WO2020208092A1

WO2020208092A1 - A heave compensating system for a floating drilling vessel

Info

Publication number: WO2020208092A1
Application number: PCT/EP2020/060063
Authority: WO
Inventors: Rune STANGHELLE; Håkon KLEPSVIK; Thomas BORSHOLM; Per Lund
Original assignee: Odfjell Drilling As
Priority date: 2019-04-10
Filing date: 2020-04-08
Publication date: 2020-10-15
Also published as: GB202114536D0; CA3136399A1; ZA202108011B; GB2596492B; GB2596492A; NO20190492A1; NO345357B1

Abstract

The present invention is directed to a heave compensating system for a floating drilling vessel. The system comprises: - a rig floor of the floating drilling vessel, - a drilling riser attached to a well via a wellhead, - a tubular extending through an opening of the rig floor, - a slips for holding the tubular, - a top drive and/or an elevator for holding the tubular at an upper end, - a telescopic joint comprising an outer barrel and an inner barrel, wherein the outer barrel is connected to a wellhead, and the inner barrel is telescopically arranged inside the outer barrel, - a riser tensioning system arranged between the drilling riser and the floating drilling vessel, wherein the heave compensating system comprises a draw work heave compensating system arranged between the top drive and/or elevator and the rig floor, and a slips heave compensating system for heave compensation of the slips, wherein the heave compensating systems may be synchronized, compensating for the floating drilling vessel's heave movement.

Description

A HEAVE COMPENSATING SYSTEM FOR A FLOATING DRILLING VESSEL

The invention is related to a heave compensating system for a floating drilling vessel.

BACKGROUND

Heave movement is a limiting factor for drilling operations from all types of floating drilling vessels, including drilling barges, drillships and semi submersible drilling rigs. Drilling operations in harsh environment like the high latitude and high current areas are mostly exposed to this challenge due to the higher occurrence of larger waves imposing a larger heave for the drilling vessel.

Without heave compensating systems, the heave motion will be imposed onto the drill string and make it impossible to control the weight on the drill bit. This may cause damage to the drill bit and the drill string. Another challenge is that the vertical movement in the drill string causes swab and surge in the well, which again can lead to collapse, fracture or instability of the wellbore and surrounding formation. Similar problems with swab and surge will be relevant when running casing and production tubing.

Accurate heave compensation is also important when landing equipment like blowout preventer (BOP) and riser onto the wellhead.

Systems for heave compensation of the drill string on rigs have existed for decades, however for most rigs passive compensators are used. These can be“in line compensators” or“crown block top compensators”, both which are based on gas springs installed either in line or on the top of the derrick. The main function of a passive compensation system is to keep constant tension in the drill line wire that is holding the main block and the tubular.

Thus, passive heave compensation systems can only give meaningful compensation when the compensated tubular is fixed to, or landed on, a bottom, e.g. when the bit is on bottom.

Active Heave Compensation (AHC) differs from Passive Heave Compensation (PHC) by having a control system that actively pulls or eases on the drill line to compensate for a measured movement at a specific point.

The heave compensating systems on floating drilling vessels today have limitations since they are not able to compensate the string in all operational modes and operations. Very often, drilling operations are postponed in waiting for better weather conditions. During some winter seasons and drilling operation in harsh environment location, the total time spent in waiting for better weather conditions can amount to as much as 20% of the total time spent on the well.

It is therefore an objective of the present invention to provide a solution for heave compensation of a floating drilling vessel that significantly reduce the operational limitations related to weather in harsh weather conditions.

SUMMARY OF THE INVENTION

The present invention is directed to a heave compensating system for a floating drilling vessel. The system comprises:

a rig floor of the floating drilling vessel,

a drilling riser attached to a well via a wellhead,

a tubular extending through an opening of the rig floor,

a slips for holding the tubular,

- a top drive and/or an elevator for holding the tubular at an upper end,

a telescopic joint comprising an outer barrel and an inner barrel, wherein the outer barrel is connected to a wellhead, and the inner barrel is telescopically arranged inside the outer barrel,

a riser tensioning system arranged between the drilling riser and the floating drilling vessel,

wherein the heave compensating system comprises a draw work heave

compensating system arranged between the top drive and/or elevator and the rig floor, and a slips heave compensating system for heave compensation of the slips, wherein the heave compensating systems may be synchronized, compensating for the floating drilling vessel’s heave movement.

The slips compensating system may be arranged between the slips and the rig floor.

The term tubular is a generic term pertaining to any type of oilfield pipe, such as drill pipe, drill collars, pup joints, casing, liner and production tubing.

A rotary table may be installed in the well center on the rig floor and is a rotating device for orienting drill pipe and tubular run from the rig. The rotary table has an open center with space for a master bushing with various insert bowls, which help to set various slip configurations to handle drill pipe, casing, and drill collars.

An iron roughneck/power tong or a casing tong may be installed on top of the slips on the rig floor to make up and break out tubular connections. The top drive is a mechanical device on a drilling rig that provides clockwise torque to the drill string to drill a borehole. It is located below the traveling block and moves vertically up and down the derrick. The top drive may be arranged for holding the upper end of the tubular.

An elevator mechanism may be closed around the tubulars to facilitate lowering them into the wellbore or lifting them out of the wellbore. The elevator may be arranged for holding the upper end of the tubular and may be attached to the top drive.

A draw-work is the primary hoisting machinery component of a rotary drilling rig. Its main function is to provide a means of raising and lowering the traveling block. The wire-rope drill line winds on the draw-work drum and over the crown block to the traveling block, allowing the drill string to be moved up and down as the drum turns. Some drilling rigs have dual draw-works, where one draw-work can pull or release the drill line from either end of the drill line. The hoisting and lowering of the top drive/drill string may also be done by hydraulic cylinders.

The draw-work heave compensating system may comprise one or more draw-work.

The slips heave compensating system may comprise a stroking arrangement, wherein a load from the tubular is held in the slips and transferred further to a tensioning means.

The slips and an iron roughneck or casing tong may be located on top of the stroking arrangement.

The stroking arrangement of the heave compensating system may comprise the inner barrel moving inside the outer barrel, and wherein the tensioning means may be connected between the rig floor and the inner barrel. The tensioning means comprises wire ropes, sheaves and wire winches.

The telescopic joint comprises the inner barrel telescopically arranged inside the outer barrel, wherein the outer barrel is connected to a wellhead via a drilling riser and a blowout preventer, and the inner barrel is connectable to the slips.

The inner barrel may be connectable to the slips via a flex joint and an inner barrel extension. The inner barrel extension may extend the inner barrel upwards to the rig floor and may slide vertically inside the inner barrel extension guides installed in the rig floor, wherein at least a section of the inner barrel is moveable through the opening of the rig floor. The iron roughneck or casing tong may be retractable to allow the top drive to drill or run the full stand. This means that top drive/elevator can run connection down to a height where the iron roughneck can grab connection and couple it together with next tubular. The iron roughneck or casing tong may thus operate on rails such that it may be retractable from the well and freeing up space for the top drive.

A riser flow diverter may be arranged below a riser tension ring for allowing diverting flow from the well away from the rig floor.

Flow lines for mud return, riser fill and trip tank fill may be attached to the riser flow diverter.

The stroking arrangement may comprise an outer guide that guides a stroking structure connected to the slips, wherein a riser spacer is arranged to allow the stroking structure to move vertically inside the drilling riser.

The stroking arrangement may be located in the master bushing / rotary bushing location in the rotary table and extends inside the flow diverter housing and a new riser spacer between the flow diverter housing and the flex joint in the riser system.

The stroking arrangement may comprise an outer guide that guides a stroking structure. The lower end of the stroking structure may be located above the flex joint and the slips and iron roughneck / casing tong is landed on top of the stroking structure. A riser spacer may be added between the flow diverter and the flex joint to allow the stroking structure to move vertically inside the riser above the flex joint, thus avoiding conflict with the inner wall of the riser when the flex joint is angled.

The stroking arrangement may have a heave compensating system for hoisting and lowering the inner structure and thus hoisting and lowering the slips and iron roughneck / casing tong. The load from the tubular may be held in the slips and transferred further to a tensioning means. The top of the inner structure may have a platform for personnel access to the well center and may have access to the platform from a telescopic access gangway.

The advantage of this embodiment is that it reduces the amount of equipment that are compensated, and it involves less changes on the riser system.

The tensioning means may comprise at least any one of: hydraulic cylinders, wire winches, tension ring, wire rope and sheaves.

The tensioning means may comprise hydraulic cylinders, wire rope and sheaves. The stroking structure may be located in a master bushing / rotary bushing location in a rotary table and extends inside a flow diverter housing and the riser spacer between a flow diverter housing and a flex joint, wherein a lower end of the stroking structure is located above the flex joint.

The heave compensating system, in operation, at least one of the draw work compensating system and/or the slips heave compensating system may be active or inactive.

In operation, the draw work heave compensating system and/or the slips heave compensating system may run in different modes depending on the operational modes of the floating drilling vessel. For example, the heave compensating modes may be; in operation, inactive, passive, constant tension, etc. The operational modes of the floating drilling vessel may be; connection, trip and drill a stand, pipe handling, etc.

The one or more draw works may comprise AHC (active heave compensation) systems.

The draw work heave compensating system and/or the slips heave compensating systems of the present invention may be AHC (active heave compensating) systems.

The Active Heave Compensating systems are real time systems that may actively pull or ease the drill line based on the measured movement at a certain location.

This movement may be measured by electronic sensors like accelerometers, magnetometers, gyroscopes and barometers. Combined, these sensors are often referred to as Motion Reference Units (MRUs). The measured movement is used as input to a computer algorithm, or model representing the physical properties of the heave compensating system. This physical model may include inertia, friction and flexibility of the wire and pulley system as well as the characteristics of the winch or hydraulic cylinders. The computer model is used to calculate the action required to counteract for the movement in order to keep the top drive and/or elevator vertically in the same position when the floating drilling vessel moves up and down.

The computer model may be incorporated into an AHC control system that operates the draw-works, winches or hydraulic cylinders, that pulls and eases on the drill wire. The control system may be used to put the AHC system into different modes such as active, inactive, constant tension or looked to bottom mode. One or more control systems may operate the AHC systems. They may be individual systems controlled and synchronized by a main control system. Each AHC system may have different modes such that they may be connected, disconnected and/or actively controlled for different operational modes of the vessel.

The slips heave compensating system may be an inner barrel heave compensating system or a stroking structure heave compensating system.

The slips heave compensating system may be an Active Heave Compensation system. This AHC system may be electronically synchronized with the draw-work heave AHC system so that both top drive and/or elevator and slips are fully synchronized and compensated for the floating drilling vessel’s heave movement. This will ensure that the distance between the top drive and/or elevator and the slips may be kept the same when this is required.

The slips AHC system and the draw-work AHC system may have independent MRUs. One control system may be used as“master” and the other control system may be used as“slave”. A third control system may also be used on top of the two AHC control systems, orchestrating the synchronization. A control loop with one or more algorithms correcting for the two systems potentially drifting apart may be included in one or more of the control systems.

The heave compensating system of the present invention provides the following advantages:

- Reduce swab and surge while tubulars are“in slips” - for increased operability in harsh environment.

- Maintaining operational efficiency when operating without compensated slips/rig floor.

- No need for a large modification of the existing rig floor.

- Can drill without a pup joint or raised backup tong (like on a fixed platform) - which simplifies drilling connections.

- Saves time in testing and rigging of the riser flow diverter.

Furthermore, the draw-work AHC system work directly on the draw-works and can also compensate while tripping and with the drill string free hanging. None of the existing solutions can compensate whilst the tubular is set in the slips. The present invention provides a solution for heave compensation of a floating drilling vessel that significantly reduce the operational limitations related to weather in harsh weather conditions.

In the following, some operational modes of the floating drilling vessel are described together with the operational modes of the hive compensated system. Event thought the exemplary embodiments described below are directed to the inner barrel heave compensating of the slips, the operational modes are also relevant and applicable to the stroking structure heave compensating system of the slips.

In a“connection” mode of the floating drilling vessel, the inner barrel and the slips may be lifted and lowered by the slips heave compensating system in such a way that the slips maintains the same vertical distance to the wellhead, while the floating drilling vessels rig floor moves up and down with the vessel heave. The inner barrel may thus be fixed in the outer barrel and in relation to the wellhead. This is achieved without transferring the tubular string weight via the riser system down to the wellhead, which can overload the wellhead and reduce the wellhead fatigue life. The slips heave compensating system may be electronically synchronized with the draw work heave compensating system so that both top drive and/or elevator and slips are fully synchronized and compensated for the floating drilling vessel’s heave movement. This will allow connection or disconnection of new sections of drill pipe to the handing drill pipe string without swabbing and surging the well.

In a“trip and drill a stand” mode of the floating drilling vessel, the draw-works may be compensated so that the tubular is always relative to earth/well. The inner barrel extension may be locked to the rig floor and the inner barrel slides on the outer barrel in the telescopic joint. The inner barrel heave compensating system may be inactive or run in passive mode. However, when tripping into or out of the well the inner barrel heave compensating system may also be active because of short time between each time the string is set in slips.

In a“pipe handling” mode of the floating drilling vessel, the draw-works may not be compensated so that sections (stands) of tubulars can be moved between the pipe handler and the top drive and/or elevator. The inner barrel extension may be compensated to keep the tubular in the well in a fixed vertical position relative to the wellhead to avoid swab and surge.

The system of the present invention may require a new access platform around the well center on top of the inner barrels extension, a bridge that may be telescopic for transport of personnel between the rig floor and the access platform, a new torque wrench for make/break of tubulars that may be possible to retract from the well center to allow access for the top drive to drill down the whole stand, a new stabbing guide installed on top of the compensated slips, as well as rerouting of the mud return, riser fill and trip tank fill lines. The system of the present invention may also require a suction tank and low return pump with control system to maintain the riser fill and trip tank functions.

The riser flow diverter may be relocated and mounted below the slip joint / outer barrel and diverted flow like shallow gas may be routed out underneath the rig.

This may simplify the handling of large hoses underneath the rig. The riser flow diverter may also be removed to make installation and operation of the riser simpler.

The mud return-, riser fill- and trip tank fill lines may be relocated to the inner barrel tension ring in order to free up space for the inner barrel extension under the rig floor and rotary table.

FIGURES

The description above, as well as further objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of the preferred embodiment which should be read in conjunction with the accompanying drawings in which:

Fig. 1 shows a drilling system according to the present invention comprising an inner barrel heave compensating system.

Fig. 2 shows a stroking structure heave compensating system.

Figs. 3 A-C shows a drilling system according to the present invention in a“trip and drill a stand” mode

Figs. 4 A-C shows a drilling system according to the present invention in a

“connection” mode

Figs. 5 A-C shows a drilling system according to the present invention in a“pipe handling” mode DETAILED DESCRIPTION OF FIGURES

Fig. 1 shows a simplified side representation heave compensating system for a floating drilling vessel, according to the present invention. The heave compensating system comprises a draw work heave compensating system 18 arranged between the top drive 19 and/or elevator and the rig floor 14, and a slips compensating system 30 comprising an inner barrel heave compensating system 25 arranged between the rig floor 14 and the inner barrel 8 for heave compensation of the slips 16.

The drilling system comprises drilling riser 2 attached to the well 3 in a seabed 4 via a wellhead 5 and a blowout preventer (BOP) 6. On top of the riser there is a telescopic joint comprising of a slip joint outer barrel 7 and a slip joint inner barrel 8 sliding inside the outer barrel, allowing the floating drilling vessel to move vertically with the varying sea levels 9.

The mass of the riser is supported vertically by a riser tensioner system 10 which are attached the drilling riser 2 in a riser tension ring 11.

A flex joint 12 allows the drilling riser to flex when the floating drilling vessel moves horizontally outside the lateral well center.

A riser flow diverter 13 may be arranged below the riser tension ring 1 1 and allows diverting flow from the well, for example shallow gas, away from the rig floor 14. Flow lines for mud return, riser fill and trip tank fill may also be attached to the riser flow diverter housing 13.

Kill and choke lines 15 connects the BOP 6 to the floating drilling vessel via pipes attached to the drilling riser and flexible lines from the riser tensioning ring 11 to the drilling fluid system (not shown).

A rotary table and slips 16 are installed for rotating and hanging off the drill string 17 in the rig floor 14. The tubular 17 can be hoisted in and out of the well with a draw work 18 and rotated using a top drive 19. The tubular can also be hoisted in and out of the well using an elevator (not shown) hanging underneath the top drive 19.

The system comprises an active heave compensated draw work 18 that compensates for vertical heave movement of the floating drilling vessel as detected by an electronic motion recording unit (MRU, not shown), thus keeping the tubular in a fixed vertical relative position to the well when the active heave compensation system is used. A pipe handler 20 may move stands of several tubular joints 21 in and out of the well center where an iron roughneck or casing tong 22 makes up and breaks out connections. The iron roughneck or casing tong may be installed on rails on the rig floor to allow it to move in and out of the well center.

Fig. 1 shows a drilling system according to the present invention on a floating drilling vessel, in a neutral or mid heave position level 4, according to the height of the rig floor above the mean sea level. The system may comprise an inner barrel extension 23 included as a vertical upper prolongation of the slip joint inner barrel 8 and may replace the rotary table. Inner barrel extension guides 24 may be included in the rig floor structure, allowing the inner barrel to slide vertically with low friction. The iron roughneck or casing tong 22 may be installed on top of the inner barrel structure. The heave compensating system further comprises an inner barrel compensation system 25, which has active heave compensation that may be synchronized with the active heave compensation system for the draw work.

The lines for mud return, riser fill and trip tank fill 27 may be attached to the inner barrel tension ring 26.

In operation, at least one of the draw work compensating system 18 and/or the inner barrel compensating system 25 may be active or inactive.

Fig. 2 shows another embodiment of the invention comprising a riser spacer 28, a stroking structure 29, a stroking structure tension ring 31, the slips 16 and iron roughneck 22, wire sheaves 32 and tension means 33.

The stroking arrangement comprises an outer guide that guides a stroking structure 29. The lower end of the stroking structure 29 may be located above the flex joint 12 and the slips 16 and iron roughneck / casing tong 22 is landed on top of the stroking structure 29. A riser spacer 28 is added between the flow diverter 13 and the flex joint 12 to allow the stroking structure 29 to move vertically inside the riser 2 above the flex joint 12, thus avoiding conflict with the inner wall of the riser 2 when the flex joint 12 is angled.

The stroking arrangement may comprise a stroking structure heave compensating system 35 for hoisting and lowering the inner structure and thus hoisting and lowering the slips 16 and iron roughneck / casing tong 22. The load from the tubular 17 may be held in the slips and transferred further to a tensioning means. The top of the inner structure may have a platform for personnel access to the well center and may have access to the platform from a telescopic access gangway.

The advantage of this embodiment is that it reduces the amount of equipment that are compensated, and it involves less changes on the riser system. The tensioning means 33 may comprise at least any one of: hydraulic cylinders, wire winches, tension ring, wire rope and sheaves.

The stroking structure 29 may be located in a master bushing / rotary bushing location in a rotary table and extends inside a flow diverter housing and the riser spacer 28 between a flow diverter housing and a flex joint 12, wherein a lower end of the stroking structure 29 is located above the flex joint 12.

Figs. 3 A-C shows the present invention on a floating drilling vessel in a“trip and drill a stand” mode, in neutral heave position (fig. 3A), upper heave position (fig. 3 B) and lower heave position (fig. 3 C). In this mode the draw work compensation is activate and the slips (inner barrel) compensation is inactivate. The inner barrel may in this mode be locked to the rig floor deck structure. This mode allows the present invention to be operated as a conventional drilling rig with active heave

compensation while tripping pipe in and out of the well and while drilling, maintaining full efficiency on the rig floor.

Figs. 4 A-C shows the present invention on a floating drilling vessel in a

“connection” mode, in neutral heave position (fig. 4A), upper heave position (fig. 4B) and lower heave position (fig. 4C). In this mode, both draw work compensation 18 and slips compensation 25 are active and synchronized to ensure that the distance between the top drive 19 and the slips 16 is the same in all positions. This mode allows a pipe stand 21 to be connected or disconnected by the iron roughneck or casing tong without the tubular moving vertically in the well.

Fig. 5 A-C shows the present invention on a floating drilling vessel in a“pipe handling” mode, in neutral heave position (fig. 5A), upper heave position (fig. 5B) and lower heave position (fig. 5C). In this mode, the draw work compensation 18 is inactive or locked and the slips compensation 25 is active. This mode allows a new pipe stand 21 to be handled by the pipe handler 20 to and from the top drive 90 or elevator, without the tubular set in the slips 16 is moving vertically in the well.

Reference number Description

1 Seabed

2 Drilling riser

3 Well

4 Neutral heave level

5 Wellhead

6 BOP

7 Telescopic (slip) joint outer barrel

8 Telescopic (slip) joint inner barrel Sea level

Riser tensioner system

Riser tension ring

Flex joint

Riser flow diverter (housing)

Rig floor

Kill and choke lines

Rotary table and slips

Tubular (drill string, landing string, casing, production tubing)

Draw work heave compensating system

Top drive

Pipe handler

Drill pipe stand

Iron rouchneck/torque wrench/casing tong

Inner barrel extension

Inner barrel extension guides

Inner barrel heave compensating system

Inner barrel tension ring

Lines for mud return, riser fill and trip tank

Riser Spacer

Stroking structure

Slips heave compensating system

Stroking structure tension ring

Wire sheave

Tension means

Stroking structure heave compensating system

Claims

1. A heave compensating system for a floating drilling vessel

comprising:

a rig floor (14) of the floating drilling vessel,

a drilling riser (2) attached to a well (3) via a wellhead (5), a tubular (17) extending through an opening of the rig floor (14), a slips (16) for holding the tubular (17),

a top drive (19) and/or an elevator for holding the tubular (17) at an upper end,

a telescopic joint comprising an outer barrel (7) and an inner barrel (8), wherein the outer barrel (7) is connected to a wellhead (5), and the inner barrel (8) is telescopically arranged inside the outer barrel (7),

a riser tensioning system (10) arranged between the drilling riser (2) and the floating drilling vessel,

wherein the heave compensating system comprises a draw work heave compensating system (18) arranged between the top drive (19) and/or elevator and the rig floor (14), and a slips heave compensating system (25) for heave compensation of the slips (16), wherein the heave compensating systems may be synchronized, compensating for the floating drilling vessel’s heave movement.

2. The heave compensating system according to claim 1, wherein the slips heave compensating system comprises a stroking arrangement, wherein a load from the tubular is held in the slips and transferred further to a tensioning means.

3. The heave compensating system according to claim 2, wherein the slips and an iron roughneck or casing tong (22) is located on top of the stroking arrangement.

4. The heave compensating system according to claim 2 or 3, wherein the

stroking arrangement is the inner barrel (8) moving inside the outer barrel (7), and wherein the tensioning means is connected between the rig floor (8) and the inner barrel (8).

5. The heave compensating system according to claim 4, wherein the tensioning means comprises wire ropes, sheaves and wire winches.

6. The heave compensating system according to any one of the preceding claims, wherein the inner barrel (8) is connected to the slips (16) via a flex joint (12) and an inner barrel extension (23) which extends the inner barrel (8) upwards to the rig floor (14).

7. The heave compensating system according to any one of the preceding

claims, wherein an iron roughneck or casing tong (22) is retractable to allow the top drive (19) to drill or run the full stand.

8. The heave compensating system according to any one of the preceding

claims, wherein a riser flow diverter (13) is arranged below a riser tension ring (11) for allowing diverting flow from the well away from the rig floor (14).

9. The heave compensating system according to claim 8, wherein flow lines for mud return, riser fill and trip tank fill are attached to the riser flow diverter (13).

10. The heave compensating system according to claim 2 or 3, wherein the

stroking arrangement comprises an outer guide that guides a stroking structure connected to the slips (16), wherein a riser spacer is arranged to allow the stroking structure to move vertically inside the drilling riser (2).

11. The heave compensating system according to claim 10, wherein the

tensioning means comprises hydraulic cylinders, wire rope and sheaves.

12. The heave compensating system according to claim 10 or 11, wherein the stroking structure is located in a master bushing / rotary bushing location in a rotary table and extends inside a flow diverter housing and the riser spacer between a flow diverter housing and a flex joint.

13. The heave compensating system according to any one of claim 10-12,

wherein a lower end of the stroking structure is located above the flex joint.

14. The heave compensating system according to any one of the preceding

claims, wherein the draw work heave compensating system (18) and/or the slips compensating system (25) are Active Heave Compensating (AHC) systems.

15. The heave compensating system according to claim 14, wherein the slips heave compensating system (25) is electronically synchronized with the draw work heave compensating system (18) so that both top drive and/or elevator and slips (16) are fully synchronized and compensated for the floating drilling vessel’s heave movement.

16. The heave compensating system according to claim 14 or 15, wherein the system comprises one or more control systems for controlling the AHC systems.

17. The heave compensating system according to claim 16, wherein a main control system controls the one or more control systems for synchronizing the system for different operational modes of the floating drilling vessel.

18. The heave compensating system according to any one of the preceding claims, wherein in operation, at least one of the draw work heave compensating system (18) and/or the slips heave compensating system (25) is active or inactive.