WO2014147406A2

WO2014147406A2 - Subsea hydraulic power generation

Info

Publication number: WO2014147406A2
Application number: PCT/GB2014/050881
Authority: WO
Inventors: Charles BRODIE
Original assignee: Geoprober Drilling Limited
Priority date: 2013-03-21
Filing date: 2014-03-20
Publication date: 2014-09-25
Also published as: GB201305161D0; WO2014147406A3

Abstract

There is disclosed a subsea hydraulic power generating apparatus, for generating hydraulic power to operate a device in a subsea environment, and an associated method. One subsea hydraulic power generating apparatus (10) disclosed herein comprises a hydraulic pump (14) which is operable to supply fluid to a hydraulic actuator associated with a subsea device in the form of a BOP (12). The apparatus also comprises a mechanical interface (20) comprising a drive member (22) coupled to a rotor (24) of the pump, for transferring an input drive force to the rotor to operate the pump. The apparatus further comprises a control assembly (26) for controlling the flow of fluid between the pump and the hydraulic actuator, to thereby control operation of the actuator, and so a desired function of the device. The pump, interface and control assembly are provided as a unit which can be releasably mounted to the device in the subsea environment, and coupled to the hydraulic actuator to provide hydraulic power when required.

Description

SUBSEA HYDRAULIC POWER GENERATION

The present invention relates to a subsea hydraulic power generating apparatus, and to an associated method. In particular, but not exclusively, the present invention relates to a subsea hydraulic power generating apparatus for generating hydraulic power to operate a device in a subsea environment. The present invention therefore also relates to a subsea device comprising a hydraulic power generating apparatus.

In the oil and gas exploration and production industry, many oil and gas deposits are found in offshore environments. This presents a number of unique challenges, not least of which is that much of the equipment required to gain access to the oil and gas deposits has to be located subsea. This can present significant difficulties, especially in the event of equipment failure. For example, during the drilling and completion phases of wellbore construction, pressure control is achieved using a device known as a blow-out preventer (BOP). The BOP includes hydraulic seal rams which can seal around a string of tubing extending into the wellbore, to provide annulus pressure control, and shear rams which can sever the tubing in an emergency situation. Where deployed from a floating surface facility such as a floating drilling rig, the BOP is positioned on a wellhead on the seabed, and is connected to the surface facility via a marine riser.

During the production phase, pressure control can be achieved using a device known as a Christmas tree, which comprises a number of valves that control the flow of fluid from the well. Again, the Christmas tree is typically installed on a wellhead on the seabed, and for this reason is generally referred to as a subsea Christmas tree.

Equipment is provided for controlling various operations of subsea devices, for example the actuation of valves in a subsea Christmas tree. Such might be achieved via electrical or hydraulic control lines extending to the surface facility. Fluid injection lines are also sometimes required, such as for injecting a treatment fluid into the well, to stimulate flow. These control and fluid lines are often provided in a bundle and contained within an outer sheath, these being known in the industry as an umbilical. The umbilical carries a stab plate at its lower end, which includes electrical and/or hydraulic connectors, for mating with corresponding connectors on the subsea device. The umbilical stab plate is coupled to a receptacle on the subsea device, which carries the mating connectors, and a hydraulic locking system is provided for locking the stab plate to the receptacle.

In all of these examples, it is necessary to provide a source of hydraulic power, so that the required function can be performed. For example, to operate the BOP rams; to actuate a valve on the subsea Christmas tree; and to lock the stab plate to the receptacle on the subsea component. Conventionally, this has been achieved using hydraulic control lines which extend to the surface facility, or in some cases by connecting the hydraulic system of a remotely operated vehicle (ROV) to the device via a hydraulic quick connect system. The control lines are delicate and tricky to install, and connection of an ROV hydraulic system to the device subsea can be very difficult.

In addition, hydraulic failure can result in serious consequences. This is particularly true in the case of BOPs and subsea Christmas trees, where hydraulic failure can result in the loss of pressure control. Such could occur through damage to the associated control lines. To this end, back-up systems are provided which can be operated in the event of hydraulic failure of primary operating systems. In certain situations, the back-up systems can be mechanical, facilitating manual override via a remotely operated vehicle (ROV) or diver. However, mechanical back-up systems are not preferred, as there is a limit on the amount of force which can be applied through mechanical systems of the type which can be provided subsea. For example, it is unlikely that it would be possible to exert sufficient force to operate a BOP shear ram mechanically.

Accordingly, hydraulic back-up systems have been developed for use in these situations. One exemplary hydraulic system employs a technique known as a 'hot stab', and uses the onboard hydraulic system in an ROV sled to provide hydraulic control of the failed equipment. In the example of a failed BOP ram operation, the technique involves mating the hydraulic system on the ROV sled with hydraulic connectors on the BOP, and using the ROV system to supply and exhaust fluid from a cylinder of the BOP ram, to advance the ram.

There are a number of disadvantages to this. These include that it can be difficult to mate the ROV sled system with the connectors on the BOP. Also, there is a significant risk of further damage to the BOP operating system, say in the event of incorrect connection with the ROV sled hydraulic system, leading to loss of hydraulic control fluid. Furthermore, there is a corresponding risk of loss of hydraulic control fluid from the hydraulic system in the ROV sled. These difficulties apply equally in situations where the ROV is used to provide primary control of the required function of the device.

It will be understood that similar difficulties are encountered with hydraulic systems on other subsea equipment, including but not limited to subsea Christmas trees and umbilical locking systems discussed above.

It is amongst the objects of at least one embodiment of the present invention to obviate or mitigate at least one of the foregoing disadvantages.

According to a first aspect of the present invention, there is provided a subsea hydraulic power generating apparatus, for generating hydraulic power to operate a device in a subsea environment, the apparatus comprising:

a hydraulic pump which is operable to supply fluid to a hydraulic actuator associated with the device;

a mechanical interface comprising a drive member coupled to a rotor of the pump, for transferring an input drive force to the rotor to operate the pump; and

a control assembly for controlling the flow of fluid between the pump and the hydraulic actuator, to thereby control operation of the actuator and so a desired function of the device;

in which the pump, interface and control assembly are provided as a unit which can be releasably mounted to the device in the subsea environment and coupled to the hydraulic actuator to provide hydraulic power when required. According to a second aspect of the present invention, there is provided a subsea device comprising:

at least one hydraulic actuator for performing at least one function of the device; and

a subsea hydraulic power generating apparatus according to the first aspect of the invention;

in which the unit of the apparatus comprising the pump, interface and control assembly is releasably mounted to the device and coupled to the hydraulic actuator (or at least one actuator where the device comprises a plurality of actuators) to provide the hydraulic power when required.

The apparatus of the invention may facilitate the operation of a subsea device without requiring the provision of hydraulic control lines extending to a surface facility, as is required with prior devices. In particular, provision of the pump, interface and control assembly as a unit which can be releasably coupled to the device may provide the ability to couple to the device which is to be controlled as and when required, without requiring a permanent connection to a surface facility.

The apparatus of the invention may additionally or alternatively provide a backup (or override) for the operation of a device in a subsea environment, in the event of a hydraulic failure of the device or a component of the device. Again, provision of the pump, interface and control assembly as a unit may which can be releasably coupled to the device may provide the ability to couple to the device which is to be controlled in the event of such a failure occurring, and without requiring a permanent connection to a surface facility.

The apparatus of the invention may have a use with any subsea device which requires an external input for controlling an operation of the device. Suitable devices may include: a BOP; a subsea tree; a locking assembly for locking an umbilical stab plate to a receptacle on a subsea component; a wellhead locking assembly; and a locking assembly for locking other subsea components to a mounting arrangement on a seabed. The interface may be a mechanical interface in that it is mechanically operated, that is by a force which is mechanically imparted on the interface. Operation of the apparatus may be achieved by rotating the drive member of the interface, and this will typically be achieved using an ROV, but may also be achieved by a diver. In the case of an ROV, a manipulator arm of the ROV may be employed. The manipulator arm may directly rotate the drive member. The manipulator arm may carry a dedicated rotary drive mechanism for rotating the drive member, which may comprise its own source of power. The rotary drive mechanism may be a hydraulic motor with its own source of hydraulic input power. Use of a dedicated rotary drive mechanism may be preferred, as ROV manipulator arms typically have a rotary speed of around 40rpm, whereas a rotary drive mechanism with its own source of power may rotate at much higher speeds.

The provision of an interface for transferring an input drive force to the pump rotor may mitigate the problems associated with existing 'hot stab' techniques, as operation of the apparatus requires only the application of an input force to the drive member, and the control assembly may employ the hydraulic fluid within the apparatus to facilitate operation of the actuator.

The hydraulic actuator may be a primary hydraulic actuator of the device. For example, the hydraulic actuator may be a ram (piston) of a BOP; a valve of a subsea tree; a locking component of a locking assembly for an umbilical stab plate, wellhead locking assembly or other locking assembly for locking the subsea device to a mounting arrangement on the seabed. The hydraulic actuator may be a secondary or override hydraulic actuator of the device. For example, the hydraulic actuator may be coupled to a ram of a BOP; a valve of a subsea tree; a locking component of a locking assembly for an umbilical stab plate, wellhead locking assembly or other locking assembly for locking the subsea device to a mounting arrangement on the seabed.

The hydraulic actuator may form part of the apparatus, and may be arranged to be permanently mounted on or provided as part of the subsea device. The unit comprising the pump, interface and control assembly may be releasably coupled to the actuator mounted/provided on the device when the provision of subsea hydraulic power (to operate the actuator) is required. This may provide a number of advantages. For example, the unit comprising the pump, interface and control assembly can be used to operate a plurality of different hydraulic actuators on the same device or different devices. The hydraulic actuator can be operated and then hydraulically locked, without requiring a permanent hydraulic pressure control system to maintain applied pressure, the unit being couplable to the actuator when required to change its operation state. The apparatus, for example the control assembly, may be arranged for coupling to a plurality of actuators, so that the apparatus can be employed to control the operation of said plurality of actuators. This may facilitate the operation of a plurality of subsea devices, via at least one actuator of each device (controlled by the apparatus), and/or the operation of a plurality of different functions of a single device, each actuator being associated with a respective function or functions. The apparatus, in particular the control assembly, may comprise flow control equipment, which may be or may include a manifold, for controlling the flow of fluid to a plurality of actuators. The flow control equipment may be provided between the unit (comprising the pump, interface and control assembly) and the actuators. The apparatus may comprise a hydraulic fluid reservoir. The reservoir may be provided as part of the unit comprising the pump, interface and control assembly which can be releasably coupled to the actuator. The reservoir may provide a source of hydraulic fluid for operation of the hydraulic actuator. The control assembly may be arranged to control the flow of fluid to and from the reservoir during operation of the actuator. The control assembly may serve for coupling the pump to the actuator in a closed loop, which may extend from the pump, through the actuator and the fluid reservoir (but not necessarily in that flow order) and back to the pump. The provision of a dedicated fluid reservoir and an interface for transferring an input drive force to the pump rotor may mitigate the problems associated with existing 'hot stab' techniques, as operation of the apparatus requires only the application of an input force to the drive member, and employs the hydraulic fluid within the apparatus and the fluid reservoir to operate the actuator. The provision of a dedicated fluid reservoir may ensure that sufficient hydraulic fluid exists for operation of the actuator, without having to rely purely on the fluid contained within the actuator. This may be important where there has been a failure of an existing operating system for the actuator resulting, potentially, in the loss of hydraulic control fluid. The control assembly may comprise a plurality of valves, and may comprise first and second outlet valves, the assembly being arranged so that each outlet valve can selectively control the flow of fluid from the hydraulic actuator. For example, where the hydraulic actuator is a linear actuator such as a ram (or piston) mounted for movement in a cylinder, the first and second outlet valves may be coupled to the cylinder and the control assembly may be arranged so that the first and second outlet valves are exposed to respective opposed faces of the ram (or piston). Where the hydraulic actuator is a rotary actuator such as a hydraulic motor, the control assembly may be arranged so that the first and second outlet valves can be coupled to respective opposed ports of the actuator (one of which ports forms an inlet port and the other an outlet port, depending on the direction of rotation of the actuator). The first and second outlet valves may be rated to open and allow flow at different pressures, and so may have different threshold pressures below which the valves restrict fluid flow. This may provide the ability to tune the apparatus so that a higher pressure is required to move the actuator in a first direction than in a second, opposed direction. Said direction may be opposed axial directions in the case of a linear actuator; or opposed rotational directions (clockwise and anti- or counter-clockwise directions) in the case of a rotary actuator.

The interface drive member may be a drive shaft coupled to the pump rotor (or impeller), and may be an input shaft of the pump rotor itself or a connecting shaft coupled to the rotor input shaft. Typically, the pump will be a rotary pump comprising a rotor arranged to rotate within a stator, but the pump could conceivably be a linear rod-type pump (in which case the interface drive member would be coupled to the pump rod).

The unit may be releasably mountable to a housing of the device, and hydraulically connected to the hydraulic actuator, such as via suitable releasable hydraulic connectors. Further features of the device of the second aspect of the invention may be derived from the text set out above relating to the apparatus of the first aspect of the invention. In particular, the subsea device may be a device selected from the list/options set out above in relation to the first aspect of the invention.

According to a third aspect of the present invention, there is provided a method of generating hydraulic power to operate a device in a subsea environment, the method comprising the steps of:

releasably mounting a unit of a hydraulic power generating apparatus to the subsea device and coupling the unit to a hydraulic actuator associated with the device, the unit comprising a hydraulic pump, an interface comprising a drive member coupled to a rotor of the pump, and a control assembly;

operating the drive member of the interface to transfer an input drive force to the rotor and thereby operate the pump; and

operating the control assembly to control the flow of fluid between the pump and the hydraulic actuator, to thereby control operation of the actuator and so a desired function of the device.

The step of operating the drive member of the interface may comprise rotating the drive member to transfer the input drive force to the rotor and thereby operate the pump.

The method may comprise the further step of, following operation of the actuator, dismounting the unit from the device and decoupling the unit from the hydraulic actuator. The method may comprise hydraulically locking the actuator in a desired operation state or condition prior to such dismounting and decoupling. The actuator may be hydraulically locked by closing a valve or valves associated with the actuator.

Following such dismounting and decoupling, the method may comprise the further step of subsequently remounting the unit on the device and:

recoupling the unit to the same actuator, to change an operation state or condition of said actuator; and/or coupling the unit to at least one further actuator of the device, to control the operation of said further actuator.

Following such dismounting and decoupling, the method may comprise the further step of releasably mounting the unit to a further subsea device and coupling the unit to a hydraulic actuator of the further device, and then repeating the steps set out above in the third aspect of the invention, for controlling the operation of the actuator of the further device.

The method may comprise the further step of, following operation of the actuator, employing the unit to control the operation of at least one further actuator associated with the device.

The step of operating the drive member of the interface may be achieved using an ROV, but could also be achieved by a diver. In the case of an ROV, a manipulator arm of the ROV may be employed. The manipulator arm may directly rotate the drive member. The manipulator arm (or diver) may carry a dedicated rotary drive mechanism for rotating the drive member, which may comprise its own source of power.

The method may comprise coupling the unit to a primary hydraulic actuator of the device. For example, the hydraulic actuator may be a ram (piston) of a BOP; a valve of a subsea tree; a locking component of a locking assembly for an umbilical stab plate, wellhead locking assembly or other locking assembly for locking the subsea device to a mounting arrangement on the seabed. The method may comprise coupling the unit to a secondary or override hydraulic actuator of the device. For example, the hydraulic actuator may be coupled to a ram of a BOP; a valve of a subsea tree; a locking component of a locking assembly for an umbilical stab plate, wellhead locking assembly or other locking assembly for locking the subsea device to a mounting arrangement on the seabed.

The method may comprise coupling the unit, for example the control assembly, to a plurality of actuators, so that the apparatus can be employed to control the operation of said plurality of actuators. The method may involve controlling the operation of a plurality of subsea devices, via at least one actuator of each device; and/or the operation of a plurality of different functions of a single device, each actuator being associated with a respective function or functions. The method may comprise controlling the flow of fluid to a plurality of actuators using flow control equipment, which may be or may comprise a manifold. The flow control equipment may be provided between the unit (comprising the pump, interface and control assembly) and the actuators.

Further features of the method of the third aspect of the invention may be derived from the text set out above relating to the apparatus and/or device of the first and/or second aspect of the invention.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic illustration of a subsea power generating apparatus in accordance with an embodiment of the invention, coupled to a hydraulic actuator;

Fig. 2 is a side view of a subsea device in the form of a BOP, for which the apparatus of Fig. 1 is to provide power;

Fig. 3 is a view similar to Fig. 1, but showing a variation in the means of operating the apparatus; Fig. 4 is a view similar to Fig. 1, showing the apparatus of Fig. 1 coupled to a plurality of hydraulic actuators;

Fig. 5 is a view of the apparatus shown in Fig. 1, illustrating a control assembly forming part of the apparatus in greater detail;

Figs. 6 and 7 are views of the apparatus shown in Fig. 5, which have been annotated to illustrate the direction of flow when a rotor of a pump of the apparatus is operated to rotate in first and second rotational directions, the solid black line indicating the direction of flow of fluid from the pump to the actuator and the dashed black line indicating the direction of return flow from the actuator to the pump; Fig. 8 is a view of the apparatus of Fig. 1, illustrating the control assembly in the same level of detail of Fig. 5, but coupled to an alternative type of hydraulic actuator;

Fig. 9 is a side view of a subsea device in the form of a subsea Christmas tree, for which the apparatus of Fig. 1 is to provide power, the drawing also illustrating an umbilical stab plate with which the apparatus of the invention has a use; and

Fig. 10 is a side view of a subsea device in the form of a wellhead connector, for which the apparatus of Fig. 1 is to provide power. Turning firstly to Fig. 1 , there is shown a schematic illustration of a subsea power generating apparatus in accordance with an embodiment of the invention, the apparatus indicated generally by reference numeral 10. The apparatus 10 is for generating hydraulic power to operate a device in a subsea environment, which in this case is BOP 12, shown in the side view of Fig. 2.

The apparatus 10 generally comprises a hydraulic pump 14 which is operable to supply fluid to a hydraulic actuator 16 associated with the BOP 12. In this instance, the actuator 16 takes the form of a ram or piston of the BOP 12, which is housed in a cylinder 18, and which is operable to provide pressure control for a subsea well. As can be seen from Fig. 2, the BOP typically comprises a pair of cylinders 18a, which house opposed seal rams (not shown) which can seal around tubing extending into the well. The BOP 12 also comprises a second pair 18b of cylinders which house opposed shear rams (also not shown), which can cut and seal a string of tubing and any associated tool extending through the BOP 12, in an emergency situation.

The apparatus 10 also comprises an interface 20 comprising a drive member in the form of an ROV-friendly handle 22, which is coupled to a rotor 24 of the pump 14. The interface 20 is a mechanical interface, and is for transferring an input drive force to the rotor 24 to operate the pump 14. The apparatus 10 also comprises a control assembly, indicated generally by reference numeral 26, for controlling the flow of fluid between the pump 14 and the hydraulic actuator 16, to thereby control operation of the actuator and so a desired function of the device. In the illustrated example of a BOP 12, the function which is to be carried out is a pressure control function, in which the ram 16 is operated to seal the well or to shear tubing extending through the BOP, as appropriate.

The pump 14, interface 20 and control assembly 26 are provided as a unit which can be releasably mounted to the BOP 12 in the subsea environment. Mounting of the unit on the BOP 12 is achieved using suitable mountings, which can be operated by an ROV or diver. As can be seen from Fig. 2, the BOP 12 is mounted on a wellhead 28 of the well at the level of a seabed 30. The unit comprising the pump 14, interface 20 and control assembly 26 is shown in Fig. 2, and denoted by reference numeral 32, and is shown mounted on a housing 34 of the BOP 12. The unit 12 is coupled to the ram 16 of the BOP 12 to provide hydraulic power for operation of the ram when required.

In the illustrated embodiment, and as discussed above, the hydraulic actuator 16 takes the form of a ram 16 of the BOP 12. Accordingly, the power generating apparatus 10 of the present invention facilitates the direct operation of the BOP ram 16 to provide the required pressure control. However, the apparatus 10 of the invention may additionally or alternatively be capable of operating a secondary or override actuator, in the event of failure of a primary ram of the BOP 12. In that situation, the actuator 16 shown in Fig. 1 would be the secondary or override actuator, and would be coupled to the ram housed in the cylinder 18a/b, to operate the primary BOP ram in the event of a hydraulic failure in the BOP 12. This could be achieved by mounting the secondary actuator cylinder 18 to the cylinder of the primary BOP ram in such a way that the secondary ram 16 can exert a force on the primary BOP ram. In general terms, the apparatus 10 is operated as follows. The ROV friendly handle 22 is designed in such a way that it can be operated by an ROV 36, through a manipulator 38. The manipulator 38 carries a coupling 40 at its end which is rotatable, typically at speeds of around 40 rpm, as is well known in the industry. The coupling 40 can engage the handle 22, to rotate the handle and thus the pump rotor 24. In a variation shown in Fig. 3, the ROV manipulator 38 can carry a dedicated rotary drive mechanism such as a torque tool 42, for rotating the handle 22 and so the rotor pump 24. The torque tool is powered by a dedicated hydraulic power source 44 carried by the ROV 36, and advantageously can be rotated at much higher speeds than is typical of the manipulator coupling 40.

The unit 32 is releasably coupled to the BOP ram 16 by means of hydraulic connectors 46 and 48, so that the unit 32 can be stabbed-in to hydraulically couple the control assembly 26 to the ram cylinder 18. The control assembly 26 is arranged so that, when the pump rotor 24 is rotated to drive the pump 14, fluid is supplied into and exhausted from the cylinder 18 in order to translate the ram 16 within the cylinder. In the illustrated embodiment, the ram 16 is shown in a retracted position and, when it is desired to operate the ram to move it to a sealing or shear position (as appropriate), the control assembly 26 is operable to supply fluid into the cylinder 18 at a first end 50, and to exhaust fluid from the cylinder at a second end 52. The ram 16 defines opposed piston faces 54 and 56 and, when fluid is supplied into the cylinder 18 at the first end 50, the fluid acts on the first piston face 54. The second piston face 56 is exposed to the fluid in the portion of the cylinder 18 associated with the second end 52. The elevated pump pressure applied to the piston face 54 is such that a pressure differential exists between the piston faces 54 and 56, and this acts to translate the ram 16 in the direction of the arrow A, to perform the seal/shear function, in a fashion known in the art. Translation of the ram 16 back to the position of Fig. 1 can be achieved by reversing the direction of flow. The invention provides the ability to dismount the unit 32 from the BOP 12 following operation of the BOP ram 16. The hydraulic connectors 46 and 48 are arranged such that, following disconnection, movement of the ram 16 is prevented as no fluid can be charged into or discharged from the cylinder 18. Accordingly, an operating state of the ram 16 is maintained, which in the described example, is the holding of the ram in a seal or shear position. When it is desired to return the ram 16 to its original operating state, shown in Fig. 1, the unit 32 can be remounted on the BOP 12 and coupled to the cylinder 18 so that the ram 16 can be translated back to its start position. The invention also provides the ability to operate a plurality of actuators, and this is illustrated in Fig. 4. Fig. 4 is a view similar to Fig. 1 but showing the apparatus 10 coupled to two separate actuators, which comprise separate seal and shear rams 16a and 16b of the BOP 12 shown in Fig. 2. This is achieved by means of optional flow control equipment, indicated generally by reference numeral 58, which takes the form of a manifold 58. The manifold 58 serves for directing fluid into and returning fluid from the selected cylinder 18a/l 8b housing the ram 16a/l 6b which is to be operated. Operation of the respective ram 16a/16b is controlled by means of suitable valves 60, 62 of the manifold 58. The valve 60 can be operated to direct hydraulic fluid into (or allow the return flow of hydraulic fluid from) branches 64 or 66 of the manifold 58 associated with the respective cylinder

18a/18b. In a similar fashion, the valve 62 can be operated to control fluid supply into (or return fluid from) branches 68 or 70 of the manifold 58. It will be understood that this provides for independent operation of the rams 16a, 16b or conceivably simultaneous operation of the rams.

The apparatus 10 and its method of operation will now be described in more detail, with reference also to Fig. 5, which is a view similar to Fig. 1, but showing further detail of the control assembly 26.

The flow control assembly 26 is of a type which is known in the field of hydraulic controls, and is commercially available from the Sun Hydraulics Corporation. The control assembly 26 comprises first and second valve arrangements, indicated generally by reference numerals 72 and 74, and which operate to permit fluid flow in the direction of the arrows 76, 78 under specified operating conditions, which will be discussed below. The control assembly 26 also comprises a network of flow lines which provide for fluid flow between the pump 14 and the BOP cylinder 18, the network of flow lines indicated generally by reference numeral 80. Fig. 6 shows the control assembly 26 in the position of Fig. 5, during an operation to translate the ram 16 in the direction of the arrow A. In this scenario, the ROV manipulator coupling 40 is operated to rotate the pump rotor 24, say in a clockwise direction. The pump 14 drives hydraulic fluid along a flow line 82 through a one-way valve 84 into flow line 86, and then into the cylinder 18 at the first end 50. Flow of fluid from the pump 14 to the cylinder 18 is indicated by a solid black line in the drawing. The pressure of the fluid in the flow line 82 is communicated through a branch line 88 to a biased valve element 90 of the second valve arrangement 74. The second valve arrangement 74 is exposed to fluid in the cylinder 18 in the portion acted on by the second piston face 56 and this, together with a spring 92, acts to normally hold the biased valve element 90 in a closed position, preventing fluid flow through the valve arrangement 74 in the direction indicated by arrow 78. Specifically, the fluid pressure is communicated to the valve arrangement 74 through a flow line 94. This fluid pressure acts on a first face of the valve element 90 (not shown) and, together with the biasing force of the spring 92, acts to maintain the valve element 90 in the closed position. However, when a second, opposed face of the valve element 90 is exposed to fluid at the pump supply pressure (in the flow line 82), via the branch line 88, this acts against the spring 92 force and the pressure in the flow line 94. This results in movement of the valve element 90 to an open position, where fluid can flow through the valve arrangement 74 in the direction 78. This fluid flows on into a flow line 96, and from there into a flow line 98 which communicates with a fluid reservoir 100 of the apparatus 10. The fluid reservoir 100 provides a source of hydraulic fluid to facilitate translation of the ram 16. The fluid then flows on through a flow line 102, through a one- way valve 104 into a flow line 106, and hence returns in a closed loop to the pump 14. The return flow of fluid from the cylinder 18 to the pump 14 is indicated in the broken black line in the drawing.

It will therefore be understood that opening of the valve element 90 of the second valve arrangement 74 serves to permit fluid flow in the closed loop. The pressure differential between the fluid supplied from the pump 14 along the flow lines 82 and 84, acting on the first piston face 54, and the fluid in the cylinder 18 acted on by the second piston face 56, is such that the ram 16 is translated in the direction A, to perform the required seal/shear function. It will be noted that the first valve arrangement 72 is, in this scenario, exposed to fluid at the pressure of the pump supply via a branch line 108. However, a biased valve element 90a is, at this time, exposed to fluid at the pressure of the pump return, via a branch line 88a. This pressure is insufficient to overcome the combined action of a spring 92a and the fluid acting on a first face of the valve 90a. Accordingly, the valve

arrangement 72 remains closed, preventing fluid flow in the direction of the arrow 76.

Fig. 7 shows flow in the reverse direction, to translate the ram 16 back to the position of Figs. 5 and 6. In this scenario, the pump rotor 24 is rotated in the opposite direction, and so an anti-clockwise or counter-clockwise direction. Fluid then flows through the flow line 106, a one-way valve 112 and flow line 94 into the cylinder 18 at the second end 52, acting on the second piston face 56. The fluid in the part of the cylinder 18 acted on by the first piston face 54 communicates with the flow line 86 and hence with the first valve arrangement 72, through branch line 108. In this scenario, a second face of the biased valve element 90a of the valve arrangement 72 is exposed to fluid at the pump supply pressure through the branch line 88a. This is sufficient to overcome the combined action of the pressure acting on the first face of the valve element 90a and the spring 92a, opening the valve arrangement 72 and permitting fluid flow in the direction 76. The fluid flows on into a flow line 114, into the flow line 98 (which communicates with the reservoir 100), and from there flows into the flow line 102, through a one-way valve 116 and back into the flow line 82 to the pump 14. In this second flow scenario, the biased valve element 90 of the second valve arrangement 74 is exposed to fluid at the return pump pressure via the branch line 88, and this is insufficient to open the valve arrangement. Accordingly, fluid flow in the direction 78 is restricted.

The control assembly 26, in particular the first and second valve arrangements 72 and 74, can be rated to open and allow flow at different pressures, and so may have different threshold pressures below which the valves restrict fluid flow. This may be achieved by providing springs 92, 92a which exert different spring forces on the respective valve elements 90, 90a. This provides the ability to tune the apparatus 10 so that a higher pressure is required to move the actuator (ram 16) in a first direction than in a second, opposed direction. For example, the valve arrangements 72 and 74 may be rated so that a higher pressure is required to retract the ram 16 from the position of Fig. 7 back to its start position (Fig. 6), compared to the force required to move the ram to its extended position (Fig. 7). This may be of use in preventing inadvertent retraction of the ram 16 following activation in an emergency shut-in of the well, as a much higher fluid pressure force is required to open the valve arrangement 74 to retract the ram. Of course, the valve arrangements may be arranged in the opposite fashion depending upon the circumstances, in particular upon the actuator which is to be operated, and so may be arranged so that a higher pressure is required to move the ram to its extended position (Fig. 7).

Turning now to Fig. 8, the apparatus 10 is shown during use in the operation of an actuator 16' in the form of a hydraulic motor. The motor 16' has an output shaft 118 which can provide a rotary output to rotate and so drive a component of a subsea device. In the illustrated embodiment, the motor 16' may have a particular utility in the operation of a valve on a subsea Christmas tree, which is shown in Fig. 9 and indicated generally by reference numeral 120. In a known fashion, the subsea tree 120 is mounted on wellhead 28 and comprises a number of valves, indicated at 122 to 128, for providing pressure control. For example, the valves 122 to 128 may allow for main and annulus pressure control and the injection of treatment fluids into the well. The unit 32 is, in this case, releasably mounted to the subsea tree 120, and coupled to the motor 16' via connectors 46' and 48'. Operation of the pump 14 supplies and exhausts fluid to and from the motor 16' to rotate the output shaft 118. This rotary drive force is transferred to an input shaft of the associated valve (not shown), to control the operation state of the valve, that is open, closed or partially open.

As also shown in Fig. 9, a number of separate apparatus 10, 10a, 10b and 10c according to the invention can be provided on the subsea tree 120, to control operation of the respective valves 122 to 128. This provides for independent actuation of the valves. Like

components of the apparatus 10a, 10b and 10c with the apparatus 10 share the same reference numerals, with the addition of the appropriate suffix 'a', 'b' or 'c'. Alternatively and following the teachings outlined in Fig. 4, a single apparatus 10 may control multiple motors 16' associated with respective valves 122 to 128, such as via a manifold (not shown). Fig. 9 also shows an alternative further use of the apparatus 10, the apparatus here being indicated by reference numeral lOd. Once again, like components of the apparatus lOd with the apparatus 10 share the same reference numerals, with the addition of the suffix 'd'. Specifically, Fig. 9 also shows an umbilical 130 carrying electrical and/or hydraulic control lines, fluid injection lines and the like (not shown), for performing a number of subsea operations. For example, control lines may be provided for operating one or more of the tree valves 122 to 128, instead of the respective apparatus 10 to 10c. The umbilical 130 carries a stab plate 132 at a lower end, which mates with a receptacle 134 on the subsea tree 120. The stab plate 132 includes a hydraulically actuated locking assembly, which includes locking dogs 138 which can be operated to engage in a latch recess 140 in the receptacle 134, to thereby lock the stab plate 132 to the subsea tree 120. The dogs 138 are hydraulically actuated, and so form the actuators which can be operated by the apparatus lOd. The apparatus lOd is operated to actuate the dogs 138 in the fashion described above in relation to Figs. 1 to 8. A unit 32d of the apparatus lOd can be releasable mounted to the stab plate 132, and coupled to the dogs 138. In this way, the unit 32d can be dismounted from the stab plate 132 and decoupled from the dogs 138 following actuation of the dogs.

Turning now to Fig. 10, there is shown a side view of a subsea device in the form of a wellhead connector 142, for which the apparatus of the present invention is to provide power. The apparatus is indicated generally by reference numeral lOe, and again like components of the apparatus lOe with the apparatus 10 share the same reference numerals, with the addition of the suffix 'e'. Fig. 10 shows the wellhead 28 in more detail, the wellhead illustrated in partial cross-section. A production tubing 144 is shown, which is to be connected to the wellhead 28, and through which well fluids are to be recovered to surface. The production tubing 144 carries the wellhead connector 142, which serves for connecting the production tubing 144 to the wellhead 28, and for sealing the production tubing relative to the wellhead.

In a conventional fashion, the wellhead connector 142 includes hydraulically operated locking dogs 146, which can be operated to engage in a latch recess 148 of the tree. The dogs 146 are urged radially outwardly by an actuator in the form of an annular piston 150, which is axially moveable within an annular cylinder 152 defined by a body 154 of the wellhead connector 142. The annular piston 150 is operated in the same way as the BOP ram 16 shown and described with reference to Figs. 1 to 7, under the control of the apparatus lOe. Translation of the piston 150 axially downwardly, in the direction of the arrow B, urges the dogs 146 radially outwardly by means of cooperating ramps 156 on the piston 150 and 158 on dogs 146. A unit 32e of the apparatus lOe can be dismounted from the wellhead connector 142 following actuation of the dogs 146 if desired.

Various modifications may be made to the foregoing without departing from the spirit or scope of the present invention.

For example, the unit may be arranged so that it is provide as a permanent part, or permanently coupled to, the subsea device whose operation is to be controlled. The unit may thus be arranged so that it is not releasably mountable.

Whilst the unit is described as comprising a pump having a rotor which is rotated to supply fluid to the actuator (and so to generate hydraulic power subsea), it will be understood that it is within the scope of the present invention to employ alternative types of pump, such as rod-type pumps. This would require an appropriate interface enabling operation by an ROV (or diver).

Other types of interfaces, which may be non-mechanical interfaces, may be employed.

Claims

1. A subsea hydraulic power generating apparatus, for generating hydraulic power to operate a device in a subsea environment, the apparatus comprising:

in which the pump, interface and control assembly are provided as a unit which can be releasably mounted to the device in the subsea environment and coupled to the hydraulic actuator to provide hydraulic power when required.

2. Apparatus as claimed in any preceding claim, in which the control assembly employs hydraulic fluid within the apparatus to operate the actuator.

3. Apparatus as claimed in any preceding claim, in which the apparatus can be coupled to and control the operation of a plurality of hydraulic actuators.

4. Apparatus as claimed in claim 3, in which the control assembly comprises flow control equipment for controlling the flow of fluid to the plurality of hydraulic actuators.

5. Apparatus as claimed in any preceding claim, comprising a hydraulic fluid reservoir, the reservoir provided as part of the unit comprising the pump, interface and control assembly.

6. Apparatus as claimed in claim 5, in which the control assembly is arranged to control the flow of fluid to and from the reservoir during operation of the actuator.

7. Apparatus as claimed in claim 6, in which the control assembly serves for coupling the pump to the actuator in a closed loop.

8. Apparatus as claimed in any preceding claim, in which the control assembly comprises a plurality of outlet valves, and in which the control assembly is arranged so that each outlet valve can selectively control the flow of fluid from the hydraulic actuator.

9. Apparatus as claimed in claim 8, comprising first and second outlet valves, the outlet valves being rated to open and allow flow at different pressures.

10. Apparatus as claimed in any preceding claim, in which the interface drive member is a drive shaft coupled to the pump rotor.

11. Apparatus as claimed in claim 10, in which the unit is releasably mountable to a housing of the device, and hydraulically connectable to the hydraulic actuator via releasable hydraulic connectors.

12. A subsea device comprising:

a subsea hydraulic power generating apparatus according to any one of claims 1 to

Π;

in which the unit of the apparatus comprising the pump, interface and control assembly is releasably mounted to the device and coupled to the hydraulic actuator to provide the hydraulic power when required.

13. The device of claim 12, in which the apparatus is arranged to provide a backup for the operation of the device.

14. The device of either of claims 12 or 13, in which the device is selected from the group comprising: a BOP; a subsea tree; a locking assembly for locking an umbilical stab plate to a receptacle on a subsea component; and a wellhead locking assembly.

15. The device of any one of claims 12 to 14, in which the hydraulic actuator is a primary hydraulic actuator of the device.

16. The device of any one of claims 12 to 14, in which the hydraulic actuator is a secondary hydraulic actuator of the device.

17. The device of either of claims 15 or 16, in which the hydraulic actuator is selected from the group comprising: a ram of a BOP; a valve of a subsea tree; and a locking component of a locking assembly.

18. The device of any one of claims 12 to 17, in which the unit comprising the pump, interface and control assembly is releasably couplable to the actuator.

19. The device of any one of claims 12 to 18, in which the hydraulic actuator is a ram mounted for movement in a cylinder; and in which the control assembly comprises first and second outlet valves, the assembly being arranged so that each outlet valve can selectively control the flow of fluid from the cylinder to operate the ram.

20. The device of any one of claims 12 to 18, in which the hydraulic actuator is a hydraulic motor; and in which the control assembly comprises first and second outlet valves, the assembly being arranged so that the first and second outlet valves can be coupled to respective opposed ports of the motor.

21. The device of either of claims 19 or 20, in which the first and second outlet valves are rated to open and allow flow at different pressures.

22. A method of generating hydraulic power to operate a device in a subsea environment, the method comprising the steps of:

23. The method of claim 22, in which the step of operating the drive member of the interface comprises rotating the drive member to transfer the input drive force to the rotor and thereby operate the pump.

24. The method of either of claims 22 or 23 in which, following operation of the actuator, the method comprises the further steps of dismounting the unit from the device and decoupling the unit from the hydraulic actuator.

25. The method of claim 24, comprising hydraulically locking the actuator in a desired operation state prior to dismounting and decoupling the unit.

26. The method of either of claims 24 or 25 in which, following dismounting and decoupling of the unit, the method comprises the further step of subsequently remounting the unit on the device.

27. The method of claim 26 comprising:

recoupling the unit to the actuator, to change an operation state of the actuator.

28. The method of either of claims 26 or 27, comprising:

coupling the unit to at least one further actuator of the device, to control the operation of said further actuator.

29. The method of either of claims 24 or 25 in which, following dismounting and decoupling of the unit, the method comprises the further steps of: releasably mounting the unit to a further subsea device;

coupling the unit to a hydraulic actuator of the further device;

operating the control assembly to control the flow of fluid between the pump and the hydraulic actuator of the further device, to thereby control operation of the actuator and so a desired function of the further device.

30. The method of any one of claims 22 to 29 in which, following operation of the actuator, the method comprises the further step of employing the unit to control the operation of at least one further actuator associated with the device.

31. The method of any one of claims 22 to 30, in which the step of operating the drive member of the interface is achieved using a manipulator arm of an ROV.

32. The method of claim 31 , in which the manipulator arm directly rotates the drive member.

33. The method of claim 31 , in which the manipulator arm carries a rotary drive mechanism which is used to rotate the drive member, the drive mechanism comprising its own source of power.

34. The method of any one of claims 22 to 33, comprising coupling the unit to a primary hydraulic actuator of the device.

35. The method of any one of claims 22 to 33, comprising coupling the unit to a secondary hydraulic actuator of the device.

36. The method of either of claims 34 or 35, in which the hydraulic actuator is selected from the group comprising: a ram of a BOP; a valve of a subsea tree; and a locking component of a locking assembly.

37. The method of any one of claims 22 to 36, comprising coupling the unit to a plurality of actuators, and employing the apparatus to control the operation of the plurality of actuators.

38. The method of claim 37, comprising controlling the operation of a plurality of subsea devices, via at least one actuator of each device.

39. The method of claim 37, comprising controlling the operation of a plurality of different functions of a single device, each actuator being associated with a respective function or functions.