The present invention relates to an offshore system for performing subsea wellbore related activities, e.g. drilling a subsea wellbore, comprising a vessel that is subjected to heave motion due to waves.

The present invention also relates to methods that are performed using the offshore system.

In the art, e.g. as marketed by the present applicant, offshore systems for performing subsea wellbore related activities, e.g. involving a riser extending between the vessel and a subsea wellbore, are known.

WO2013/169099 discloses an offshore vessel with a floating hull comprising a moonpool, wherein a tower is positioned on the hull at or near the moonpool. A tubular string main hoisting device comprises a main hoisting winch and a main cable driven by said main hoisting winch, a crown block mounted at the top end of the tower, and a travelling block suspended from the crown block via the main cable. The travelling block is adapted to suspend a tubulars string along a firing line through the moonpool. The known vessel is equipped with a vertically mobile working deck that is positioned above the moonpool and is vertically movable with respect to the drilling tower along the firing line within a motion range including a heave compensation motion range. A heave compensation connection system is provided, which is adapted to connect the working deck to the travelling block, such that the hoisting device can move the working deck when the working deck is connected to the travelling block between a lowered riser assembly position allowing the assembly of a riser string, and in which the working deck is supported by the hull, and a raised heave compensated position, in which the working deck is connected to the travelling block. Heave compensation of the travelling block is provided for by means of heave compensator cylinder(s) having a sheave that acts on the main cable. Due to the connection system, the working deck is then also heave compensated.

WO2016/062812 discloses an offshore vessel with a floating hull comprising a moonpool wherein a tower is positioned on the hull at or near the moonpool. A tubular string main hoisting device comprises a main hoisting winch and a main cable driven by said main hoisting winch, a crown block mounted at the top end of the tower, and a travelling block suspended from the crown block via the main cable. The travelling block is adapted to suspend a tubulars string along a firing line through the moonpool. The known vessel is equipped with a vertically mobile working deck that is positioned above the moonpool and is vertically movable with respect to the drilling tower along the firing line within a motion range including a heave compensation motion range. An integrated heave compensation system is provided which is configured to cause, in operation thereof, a heave compensated motion of the vertically mobile working deck relative to the hull within said heave compensation motion range and a synchronous heave compensated motion of the travelling block in order to obtain synchronous heave compensated motions of the working deck and the travelling block.

US2017/074065 discloses an offshore vessel with a floating hull comprising a moonpool wherein a tower is positioned on the hull at or near the moonpool. A tubular string main hoisting device comprises a main hoisting winch and a main cable driven by said main hoisting winch, a crown block mounted at the top end of the tower, and a travelling block suspended from the crown block via the main cable. The travelling block is adapted to suspend a tubulars string along a firing line through the moonpool. The known vessel is equipped with a vertically mobile working deck that is positioned above the moonpool and is vertically movable with respect to the drilling tower along the firing line within a motion range including a heave compensation motion range. In an embodiment disclosed in US2017/074065 the working deck is suspended directly from a heave compensated crown block, so as to provide heave compensation of both the travelling block and the working deck.

The present invention aims to provide at least an alternative for the prior art solutions.

The present invention also aims to provide a structurally simple solution for integrated heave compensation on the offshore vessel.

The present invention provides an offshore system for performing subsea wellbore related activities, the offshore system comprising a vessel with:

- a floating hull comprising a moonpool;

- a tower positioned on said hull at or near the moonpool;

- a tubular string main hoisting device comprising:

- a main hoisting winch and a main cable driven by said main hoisting winch;

- a crown block;

- a travelling block suspended from said crown block via said main cable, which travelling block is adapted to suspend a tubulars string therefrom along a firing line through said moonpool; - a vertically mobile working deck vertically movable with respect to the tower along the firing line within a motion range including a heave compensation motion range; wherein the crown block is supported via a heave compensating crown block support device relative to the tower, wherein the offshore system comprises a mechanical linkage suspending the vertically mobile working deck directly from the heave compensating crown block support device, so that the heave compensating crown block support device provides, in operation thereof, synchronous heave compensating motions of the crown block, of the travelling block, as well as of the vertically mobile working deck within said heave compensation motion range relative to the hull.

In the inventive system the working deck, and any load thereon, said load e.g. being formed by equipment on the working deck and/or a load suspended from the working deck, e.g. such as a riser and/or a drill string, is suspended directly from the heave compensating crown block support device. Therefore, no extra load is placed on the travelling block and the main cable as done in WO2013/169099, where the working deck is suspended from the travelling block. Also, compared to WO2016/062812, the provision of one or more working deck compensator cylinders between the deck and the hull can be dispensed with. The latter, e.g. allows for enhanced accessibility of the moonpool.

In an embodiment, the mechanical linkage is adjustable in length whilst the working deck is suspended thereby. For example, this length adjustment allowing to raise the working deck from a lower stationary position wherein the working deck is resting on the hull into the heave compensation motion range which lies higher than said lower stationary position. For example, the mechanical linkage comprises a fixed length linkage structure, e.g. of rods, and in addition an extendible and retractable structure, e.g. a cable part with a winch, allowing for the mentioned adjustment of the length.

As preferred, the mechanical linkage is devoid of heave compensation functionality, so in operation of the heave compensating crown block support device the length of the mechanical linkage is kept constant. The mentioned adjustment of the length is, for example, performed with the crown block in stationary, non-heave compensated, position, for example the length being increased to lower the working deck into its stationary lower position supported on the hull.

For example, a minimum length of the mechanical linkage is 25 meters. In an embodiment, the mechanical linkage can be composed of one or more of cable, chain, rigid link, rod, tubular rod, etc.

In an embodiment, the mechanical linkage is composed of mechanical linkage parts that are interconnected in series to make up a desired length of the mechanical linkage. For example, a mechanical linkage comprises linkage parts that are screwed onto one another to make up a desired length of the mechanical linkage. For example, linkage parts are configured to be screwed together using an iron-roughneck device of the system.

For example, the mechanical linkage comprises one or more rods, e.g. tubular rods, e.g. drill pipe like tubular rods interconnectable by screwing to one another.

In an embodiment, the mechanical linkage comprises one or more fibre-reinforced mechanical linkage parts or, for example, (high strength) synthetic fibre rope parts.

In an embodiment, the tower is a mast having a top and a base, the base being fixed on the hull adjacent the moonpool.

In an embodiment, the heave compensating crown block support device comprises a rocker arm frame that is pivotally mounted relative to the top of the tower about a horizontal pivot axis, wherein the heave compensating crown block support device comprises one or more hydraulic compensator cylinders that are mounted between the tower and the rocker arm frame, e.g. engaging on the rocker arm frame at a position intermediate the horizontal pivot axis and the crown block.

In an embodiment, the tower has a front side facing the moonpool and a rear side opposite said front side, wherein the pivot axis is located in proximity of said rear side, and wherein the one or more hydraulic compensator cylinders are mounted in proximity of the front side, e.g. within the mast in proximity of the front side.

In another embodiment, the tower is embodied as a derrick that stands over the moonpool.

In an embodiment, the mobile working deck is provided with an opening therein that is aligned with said firing line, wherein the mobile working deck is provided with a drill string slip device that is configured to suspend a drill string, e.g. including interconnected drill pipe sections, in the firing line. In an embodiment, the vessel further comprises a drilling tubulars storage rack for storage of at least drill pipe sections therein, wherein the drilling tubulars storage rack is mounted on the hull. In an embodiment, as preferred, the vessel further comprises a heave motion compensating pipe racker system comprising at least one pipe racker device that is adapted to move a drill pipe section between the drilling tubulars storage rack and a position wherein the drill pipe section is in the firing line and between the vertically mobile working deck and the travelling block. In an embodiment, the pipe racker system is configured to, in operation thereof, bring a drill pipe section that has been retrieved from the drilling tubulars storage rack into a vertical motion that is synchronous with the heave compensating motion of the mobile working deck and of the slip device provided on the mobile working deck as caused by the heave compensating crown block support device in operation thereof.

In an embodiment, the heave motion compensating pipe racker system comprises one or more vertical elongated support members, on which one or more vertical elongated support members one or more racker assemblies are arranged, e.g. multiple racker assemblies on a common vertical elongated support member, each racker assembly comprising a motion arm and a gripper member held by said motion arm and adapted to grip a drill pipe section, wherein each racker assembly is vertically mobile relative to the associated vertical elongated support member via a vertical drive engaging on said vertical elongated support member, and wherein the one or more vertical elongated support members are suspended from the heave compensating crown block support device so that the heave compensating crown block support device provides, in operation thereof, synchronous heave compensating motions of the crown block, of the travelling block, of the vertically mobile working deck, as well as of the one or more vertical elongated support members of the pipe racker system relative to the hull.

In an embodiment, one or more mechanical linkage parts are configured for vertically oriented storage thereof in a drilling tubulars storage rack of the system.

In an embodiment, it is envisaged that the pipe racker system is used to move the one or more mechanical linkage parts between the drilling tubulars storage rack on the one hand and the operative position of the mechanical linkage. This allows for effective storage and handling of the mechanical linkage, e.g. in particular when the mechanical linkage is composed of one or more rigid parts, e.g. rods, tubular rods, etc. The storage, when not in use, of one or more mechanical linkage parts in the drilling tubulars storage avoids use of precious deck space or the like on the vessel. Handling of the, practically rather lengthy, mechanical linkage parts by the pipe racker system avoids undue efforts and time of personnel on-board the vessel. In embodiments, a mechanical linkage is composed of parts that are screwed onto one another to make up a desired length of the linkage. In embodiments, an iron-roughneck device of the system is applied in said process to make up and/or break up the connection between linkage parts.

In an embodiment, the offshore system further comprises one or more of: a telescopic joint configured for compensating a length of a riser extending between the vessel and a subsea wellbore during a subsea wellbore related activity, the telescopic joint comprising an outer barrel adapted to be connected to a fixed length section of the riser, and an inner barrel movable relative to the outer barrel; a diverter configured to divert a hydrocarbon and/or drilling mud stream flowing up through a riser extending between the vessel and a subsea wellbore during a subsea wellbore related activity; e.g. the inner barrel of the telescopic joint being secured to the diverter via a flexible joint of the system, for example the diverter being configured for mounting thereof to the floating hull at a stationary operable position in the moonpool; e.g. a diverter carrier being provided for the diverter, allowing the diverter to move between the operational position and a moonpool clearance position, a riser tensioning system comprising a tension ring connectable to a fixed length section of the riser or to an outer barrel of a telescopic joint, and tension members connectable to said tension ring and to the floating hull;

In an embodiment, the firing line extends through an opening in the working deck, such that the hoisting device can raise and lower a load, such as a drill string and/or a riser string, through the opening in the working deck.

In an operational modus of an embodiment of the system, the diverter is connected stationary to the floating hull.

The crown block heave motion compensating device may be configured to provide passive heave compensation, active heave compensation, or both.

In an embodiment, in addition to the crown block heave motion compensating device, a heave compensation of the main cable is provided for. This, for example, allows to provide for heave compensation when the crown block, and the working deck, is held stationary. In addition, this may allow for redundancy of the vessel’s heave compensating capabilities. One may also seek to operate one heave compensation system in passive mode and the other in active mode, or one may seek to achieve enhanced responsiveness of the heave compensation by superimposing the two heave compensation system, for example using an active heave compensation of the main cable that is a faster in its response than an active heave compensation of the crown block.

In embodiments, a hydraulic main cable compensator is provided that engages on the one or more main cables and is configured to provide a heave compensated motion of the travelling block. In an alternative, or in combination, one can make use of an active heave compensated main cable winch.

Advantageously, the offshore system can be employed for managed pressure drilling.

For example, the heave compensation system provides a range of between 5 and 15 meters, e.g. of 6 meters.

In an embodiment, the vessel is a mono-hull vessel with the moonpool extending through the design waterline of the vessel. In another embodiment, for example, the vessel is a semi- submersible vessel having submergible pontoons with columns thereon that support an above-waterline deck box structure. The moonpool may then be arranged in the deck box structure.

In an embodiment, the main hoisting device comprises a first main hoisting winch and a second main hoisting winch, wherein the main cable is connected at either end thereof to a respective one of the first and second main hoisting winches. This e.g. allows for redundancy of the winches in the main hoisting device. In such an embodiment, the first heave motion compensation system possibly comprises a first main cable heave compensation sheave in the path between the first main hoisting winch and the travelling block, a first hydraulic compensator connected to said first main cable heave compensation sheave, and a second main cable heave compensation sheave in the path between the second main hoisting winch and a travelling block, a second hydraulic compensator being connected to said second main cable heave compensation sheave.

The working deck may be provided with a rotary table.

A slip device is, preferably, arranged on the vertically mobile working deck. The slip device is adapted to suspend therefrom a drilling tubulars string, e.g. a drill string, along the firing line, e.g. through a riser. In an embodiment, the system comprises a pipe racker system provided with a heave motion synchronisation system adapted to bring a drill pipe section retrieved from a drilling tubulars storage rack into a vertical relative motion that is synchronous with a heave compensating motion of the working deck, thereby allowing to interconnect the drill pipe section to a drill pipe string suspended from a slip device on the working deck.

In an embodiment, the vessel is provided with a drilling tubulars, e.g. drill pipes, storage rack, e.g. a carousel, adapted for storage of drilling tubulars, e.g. at least drill pipes, in vertical orientation therein, the drilling tubulars storage rack being mounted on the hull so as to be subjected to heave motion along with the hull. A pipe racker system is provided that is adapted to move a pipe section between the drilling tubulars storage rack and a position in the firing line between the working deck and the travelling block. A slip device is provided that supports the suspended drill string, e.g. within a riser, when the drill string is disconnected from the travelling block, e.g. from the topdrive, in view of the connection of a new drill pipe to the suspended drill string.

In embodiment, the vessel is provided with an iron roughneck device arranged on the vertically mobile working deck. This e.g. allows the use of the iron roughneck deck for make up or break-up of the threaded connection between drill pipes or other tubular bodies.

In an alternative embodiment, the vessel has an iron roughneck device that is not mounted on the working deck, but is instead independently supported from the hull of the vessel, e.g. vertically mobile along a rail mounted to the tower by means of a vertical drive. The iron roughneck device is then provided with a heave motion vertical drive adapted to move the iron roughneck device in heave motion in synchronicity with the heave motion of the suspended drill string, so that the iron roughneck device can operate whilst in heave motion. For example, as preferred, the iron roughneck device is mounted vertically mobile on a vertical elongated support member that also has mounted thereon one or more motion arms as described herein. As discussed herein, the vertical elongated support member may be coupled to the crown block heave compensation support device to achieve synchronous heave compensated motion of the iron roughneck device.

The heave motion compensating pipe racker system can be used to move drill pipes, e.g. single, double or triple pipe stands, between the drilling tubulars storage rack and the firing line so as to connect a new drill pipe to the pipe string held by the slip device whilst in heave motion. It is envisaged that this may be of great value for managed pressure drilling wherein highly accurate control of borehole pressure is desired.

In an embodiment, the vessel further comprises a driller’s cabin deck and a driller’s cabin thereon. Preferably, the lower stationary position of the working deck is at said driller’s cabin deck level.

The invention also relates to an offshore vessel as described herein.

The invention also relates to a method for performing a subsea wellbore related activity, wherein use is made of an offshore system as described herein.

The invention will now be explained with reference to the drawings. In the drawings:

Fig. 1 shows schematically in vertical cross-section an offshore system according to the invention,

Fig. 2 shows schematically a portion of the vessel with the mast, mobile working deck, as well crown block heave compensating device,

Fig. 3 shows schematically and in a perspective view the mast, crown block heave compensating device, drill pipe storage carousels, pipe racker system of the vessel of figures 1 and 2,

Fig. 4 illustrates the mast of the vessel of figure 1 with the mobile working deck, the mast being provided with vertical elongated support members whereon mobile pipe racker devices and a mobile iron roughneck device are mobile,

Fig. 5 shows schematically in a cross sectional view a riser, a telescopic joint, and the vessel of figure 1 with the working deck lowered onto the hull,

Fig. 6 illustrates schematically the inventive concept applied to a vessel having a derrick.

With reference to the figures 1 - 5 an example of an offshore system for performing subsea wellbore related activities will be discussed.

The system comprises an offshore vessel 1 having a floating hull 2 subjected to heave motion, the hull comprising a moonpool 5, here the moonpool having a fore portion 5a and an aft portion 5b that are forward and aft of a mast 10 respectively. Other arrangements are also envisaged. The hull has a main deck 12 in proximity to the top opening(s) of the moonpool 5.

In another embodiment, for example, the vessel is a semi-submersible vessel having one or more submergible pontoons, possibly an annular pontoon, with columns thereon that support an above-waterline deck box structure. The moonpool may then be arranged in the deck box structure.

The vessel 1 is equipped with a tower 10 at or near the moonpool 5.

In this example, as is preferred, the tower 10 is a mast having a closed outer wall and having a top and a base. The base of the mast 10 is secured to the hull 2, e.g. to the main deck 12 of the hull 2.

In this example, the mast 10 is mounted above the moonpool 5 with the base spanning the moonpool 5 in a transverse direction.

In another embodiment, illustrated in figure 6, the tower 10 can be embodied as a derrick, e.g. with a latticed derrick frame standing over the moonpool 5.

The vessel 1 is provided with a tubular string main hoisting device, here operative at the side of the moonpool portion 5a relative to the tower/mast 10, the tubular string for example being a drill pipe string of pipe sections 15.

As known in the art, a second firing line at the opposite side of the mast 10, associated with moonpool portion 5b, and associated hoisting device may allow for assembly and disassembly of a riser string. A moonpool cart, not shown, may be present to allow for displacement of a riser string between the firing lines. It will be appreciated that the present invention is equally applicable to vessels having a single firing line.

The shown configuration of the main hoisting device comprises: a main hoisting winch 20 (in figure 6 first and second main hoisting winches 20, 21), and a main cable 22 that is driven by the one or more main hoisting winches 20, 21, a crown block 23, a travelling block 24 that is suspended from the crown block 23, here in a multiple fall arrangement, by the main cable 22.

In an embodiment, one or more main cable sheaves connected to the travelling block 24 have an individual lower latching device allowing to connect and disconnect the individual sheave to and from the travelling block 24. Preferably, these one or more sheaves also have an upper latching device allowing to latch the sheave to the crown block if the sheave is disconnected from the travelling block. This “splittable block” arrangement is known in the art. The travelling block 24 is adapted to suspend a tubular string, e.g. the drill string of sections 15, therefrom along a firing line 16, here shown (as preferred) with an intermediate topdrive 18 that is supported by the travelling block 24 and that is adapted to provide a rotary drive for the drill string.

A vertically mobile working deck 70 is movable along the firing line 16 within a motion range including a heave compensation motion range 72.

The range 72 lies higher than the deck 12.

For example, as preferred, the working deck 70 is vertically guided along one or more guide rails 73 mounted along the tower 10, e.g. at the front side 10a of the mast 10, in a trajectory in vertical projection above the moonpool.

As preferred, the travelling block 24 is combined with a trolley that travels along on or more vertical rails along the tower, e.g. along rails 73. The trolley may also support, or assist in the support of, a topdrive 18.

The crown block 23 is supported via a heave compensating crown block support device 40 on the tower 10, preferably on the top of the tower, e.g. the top of the mast 10.

The offshore system comprises a mechanical linkage 45 suspending the vertically mobile working deck 70 directly from the heave compensating crown block support device 40, so that the heave compensating crown block support device provides, in operation thereof, synchronous heave compensating motions of the crown block 23, of the travelling block 24 suspended via cable 22, as well as of the vertically mobile working deck 70 within said heave compensation motion range relative to the hull 2.

For example, a pair a mechanical linkage members 45 extends on opposite sides of the working deck, e.g. in a vertical plane encompassing the firing line 16.

For example, the mechanical linkage includes a pair of cables 45, rods, tubular rods, etc.

In an embodiment, the mechanical linkage 45 is adjustable in length whilst the working deck 70 is suspended thereby from the crown block support device 40. This allows, for example, the adjust the general position of the working deck 70, e.g. relative to deck 12, and/or to adjust the height of the space above the working deck, e.g. in view of the height of equipment to be arranged on the working deck.

For example, coiled tubing equipment is to be placed on the working deck 70, for performing a coiled tubing activity.

For example, the adjustability of the length of the mechanical linkage whilst supporting the deck 70 allows to raise the working deck 70 from a lower stationary position wherein the working deck is resting on the hull (see e.g. figure 5) into the heave compensation motion range 72 which lies higher than this lower stationary position 71. The lower stationary position may, for example, be flush with a deck area 12 adjoining the top of the moonpool, but could also, in embodiments, be at another height relative to the top of the moonpool. For example, the lower stationary position could be lower that said moonpool top opening or higher.

In the figure 2, it is illustrated that the working deck 70 is in a heave compensation motion range that lies higher than the lower stationary position of the deck 70 which is shown in figure 5.

In the heave compensation motion range the working deck 70 can perform heave compensation motion relative to the hull of the vessel. For example, the heave compensation motion range is between 5 and 10 meters, e.g. 6 meters.

As shown, in an embodiment, the heave compensating crown block support device 40 comprises a rocker arm frame 41 that is pivotally mounted relative to the top of the mast about a horizontal pivot axis 42. The rocker arm frame 41 supports the one or more sheaves of the crown block 23. The frame 41 can basically rock up and down to cause the heave compensating motion over a generally vertical stroke. The frame 41 is supported by one or more hydraulic compensator cylinders 43 that are mounted between the mast 10 and the rocker arm frame 41, e.g. at the top of the mast 10, e.g. within a top interior portion of the mast. The one or more cylinders 43 here engage on the rocker arm frame at a position intermediate the horizontal pivot axis 42 and the crown block 23.

It is shown that a guide sheave 26 for the main cable 22 is mounted on the axis 42 so that the length of the cable path between the winch 20 and the crown block 23 is not affected by the rocking motion of the arm frame 41. In figure 2 reference numeral 23’ is indicative of a lower position of the crown block 23 during heave compensation mode. It is shown that the tower 10 has a front side 10a facing the moonpool 5 and a rear side 10b opposite said front side. The pivot axis 42 is located in proximity of the rear side 10b. The one or more hydraulic compensator cylinders 43 are mounted in proximity of the front side 10a, here within the mast 10 in proximity of the front side.

Instead of a rocker arm frame, also a merely vertically mobile support frame supporting the sheaves of the crown block 23 could be employed. Articulated support frames for the crown block are also envisaged within the scope of the inventive concept.

The mobile working deck 70 is provided with an opening 75 therein that is aligned with the firing line 16.

The mobile working deck 70 is provided with a drill string slip device 77 that is configured to suspend a drill string, e.g. including interconnected drill pipe sections 15, in the firing line 16, e.g. within a riser 19 extending between the vessel 1 and a subsea wellbore.

Figure 3 illustrates the presence on the vessel 1 of one or more drilling tubulars storage rack 110, 111 for vertical storage of drill pipe sections 15 therein, e.g. multiple jointed stands of drill pipe sections. The one or more drilling tubulars storage racks are mounted on the hull 2 and subject to the heave motion induced by waves. For example, as shown, the racks are embodied as carousels.

The vessel 1 further comprises a heave motion compensating pipe racker system comprising at least one pipe racker device that is adapted to move a drill pipe section 15 between the drilling tubulars storage rack 110, 111 and a position wherein the drill pipe section is in the firing line 16 and between the vertically mobile working deck 70 and the travelling block 24.

The pipe racker system is configured to, in operation thereof, bring a drill pipe section 15 that has been retrieved from the drill pipe storage rack 110, 111 into a vertical motion that is synchronous with the heave compensating motion of the mobile working deck 70 and of the drill string slip device 77 provided on the mobile working deck 70 as caused by the heave compensating crown block support device 40 in operation thereof.

In more detail, it is illustrated that the heave motion compensating pipe racker system comprises one or more vertical elongated support members 145, 145’ on which one or more racker assemblies 141, 14T, 142, 142’, are arranged, e.g. multiple racker assemblies on a common vertical elongated support member. Each racker assembly 141, 141’, 142, 142’ comprises a motion arm and a gripper member adapted to grip a drill pipe section 15. Each racker assembly is vertically mobile relative to the associated vertical elongated support member 145, 145’ via a vertical drive engaging on the member, e.g. the vertical elongated support member having teeth, e.g. like a toothed rack, and the drive having a pinion or the like allowing the racker assembly to be moved up and down along the member. For example, each drive of a racker assembly is operable independent from other racker assemblies of the system.

Figures 2 and 3 illustrate that the one or more vertical elongated support members 145, 145’ are suspended from the heave compensating crown block support device 40 so that the heave compensating crown block support device provides, in operation thereof, synchronous heave compensating motions of the crown block 23, of the travelling block 24, of the vertically mobile working deck 70, as well as of the one or more vertical elongated support members 145, 145’ of the pipe racker system relative to the hull. It may be that the effective stroke of the one or more vertical elongated support members 145, 145’ is not the same as that of the crown block sheaves. In such an embodiment, the vertical drives of the racker assemblies may be employed to achieve synchronicity.

The lower assembly 143, 143’ on at least one of the elongated support members 145, 145’ carries an iron roughneck device 150, 150’ that may be employed in make up or breaking up a connection between a drill string held by the slip device 77 and a pipe section 15 that is to be connected thereto or released therefrom.

In fig. 4 the assembly of a drill string using drill pipe sections 15 is illustrated, which assembly can be done whilst the working deck 70 and the slip device 77 holding the already assembled part of the drill string are being heave compensated as described herein.

The pipe racker system is provided with a heave motion synchronization system that brings the drill pipe section 15 that has been retrieved from a drilling tubulars storage rack 110 or 111 into a vertical motion that is synchronous with the heave motion of the upper end of the drill string held by slip device 77, thereby allowing the interconnect the drill pipe 15 to a drill pipe string suspended from the slip device 77, e.g. using iron roughneck 150 or 150’.

In fig. 4, racker assemblies 143 and 143’ and 141 and 14T are visible, wherein racker assembly 14T grips the drill pipe 15. The slip device 77 on the working deck 70 holds the drill string in the firing line. As shown best in figure 5, the vessel is furthermore provided with a riser tensioning system that is adapted to connect to a riser 19 extending along the firing line 16 between a subsea wellbore, e.g. a BOP on the subsea wellhead, and the vessel 1. The riser tensioning system comprises a tension ring 60 and tensioner members 61 connected to the tension ring 60. In the depicted example a wire line tensioning system is shown, with the members 61 being wires that run from the ring 60 upward to sheaves 62 and then to a tensioning arrangement, e.g. including cylinders 63 and a gas buffer.

The drawings further show the presence of a telescopic joint 50 having a lower outer telescopic joint barrel 51 and an upper inner telescopic joint barrel 52. As is known in the art the outer barrel 51 is adapted to be connected at its lower end, e.g. via bolts, to a fixed length section of the riser 19 extending to the seabed. As is known in the art and not shown in detail here the telescopic joint is provided with a locking mechanism 53, e.g. including hydraulically activated locking dogs, which is adapted to lock the telescopic joint in a collapsed position. As explained in the introduction the telescopic joint has a higher pressure rating when collapsed and locked that in dynamic stroking mode, e.g. as the locked position includes an operative metal-to-metal seal in the telescopic joint.

As is known in the art the tension ring 60 of the riser tensioning system is adapted to be connected to the outer barrel 51 of the telescopic joint 50, thereby allowing to absorb the effective weight of the riser.

In fig. 5, a diverter 55 is shown, configured to divert a hydrocarbon and/or drilling mud stream flowing up through the riser; wherein the inner barrel 52 of the telescopic joint is secured to the diverter. According to the invention, the diverter 55 is connected stationary to the floating hull. The upper inner barrel 52 is secured to the diverter 55 via a flex joint, not shown in this drawing.

Figure 5 illustrates that the working deck 70 is in its lower stationary position, wherein the working deck is used as a drill floor deck stationary with respect to the hull of the vessel. This position of the working deck 70 is also called a regular position of the working deck in which the working deck 70 is aligned with main deck 12 of the hull in proximity of the moonpool.

The diverter 55 is connected stationary to the floating hull, and is provided right below the working deck 70, in particular below the slip device 77 on said deck 70.