The present invention relates to hydraulic systems and methods for a tensioning system, including but not limited to a tensioning system for a drill string used on an offshore drill rig for oil and gas exploration and production.

BACKGROUND

As subsea oil and gas fields at great water depths are being developed, the facilities used in drilling and production of hydrocarbons will increasingly be floating structures such as drilling ships, semi-submersible platforms and drilling rigs, etc. These vessels move under the influence of waves, winds and currents and risers or pipes suspended by the vessel or linking the vessel with the subsea wells are also influenced by, for example, sea currents. Such risers are commonly supported by a riser tensioner system, for example as described in WO 2012/016765 A1.

In many operating areas, severe weather conditions often develop rapidly, leaving only little time to secure or pull the riser. This includes wind, sea states, or sea currents, which can change within very short time windows. This may require an adjustment of the riser suspension system to adapt it to the new conditions, in order to avoid damage or excessive loads on the riser and associated equipment. In addition, the different types of operations carried out by a rig or vessel may require changes in the operating conditions under which the suspension system serve.

Further documents which may be useful for understanding the field of technology include: US 4 351 261 A which shows a recoil system and a method for supporting a marine riser which is extended from offshore well head equipment to a floating platform; WO 2014/090682 A2 which shows a hydraulic cylinder unit for connection to a wire line riser system having multi-capacity properties; WO 2014/090682 A2 which shows a method for switching a hydraulic cylinder unit between a hydraulic cylinder unit with low tension capabilities and a hydraulic cylinder unit with high tension capabilities; and WO 2018/111114 A1 which shows a wireline tensioner having at least on sheave and a hydraulic cylinder unit operatively connected to the at least on sheave, where the hydraulic cylinder unit is fluidly connected to a first accumulator unit and to a second accumulator unit via a hydraulic distribution system. There is a need for further improved systems and techniques to be able to handle such varying operating conditions in a better manner compared to known solutions. The present invention has the objective to provide methods and systems with advantages compared to such conventional solutions, or at least to provide an alternative to known technology.

SUMMARY

In an aspect, there is provided a hydraulic system for a wireline tensioner configured for use on a floating vessel, the hydraulic system comprising: a compensator cylinder forming part of the wireline tensioner, the compensator cylinder having a first hydraulic chamber and a compensator piston operable therein; an accumulator cylinder having a gas chamber, a second hydraulic chamber and an accumulator piston operable therein, the second hydraulic chamber being fluidly connected to the first hydraulic chamber; a gearing cylinder having a gearing cylinder piston which is mechanically connected via a rod to either (i) the compensator piston, or (ii) the accumulator piston; and a hydraulic supply comprising a hydraulic controller operable to control a supply of hydraulic fluid to and from the gearing cylinder, whereby the gearing cylinder piston can provide a force on the compensator piston or accumulator piston via the rod.

The gearing cylinder may comprise a third hydraulic chamber, the third hydraulic chamber being a rod side chamber or a piston side chamber.

The hydraulic controller may have a first operational setting in which the third hydraulic chamber is fluidly connected to the second hydraulic chamber, and a second operational setting in which the third hydraulic chamber is fluidly connected to an accumulator.

The gearing cylinder may comprise a third hydraulic chamber, the third hydraulic chamber being a piston side chamber, and a fourth hydraulic chamber, the fourth hydraulic chamber being a rod side chamber.

The hydraulic controller may have at least two of: a first operational setting in which the third hydraulic chamber is fluidly connected to an accumulator and the fourth hydraulic chamber is fluidly connected to the second hydraulic chamber; a second operational setting in which the third hydraulic chamber and the fourth hydraulic chamber are fluidly connected to each other and to the accumulator; a third operational setting in which the fourth hydraulic chamber is fluidly connected to the accumulator and the third hydraulic chamber is fluidly connected to the second hydraulic chamber, or a fourth operational setting in which the third hydraulic chamber and the fourth hydraulic chamber are fluidly connected to each other and to the second hydraulic chamber.

The hydraulic controller may have at least three of the first, second, third or fourth operational settings, or all four of the first, second, third or fourth operational settings.

The hydraulic system may comprise a controller operable to regulate the hydraulic controller to actively drive the gearing cylinder piston in response to an input from a sensor.

The controller may be a heave compensation controller and the input from the sensor may represent a variable indicative of a vessel heave motion. The compensator cylinder may comprise a compensator piston rod extending from the compensator piston and out of the compensator cylinder.

At least one sheave may be fixed to and movable with the compensator piston rod. The compensator cylinder may comprise a compensation volume.

The compensation volume may be fluidly connected to a low pressure accumulator.

The hydraulic supply may comprise a hydraulic supply line arranged to supply hydraulic fluid from a hydraulic power unit to the first and second hydraulic chambers.

The hydraulic system may comprise the wireline tensioner or a plurality of wireline tensioners.

In one aspect, there is provided use of a hydraulic system to support a riser suspended from a floating vessel. In one aspect, there is provided a floating vessel comprising at least one wireline tensioner with a hydraulic system. The appended dependent claims and the detailed description below disclose further embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Various characteristics will become clear from the following description of illustrative embodiments, given as non-restrictive examples, with reference to the attached drawings, in which

Fig. 1 shows a hydraulic tensioning system for a floating vessel,

Fig. 2 shows another embodiment of a hydraulic tensioning system,

Figs 3-7 illustrate different operation modes of a hydraulic tensioning system, and

Fig. 8 shows a floating vessel with a hydraulic tensioning system and a riser arrangement.

DETAILED DESCRIPTION Figure 1 discloses a preferred embodiment of a hydraulic system 10 for a wireline tensioner 100,600 on a floating vessel 500. (See also Fig. 8 and the description below.) The hydraulic system 10 comprises a hydraulic power unit 12, a valve block 14, and a low pressure accumulator 16. The low pressure accumulator 16 may be an accumulator with a low pressure setting, or it may be, for example, simply a hydraulic expansion tank, storage or the like. The hydraulic power unit 12 is connected to the valve block 14 via a hydraulic connection lines 54,55. The low pressure accumulator 16 is similarly connected to the valve block 14. These components make up a hydraulic supply arrangement 9 for the hydraulic system 10.

An accumulator cylinder 20 comprises a high pressure chamber 22 and a gas chamber 36, separated by a piston 24. The high pressure chamber 22 is supplied with hydraulic oil from the supply arrangement 9 via a hydraulic line 18, such that, for example, a top-up of hydraulic oil in the system can be effectuated. The gas chamber 36 is a closed chamber comprising a volume of gas, such as nitrogen or air, which is compressible as the piston 24 moves in the accumulator cylinder 20. Optionally, the gas chamber 36 can be fluidly connected to a gas vessel, supply or storage external to the accumulator cylinder in order to, for example, provide a higher gas volume for compression. (E.g. similarly as gas storage units 205,305 in Fig. 1 of the abovementioned WO 2018/111114 A1 .)

A compensator cylinder 40 has a compensator piston 42 movable in the compensator cylinder 40 and connected to a piston rod 44. The piston rod is connected to a sheave assembly having at least one sheave (not shown in Fig. 1 , but visible on wireline tensioners 100,600 in Fig. 8) which is movable with the piston 42 and rod 44. Tensioning wires will thus be wound around the movable sheave and typically around a second set of sheaves which are fixed in relation to the compensator cylinder 40 (which can also be seen in Fig. 8) such that the compensator cylinder 40 effects a tensioning force between the sheave sets and thereby on the wire(s). This is the conventional setup of a wireline tensioner unit, which will be known to persons familiar with tensioning systems.

The compensator cylinder 40 has a high pressure chamber 41 which is hydraulically connected to the high pressure chamber 22 of accumulator cylinder 20 via a hydraulic connection 35. In this embodiment, the high pressure chamber 41 is provided on the piston side of the piston 42 in the compensator cylinder 40. Pressurized hydraulic fluid in the chambers 22 and 41 thus effects a force on the piston 42 and thus on the rod 44. On the rod side of the compensator cylinder 40 there is a compensation volume 46 which may be oil-filled and supplied from a low-pressure accumulator 50 via a supply line 53.

The system 10 further comprises a gearing cylinder 34. The gearing cylinder 34 comprises a gearing cylinder piston 26 movable within the gearing cylinder 34. The gearing cylinder piston 26 is mechanically connected to the accumulator piston 24 via a piston rod 32 so that the accumulator piston 24 and the gearing cylinder piston 26 moves in unison, and the gearing cylinder piston 26 can effect a force on the accumulator piston 24. The gearing cylinder 34 has a piston side chamber 37 and a rod side chamber 38, separated by the gearing cylinder piston 26. The piston side chamber 37 is supplied with hydraulic fluid from the valve block 14 via a supply line 31 , and the rod side chamber 38 is supplied with hydraulic fluid from the valve block 14 via a supply line 33.

By means of the system 10 shown in Fig. 1 , the gearing cylinder 34 is operable to effect a force on the accumulator piston 24, thereby influencing the operating characteristics of the accumulator cylinder 20 and how it influences the compensator cylinder 40 during operation. Figure 2 illustrates another embodiment comprising a number of the same components as the embodiment described in relation to Figure 1 , which have been given the same reference numeral. In the embodiment shown in Fig. 2, the piston rod 32 is mechanically connected to the compensator piston 42 and not to the accumulator piston 24, as in Fig. 1 . Figure 2 also illustrates the sheaves 60,61 which are part of the wireline tensioner, as described above, one sheave 60 being a movable sheave connected to the compensator piston rod 44 and one sheave 61 being a fixed sheave which is stationary and fixed in relation to the compensator cylinder 40. (See also Fig. 8.)

In Fig. 2, the gearing cylinder piston 26 is fixed to the compensator piston 42 via the structure holding the movable sheave 60, however the gearing cylinder piston 26 may be connected to the compensator piston 42 via a different path, for example from below or directly interfacing the compensator piston rod 44.

Consequently, in this embodiment, the gearing cylinder piston 26 is operable to effect a force on the compensator piston 42, determined by the pressure conditions in the gearing cylinder chambers 37,38.

Figures 3-7 illustrates various operating modes of the system 10, which will be described in the following. The valve block 14 is operable to control the distribution of hydraulic fluid from the hydraulic supply arrangement 9. The valve block 14 can supply hydraulic fluid to the accumulator high-pressure chamber 22 and compensator cylinder high-pressure chamber 41 via hydraulic line 18. In this way, the valve block 14 can be operated to control the amount of hydraulic fluid in the chambers 22,41 . Further, the valve block 14 is operable to control a hydraulic fluid supply or a hydraulic fluid connection to at least one of the gearing cylinder chambers 37,38. In the embodiments shown, the valve block 14 controls the hydraulic supply to both chambers 37,38 via respective hydraulic lines 31 ,33. Alternatively, one side of the gearing cylinder 34 (i.e. one side of the gearing cylinder piston 26) may be arranged to vent to atmosphere or be continuously connected to an accumulator or the like.

The operating modes in Figs 3-7 have been illustrated in relation to the embodiment shown in Fig. 1 above, however the different valve block 14 settings may be applied equivalently in the embodiment shown in Fig. 2 to provide the same effects. Figs 3-7 and the description below should therefore be read as being applicable to both the embodiment shown in Fig. 1 and that shown in Fig. 2.

Valve block 14 can be operated manually or via a controller arrangement, such as an electronic controller operated by a rig operator or the like, in order to set a desired operational setting for the system 10 at any given time.

Fig. 3 shows the hydraulic system 10 of Fig. 1 in a first operational mode. Reference is made to the schematically illustrated hydraulic connections provided by valve block 14. In this first operation mode, both the rod side 38 and the piston side 37 of the gearing cylinder 34 are hydraulically connected to the low pressure accumulator 16. The first operational mode can be considered an idle mode, wherein the pressure on each side of the gearing cylinder piston 26 is the same due to the rod side 38 and piston side 37 being interconnected, and substantially no force contribution is provided from the gearing piston 26 on the accumulator piston 24.

The low pressure accumulator 16 may be an accumulator having a low pressure, or it may be merely an expansion volume to account for the different fluid volumes on the rod side 38 and the piston side 37 of the gearing cylinder 34. Fig. 4 shows the hydraulic system 10 of Fig. 1 in a second operational mode. In the second operation mode gearing cylinder 34 is operated to provide active heave compensation for the tensioner via the compensator cylinder 40. This is obtained by arranging the hydraulic supply arrangement 9 to actively control a supply of hydraulic fluid to each of the gearing cylinder chambers 37,38. Pressurised hydraulic fluid for this purpose can be provided by the HPU 12.

If the system 10 is provided with active heave compensation capability, a controller 70 can be provided to automatically control the operation of the valve block 14. The controller 70 may be integrated with the valve block 14, or may be separate from the valve block 14, for example, as an add-on element. In the illustrated embodiment, the controller 70 is an add-on unit to the valve block 14 and receives hydraulic power from the HPU 12 to control the hydraulic supply to gearing cylinder chambers 37,38. The controller 70 may receive its input from a sensor 71 (or a processed sensor signal or a demand signal from another source, such as a rig control system). The sensor (or equivalent) signal may indicate a request for compensating action to be provided by the tensioner, whereby the valve block 14 can be controlled to provide a cyclic output to actively drive the gearing cylinder 34 in order to provide a compensating effect on the compensator cylinder 40, for example to match a wave heave period to which the vessel or rig is exposed.

Fig. 5 shows a third operational mode of the hydraulic system 10. In this third operational mode the piston side 37 of the gearing cylinder 34 is connected to the low pressure accumulator 16 and the rod side 38 of the gearing cylinder 34 is connected to the high pressure chamber 22 of the accumulator cylinder 20. In this operational mode the pressure acting on the rod side 38 of the gearing cylinder 34 will be substantially higher than that acting on the piston side 37, thus resulting in an upward force contribution from the gearing cylinder 34 on the accumulator piston 24.

Fig. 6 shows a fourth operational mode of the hydraulic system 10. In this fourth operational mode, both the rod side 38 and the piston side 37 of the gearing cylinder 34 are hydraulically connected to the high-pressure chamber 22 of the compensator cylinder 20, and interconnected to each other. The pressure on each side of the gearing cylinder piston 26 is thus the same, and equal to the pressure in the high- pressure chamber 22. A moderate downward force contribution is provided from the gearing cylinder piston 26 on the accumulator piston 24 due to the higher piston area acting towards the piston side chamber 37 compared to the downward-facing piston area against the rod side chamber 38. The gearing cylinder 34, piston 26 and rod 38 may be designed in order to provide a desired force contribution in this mode of operation, for example by making the diameter of the rod 38 larger. Fig, 7 shows a fifth operational mode of the hydraulic system 10. In this fifth operational mode, the piston side 37 of the gearing cylinder 34 is hydraulically connected to the high pressure chamber 22 of the accumulator cylinder 20 and the rod side 38 of the gearing cylinder 34 is connected to the low pressure accumulator 16. In this operational mode, the hydraulic pressure on the piston side 37 of the gearing cylinder 34 is higher than the hydraulic pressure on the rod side 38 of the gearing cylinder 34, resulting in a downwards force contribution from the gearing cylinder 34 on the accumulator piston 24. By means of control of the valve block 14, the tensioning effect and operational characteristics of the system 10 can thus be modified during operation or between operations. The valve block 14 can provide a “gearing” which influences the operational characteristics of the compensator cylinder 40, which can thereby be adapted according to operational requirements. For example, a stiffness of the tensioning system can be influenced by control of valve block 14. By enabling this “gearing” to be effectuated by hydraulic valve control provides operational flexibility, in that any changes can be done quickly and without, for example, requiring physical reconfiguration of system components.

While the shown embodiments control the hydraulic fluid connection to both sides of the gearing cylinder 34 (i.e. , both the rod side 38 and piston side 37), in principle the system can be implemented with control of only one side 37 or 38, and with the other side, for example, venting to air or permanently connected to an accumulator. Controlling both sides 37,38 provides more operational flexibility, however in some applications it may be sufficient to have only one of the sides 37 or 38 actively controlled. For example, only the piston side 37 can be used for this purpose and the valve block 14 can be operable to switch between two operational modes: (i) the piston side chamber 37 connected to the hydraulic line 18 and thus to chamber 22, and (ii) the piston side chamber 37 connected to the low pressure accumulator 16. Such a setup can provide “two gears” for the compensator cylinder 40. Preferably the system comprises more than two operational modes, for example arranging the valve block 14 to be able to switch between the third, fourth and fifth operational modes as shown in Figs 5, 6 and 7, provides a system with “three gears”. By including an operational setting as in Fig. 3, four different settings (or “gears”) can be realised: an “idle” mode with substantially zero contribution from the gearing cylinder 34 (Fig. 3); a negative (upwards) force contribution on the accumulator piston 24 (Fig. 5); a moderate positive (downwards) force contribution (Fig. 6); and a high positive force contribution (Fig. 7). An operator may thus control the stiffness and operational characteristics of the tensioning system between these modes according to the operational requirements at any given time. Alternatively, or additionally, the second operational mode can be used to provide active control, e.g. for heave compensation or for continuous adjustment of the tensioning system characteristics.

Fig. 8 shows an illustrative example of a floating vessel 500 having wireline tensioners 600 to provide tensioning for a riser 401 . The riser 401 is suspended from the vessel 500, for example a drilling rig or a drillship, and longitudinal (vertical) tensioning is provided by wireline tensioners 600 providing a substantially longitudinal tensioning force on the riser via wirelines 402a, b acting on tensioning ring 403. In this example, further wireline tensioners 100 are provided to control the transverse (horizontal) motion of the riser 401 by exerting a substantially transverse tensioning force on the riser 401 via wirelines 404a, b acting on tensioning ring 405. Such transverse tensioning may be used in particularly demanding offshore conditions, and the vessel 500 may only comprise the longitudinal tensioners 600. A system 10 as described above may be used in relation to one or more of the tensioners 100,600 on a vessel 500 from which a riser 401 is suspended.

In use, by proving a wireline tensioner 600,100 with a hydraulic system 10 according to the embodiments described herein, it is thereby possible to adjust the pressure of the hydraulic system 10 to adapt the operational characteristics of the wireline tensioner 600,100 according to given operational requirements. These may vary according to the type of operation, the length of the riser 401 , weather conditions, wave-induced heave motion of the vessel 500, etc. By adjusting the hydraulic supply to the gearing cylinder 30 via the hydraulic supply arrangement 9, the tensioning force and the force characteristics acting on the wirelines 402a, b, 404a, b can be set or adjusted.

The invention is not limited by the embodiments described above; reference should be had to the appended claims.