Heave compensation

Abstract

A method of performing heave compensation on a floating vessel (10), the method comprising: measuring a total heave value (b) of the floating vessel (10); and applying active heave compensation by means of a hoisting heave compensation system (20) and a hydraulic heave compensation system (30) according to a control process (100), wherein the control process (100) comprises: providing a first input control signal (110) to the hydraulic heave compensation system (30) and a second input control signal (120) to the hoisting heave compensation system (20), the first and second input control signals (110,120) comprising at least one of the total heave value (b), a partial heave value (c,e) or a control deviation value (dh,, dhy). Also provided is a heave compensation installation (15) for heave compensation on a floating vessel (10).

Description

[0001] HEAVE COMPENSATION

[0002] The present disclosure relates to heave compensation systems and methods, particularly with reference to heave compensation on floating structures used for drilling, installing, servicing or maintenance of subsea oil and gas wells.

[0003] BACKGROUND

[0004] Floating vessels, e.g. ships or platforms, are commonly used for drilling operations and auxiliary processes at subsea oil and gas wells. For instance, a vertical load such as a riser, a drill string or an item to be installed at or adjacent a well may be suspended from the floating vessel and extend to a subsea wellhead on the seabed. Since the floating vessel may move in the water, for example due to sea swell, the distance between the floating vessel and the subsea well may vary considerably. It is therefore often required to provide heave compensation regarding the respective connections between the vessel and the vertical load in order to ensure that the vessel movement does not cause negative consequences for the operation.

[0005] Commonly, it is known to provide hydraulic heave compensation systems comprising at least one hydraulic cylinder to decouple the connection between the vessel and the vertical load from the vessel movement. Examples of hydraulic heave compensation systems are known as Crown Mounted Compensator (CMC) or Drill String Compensator (DS). Hydraulic heave compensation systems may be implemented as passive systems or active systems. Passive hydraulic heave compensation systems may comprise at least one hydraulic cylinder which is preloaded by gas pressure, thus acting like a hydropneumatic spring and balancing the load with the cylinder force. Active hydraulic heave compensation systems include measuring the vertical heave of the vessel and using the measured heave value as a control parameter for active control of the hydraulic pressure, thus moving a piston in the hydraulic cylinder for maintaining the load in a substantially constant vertical position.

[0006] Further systems and methods for heave compensation include hoisting heave compensation systems comprising a drawworks (i.e., a hoisting winch). Hoisting heave compensation systems are commonly implemented as active heave compensation systems. The drawworks may comprise a rotatable drum for winding and unwinding a hoisting line and may generally be used to suspend the vertical load from the vessel and to retrieve it, either directly or via a stringed block arrangement. By actively controlling the drawworks for moving the load contrarily to the vessel movement, the vertical load position can be maintained constant or substantially constant relative to the seabed. Examples of heave compensation methods and systems which may be useful for understanding the field of technology include WO 2013 / 076207 A1 ; WO 2015 / 007412 A2; EP 3 363 989 A1 ; and WO 2015 / 189368 A2.

[0007] Both hoisting heave compensation systems and hydraulic heave compensation systems may be technically limited due to their structure. For instance, hydraulic heave compensation may be limited regarding the compensation capacity since the maximum compensation movement may depend directly on the limited cylinder stroke. Furthermore, hoisting heave compensation requires high rotation speeds by the drawworks, which leads to high driving power requirements due to system inertia. Approaches exist which are based on a combination of both compensation concepts in order to improve heave compensation.

[0008] For instance, in WO 2015 / 189368 A2, hoisting systems and methods relating to heave compensation are described. According to an aspect of the publication, the hoisting system comprises both active heave control via a drawworks of the hoisting system and a passive heave compensation system coupled to the drawworks. According to an embodiment, the passive heave compensation system may comprise a hydraulic cylinder.

[0009] There is a continuous need for improved technology to make heave compensation more effective, in particular by increasing the capacity and accuracy of heave compensation systems and methods. It is an aim of the present disclosure to provide such improvements, or at least useful alternatives, to known technology.

[0010] SUMMARY

[0011] In an example, there is provided a method of performing heave compensation on a floating vessel having a hoisting heave compensation system with a drawworks and a hydraulic heave compensation system with a hydraulic cylinder, the method comprising: measuring a total heave value of the floating vessel; and applying active heave compensation by means of the hoisting heave compensation system and the hydraulic heave compensation system according to a control process, wherein the control process comprises: providing a first input control signal to operate the hydraulic heave compensation system; and providing a second input control signal to operate the hoisting heave compensation system, wherein the first and second input control signals comprise at least one of the total heave value, a partial heave value or a control deviation value.

[0012] There are also provided a heave compensation installation for performing heave compensation on a floating vessel. The detailed description below and appended claims outline further inventive aspects and embodiments.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other characteristics will become clear from the following description of illustrative embodiments, given as non-restrictive examples, with reference to the attached drawings, in which:

[0015] Fig. 1 illustrates a schematic side view of a heave compensation installation comprising a hoisting heave compensation system and a hydraulic heave compensation system according to an example.

[0016] Fig. 2 schematically depicts a control process for applying heave compensation by means of the hoisting heave compensation system and the hydraulic heave compensation system according to a first example.

[0017] Fig. 3 schematically shows a control process for applying heave compensation by means of the hoisting heave compensation system and the hydraulic heave compensation system according to a second example.

[0018] Fig. 4 schematically illustrates a control process for applying heave compensation by means of the hoisting heave compensation system and the hydraulic heave compensation system according to a third example.

[0019] Fig. 5 schematically depicts a control circuit for applying heave compensation by means of the hoisting heave compensation system according to a fourth example.

[0020] Fig. 6 shows a schematic diagram with example acceleration patterns over time resulting from the control circuit according to the fourth example.

[0021] Figs. 7 and 8 illustrate schematic example diagrams comparing heave patterns over time without setpoint correction and with setpoint correction resulting from the control circuit according to the fourth example.

[0022] DETAILED DESCRIPTION

[0023] The following description may use terms such as “horizontal”, “vertical”, etc. These terms generally refer to the views and orientations as shown in the drawings and that are associated with a normal use of the invention. The terms are used for the reader’s convenience only and shall not be limiting.

[0024] The following description provides improved heave compensation concepts comprising advantageous methods of performing heave compensation on floating vessels. Furthermore, the following description provides beneficial heave compensation installations comprising a hoisting heave compensation system and a hydraulic heave compensation system. The described heave compensation concepts beneficially combine active heave compensation by means of the hoisting heave compensation system with active heave compensation by means of the hydraulic heave compensation system. Using the invention, it is possible to increase the overall capacity of the heave compensation installation by combining the individual capacities of the hoisting heave compensation system and the hydraulic heave compensation system. Furthermore, it is possible to increase the accuracy of the heave compensation installation by decreasing a control deviation of one of the hoisting heave compensation system and the hydraulic heave compensation system by compensation of the other system. In addition, the following description provides suitable control concepts and control circuits for the implementation of the suggested heave compensation concepts.

[0025] Fig. 1 illustrates a schematic side view of a heave compensation installation 15 comprising a hoisting heave compensation system 20 and a hydraulic heave compensation system 30 according to an example. The heave compensation installation 15 is arranged on a floating vessel 10, for instance on a floating ship or floating platform for drilling operations. The hoisting heave compensation system 20 comprises a drawworks 21 for winding and unwinding a hoisting line 22 over a tackle 25 in order to suspend a vertical load 23 from the vessel 10 via a multiple stringed block arrangement. The other end of the hoisting line 22 (the “dead end”) which is not attached to the drawworks 21 may be fixed to the vessel 10 as illustrated. For instance, the drawworks 21 may comprise a rotatable drum which is turned around a defined rotation angle for lifting or lowering the vertical load 23 by a given lifting or lowering distance a. As depicted in Fig. 1 , the given lowering distance a may correspond to the distance a between the vertical load 23 and the seabed 11 . If the vertical load 23 is a drill string extending into a subterranean well, the distance a may correspond to a distance between the end of the drill string and the bottom of the wellbore. Furthermore, the drawworks 21 is configured to perform active heave compensation in order to maintain a constant vertical position of the vertical load 23 with reference to the seabed 11 (or wellbore) if the floating vessel 10 is exposed to vertical heave movements, e.g. due to sea swell.

[0026] The hydraulic heave compensation system 30 comprises a hydraulic cylinder 31 for balancing the vertical load 23 against heave variations with hydraulic pressure. The hydraulic pressure of the hydraulic cylinder 31 may be actively controllable thus allowing the hydraulic heave compensation system 30 to perform active heave compensation by means of a movable piston. As illustrated, the hydraulic cylinder 31 may be configured as a top-mounted compensator mounted to the top of a derrick 16. Alternative embodiments may comprise other suitable mounting positions of the hydraulic cylinder 31 .

[0027] In order to perform heave compensation, the drawworks 21 and the hydraulic cylinder 31 each comprise a signal connection 52 to a control unit 50. The control unit 50 may receive a measured total heave value b of the floating vessel 10 from a sensor unit 40. The total heave value b may preferably correspond to a vertical heave value of the vessel’s movement in the water. The control unit 50 and the sensor unit 40 may be arranged on the floating vessel 10 and connected to each other by a further signal connection 52. The sensor unit 40 may comprise suitable heave measuring means as e.g. an acceleration sensor or an altimeter. The control unit 50 may be configured to control the hoisting heave compensation system 20 and the hydraulic heave compensation system 30 in accordance with a predefined control process 100 as will be further explained below with reference to Figs. 2 to 8.

[0028] According to the example of Fig. 1 , the hoisting heave compensation system 20 and the hydraulic heave compensation system 30 are connected in parallel which means that the signal connections 52 between the control unit 50 and the hoisting heave compensation system 20 as well as between the control unit 50 and the hydraulic heave compensation system 30 run in parallel, thus providing parallel signal paths and parallel control signals to both systems. In addition or alternatively, it is conceivable to provide signal connections 52 between the hoisting heave compensation system 20 and the hydraulic heave compensation system 30 in order to enable serial or partly serial control processes 100 as will be explained further with reference to Figs 2 to 4. The signal connections 52 may, for instance, be configured as wired signal lines or as wireless signal paths.

[0029] The heave compensation installation 15 depicted in Fig. 1 may be suitable to apply heave compensation by means of the hoisting heave compensation system 20 and the hydraulic heave compensation system 30 according to a defined control process 100 as will be further explained in the following with reference to Figs 2 to 8. The hoisting heave compensation system 20 and the hydraulic heave compensation system 30 are provided as active compensation systems configured to be actively controlled on the basis of input signals.

[0030] Generally, the control process 100 may comprise providing a first input control signal 110 to the hydraulic heave compensation system 30 and providing a second input control signal 120 to the hoisting heave compensation system 20. For instance, the first input control signal 110 or the second input control signal 120 may comprise (i.e. represent and / or be a function of) the total heave value b. The control process 100 may comprise dividing the measured total heave value b into a first partial heave value c and a second partial heave value e. Thus, the first input control signal 110 may for instance comprise the first partial heave value c and the second input control signal 120 may comprise the second partial heave value e. In Fig. 1 , the first partial heave value c is schematically indicated next to the hydraulic cylinder 31 and the second partial heave value e is schematically indicated at the drawworks 21 and at the hoisting line 22. Furthermore, the total heave value b, the first partial heave value c and the second partial heave value e are indicated together by way of illustration next to the load suspension point 24 of the vertical load 23. As illustrated, the total heave value b may correspond to a sum of the first partial heave value c and the second partial heave value e. In order to provide compensation, the first partial heave value c and the second partial heave value e are opposed to the total heave value b. As suggested, the first partial heave value c may be transformed to a corresponding piston movement c of the hydraulic cylinder 31 and the second partial heave value e may be transformed to a corresponding hoisting line movement by the distance e by means of the drawworks 21 . In this manner, the vertical load 23 can be maintained in a substantially constant vertical position relative to the seabed 11 . In addition, the drawworks 21 may be configured to provide additional lifting or lowering movements of the vertical load 23 by a given distance a if a change in vertical position of the vertical load 23 is required.

[0031] According to a further example, the first input control signal 110 or the second input control signal 120 may comprise a control deviation value dho, dhyof one of the systems as will be further explained in the following. It is also conceivable that the first input control signal 110 or the second input control signal 120 comprises more than one of the total heave value b, the partial heave values c, e and the control deviation value dho, dhy. In addition, it may be possible to provide further input control signals.

[0032] Reference is now made to Figs. 2 to 4 depicting schematic control processes 100 for applying heave compensation by means of the hoisting heave compensation system 20 and the hydraulic heave compensation system 30 according to a first, second and third example. Fig. 2 illustrates a substantially parallel control configuration for controlling the hoisting heave compensation system 20 and the hydraulic heave compensation system 30. Figs. 3 and 4 illustrate substantially serial control configurations for controlling the hoisting heave compensation system 20 and the hydraulic heave compensation system 30. The control processes 100 may, for instance, be carried out by the control unit 50. For example, the control unit 50 may comprise a processor and a memory device storing instructions, which when executed by the processor, causes the control unit 50 to carry out the control process 100. According to Fig. 2, a measured total heave value b is provided, e.g. by the sensor unit 40 of the heave compensation installation 15. The indicated waveform of the total heave value b and further depicted values may, by way of illustration, demonstrate the fluctuating heave of the vessel 10 on the water surface 12 over time. As depicted, the total heave value b is divided into the first partial heave value c and the second partial heave value e. The first partial heave value c is provided as part of the first input control signal 1 10. The second partial heave value e is provided as the second input control signal 120, which is provided to the hoisting heave compensation system 20 for compensation by means of the drawworks 21 , which for instance may wind and unwind the hoisting line 22 according to the required compensation distance given by the second input control signal 120.

[0033] Since the compensation provided by the hoisting heave compensation system 20 may be technically limited, a control deviation value dho may remain after performing compensation by means of the hoisting heave compensation system 20. According to the example illustrated in Fig. 2, the remaining control deviation value dho of the hoisting heave compensation system 20 is provided as a third input control signal 130 and merged with the first partial heave value c to form a combined partial heave value c+dho- The combined partial heave value c+d o is provided as the first input control signal 1 10 to the hydraulic heave compensation system 30 for compensation by means of the hydraulic cylinder 31 , which for instance may result in a moving piston by controlling hydraulic pressure in the hydraulic cylinder 31 according to the required compensation distance. Since the compensation provided by the hydraulic heave compensation system 30 may be technically limited, a control deviation value dhy may remain after performing compensation by means of the hydraulic heave compensation system 30.

[0034] According to alternative examples, it may also conceivable to provide the remaining control deviation value dhy of the hydraulic heave compensation system 30 as the third input control signal 130 instead of the remaining control deviation value d o of the hoisting heave compensation system 20. The remaining control deviation value dhy of the hydraulic heave compensation system 30 may in such a case be combined with the second partial heave value e to form a combined partial heave value e+dhy. The combined partial heave value e+dhy may be provided as the second input control signal 120 to the hoisting heave compensation system 20 for compensation by means of the drawworks 21 . According to further alternative embodiments, it is also conceivable to carry out the control process 100 without any third input control signal 130, rather implementing a pure parallel control configuration. In such a case, the first partial heave value c is provided as the first input control signal 1 10. The control deviation values dhyand dho may be derived through sensor signals representative of the actual motion of the heave compensation systems 20,30, for example linear sensors indicating the position of a hydraulic cylinder in the hydraulic heave compensation system 30, measuring position(s) of a crown block and / or a traveling block in the hoisting system, or an encoder indicating the winch drum position / motion of the hoisting heave compensation system 20. The control deviation values may, alternatively, be indirectly derived from other measurements. In this manner, the deviation between the demanded compensation action (which may aim to fully eliminate the heave values b,c,e) and the actually executed motion can be determined and fed forward as control signals in the form of the control deviation values dhy and dho-

[0035] The total heave value b may be divided into the first partial heave value c and the second partial heave value e according to a static dividing scheme. For instance, the ratio can be a fixed ratio of at least 70% of the total heave value b for the first partial heave value c and a maximum of 30% of the total heave value b for the second partial heave value e. Other ratios may be applicable, for instance 50% / 50% or at least 60% of the total heave value b for the first partial heave value c and a maximum of 40% of the total heave value b for the second partial heave value e. The selected ratio may depend on the individual system properties or predefined system specifications of the hoisting heave compensation system 20 and the hydraulic heave compensation system 30.

[0036] According to further examples, it is conceivable to provide dynamic dividing schemes which may select varying ratios according to varying heave conditions, e.g. small or large heave fluctuation. For example, the measured total heave value b can be dynamically divided into the first partial heave value c and the second partial heave value e as a function of the measured total heave value b. The control process 100 may, for example, be set up such that for low heave values (calm weather), only one of the heave compensation systems 20,30 is active (a ratio 0% / 100%), while for increasing heave motion the ratio is adjusted. In this manner, the heave compensation performance can be optimized based on the ratio giving the best performance at the weather condition experienced at a given time.

[0037] By means of a control configuration as for instance depicted in Fig. 2 it is possible to increase the overall compensation capacity of the heave compensation installation 15. The individual capacity of the hoisting heave compensation system 20 and the individual capacity hydraulic heave compensation system 30 can be exploited concurrently by means of the suggested control process 100. By this, it is possible to jointly compensate even strong swell leading to high vertical heave motion of the vessel 10, thus increasing the vessel’s operational capability for challenging weather conditions. By additionally signaling a remaining control deviation value dho, dhy of one of the hoisting heave compensation system 20 and the hydraulic heave compensation system 30 to the other system, it is furthermore possible to increase the overall accuracy of the heave compensation installation 15. In this case, the overall accuracy only depends on the individual accuracy of the system processing the provided addition control deviation value dho, dhy, whereas the maximum heave compensation capacity is defined by the added up individual system capacities.

[0038] Now referring to Fig. 3, a substantially serial control configuration for controlling the hoisting heave compensation system 20 and the hydraulic heave compensation system 30 is explained in the following. According to Fig. 3, a measured total heave value b is provided, e.g. by the sensor unit 40 of the heave compensation installation 15. As depicted, the total heave value b is provided as the first input control signal 1 10 to the hydraulic heave compensation system 30. Since the compensation provided by the hydraulic heave compensation system 30 may be technically limited, a control deviation value dhy may remain after performing compensation by means of the hydraulic heave compensation system 30. According to the depicted control process 100, the control deviation value d y is subsequently provided to the hoisting heave compensation system 20 as the second input control signal 120. Since the compensation provided by the hoisting heave compensation system 20 may be technically limited, a control deviation value dho may remain after performing compensation by means of the hoisting heave compensation system 20, but due to the serial processing the remaining control deviation value dho may be very low.

[0039] Now referring to Fig. 4, a further substantially serial control configuration for controlling the hoisting heave compensation system 20 and the hydraulic heave compensation system 30 is explained in the following. According to Fig. 4, a measured total heave value b is provided, e.g. by the sensor unit 40 of the heave compensation installation 15. As depicted, the total heave value b is provided as the second input control signal 120 to the hoisting heave compensation system 20. Since the compensation provided by the hoisting heave compensation system 20 may be technically limited, a control deviation value dho may remain after performing compensation by means of the hoisting heave compensation system 20. According to the depicted control process 100, the control deviation value dho is subsequently provided to the hydraulic heave compensation system 30 as a first input control signal 1 10. Since the compensation provided by the hydraulic heave compensation system 30 may be technically limited, a control deviation value dhy may remain after performing compensation by means of the hydraulic heave compensation system 30, but due to the serial processing the remaining control deviation value dhy may be very low.

[0040] By means of substantially serial control configurations as for instance depicted in Figs. 3 and 4 it is possible to increase the overall compensation accuracy of the heave compensation installation 15. The generally already low control deviation value dhy, dho of one of the hoisting heave compensation system 20 and the hydraulic heave compensation system 30 can be further reduced by means of the other system, thus resulting in very precise heave compensation. For many operations, the overall compensation accuracy may be of great importance, for instance regarding drilling operations in sensible areas or regarding high- precision underwater works.

[0041] Since the control processes 100 depicted in Figs. 2 to 4 substantially differ only in terms of controller setup, the described examples may be implemented with the same heave compensation installation 15 if suitable parallel and / or serial signal connections 52 are provided. For switching to a different control concept, it may be sufficient to reconfigure the control unit 50 accordingly. (As the skilled reader will recognize, the arrangement of Fig. 4 can be implemented by the system of Fig. 2 by setting the ratio between c and e to 0% / 100%.)

[0042] Now turning to Figs. 5 to 8, control concepts are described with enhanced consideration of system limitations. The control concepts may be used in conjunction with examples described above or with different configurations.

[0043] Both the hoisting heave compensation system 20 and the hydraulic heave compensation system 30 may be subject to technical limitations according to predefined system specifications, e.g. maximum available speeds or maximum allowable accelerations. These and other limitations may potentially affect the achievable heave compensation effect. It may thus be desirable to provide a further improved control process 100 considering such limitations. It is therefore suggested that the control process 100 further comprises adapting at least one of the first input control signal 110 and the second input control signal 120 to predefined system specifications of at least one of the hoisting heave compensation system 20 and the hydraulic heave compensation system 30. For instance, the control process 100 may be adapted to provide input control signals 110,120,130 leading to movements of the drawworks 21 or to piston movements of the hydraulic cylinder 31 falling within the range of feasible and permitted movements. Thus, stable behavior of the hoisting heave compensation system 20 and the hydraulic heave compensation system 30 may be promoted and the movements resulting from the various input control signals 110,120,130 are precisely coordinated and readjusted in order to remain in phase with the vessel’s movement.

[0044] Accordingly, Fig. 5 depicts an example of a schematical control circuit 60 which may be implemented in the control unit 50 for applying heave compensation by means of the hoisting heave compensation system 20 by way of illustration. Although primarily discussed in the following with reference to the hoisting heave compensation system 20, comparable suitable control circuits 60 may be developed for the hydraulic heave compensation system 30. The control concept implemented by the control circuit 60 depicted in Fig. 5 by way of illustration takes into consideration the driving power, the acceleration, the jolt and the speed of the drawworks 21 of the hoisting heave compensation system 20.

[0045] Generally, the control concept according to Fig. 5 is based on converting the total heave value b or a partial heave value e to be compensated by the hoisting heave compensation system 20 by means of mathematical functions in order to determine a required motor acceleration 64 of the drawworks 21 . As depicted, starting with the total heave value b or the partial heave value e, an initial setpoint position 61 is provided. Subsequently, a speed setpoint 62 and an acceleration setpoint 63 are determined in order to calculate the required motor acceleration 64. Subsequently, the motor acceleration 64 is limited according to the maximum feasible or permitted motor acceleration 64 given by the system specifications such that a limited motor acceleration 65 is provided. By integration of the limited motor acceleration 65, a motor rotation speed 66 is provided, which may be further converted to a limited motor rotation speed 67 if required by the system specifications. Subsequently, a motor rotation angle setpoint 68 may be determined. As a result, a corrected setpoint position 69 is provided to the hoisting heave compensation system 20, e.g. to a position controller of the drawworks 21 . With the corrected setpoint position 69, the drawworks 21 is enabled to perform the required heave compensation within given system limitations. If the initial setpoint position 61 is already realizable within the given limitations, the corrected setpoint position 69 may correspond to the initial setpoint position 61 .

[0046] Upon reaching a technical limitation of the predefined system specifications, the calculated setpoint motion may deviate from the initial setpoint motion which might lead to inaccurate positioning. Figs. 6 and 7 illustrate examples of such a deviation. Fig. 6 depicts the motor acceleration pattern of the setpoint motion before and after limitation, as indicated by the graph 70 representing the motor acceleration and by the graph 71 representing the limited motor acceleration. As a consequence of the deviating acceleration patterns, drifting setpoint positions may occur as illustrated in Fig. 7, which may affect the heave compensation accuracy. As depicted, the graph 72 represents the initial setpoint, whereas the graph 73 represents the motion without correction.

[0047] This behavior may be advantageously counteracted by means of an additional control loop 75 integrated in the control circuit 60. As depicted in Fig. 5, the control loop 75 may be implemented as a FID controller 51 with a P controller 51a, an I controller 51 b and a D controller 51c. By means of the PID controller 51 , the corrected setpoint position 69 is compared with the initial setpoint position 61 and deviations are returned to the control circuit part before determination of the limited motor acceleration 65, thus limiting the deviation between the corrected setpoint position 69 and the initial setpoint position 61 . By this, as illustrated in Fig. 8, the differences between the initial setpoint 72 and the corrected setpoint 74 may be maintained on a minimum level over time. Furthermore, the center position can be precisely maintained and the phase shift between both curves remains low. By means of the described heave compensation systems and methods, improved heave compensation with increased overall compensation capacities as well as enhanced overall accuracy may be beneficially provided. For example, the system operation can be optimized for best performance and / or minimum energy usage at any given operational conditions. For challenging weather conditions, the two active heave compensation systems 20,30 can be operated concurrently for better performance, for example in the event that one of the systems 20,30 meets its operational limits or by selecting the most desirable relative distribution of compensation action between the two systems.

Claims

CLAIMS1 . A method of performing heave compensation on a floating vessel (10) having a hoisting heave compensation system (20) with a drawworks (21 ) and a hydraulic heave compensation system (30) with a hydraulic cylinder (31), the method comprising:- measuring a total heave value (b) of the floating vessel (10); and- applying active heave compensation by means of the hoisting heave compensation system (20) and the hydraulic heave compensation system (30) according to a control process (100), wherein the control process (100) comprises:- providing a first input control signal (110) to operate the hydraulic heave compensation system (30); and- providing a second input control signal (120) to operate the hoisting heave compensation system (20), wherein the first and second input control signals (110,120) comprise at least one of the total heave value (b), a partial heave value (c,e) or a control deviation value (dho, dhy).

2. The method according to claim 1 , wherein the control process (100) further comprises dividing the measured total heave value (b) into a first partial heave value (c) and a second partial heave value (e) and wherein the first input control signal (110) comprises the first partial heave value (c) and the second input control signal (120) comprises the second partial heave value (e).

3. The method according to claim 2, wherein the measured total heave value (b) is dynamically divided into the first partial heave value (c) and the second partial heave value (e) as a function of the measured total heave value (b).

4. The method according to claim 2 or 3, wherein the control process (100) further comprises providing a control deviation value (dho) of the hoisting heave compensation system (20) and the first input control signal (110) comprises a combination of the first partial heave value (c) and the control deviation value (d o).

5. The method according to claim 2 or 3, wherein the control process (100) further comprises providing a control deviation value (dhy) of the hydraulic heavecompensation system (20) and the second input control signal (120) comprises a combination of the second partial heave value (e) and the control deviation value (dhy).

6. The method according to claim 1 , wherein the first input control signal (1 10) comprises the total heave value (b) and the second input control signal (120) comprises a control deviation value (dhy) of the hydraulic heave compensation system (30).

7. The method according to claim 1 , wherein the second input control signal (120) comprises the total heave value (b) and the first input control signal (110) comprises a control deviation value (dho) of the hoisting heave compensation system (20).

8. The method according to any preceding claim, wherein the control process (100) further comprises adapting at least one of the first input control signal (1 10), the second input control signal (120) or the third input control signal (130) to predefined system specifications of at least one of the hoisting heave compensation system (20) and the hydraulic heave compensation system (30).

9. The method according to claim 8, wherein a corrected setpoint position (69) for a drawworks (21 ) of the hoisting heave compensation system (20) is calculated from an initial setpoint position (61 ) comprising converting a determined motor acceleration (64) to a limited motor acceleration (65) and / or converting a determined motor rotation speed (66) to a limited motor rotation speed (67).

10. The method according to claim 9, wherein a deviation between the corrected setpoint position (6) and the initial setpoint position (62) is returned to the control process (100) by means of an additional control loop (75), particularly using a PID controller (51 ).1 1. A heave compensation installation (15) for performing heave compensation on a floating vessel (10), comprising:- a hoisting heave compensation system (20) having a drawworks (21 );- a hydraulic heave compensation system (30) having a hydraulic cylinder (31 );- a sensor unit (40) for measuring a total heave value (b) of the floating vessel (10); and- a control unit (50) configured to control the hoisting heave compensation system (20) and the hydraulic heave compensation system (30), wherein the control unit (50) is adapted to carry out the control process (100) of the method according to any preceding claim.

12. The heave compensation installation (15) according to claim 11 , wherein the hoisting heave compensation system (20) and the hydraulic heave compensation system (30) comprise a substantially parallel control configuration.

13. The heave compensation installation (15) according to claim 11 , wherein the hoisting heave compensation system (20) and the hydraulic heave compensation system (30) comprise a substantially serial control configuration.

14. The heave compensation installation (15) according to any one of claims 11 to 13, wherein the control unit (50) comprises a PID controller (51 ).

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