GB2546090A

GB2546090A - A subsea, stand-by installation

Info

Publication number: GB2546090A
Application number: GB1600291.7A
Authority: GB
Inventors: Stuart Elliot Keith; James Bolton Adam
Original assignee: Allspeeds Holdings Ltd
Current assignee: Allspeeds Holdings Ltd
Priority date: 2016-01-07
Filing date: 2016-01-07
Publication date: 2017-07-12
Also published as: GB201600291D0

Abstract

A subsea, stand-by installation having a stand-by tool 1 and a hydraulic drive system 2 therefor. The tool 1 has a hydraulic actuator 4 that is supplied with hydraulic fluid from the hydraulic drive system 2. The hydraulic drive system 2 has a pump in the form of a hydraulic cylinder with a cylinder barrel 10 defining a first fluid inlet or outlet port 11 at one end and containing a piston 14 secured to a piston rod 15 that projects from one end of the cylinder barrel 10. The projecting end of the piston rod 15 being adapted for connection to one end of a tether 16 the other end of which tether is intended for securement to equipment or an attachment point from which the installation is to be separated on operation of the tool. In use a pulling force on the tether 16 moves the piston rod 15 and thereby the piston 14 along the cylinder barrel 10 to pump hydraulic fluid contained in the cylinder barrel 10 via the fluid inlet or outlet port 11 to the actuator 4 to operate the tool 1. Optionally, the tool is a cutting tool for severing umbilicals or hoses contained within.

Description

A SUBSEA, STAND-BY INSTALLATION

The present invention relates to a subsea, stand-by installation for use in an emergency situation.

In offshore industries, for example in oil and gas drilling industries, surface vessels are often connected to seabed installations and to the seabed itself by lines such as umbilicals, hydraulic hoses, tethers, moorings, towing lines and the like. Should an emergency situation arise, for example in heavy seas, it is sometimes necessary to sever these lines to disconnect the vessel from the installation or the seabed. Conventionally, connectors may be used in these lines that are designed to pull apart if the surface vessel unintentionally moves away from the installation, for example in heavy seas, otherwise the lines may rip out equipment from the installation as the vessel moves away. Stand-by hydraulic tools that are used in such installations are usually fed with hydraulic fluid through hoses that are connected to the surface vessel. In the past, the severing of the hydraulic hose took place on or close to the vessel but this had the unfortunate consequence that the severed hose fell to the seabed and the hydraulic fluid it contained spilt into the sea. The heavy, severed end of the hose could also cause considerable damage to the installation itself as it fell to the seabed. Thereafter, the hose had to be recovered by divers for reconnection. The same applied to other umbilicals and lines connected to the vessel. More recently, cutting tools have been deployed as part of a subsea rig so that the hydraulic hoses and lines can be severed close to the rig and then reeled back into the vessel. This permits the hydraulic fluid to be contained and divers do not need to recover the hoses and lines prior to reconnection, which is usually accomplished by a remotely operated vehicle (ROV). However, it is not always possible in an emergency situation for the surface vessel to pump hydraulic fluid to the seabed to actuate such an emergency cutting tool.

An object of the present invention is to overcome or substantially mitigate the aforementioned disadvantages and to provide a subsea, stand- installation for use in an emergency situation that does not rely on hydraulic fluid being pumped from a remote source.

According to the present invention there is provided a subsea, standby installation comprising a stand-by tool and a hydraulic drive system therefor, the tool comprising a hydraulic actuator that is supplied with hydraulic fluid from the hydraulic drive system, and the hydraulic drive system comprising a pump in the form of a hydraulic cylinder with a cylinder barrel defining a first fluid inlet/outlet port at one end and containing a piston secured to a piston rod that projects from one end of the cylinder barrel, the projecting end of the piston rod being adapted for connection to one end of a tether the other end of which tether is intended for securement to equipment or an attachment point from which the installation is to be separated on operation of the tool whereby in use a pulling force on the tether moves the piston rod and thereby the piston along the cylinder barrel to pump hydraulic fluid contained in the cylinder barrel via the fluid inlet/outlet port to the actuator to operate the tool.

Preferably, the projecting end of the piston rod is adapted for connection to the tether by the provision of a mechanical link that is adapted to disconnect from the piston rod or from the tether when a predetermined pulling force is reached.

Preferably also, the first and second hydraulic accumulators are provided with appropriately biased pressure settings relative to each other whereby the hydraulic drive system and the actuator automatically reset after use.

Preferably also, the tool is a cutting tool.

Other preferred but non-essential features of the present invention are described in the dependent claims appended hereto.

The present invention will now be described by way of example with reference to the accompanying drawing in which is a schematic view, in partial cross-section, of an embodiment of a subsea, stand-by installation.

The embodiment of the present invention shown in the drawing is of a subsea, stand-by installation comprising a subsea cutting tool l and a hydraulic drive system 2 for use in the emergency severing of umbilicals, hydraulic hoses, tethers, moorings, towing lines and the like that are connected between a surface vessel and a subsea installation. However, it will be appreciated that other forms of hydraulic stand-by tool may be substituted for the cutting tool 1 as appropriate in other circumstances. The installation is typically mounted on a lower riser package or frame, part of which is shown at 3, that is tethered or otherwise secured to a surface vessel or semi-submersible rig.

The stand-by cutting tool 1 is driven by a hydraulic actuator 4 that is connected directly to it. In the case of a cutting tool as shown in the drawing and as further described below, the actuator 4 comprises a hydraulic piston (not shown) located within a housing that is attached to directly to a body 5 of the cutting tool 1, preferably by screwing. The actuator 4 has first and second hydraulic fluid inlet/outlet ports 6 and 7 respectively. The port 6 is supplied with hydraulic fluid from the hydraulic drive system 2 by a hose 8. The port 7 is linked to a receptacle or reservoir 9 of hydraulic fluid as further described below. When supplied with hydraulic fluid the actuator 4 acts to operate the cutting tool 1 by moving a blade (not shown) of the tool (1) in a cutting action. Conversely, when supplied with hydraulic fluid via the port 7 from the reservoir 9, the actuator 4 acts to reset the position of the blade back to a stand-by position ready for another cutting action.

The hydraulic drive system 2 comprises a pump in the form of a hydraulic cylinder with a cylinder barrel 10 that in use is typically secured at in a vertical or near vertical position to the lower riser package or frame 3.

The barrel 10 defines fluid inlet/outlet ports n and 12 at opposite ends, the port 11 being connected to the hose 8 and the port 12 being preferably connected to a reservoir 13 of hydraulic fluid, as is further described below. Within the barrel 10 is a piston 14 secured to a piston rod 15 that projects from an end of the barrel 10. The projecting end of the piston rod 15 is adapted for connection to one end of a tether 16, the other end of which is intended for securement to fixed subsea equipment, such as a subsea blowout preventer (BOP) or subsea Christmas tree, or other attachment point from which the installation is to be separated on operation of the tool 1. Preferably, a mechanical link 17 is used to connect the piston rod 15 to the tether 16, which link 17 is adapted to disconnect from the piston rod 15 or from the tether 16 when a predetermined pulling force on the tether 16 is reached. This pulling force has to be predetermined to be greater than that required to operate the hydraulic drive system 2 but not so great that the tether 16 is not disconnected from the piston rod 15 before damage to the cylinder barrel 10 and the fixed subsea equipment can occur.

The size of the cylinder barrel 9, that is its length L and internal diameter D is determined by the pressure and quantity of hydraulic fluid required to be pumped to the actuator 4 to operate the tool 1. The volume of the barrel 9, taking into account the volume taken up by the piston rod 15 as determined by its diameter d, needs to be sufficiently large to accommodate the quantity of fluid required and the cross-sectional area of the barrel 9 needs to be such that the required pressure can be achieved when an appropriate pulling force P is applied to the tether 16 by the surface vessel. Hence, the length L and the internal diameter D of the barrel 9 are dependent on the operating requirements of the actuator 4. As an example, a typical pulling force P on the tether 16 by a surface vessel moving away from the installation 3 may be of the order of 5 tonnes. Hence, to produce a cutting force of 20 tonnes by the actuator 4, which force is required to sever umbilicals, steel ropes and the like, the barrel 9 needs to have a length or around 895 mm and an internal diameter D of around 40 mm, given a piston rod diameter d of 25 mm, to produce a 4:1 mechanical advantage to operate the actuator 4.

In use, the hydraulic drive system 2 is set up with the piston rod 15 inserted fully into the barrel 10 so that the piston 14 is located at the end of the cylinder barrel 10 adjacent the inlet/outlet port 12. When an appropriate pulling force P is applied to the tether 16 by movement of the surface vessel away from the subsea installation, the tether 16 pulls the piston rod 15 out of the barrel 10 so that the piston 14 pumps the hydraulic fluid in the barrel out through the inlet/outlet port 11 along the hose 8 to the actuator 4. The actuator 4 then causes operation of the tool 1. As the piston 14 moves through the barrel 10, hydraulic fluid from the reservoir 13 floods into the barrel 10 below the piston 14 to replace that which is being pumped out. Similarly, hydraulic fluid from the actuator is forced out through the port 7 into the reservoir 9.

It will be appreciated that an arrangement set up as described above is a basic one and, in fact, the reservoirs 9 and 13 could be the same or separate reservoirs of hydraulic fluid. Preferably, however, the installation is made more sophisticated by the provision of first and second hydraulic accumulators with appropriately biased pressure settings relative to each other whereby the tool 1 and the hydraulic drive system 2 will automatically reset after use. In this case the reservoirs 9 and 13 are separate and comprised in such accumulators. The first accumulator is therefore connected via a hose 18 to the inlet/outlet port 12 of the cylinder barrel 10 and comprises the reservoir 13. The second accumulator is connected via a hose 19 to the inlet/outlet port 7 of the actuator 4 and comprises the reservoir 9. Hence, on operation of the hydraulic drive system 2 fluid from the first accumulator 13 is pumped into the second accumulator 9 via the actuator 4. The second accumulator 9 can then act to pump the fluid in the reverse direction to reset the actuator 4 and the position of the piston 14 and piston rod 15 in the cylinder barrel 9. The tether 16 can then be reattached to the piston rod 15 via the mechanical link 17 using an ROY, which is also used to reset the stand-by tool 1 by reattaching the lines such as umbilicals, hydraulic hoses, tethers, moorings, towing lines and the like between the subsea installation 3 and the fixed subsea equipment by securing them to the tool 1.

When the stand-by tool 1 is a cutting tool, its body 5 is preferably bifurcate and defines a blade chamber (not shown) adjacent and first and second arms 20 and 21 between which is a substantially U-shape, cutting aperture 22. An anvil 23 is detachably located between the arms 20, 21 by an appropriate securement means 24. In this operative position the anvil 23 bridges the arms 20 and 21 and thereby traps any item it is desired to sever within the aperture 22. The blade (not shown) of the cutting tool 1 comprises a guillotine blade that is mounted in the blade chamber such that on actuation by the actuator 4 it is driven out of the chamber between the arms 20, 21 to contact the anvil 23 thereby severing any item or items located within the cutting aperture 22. It will be appreciated that for standby use to sever lines in emergency subsea situations, these lines are permanently located within the cutting aperture 22 of the tool 1 ready to be severed by operation of the tool 1 at a moment’s notice, the tool 1 being solely deployed on stand-by for this purpose. The size of the tool 1 and therefore the aperture 22 may be varied as required but typically in situations similar to those described above wherein the actuator 4 requires a cutting force of around 20 tonnes, the width W of the tool 1 between the arms 20, 21 maybe of the order of 150 mm. Reconnection of reinstated lines to the tool 1 after use, for example by an ROV, is facilitated by the provision of a spring clip 25 that is attached to the body 5 adjacent the arms 20, 21 and that can be used to retain the lines in the aperture 22 during resecurement of the anvil 23 between the arms 20, 21 by the securement means 24.

The invention has several advantages over conventional systems. First, it can be made to automatically reset in situ by appropriately biasing the first and second hydraulic accumulators comprising the reservoirs 13, 9 without requiring any part of the installation to be brought up to the surface vessel. Second, a relative small pulling force P on the tether 16 is required to produce a significantly higher actuation force in view of the mechanical advantage provided by the dimensions of the hydraulic drive system 2. This makes the arrangement much more efficient and reliable than conventional arrangements using severable or frangible mechanical links. Finally, operation of the invention is depth independent, as there is little external influence on the operation of the various component parts of the installation other than on the projecting part of the piston rod 15, which does not significantly affect operation of the hydraulic drive system 2.

Whilst in most cases the installation comprising the stand-by tool 1 and the hydraulic drive system 2 will mounted on a lower riser package or frame 3 so that it remains attached to a surface vessel or semi-submersible rig when the latter moves away from the fixed subsea equipment, it will be appreciated that it is possible to set the installation up so that the tether 16 is secured to the surface vessel or semi-submersible rig and the stand-by tool 1 and the hydraulic drive system 2 are secured to the fixed subsea equipment. In either case, the end of the tether 16 remote from the piston rod 15 may also be connected to equipment or an attachment point via another separable or frangible link (not shown).

Claims

1. A subsea, stand-by installation comprising a stand-by tool and a hydraulic drive system therefor, the tool comprising a hydraulic actuator that is supplied with hydraulic fluid from the hydraulic drive system, and the hydraulic drive system comprising a pump in the form of a hydraulic cylinder with a cylinder barrel defining a first fluid inlet/outlet port at one end and containing a piston secured to a piston rod that projects from one end of the cylinder barrel, the projecting end of the piston rod being adapted for connection to one end of a tether the other end of which tether is intended for securement to equipment or an attachment point from which the installation is to be separated on operation of the tool whereby in use a pulling force on the tether moves the piston rod and thereby the piston along the cylinder barrel to pump hydraulic fluid contained in the cylinder barrel via the fluid inlet/outlet port to the actuator to operate the tool.

2. An installation as claimed in Claim 1, wherein the projecting end of the piston rod is adapted for connection to the tether by the provision of a mechanical link that is adapted to disconnect from the piston rod or from the tether when a predetermined pulling force is reached.

3. An installation as claimed in Claim 1 or Claim 2, wherein the cylinder barrel defines a second fluid inlet/outlet port at its other end that is connected to a first reservoir of hydraulic fluid.

4. An installation as claimed in Claim 3, wherein the first reservoir of hydraulic fluid is contained in a first hydraulic accumulator.

5. An installation as claimed in any of Claims 1 to 4, wherein the hydraulic actuator comprises first and second inlet/outlet ports, of which the first inlet/outlet port is connected to said first fluid inlet/outlet port of the cylinder barrel and the second inlet/outlet port is connected to a second reservoir of hydraulic fluid.

6. An installation as claimed in Claim 5 when dependent on Claim 3, wherein the first and second reservoirs are the same reservoir or hydraulic fluid.

7. An installation as claimed in Claim 5, wherein the second reservoir of hydraulic fluid is contained in a second hydraulic accumulator.

8. An installation as claimed in Claim 7, wherein the first and second hydraulic accumulators are provided with appropriately biased pressure settings relative to each other whereby the hydraulic drive system and the actuator automatically reset after use.

9. An installation as claimed in any of Claims 1 to 8, wherein the tool is a cutting tool.

10. An installation as claimed in Claim 9, wherein the tool comprises a body defining a blade chamber and a cutting aperture, an anvil retained or defined by the body, and a blade that is located within the blade chamber and that is moveable therefrom by the hydraulic actuator to contact the anvil in order to sever one or more items located within the cutting aperture.

11. An installation as claimed in Claim 10, wherein the tool is provided with a spring clip that is adapted to retain the item or items to be severed within the cutting aperture.

12. A subsea, stand-by installation comprising a stand-by tool and a hydraulic drive system therefor substantially as described herein with reference to the accompanying drawing.