axis of two of the rig units. Alternatively, or in addition, the at least two rig units may be substantially linearly arranged, or linearly arranged.

The at least two rig units may comprise at least one drilling rig unit for handling a drill string when the well center is aligned with the vertical axis of the drilling rig unit.

The at least two rig units may comprise two drilling rig units, each for handling a drill string when the well center is aligned with the vertical axis of the respective drilling rig unit. In this way, the risk for downtime due to equipment failure is reduced.

The at least two rig units may comprise a casing rig unit for handling a casing string when the well center is aligned with the vertical axis of the casing rig unit. The at least two rig units may comprise a riser rig unit for handling a riser when the well center is aligned with the vertical axis of the riser rig unit.

The at least two rig units may comprise a workover rig unit for handling workover tools when the well center is aligned with the vertical axis of the workover rig unit.

The arrangement may comprise at least three rig units. At least two of the rig units may be configured to carry out different tasks. Alternatively, or in addition, at least two of the rig units may be configured to carry out the same task. Each rig unit may be arranged to perform drilling and/or other wellbore related activities.

The arrangement may further comprise a storage device configured to store tubulars, wherein the storage device is movable between a position associated with each of two or more of the at least two rig units. The storage device may be movable to and from a storage device storage area distanced from each rig unit.

According to one example, the storage device is movable by means of the drive mechanism in common with the suspension structure to the active rig unit. As an alternative, the storage device may be moved by a dedicated moving device independently of the suspension structure. The arrangement may comprise one or several storage devices. Alternatively, or in addition, each storage device may comprise a fingerboard device adapted to store tubulars.

The arrangement may further comprise a moon pool, wherein the support table is movable within the moon pool. The drive mechanism may comprise a rack and pinion device arranged to move the support table.

The suspension structure may comprise a diverter connected to the support table. The diverter may be detachably connected to the support table. By detaching the diverter from the suspension structure and "parking" the diverter, the support table can be moved independently of the diverter. The suspension structure may further comprise a flowline connected to the diverter.

The suspension structure may comprise riser tensioners. The riser tensioners may be detachably arranged in the suspension structure. By detaching the riser tensioners from the suspension structure and "parking" the riser tensioners, the support table can be moved independently of the riser tensioners. The suspension structure may further comprise a tensioning system for tensioning the riser tensioners. According to a further aspect, there is provided a drilling system, such as an offshore drilling rig, comprising an arrangement according to the present disclosure.

According to a further aspect, there is provided a method of operating an arrangement for a drilling system, such as an offshore drilling rig, the method comprising suspending a string of tubulars by means of a suspension structure at a first position at a first rig unit, the suspension structure comprising a support table for holding a string of tubulars through a well center in the support table, the first rig unit having at least one first lifting device configured to lift and lower a load along a first vertical axis, and wherein the well center is aligned with the first vertical axis of the first rig unit at the first position; and moving the suspension structure from the first position to a second position at a second rig unit, the second rig unit having at least one second lifting device configured to lift and lower a load along a second vertical axis, and wherein the well center is aligned with the second vertical axis of the second rig unit at the second position.

The method may further comprise tripping out a string of tubulars through the well center by means of the first rig unit when the suspension structure is in the first position. The method may further comprise tripping out a string of tubulars through the well center by means of the second rig unit when the suspension structure is in the second position. The above two step may be alternated repeatedly. According to one example, the first rig unit is a drilling rig unit for handling drill tubulars and the second rig unit is a casing rig unit for handling casing tubulars.

Brief Description of the Drawings Further details, advantages and aspects of the present disclosure will become apparent from the following embodiments taken in conjunction with the drawings, wherein:

Fig. 1: schematically represents a side view of a drilling system comprising a drilling rig and an arrangement; Fig. 2: schematically represents a perspective view of the arrangement; Fig. 3: schematically represents a side view of the arrangement comprising a suspension structure;

Fig. 4: schematically represents a side view of the arrangement after movement of the suspension structure; Fig. 5: schematically represents a perspective view of the arrangement in Fig. 4; Fig. 6: schematically represents a side view of the arrangement after further movement of the suspension structure; and

Fig. 7: schematically represents a top view of the arrangement. Detailed Description

In the following, an arrangement for a drilling system, a drilling system comprising an arrangement, and a method of operating an arrangement for a drilling system, will be described. The same or similar reference numerals will be used to denote the same or similar structural features. Fig. 1 schematically represents a side view of a drilling system 10. The drilling system 10 of this example is an offshore floating drilling rig 12 having an arrangement 14. The drilling system 10 comprises a riser 16 and a blow-out preventer (BOP) 18 connected to a wellhead assembly 20 on a seabed 22 above a reservoir 24 containing oil or gas. The reservoir 24 may be located at a depth of up to 5000 m below the seabed 22. The drilling rig 12 floats on a surface 26 of the sea 28. The drilling rig 12 is here exemplified as a semi- submersible platform, but the drilling rig 12 may alternatively be provided on a ship, on a jackup rig, or on other rigs with flexible connection between the seabed 22 and the rig.

Fig. 2 schematically represents a perspective view of the arrangement 14. The arrangement 14 of this example comprises a riser rig unit 30, a first drilling rig unit 32, a second drilling rig unit 34 and a casing rig unit 36. The second drilling rig unit 34 is optional and is used as backup should the first drilling rig unit 32 fail. In this example, each rig unit 30, 32, 34, 36 is secured relative to a deck 38 over a moon pool on the drilling rig 12. The rig unit 30, 32, 34,

36 are arranged in a straight line.

The arrangement 14 further comprises a storage device 40 storing tubulars 42. To this end, the storage device 40 comprises a fingerboard (not denoted) for holding the tubulars 42.

As shown in Fig. 2, the drilling system 10 further comprises a garage 44. The garage 44 may for example accommodate the BOP 18 prior to lowering and/or a subsea workover rig unit (not shown) for handling workover tools.

In Fig. 2, some lifting devices 46 can also be seen. Fig. 3 schematically represents a side view of the arrangement 14. The arrangement 14 comprises a suspension structure 48. The suspension structure 48 is arranged to suspend the riser 16. As shown in Fig. 3, the riser 16 is a string of tubulars 42. The suspension structure 48 comprises a support table 50, here exemplified as a rotary table. The support table 50 comprises a well center 52 constituting an interface to the well equipment.

The arrangement 14 in Fig. 3 comprises only one single well center 52. Moreover, the arrangement 14 comprises only one support table 50. The support table 50 comprises slips 54. By tightening the slips 54, a string of tubulars 42 can be held in the well center 52 by the support table 50. As shown in Fig. 3, each rig unit 30, 32, 34, 36 comprises a lifting device 46. Each rig unit 30, 32, 34, 36 may comprise one or several lifting devices 46. Each rig unit 30, 32, 34, 36 may further comprise makeup and breaking equipment (not shown). Each lifting device 46 is here exemplified as a top drive for rotating a tubular 42. The top drive can be driven vertically relative to the respective rig unit 30, 32, 34, 36 in order to perform drilling and tripping operations. The lifting device 46 of the riser rig unit 30 does however not need to be a top drive or have makeup and breaking equipment. The lifting device 46 of the casing rig unit 36 may however comprise makeup equipment.

Each lifting device 46 is configured to lift and lower a load along a respective vertical axis 56. To this end, the lifting devices 46 may be driven along vertical rails (not denoted) by means of a vertical motion drive. Each vertical axis 56 is positioned over a moon pool 58. In this example, each vertical axis 56 is centered with a respective rig unit 30, 32, 34, 36.

The suspension structure 48 further comprises a drive mechanism 60. The drive mechanism 60 is arranged to horizontally move the suspension structure 48 relative to the four rig units 30, 32, 34, 36. In this way, the suspension structure 48 can be moved such that the well center 52 moves from a first position, aligned with the vertical axis 56 of one of the rig units 30, 32, 34, 36, to a second position, aligned with the vertical axis 56 of any of the other rig units 30, 32, 34, 36.

In Fig. 3, the BOP 18 has first been lowered to the seabed 22. The BOP 18 may for example be lowered by means of the first drilling rig unit 32 or the second drilling rig unit 34 by connecting the BOP 18 to a tubular 42 and tripping down further tubulars 42. For this operation, the support table 50 may not be needed, e.g. if the rig unit has two lifting devices 54 with slips function. The riser 16 may then have been lowered by the riser rig unit 30 and now needs to be connected to the BOP 18. When the riser 16 has been lowered, the suspension structure 48 may be completely assembled.

The suspension structure 48 comprises a diverter 62. A flowline 64 is connected to the diverter 62. The suspension structure 48 further comprises universal joint 66, here exemplified as a ball joint. The suspension structure 48 further comprises a telescopic joint 68. The telescopic joint 68 comprises an upper inner barrel 70 and a lower inner barrel 72.

The suspension structure 48 further comprises riser tensioners 74. The riser tensioners 74 form part of a tensioning system (not illustrated) for tensioning the riser 16. The tensioning system may further comprise a support secured to the drilling rig 12. The riser tensioners 74 may be wires driven by hydraulic cylinders. Vertical movements of the riser 16 are taken by the telescopic joint 68 and tilting movements of the riser 16 are taken by the universal joint 66. Fig. 3 further shows a riser coupling 76 to the riser 16.

During assembly of the suspension structure 48 under the riser rig unit 30, the first drilling rig unit 32 is prepared. The preparations may for example include moving the storage device 40 of tubulars 42 to a position close to the first drilling rig unit 32 and make all drilling equipment ready for drilling. Since the suspension structure 48 with the support table 50 and the well center 52 is aligned with the riser rig unit 30, the riser rig unit 30 is active. When the riser rig unit 30 is active, the riser rig unit 30 can perform an operation on the riser 16. In Fig. 3, the support table 50 is aligned with the riser rig unit 30 such that the vertical axis 56 of the riser rig unit 30 passes through the well center 52.

Fig. 4 schematically represents a side view of the arrangement 14 after movement of the suspension structure 48. Fig. 5 schematically represents a perspective view of the arrangement 14 in Fig. 4. With collective reference to Figs. 4 and 5, the entire structure below the suspension structure 48 (in this example the support table 50, the diverter 62, the universal joint 66, the telescopic joint 68, the riser tensioners 74 and the top part of the riser 16) has been moved or skidded horizontally from the riser rig unit 30 to the first drilling rig unit 32. However, it is possible to detach one or several parts from the suspension structure 48 (e.g. the diverter 62 and the riser tensioners 74) prior to moving the support table 50 without these detached parts.

The suspension structure 48 has been moved from the riser rig unit 30 to the first drilling rig unit 32 by driving the support table 50 by means of the drive mechanism 60. During the movement, the support table 50 moves within the moon pool 58. In Figs. 4 and 5, the support table 50 is aligned with the first drilling rig unit 32 such that the vertical axis 56 of the first drilling rig unit 32 passes through the well center 52.

Since the suspension structure 48 with the support table 50 and the well center 52 is now aligned with the first drilling rig unit 32, the first drilling rig unit 32 is active and the riser rig unit 30 is now passive. When the first drilling rig unit 32 is active, the first drilling rig unit 32 can perform an operation on a drill string 78, such as a tripping or drilling operation.

In this example, the second drilling rig unit 34 has the same configuration as the first drilling rig unit 32. The second drilling rig unit 34 can be used in the same way as the first drilling rig unit 32 if needed, e.g. if the first drilling rig unit 32 should fail.

As the first drilling rig unit 32 performs an operation on the drill string 78, the casing rig unit 36 is prepared. The preparations may for example include moving the storage device 40 of tubulars 42 to a position close to the casing rig unit 36 and make all equipment ready for running casing. Fig. 6 schematically represents a side view of the arrangement 14 after further movement of the suspension structure 48. In Fig. 6, the support table 50 is aligned with the casing rig unit 36 such that the vertical axis 56 of the casing rig unit 36 passes through the well center 52. Since the suspension structure 48 with the support table 50 and the well center 52 is now aligned with the casing rig unit 36, the casing rig unit 36 is active and the first drilling rig unit 32 is now passive. When the casing rig unit 36 is active, the casing rig unit 36 can perform an operation associated with the casing string 80, such as a tripping in and setting the casing.

The entire structure below the suspension structure 48 (in this example the support table 50, the diverter 62, the universal joint 66, the telescopic joint 68, the riser tensioners 74 and the top part of the riser 16) has been moved or skidded further horizontally from the first drilling rig unit 32 to the casing rig unit 36.

During setting of a casing string 80 by the casing rig unit 36, the first drilling rig unit 32 is prepared again. For each casing run, casing tubulars 42 with successively smaller diameters are used. The drilling by the first drilling rig unit 32 and the casing setting by the casing rig unit 36 may be alternated in this way until the reservoir 24 is reached. In this way, the use of the equipment and personnel is optimized. That is, work through the well center 52 by an active rig unit 30, 32, 34, 36 and preparation work on a passive rig unit 30, 32, 34, 36 can be carried out in parallel. Thus, a part of the activities for assembling a casing string 80 or drill string 78 is carried out simultaneously with other activities, instead of in succession, as normally occurs in the prior art. By reducing the "flat periods" in this way, the activities result in a considerable gain of time. By utilizing technology described in international patent application WO 2018010980 Ai, the tripping speed can be increased, for example from 900 m/h to 1800 m/h, further generating a considerable gain of time.

Fig. 7 schematically represents a top view of the arrangement 14. As shown in Fig. 7, the drive mechanism 60 comprises a rack 82 and pinion 84. The rack 82 is secured to one side of the moon pool 58. The pinion 84 is provided on the support table 50. The drive mechanism 60 further comprises a motor 86 for driving rotating the pinion 84 engaging with the rack 82 to move the support table 50 and the suspension structure 48. The support table 50 thereby moves along support table rails 88 in the moon pool 58. The motor 86 may be an electric motor.

The storage device 40 is movable on storage device rails 90 on the deck 38, e.g. by means of a motor (not shown) or in common with suspension structure 48 by means of the drive mechanism 60. The storage device 40 can be moved to a position adjacent each active rig unit 30, 32, 34, 36. Although not illustrated, the arrangement 14 may comprise a storage device 40 on each side of the moon pool 58.

While the present disclosure has been described with reference to exemplary embodiments, it will be appreciated that the present invention is not limited to what has been described above. For example, it will be appreciated that the dimensions of the parts may be varied as needed. Accordingly, it is intended that the present invention may be limited only by the scope of the claims appended hereto.