WO2010018410A1

WO2010018410A1 - Seismic network installation

Info

Publication number: WO2010018410A1
Application number: PCT/GB2009/051015
Authority: WO
Inventors: Peter Miles Roberts
Original assignee: Verderg Limited
Priority date: 2008-08-15
Filing date: 2009-08-13
Publication date: 2010-02-18
Also published as: GB0814906D0; GB2462641A

Abstract

An apparatus and method for installing and maintaining an array of spaced apart workpieces (1) on the seabed amongst pre-existing subsea facilities (6, 7, 8). Each workpiece (1) is connected to at least one other workpiece (1) by a tubular element (2), wherein the tubular elements (2) are buoyant such that they form catenary arches. A fibre optic wet connector system mounted to the subsea structures permits coupling of the tubular elements and workpieces.

Description

SEISMIC NETWORK INSTALLATION

Technical field

[0001] This invention relates to apparatus and methods for installing and maintaining an array of workpieces on a seabed, in particular for overlying a network over an existing network of production facilities.

Background art

[0002] Offshore oil and gas field development results in various forms of production hardware being placed on the sea bed generally above the location of the hydrocarbons reservoir, and interconnected with pipes and cables of various sorts. Frequently, and increasingly commonly in the very deep water now being met, floating production facilities are moored by chains and/or cables to the sea bed above the field and connected by cables and risers into the network of pipes and cables on the sea floor.

[0003] The initial development project for an oil or gas field offshore is to drill the wells and commission the field facilities that permit production and export of the best defined or most accessible part of the hydrocarbon reserves. It is commonly the case that significant uncertainty will still exist, even when production starts, about the geographical extent of the reservoir, the total amount of hydrocarbons in place, and about the proportion of that volume of hydrocarbon that can be recovered before the operating costs rise and/or the production rate falls to a point where the field is no longer economic.

[0004] As the price of hydrocarbons has risen in recent years, and technology has advanced, various technologies have emerged that economically permit the proportion of reservoirs that can be usefully recovered to increase. Characteristically, if 50% of the hydrocarbons in a given field could have been economically recovered 25 years ago, it might now be possible to economically recover, say 60% of the hydrocarbons in place. If a field contains 100 million barrels and each barrel is worth $100, then every one percent recovery improvement is worth $100 million. A 10% improvement in recovery, as in this hypothetical case, would be worth $1 billion, aside from the environmental benefits of getting more energy from a fixed infrastructure investment. There is thus a significant financial incentive to maximise reservoir recovery, and in response, there is a growing set of enabling technologies to achieve it.

[0005] As this trend continues, driven by the continuing high cost of energy and advancing technology, the complexity and sophistication of the hardware required to be placed on the sea floor advances. The congestion of the hardware increases and it becomes more difficult to install economically without damage, particularly in the very deep water increasingly being met, which may be up to 3000m deep.

[0006] Typically there is a need to place on or under the sea bed an array of regularly spaced assemblies forming a grid of similar or identical devices, possibly linked together with a network of pipes or cables. One example of such a regular grid is where hydrophones are placed in a regular pattern over a reservoir, on or just below the sea bed and linked together by electrical or fibre optic cables to monitor over time the hydrocarbon-water interface in the depleting reservoir. Survey vessels are used to emit seismic charges; the reflected waves being detected by hydrophones. The installation of an array of hydrophones permits the detection of oil fields by seismic mapping.

[0007] It is also possible that "shallow gas" or methane hydrate deposits may be recovered using a regularly spaced array of shallow wells, possibly in conjunction with heating and/or local de-pressuhzation facilities that require manifolding of several services from well to well. Further future embodiments are expected to be developed which have requirements for regular arrays of seabed assemblies.

[0008] The installation and maintenance of hydrophone arrays presents various challenges. Difficulties exist where the regular grid of linked assemblies being installed are superimposed over existing field facilities with production hardware linked by cables and pipes. There will be circumstances where one network is to be installed over another network with multiple crossing points, where clash damage can occur. Damage to the first network may also be caused by the installation equipment used to install the second network. A method to overcome this is to bury the underlying network under the seabed at all clash points or to separate the clash points physically with grout bags or concrete mattresses. However both techniques are expensive and cumbersome.

[0009] Furthermore the underlying production network may need to be continually updated, re-configured and extended, necessitating regular temporary removal of sections of the overlying new network. Mention is also made of the potential attraction of using sea bed crawler machines that move on powered tracks to install complex sea bed service networks. Such machines exist and continue to be developed. They are disadvantaged, however, where the sea bed they need to crawl across is already obstructed by existing production equipment, that may either be damaged when crossed or which precludes access by the crawler to the required target location.

[0010]This invention seeks to overcome the difficulties outlined above by providing apparatus and methods for installing and maintaining a workpiece array on the seabed.

Disclosure of the invention

[0011] A first aspect of this invention provides a method for placing an array of spaced apart workpieces on the seabed amongst pre-existing subsea facilities, the method comprising placing a workpiece on the seabed; connecting the workpiece to at least one other workpiece on the seabed by a tubular element, wherein the tubular elements are buoyant such that the tubular elements extend above the seabed between the workpieces and above the pre-existing subsea facilities located between adjacent workpieces.

[0012] The method can further comprise connecting tubular elements laterally to a central tubular element; and connecting the workpieces to the lateral tubular elements.

[0013] One end of the central tubular element can be connected to a floating vessel. In one embodiment the method may comprise running one end of the central tubing to the shore for connection.

[0014] The method further comprises connecting the lateral tubular elements to the central tubular elements and/or the workpiece by a subsea connector.

[0015] A second aspect of this invention comprises an array of spaced apart workpieces for placing amongst pre-existing subsea facilities located on the seabed, wherein each workpiece is connected to at least one other workpiece by a tubular element, wherein the tubular elements are buoyant such that when the workpieces are positioned on the seabed the tubular elements extend above the seabed between the workpieces and above the pre-existing subsea facilities located between adjacent workpieces. [0016] The tubular elements may form a catenary arch between the workpieces when the workpieces are positioned on the seabed. [0017] The tubular element between two workpieces may be reversibly disconnectable from the workpieces. [0018] The workpiece array comprises a central tubular element and lateral tubular elements extending from both sides of the central tubular element, wherein the workpieces are attached to the lateral tubular elements in a spaced apart arrangement. [0019] The workpieces are about located about every 50m along the length of the lateral tubular elements, although other spacings are also envisaged. [0020] The workpieces may be hydrophones. [0021] One end of the central tubular element is attached to a floating vessel or runs to shore. [0022] The lateral tubular elements extend from the central tubular element about every 300 to 500m although other spacings are also envisaged. [0023] The lateral tubular elements are connected to the central tubular element or the workpiece by a subsea connector. [0024] The tubular elements may comprise fibre optic cables and the connector may comprise a fibre optic wet connector system for subsea installation. [0025] The connector system may comprise: a first connector assembly comprising a first fibre optic cable, and a first latching device; and

-a second connector assembly comprising a second fibre optic cable and a second latching device; the first and second latching devices being complimentary to each other to join the first and second connector assemblies together such that the first and second fibre optic cables can be coaxially connected; wherein the first and second fibre optics cables each comprise a lens attached to the end of the fibre optic cable to be connected together such that the lens can spread out the light beam in each fibre.

[0026] A third aspect of this invention provides a system for placing structures on the seabed comprising an overlay network and an underlay network, wherein the overlay network comprises an array as described above and the underlay network comprises subsea facilities on the seabed, wherein the tubular elements of the overlay network extend over the underlay facilities positioned between adjacent workpieces.

[0027] A fourth aspect of this invention provides a fibre optic wet connector system for subsea installation comprising: a first connector assembly comprising a first fibre optic cable, and a first latching device; and a second connector assembly comprising a second fibre optic cable and a second latching device; the first and second latching devices being complimentary to each other to join the first and second connector assemblies together such that the first and second fibre optic cables can be coaxially connected; wherein a lens is attached to at least one of the ends of the first or second fibre optic cable such that the lens can spread out the light beam in the fibre.

[0028] The second connector assembly comprises a probe and the first connector assembly comprises a docking funnel in which the probe can be inserted on the first connector assembly.

[0029] Preferably the lens is a fish eye lens.

[0030] The first connector assembly can be mounted to a subsea structure.

[0031] A fifth aspect of the invention comprises a method for connecting fibre optic cables in a subsea environment using a fibre optic wet connector system as described above, the method comprising: positioning the second connector assembly in close proximity to the first connector assembly; aligning the second fibre optic cable with the first optic cable; and forming a connection between the first and second connector assemblies to join the first and second fibre optic cables together. [0032] The method comprises using a remotely operated vehicle (ROV) to connect the second connector assembly to the second connector assembly.

Brief description of the drawings

[0033] Figure 1 shows field production facilities and an array of workpieces placed on the seabed;

Figure 2 shows a fibre optic wet connector system; and Figure 3 shows the latching device of the first connector assembly of the fibre optic wet connector system.

Mode(s) for carrying out the invention

[0034] Figure 1 shows field production facilities and an array of workpieces (1 ) placed on the seabed. Each workpiece is positioned at a target location on the seabed at a fixed distance from other workpieces in the array. The workpieces are connected by tubular elements such that each workpiece is connected to at least one other workpiece. The tubular elements may comprise pipes or cables. The tubular elements between the workpieces are made slightly buoyant such that they form catenary arches between the connected array of workpieces, floating off the seabed and out of potentially harmful contact with any underlying network of field production facilities. Such facilities may include product jumper lines (3), umbilicals (4), export pipelines (5), a manifold (6), a tree and wellhead (7) and mooring lines to the surface (8). Using buoyant tubular elements eliminates physical clashes with underlying facilities by introducing a third dimension into the configuration.

[0035] The tubular elements are capable of being reversibly connected from the workpiece itself thus permitting temporary removal of the local section of the overlying network. This may be instigated to facilitate subsea installation of new production facilities or for the repair of pre-existing facilities lying underneath. The ability to remove and replace local sections of the overlying network also permits local sections to be repaired if damaged, for example by fishing activities.

[0036] The workpieces may perform a variety of different functions. In one embodiment of the invention the workpieces may be an assembly of concentric pipes drilled at regular centres into the seabed and function to recover methane from shallow deposits of methane hydrates. Facilities for depressurising and heating such deposits to release the methane from its clathrate are anticipated. The interconnecting pipes and tubes permit networked manifolding of necessary services; these include but are not limited to electric and hydraulic power, steam, hot water or solvent injection and formation water offtake. A further network of pipes may be incorporated to carry the methane produced from each workpiece to a common processing and export facility.

[0037] In a further embodiment of the invention the workpieces may form an array of subsea hydrophones which are typically buried at a depth of up to 2 meters below the seabed. The hydrophones permit the monitoring of reservoir seismic conditions by periodically measuring the seismic reflections from the hydrocarbon-water interface in the reservoir of a sonic signal actuated in the water column. The electrical or fibre optic cables that network each workpiece into a data collection grid may be attached and disconnected from the workpieces as required. This may be achieved by using suitable wet connectors mounted on a suitable combination of inboard and outboard latching assemblies that permit diver-less connection and disconnection.

[0038] The workpiece array comprises a central tubular element (9) which is attached to a floating vessel or runs to shore at one end; lateral tubular elements (10) extend out from the central tubular element at intervals of about 300 to 500m. The lateral tubular elements are connected to the central cable by means of subsea connectors (11 ). Workpieces are located characteristically about every 50m along the lengths of the lateral tubular elements. Where the tubular elements comprise fibre optic cables the subsea connector is a fibre optic wet connector system. The tubular elements and subsea connectors may alternatively incorporate hydraulic or electric systems. The individual workpieces may also incorporate terminal subsea connectors making them reversibly connectable with tubular elements as required after installation. This feature also permits the deployment and installation of the workpieces.

[0039] Figure 2 shows a fibre optic connector system which permits diver-less subsea installation and subsequent reconfigurations of a workpiece array. The first connector assembly (12) is mounted to a subsea workpiece or structure and comprises a mounting plate having a first fibre optic cable (13) and a first latching device (14). The second connector assembly (15) has a mounting plate comprising a bundle of fibre optic cables (16) diverging from a master cable (17) and a second latching device (18). The first and second latching devices are complimentary to each other such that the first and second connector assemblies may be joined sub-sea without using divers and the first and second fibre optic cables can be coaxially connected. The second connector assembly is guided into place by locating a probe (19) to the complimentary docking funnel (20) on the first connector assembly which permits subsea diver-less coupling. The docking funnel and probe also help with the alignment of the cables to be connected. Figure 3 shows the latching device of the first connector assembly; the first latching device is equivalent but complimentary to the second latching device. Fibre optic connectors (21 ) couple with fibre optic connectors on the second connector assembly. In addition to the locator probe and docking funnel; features on the mounting plate also facilitate correct locating and coupling of the first and second assemblies. The slotted profile (22) matches with a nose and dowel pins (23) match with receptacles on the second latching device. The latching device helps maintain the first and second connector assemblies together and also helps the alignment of the fibre optic cables. The fibre optic cables of the first and second connector assemblies are thus coupled together. The fibre optic cables each comprise a fish eye lens at their terminal end which permits the joining of the fibres by causing the light beam in each fibre to spread out. This increases the target area when connecting the first and second fibre optic cables. Having a larger target area for aligning the fibre optic cables makes it easier to remotely connect the fibre optic cables, for example by using a remotely operated vehicle (ROV). Therefore divers are not required to ensure the correct connection is made between the cables.

Claims

1. A method for placing an array of workpieces on the seabed amongst preexisting subsea facilities, comprising: placing a workpiece on the seabed; and connecting the workpiece to at least one other workpiece on the seabed by a tubular element; wherein the tubular elements are buoyant such that the tubular elements extend above the seabed between the workpieces and above pre-existing subsea facilities located between adjacent workpieces.

2. A method according to claim 1 comprising connecting the tubular elements laterally to a central tubular element; and connecting the workpieces to the lateral tubular elements.

3. A method according to claim 2 comprising attaching one end of the central tubular element to a floating vessel.

4. A method according to claim 2 comprising running one end of the central tubing to the shore for connection.

5. A method according to any of claims 2-4 comprising connecting the lateral tubular elements to the central tubular elements and/or the workpiece by a subsea connector.

6. An array of spaced apart workpieces for placing amongst pre-existing subsea facilities located on the seabed, wherein each workpiece is connected to at least one other workpiece by a tubular element, wherein the tubular elements are buoyant such that when the workpieces are positioned on the seabed the tubular elements extend above the seabed between the workpieces and above the pre-existing subsea facilities located between adjacent workpieces.

7. An array according to claim 6 wherein the tubular elements form a catenary arch between the workpieces when the workpieces are positioned on the seabed.

8. An array according to claims 6 or 7 wherein the tubular element between two workpieces is reversibly connectable from the workpieces.

9. An array according to any of claims 6, 7, or 8 comprising a central tubular element and laterals tubular elements extending from both sides of the central tubular element, wherein the workpieces are attached to the lateral tubular elements in a spaced apart arrangement.

10. An array according to claim 9 wherein the workpieces are located about every 50m along the length of the lateral tubular elements.

11. An array according to claims 9 or 10 wherein one end of the central tubular element is attached to a floating vessel or runs to shore.

12. An array according to any one of claims 9 to 11 wherein the lateral tubular elements extend from the central tubular element about every 300 to 500m.

13. An array according to any one of claims 9 to 12 wherein the lateral tubular elements are connected to the central tubular element or the workpiece by a subsea connector.

14. An array according to claim 13 wherein the tubular elements are fibre optic cables and the connector is a fibre optic wet connector system for subsea installation.

15. An array according to claim 14 wherein the connector system comprises: a first connector assembly comprising a first fibre optic cable, and a first latching device; and a second connector assembly comprising a second fibre optic cable and a second latching device; the first and second latching devices being complimentary to each other to join the first and second connector assemblies together such that the first and second fibre optic cables can be coaxially connected; wherein the first and second fibre optics cables each comprise a lens attached to the end of the fibre optic cable to be connected together such that the lens can spread out the light beam in each fibre.

16. An array according to any of claims 6 to 15 wherein the workpieces are hydrophones.

17. A system for placing structures on the seabed comprising an overlay network and an underlay network, wherein the overlay network comprises an array according to any of claims 6 to 16 and the underlay network comprises subsea facilities on the seabed, wherein the tubular elements of the overlay network extend over the underlay facilities positioned between adjacent workpieces.

18. An fibre optic wet connector system for subsea installation comprising: a first connector assembly comprising a first fibre optic cable, and a first latching device; and a second connector assembly comprising a second fibre optic cable and a second latching device; the first and second latching devices being complimentary to each other to join the first and second connector assemblies together such that the first and second fibre optic cables can be coaxially connected; wherein a lens is attached to at least one of the ends of the first or second fibre optic cable such that the lens can spread out the light beam in the fibre.

19. A connector system according to claim 18 wherein the second connector assembly comprises a probe and the first connector assembly comprises a docking funnel in which the probe can be inserted on the first connector assembly.

20. A connector system according to claim 18 or 19 wherein the lens is a fish eye lens.

21. A connector system according to claim 18, 19 or 20 wherein the first connector assembly is mounted to a subsea structure.

22. A method for connecting fibre optic cables in a subsea environment using a fibre optic wet connector system as claimed in any of claims 18-21 comprising: positioning the second connector assembly in close proximity to the first connector assembly; aligning the second fibre optic cable with the first optic cable; and forming a connection between the first and second connector assemblies to join the first and second fibre optic cables together.

23. A method according to claim 22 comprising using a remotely operated vehicle to connect the second connector assembly to the second connector assembly.