WO2014072521A2

WO2014072521A2 - Subsea actuating device and system for actuating hydraulically operated well tools

Info

Publication number: WO2014072521A2
Application number: PCT/EP2013/073576
Authority: WO
Inventors: Trond LØKKA; Scott Hamilton
Original assignee: Fmc Kongsberg Subsea As
Priority date: 2012-11-12
Filing date: 2013-11-12
Publication date: 2014-05-15
Also published as: AU2013343453A1; EP2923029B1; WO2014072521A3; AU2013343453B2; EP2923029A2; NO334934B1; NO20121327A1

Abstract

A subsea actuating device for actuating a hydraulically operated well tool or function device comprises a fluid-filled hydraulic cylinder, supplying hydraulic pressure to the well tool or function device, a piston slidably arranged in the hydraulic cylinder, a piston rod attached to the piston, an electrical motor rotationally driving a drive shaft; and a transmission device, including a rotational to linear motion converter, arranged to convert a rotational motion of the drive shaft to a linear motion of the piston rod. A plurality of such subsea actuating devices are included in a subsea actuating system for actuating a plurality of hydraulically operated well tools or function devices, wherein each subsea actuating device is attached to a central shaft section. In particular, the central shaft section may be a section of a riser extending from a subsea wellhead to a surface location.

Description

SUB SEA ACTUATING DEVICE AND SYSTEM FOR ACTUATING

HYDRAULICALLY OPERATED WELL TOOLS

TECHNICAL FIELD

The present invention relates in general to equipment for performing operations on subsea wellheads.

More specifically, the invention relates to a subsea actuating device for actuating a hydraulically operated well tool or function device and a subsea actuating system for actuating a plurality of hydraulically operated well tools or function devices.

BACKGROUND In the oil and gas industry there is a need for subsea installed well tools and hydraulically operated function devices to function quickly and with high reliability.

Such hydraulically operated well tools or function devices may include well completion equipment, wellhead equipment and safety equipment. They may, e,g, include well barriers, safety valves, blowout preventers (BOP's), landing strings, emergency disconnect packages (EDP's) and lower riser packages (LRP's).

Safety-related well tools are necessary to safeguard e.g. vessel, equipment, people and environment. They may e.g. serve to provide a conduit from the seabed to the surface vessel, while providing well barriers that can close and seal off the hydrocarbons as well as disconnecting the vessel from the seabed, thus preventing hydrocarbons from leaking to the environment.

Subsea installed well tools are typically operated via hydraulic power.

Conventionally, hydraulic power has been supplied to the well tools from the surface, e.g. a surface rig, through an umbilical. In order to facilitate fast response in operating the well tools, gas-filled hydraulic accumulators may in addition be arranged at the seabed.

Such conventional hydraulic systems for operating well tools are seen as very reliable but have certain disadvantages. The use of hydraulic lines from the surface to the seabed requires extensive material use which is heavy and expensive. At deep water, a long hydraulic supply line through an umbilical is necessary. This will lead to increased flexural compliance in the hydraulic line, which is a disadvantage in the operation of the hydraulic well tools. There is also a risk of leakage in hydraulic lines or components. Such leakages may be difficult to detect effectively by the use of pressure measurements, since a significant volume loss may lead to a relatively small pressure loss.

The use of gas accumulators at the seabed leads to increased weight, cost and complexity of the overall system. Also, the use of high pressure gas may be dangerous and requires special design and operational procedures to ensure that no accidents occur.

On more recent systems for deep water applications, electrically driven hydraulic subsea pumps have been installed with a subsea reservoir of hydraulic fluid. This way, only electric power and control signals needs to be deployed from the surface.

An example of such a system has been disclosed in GB-2341504.

Such electro hydraulic systems still have certain disadvantages. For instance, the subsea pumps can be unreliable as a result of the high cycles required to supply sufficient high pressure hydraulic fluid. Also, a reservoir of hydraulic fluid is usually required locally at the pump.

US-2007/0056745 discloses a trigger system for controlling operation of a well tool deployed in a wellbore. A valve may be selectively moved from a closed position to an open position, enabling flow of an actuating fluid from an external fluid supply through the trigger system to the tool to be activated. A disadvantage of such a system is that an external supply of pressurized actuating fluid is necessary, usually through a long hydraulic supply line.

SUMMARY

The subsea actuating device and subsea actuating system have been defined by the appended claims. Hence, a subsea actuating device for actuating a hydraulically operated well tool or function device has been disclosed. The subsea actuating device comprises a fluid- filled hydraulic cylinder having a hydraulic fluid outlet, a piston slidably arranged in the hydraulic cylinder, and means for moving the piston in the cylinder, the means comprising an electric motor and transmission to convert the rotation of the motor to a linear motion of the piston. The hydraulic fluid outlet is connected to a fluid line for supplying hydraulic pressurized fluid to the well tool or function device.

The hydraulically operated well tool or function device may be selected from the set consisting of: a safety valve, a well barrier, a locking means, a seal actuator or energizer, a landing string running tool, a tubing hanger running tool, a blowout preventer, BOP, an emergency disconnect package, EDP, and a lower riser package, LRP.

In an aspect, the rotational to linear motion converter includes a planetary roller screw. In such an aspect, at least a portion of the piston rod is provided with external threads and adapted to operate as a threaded shaft in the planetary roller screw.

The drive shaft and the piston rod may be arranged with identical axes, or alternatively, the drive shaft and the piston rod may be arranged with parallel and displaced axes. In the latter case, the transmission device may include a gear device arranged to transfer rotational motion of the drive shaft to a rotational motion of the rotational to linear motion converter. Further, the gear device may include a first sprocket attached to the drive shaft, a second sprocket attached to the rotational to linear motion converter, and an endless chain interconnecting the first and second sprockets.

In any one of the aspects wherein the drive shaft and the piston rod are arranged with parallel and displaced axes, the subsea actuating device may further comprise an additional piston slidably arranged in the hydraulic cylinder and an additional piston rod attached to the additional piston. The rotational to linear motion converter may in this case further provide linear motion of the additional piston rod.

The subsea actuating device may further comprise a pressure compensator.

In any one of the disclosed aspects and embodiments, the subsea actuating device may further comprise an electrical energy supply connected to the electrical motor.

Also disclosed is a subsea actuating system for actuating a plurality of hydraulically operated well tools or function devices. The system comprises a plurality of subsea actuating devices of the type disclosed in the present disclosure. In the system, each subsea actuating device is attached to a central shaft section. In a particular aspect, the central shaft section is a section of a riser which extends from a subsea wellhead to a surface location. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic cross-sectional view illustrating a first embodiment of a subsea actuating device;

Figure 2 is a schematic, partially cut perspective view illustrating principles of a planetary roller screw. Figure 3 is a schematic view illustrating aspects of a subsea actuating system for actuating a plurality of hydraulically operated well tools or function devices.

Figure 4 is a schematic view illustrating further aspects of a subsea actuating system for actuating a plurality of hydraulically operated well tools or function devices. Figure 5 is a schematic view illustrating a section of a riser which includes a plurality of subsea actuating devices;

Figure 6 is a schematic perspective view illustrating a second embodiment of a subsea actuating device;

Figure 7 is a schematic cross-sectional view illustrating further details of the second embodiment of a subsea actuating device; and

Figure 8 is a schematic cross-sectional view illustrating a third embodiment of a subsea actuating device.

DETAILED DESCRIPTION

Figure 1 is a schematic cross-sectional view illustrating a first embodiment of a subsea actuating device 100 for actuating a hydraulically operated well tool or function device.

The first embodiment of the subsea actuating device 100 includes a fluid-filled hydraulic cylinder 120. A piston 130 is slidably arranged in the hydraulic cylinder, and a piston rod 140 is attached to the piston. An electrical motor is included in the subsea actuating device 100. The motor rotationally drives a drive shaft. A transmission device, which includes a rotational to linear motion converter, is arranged in the subsea actuating device 100 to convert a rotational motion of the drive shaft to a linear motion of the piston rod 140.

When the drive shaft moves the piston pressurized hydraulic fluid is supplied to the well tool or function device. The hydraulically operated well tool or function device, which is actuated by the actuator, may e.g. a safety valve, a well barrier, locking means, a seal actuator or energizer, a landing string running tool, a tubing hanger running tool, a blowout preventer (BOP), an emergency disconnect package (EDP) and a lower riser package (LRP), or another type of hydraulically operated function device.

In the first embodiment of the subsea actuating device the rotational to linear motion converter includes a planetary roller screw. At least a portion of the piston rod may be provided with external threads and be adapted to operate as a threaded shaft in the planetary roller screw. In the first embodiment of the subsea actuating device 100, the motor's drive shaft and the piston rod 140 are arranged with identical axes.

More specifically, in the first embodiment, the subsea actuating device 100 includes a cylinder housing 1 10, which may be composed of a plurality of cylinder housing sections. The cylinder housing 1 10 encloses a fluid- filled hydraulic cylinder 120 which, in operation, may be fluidly connected to a hydraulically operated well tool, or function, (not shown) through a hydraulic fluid outlet 1 12.

The cylindrical piston 130 is slidably arranged in the hydraulic cylinder 120. A free end of the piston 130 is arranged in the direction towards the hydraulic fluid outlet 1 12, i.e., downwards as shown on figure 1. A piston rod 140 is attached to the piston 130 at the opposite side of the piston 130, i.e., at the upper part of the piston 130 as shown on figure 1.

Included in the cylinder housing 1 10, or alternatively as an axial extension of the cylinder housing 1 10, is attached the cylindrical motor housing 160 which includes an electrical motor 170, which rotationally drives a drive shaft that is arranged axially within the motor housing 160.

The drive shaft may be connected to a gearbox 180 which converts the speed and torque of the motor's drive shaft to a suitable speed and torque of a torque transferring member 184, e.g. a tubular cylinder, which transfers the rotational torque from the gearbox, or alternatively, from the motor itself, to the rotational input of a rotational-to-linear motion converter 150.

The rotational-to-linear motion converter 150 is arranged to convert the rotational motion of the motor and possibly the gear box to a linear motion of the piston rod 140 included in the cylinder housing 1 10. By such a transmission arrangement, it will be clear that the rotational motion of the drive shaft of the motor 170 is converted to a linear motion of the piston rod 140.

The rotational to linear motion converter 150 may include a roller screw, such as a planetary roller screw, e.g. of the type which is illustrated and further described by example with reference to figure 2 below. In this case, at least a portion of the piston rod 140 is provided with external threads and adapted to operate as a threaded shaft in the planetary roller screw. Moreover, the above-mentioned rotational input of the rotational to linear motion converter 150 will be the roller screw's nut.

Possible alternatives to the use of a roller screw for implementing the rotational to linear motion converter 150, may include the use of a ball screw, a pinion-and-rack coupling, etc. The transmission ratio between the motor's drive shaft and the second sprocket may be modified by the configuration of the gearbox 180. Moreover, the overall transmission ratio between the motor's drive shaft and the linear movement of the piston may also, or alternatively, be adjusted by configuring the pitch of the threads of the threaded piston rod 140 and the corresponding pitch of rollers included in the roller screw.

The cylinder housing 1 10 may, in the illustrated embodiment, be composed of four sections along its length. The interconnection between each cylinder section and the next cylinder section is made fluid-tight and pressure-proof. A first cylinder housing section 122 forms the lower end of the cylinder housing 1 10. An end piece of the first cylinder housing, i.e. the lowermost end of the cylinder housing as shown in figure 5, is provided with a central aperture which forms the hydraulic fluid outlet 1 12. The fluid outlet 1 12 may be suitably provided with a connection device to provide an appropriate fluid-tight and pressure-proof connection to the hydraulic supply line (not shown).

A second cylinder housing section 132 is connected to the first cylinder housing section 1 12.

A third cylinder housing section 152 is further connected to the second cylinder housing section 132. A fourth cylinder housing section 154 is further connected to the third cylinder housing section 152.

The motor housing 160 is further connected to the fourth cylinder housing section 154.

The subsea actuating device illustrated in figure 1 may further comprise a pressure compensator 190.

In any one of the embodiments of the subsea actuating device, the subsea actuating device further comprises an electrical energy supply connected to the electrical motor. The electrical energy supply may include a cable extending from the surface to the location of the subsea actuating devices and electrical connection elements. The electrical energy supply may further include batteries, e.g. electrical accumulators.

Figure 2 is a schematic, partially cut perspective view illustrating principles of a planetary roller screw.

The illustrated planetary roller screw is an exemplary implementation of the rotational to linear motion converter 150 which has been referred to in the descriptions of the above first embodiment. The planetary roller screw 150 may however also be used in other embodiments. A planetary roller screw is also known as a satellite roller screw, or just a roller screw.

Another type of rotational to linear motion converter is known as a ball screw. In a ball screw, an endless channel is provided between a threaded shaft and a nut, the channel containing a plurality of bearing balls which may move along the channel, between the nut and the threaded shaft, with low friction.

A planetary roller screw has certain resemblance to a ball screw, but the planetary roller screw uses planetary rollers, or satellite rollers, or just rollers, as the load transfer elements between nut 157 and screw (i.e., the threaded shaft 140) instead of balls. The rollers are typically threaded. Alternatively, the rollers may be grooved. In figure 2 only one roller has been identified at 156, but it will be understood that the roller screw includes a plurality of rollers arranged evenly about the threaded shaft 140, e.g., 8 or 10 or any other appropriate number of rollers. In use, the rollers spin and serve as low-friction transmission elements in contact with the threaded shaft 140 and the nut 157.

The nut 157 is further rotatably arranged in an outer, non-rotatable ring structure which constitutes or is a portion of the third cylinder housing section 152, i.e., when assembled, a part of the cylinder housing 1 10. As illustrated in figure 2, the rotatable arrangement of the nut in the third cylinder housing section 152 may be embodied by the use of ball bearings, illustrated by, e.g., the bearing ball 158.

It will be understood that rotation of the nut 157 with respect to the cylinder housing 1 10 results in linear travel of the threaded shaft 140.

Figure 3 is a schematic view illustrating aspects of a subsea actuating system for actuating a plurality of hydraulically operated well tools or function devices. The illustrated system 300 is a subsea actuating system for actuating two

hydraulically operated well tools or function devices. The system includes two subsea actuating devices according to the present disclosure, e.g. subsea actuating devices 100 of the type described and illustrated with reference to figure 1 and 2 above. It will be understood that any suitable number of subsea actuating devices 100 may be arranged in the system, although two such devices have been shown by example.

Each device 100 has been attached to a central shaft section 310. The central shaft section 310 may e.g. be a section of a riser which extends from a subsea wellhead to a surface location. Each subsea actuating device 100 is provided with a hydraulic fluid outlet 1 12, as already explained with reference to figure 1 above. The fluid outlet 1 12 may be suitably provided with a connection device to provide an appropriate fluid-tight and pressure-proof connection to a hydraulic supply line, which is further connected to the hydraulically operated well tools or function devices, 302 and 304 respectively.

Figure 4 is a schematic view illustrating a system 400 comprising a number of subsea actuating devices 100 arranged concentrically around a central axis. The central axis may be an axis of a central shaft section 310 may e.g. be a section of a riser which extends from a subsea wellhead to a surface location.

This may be used for actuating a plurality of hydraulically operated well tools or function devices where each sylinder is connected to a well tool or function device. For simplicity, and as an example, only two such tools are shown in Fig. 4.

It will be understood that any suitable number of subsea actuating devices 100 may be arranged in the system, such as one, two, three, four, five, six, or seven, or even more than eight, although eight subsea actuating devices have been shown in figure 4 by example. The example shows two different subsea actuating devices according to the present disclosure, where one may be for an "as is" function and the other, shown having a return spring, for a failsafe function, for example a failsafe valve In the first example the function will move to its intended position and stay there regardless. In the other example, when power to the motor is cut off the spring will force the hydraulic fluid back into the cylinder. Alternatively the valve can be held in position using a solenoid latch in the motor which is well known in the art.

Figure 5 is a schematic view similar to Fig. 4 also illustrating a subsea actuating system for actuating a plurality of hydraulically operated well tools.

The subsea actuating system 500 comprises a plurality of actuating devices 200, 400 that are attached to a central shaft section 510. In a typical application, the central shaft section 510 may be a section of a riser which extends from a wellhead positioned at the seabed to e.g. a surface rig.

Some well tools, e.g. safety equipment, may be arranged in the wellhead. Other well tools, in particular well completion devices, e.g. a tubing hanger running tool, may be configured to be lowered through the riser down to the wellhead to perform an operation on the wellhead assembly.

Further exemplary embodiments of subsea actuating devices, such as the devices 200, 400 shown in figure 5, have been described in closer detail in the following.

Figure 6 is a schematic perspective view illustrating a second embodiment of a subsea actuating device 200 for actuating a hydraulically operated well tool or function device. The subsea actuating device 200 includes a cylinder housing 210 which surrounds a fluid-filled hydraulic cylinder that supplies hydraulic pressure to the well tool or function device. A piston is slidably arranged in the hydraulic cylinder, and a piston rod is attached to the piston. Adjacent to the cylinder housing 210 is attached a cylindrical motor housing 260 which includes an electrical motor, rotationally driving a drive shaft. The motor housing 260 is attached to the cylinder housing 210 by means of an attachment device.

A transmission device which includes a rotational to linear motion converter is arranged to convert a rotational motion of the motor's drive shaft to a linear motion of the piston rod included in the cylinder housing 210.

The subsea actuating device 200 is configured to be attached to a central shaft section 1 10, e.g. a section of a riser as explained above with reference to fig. 5.

Figure 7 is a schematic cross-sectional view illustrating further details of the second embodiment of a subsea actuating device.

The subsea actuating device 200 includes a cylinder housing 210, composed of a plurality of cylinder housing sections. The cylinder housing 210 encloses a fluid- filled hydraulic cylinder 220 which, in operation, may be fluidly connected to a hydraulically operated well tool or function device (not shown) through a hydraulic fluid outlet 212 and a hydraulic supply line (not shown).

A cylindrical piston 230 is slidably arranged in the hydraulic cylinder 220. A free end of the piston 230 is arranged in the direction towards the hydraulic fluid outlet 212, i.e., downwards as shown on figure 7. A piston rod 240 is attached to the piston 230 at the opposite side of the piston 230, i.e., at the upper part of the piston 230 as shown on figure 7.

Adjacent to the cylinder housing 210 is attached a cylindrical motor housing 260 which includes an electrical motor 270, rotationally driving a drive shaft arranged axially within the motor housing 260. In this embodiment, the motor's drive shaft and the piston rod 240 are arranged with parallel and displaced axes. It will be understood that these axes correspond to the axes of the motor housing and the cylinder housing, respectively.

The drive shaft may be connected to a gearbox 280 which converts the speed and torque of the motor's drive shaft to a suitable speed and torque of a first sprocket 282. Alternatively, the drive shaft of the motor 270 may be connected directly to the first sprocket 282. The first sprocket 282 drives an endless chain which in turn drives a second sprocket 242 which is arranged to rotate about an axis which is identical to the axis of the cylinder housing 210. More specifically, the sprocket 242 is attached to the rotational input of a rotational to linear motion converter 250, which is arranged to convert the rotational motion of the second sprocket to a linear motion of the piston rod 240 included in the cylinder housing 210. By such a transmission arrangement, it will be clear that the rotational motion of the drive shaft of the motor 270 is converted to a linear motion of the piston rod 240.

Possible alternatives to the use of sprockets and endless chain, for transferring rotational motion from the axis of the motor housing to the axis of the cylinder housing, may include the use of pulleys and belt, a gear tooth coupling, etc.

The rotational to linear motion converter 250 may be as described earlier with reference to Fig. 2.

The transmission ratio between the motor's drive shaft and the second sprocket may be modified by the configuration of the number of teeth of the first and second sprockets. Moreover, the overall transmission ratio between the motor's drive shaft and the linear movement of the piston may also, or alternatively, be adjusted by configuring the pitch of the threads of the threaded piston rod 240 and the corresponding pitch of rollers included in the roller screw. The cylinder housing 210 is composed of four sections 222, 232, 252, 254 along its length, similar to the one that has been described earlier with reference to Fig. 1.

The subsea actuating device illustrated in figure 7 may further comprise a pressure compensator 290.

In the embodiment of figure 8, the subsea actuating device 400 further comprises a cylinder divided into two chambers 420 and 421. In each chamber is arranged a piston 430 resp. 431. The two pistons are interconnected using a common piston rod 440. This enables the device to be used in a two-way hydraulic function, for example connectors or locking dogs where it is necessary to provide pressurized fluid to alternative sides or to two actuators, for example for a lock/unlock function

Hence, many of the elements of figure 8 have their corresponding counterparts in elements already described above with reference to figure 7. The subsea actuating device 400 includes a cylinder housing 410, composed of a plurality of cylinder housing sections. The cylinder housing 410 has a fluid outlet 412 resp. 413 at each end. Adjacent to the cylinder housing 410 is attached a cylindrical motor housing 460 which includes an electrical motor 470, rotationally driving a drive shaft arranged axially within the motor housing 460. The motor's drive shaft and the piston rod 440 are arranged with parallel and displaced axes. It will be understood that these axes correspond to the axes of the motor housing and the cylinder housing, respectively. When the motor is operated it will drive the piston rod 440 and hence the pistons 430 and 431 in the same direction.

Alternatively the motor can be arranged inside the cylinder with its axis

corresponding to the cylinder axis, as described in Fig. 1. The drive shaft may be connected to a gearbox in the same manner as earlier described with reference to Fig. 7 and operates in an identical manner. As will be understood, the piston 430 and the additional piston 431 will always move in the same direction and with the same speed, since they are both attached to the piston rod 454. Such system may be used when there is a need for a two-way function. An example of such a function is a lock/unlock function. The function is realized by reversing the motor.

As a result, if the hydraulic fluid outlet 412 and the additional hydraulic fluid outlet are connected to opposite sides of a piston in the hydraulic tool or function device, a balanced operation of the hydraulic tool or function device, for instance for performing a cyclic function of the tool or device, may be achieved.

In embodiments disclosed herein, no external supply line for hydraulic fluid is necessary to obtain the actuating function of the actuating device. The fluid- filled hydraulic cylinder may be pre-filled with the required amount of fluid necessary to perform the desired function when the electric motor is actuated. The fluid at the fluid outlet, which is supplied to the well tool or function device, is pressurized by the piston in the cylinder, the pressurization of the fluid being due to mechanical motion provided by the electric motor and transmission. The actuating device may more conveniently be located close to the well tool or function device, since a hydraulic supply line is not necessary.

Claims

1. Subsea actuating device for actuating a hydraulically operated well tool or function device, the subsea actuating device comprising a fluid-filled hydraulic cylinder having a hydraulic fluid outlet, a piston slidably arranged in the hydraulic cylinder, a piston rod attached to the piston, means for moving the piston in the cylinder, said means comprising an electric motor, the motor driving a drive shaft, and transmission to convert the rotation of the drive shaft to a linear motion of the piston rod, wherein the hydraulic fluid outlet is connected to a fluid line for supplying hydraulic pressurized fluid to the well tool or function device.

2. Subsea actuating device according to claim 1 ,

wherein the hydraulically operated well tool or function device is selected from the set consisting of: a safety valve,

a well barrier,

a locking means,

a seal actuator or energizer,

a landing string running tool,

a tubing hanger running tool,

a blowout preventer, BOP,

an emergency disconnect package, EDP, and

a lower riser package, LRP.

3. Subsea actuating device according to one of the claims 1-2,

wherein the rotational to linear motion converter includes a planetary roller screw, and

wherein at least a portion of the piston rod is provided with external threads and adapted to operate as a threaded shaft in the planetary roller screw.

4. Subsea actuating device according to one of the claims 1-3,

wherein the drive shaft and the piston rod are arranged with identical axes.

5. Subsea actuating device according to one of the claims 1-3,

wherein the drive shaft and the piston rod are arranged with parallel and displaced axes.

6. Subsea actuating device according to claim 5,

wherein the transmission device includes a gear device arranged to transfer rotational motion of the drive shaft to a rotational motion of the rotational to linear motion converter.

7. Subsea actuating device according to claim 6,

the gear device including a first sprocket attached to the drive shaft, a second sprocket attached to the rotational to linear motion converter, and an endless chain interconnecting the first and second sprockets.

8. Subsea actuating device according to one of the claims 5-7,

further comprising an additional piston slidably arranged in the hydraulic cylinder and an additional piston rod attached to the additional piston, wherein the rotational to linear motion converter further provides linear motion of the additional piston rod.

9. Subsea actuating device according to one of the claims 5-7, further comprising a pressure compensator.

10. Subsea actuating device according to one of the claims 1-9,

further comprising an electrical energy supply connected to the electrical motor.

1 1. Subsea actuating system for actuating a plurality of hydraulically operated well tools or function devices, the system comprising

said plurality of subsea actuating devices as set forth in one of the claims 1- 10, each subsea actuating device being attached to a central shaft section.

12. Subsea actuating system according to claim 1 1 ,

wherein said central shaft section is a section of a riser extending from a subsea wellhead to a surface location.

13. Subsea actuating system according to one of the preceding claims, wherein, in order to actuate the hydraulically operated well tool or function device, the pressurised hydraulic fluid is supplied to the well tool or function device by linear movement of the piston, the movement being provided by the motor, drive shaft and transmission.