METHOD AND SYSTEM

FIELD OF THE INVENTION

The invention relates to Underwater Intervention Drones (UIDs) including Autonomous Underwater Vehicles (AUVs) and Remotely Operated Vehicles (ROVs). In particular, the invention relates to docking of such vehicles or drones on a subsea node, especially a subsea node connected for receiving direct current and fibre optic communication, a so called DC/FO node.

BACKGROUND

Prior ROVs were manually operated devices where the operator controlled the device either“on-site” on a vessel or a rig, or more remotely from an on-shore site; the latter being possible with modern communication techniques. Also known are AUVs that are operated in a non-autonomous, i.e. supervised, mode. Since these AUVs are not autonomous they are more correctly called semi-automatic underwater vehicles; the devices generally follow a program but are still monitored by a controller.

Typical applications of UIDs include: pipeline surveys, seabed mapping, environmental surveys, Inspection Maintenance and Repair (IMR).

The support vessel is the main cost driver in the performance of many off-shore operations performed with the aid of a ROV or AUV, for example, seabed mapping, inspection, maintenance etc. Remove the need for the vessel and a significant percentage of the cost of operations is removed.

Consequently, it would be desirable to have resident systems where the power and communications were supplied to the UID from a subsea node. In other words, it is desirable for the UID to be hosted below sea line, in particular on the seabed. IN this case, improvements can be envisaged in:

• Response times: because the UID is hosted near the subsea installations (“24/7”) there will be increased production efficiency; • Effectiveness: more cost effective acquisition of seabed mapping, pipeline survey and environmental data;

• Operating costs: in particular for challenging prospects, in harsh conditions, long distance from shore, remote areas, and deep water;

• Capital expenditure: for new fields - provides possibility for simplified and less complex Subsea Production Systems (SPS);

• Health and safety: fewer site based people

• Security: On site UID could provide a surveillance function;

• Environment: Fewer vessel trips therefore reduced emissions; no more wait on weather (WOW); oil spill monitoring and response possibilities;

• Quality: more information, more data - better decision making in respect of the subsea installation and processes.

The possibility of providing docking stations on Subsea Production Systems (SPS) has been proposed by Statoil,“How we think UIDs will be used by Statoil in the future” (IOGP Geomatics Industry Day, Stavenger, 26 ^th April 2017).

In a collaboration between Batelle and OceanWorks, a subsea docking, re-charging and communications station is disclosed in“Resident AUV system with subsea dock in development”, Offshore (RTM) Mag (04/10/2014) - https ://www.offshore- mag.com/1/volume-74/issue-4/subsea/resident-auv-svstem-with- subsea-dock-in- development/resident-auv-svstem-with-subsea-dock-in-developm ent-full.html

The Batelle and OceanWorks proposal is intended to enable persistent AUV operations from a seafloor node network that incorporates a subsea docking, recharging, and communications. Such a system would enable resident AUV presence on the seafloor, providing cost-effective support for a variety of oil and gas exploration and production activities. In the system a Bluefin Robotics AUV was equipped with a device enabling it to home in and then dock for data exchange and recharging. Once docked, the vehicle used a Wi-Fi connection to download data and upload its next mission profile. Inductive coils on the vehicle and dock transferred energy from the dock to the vehicle - without the need for metal-to-metal contacts.

Referring to Figure 1 , there is illustrated schematically a network of subsea wells connected to a host production facility 1. Several subsea umbilicals 2, 3, 4, 5 are connected to the host production facility 1. Each umbilical connects several subsea wells (shown in Figure 1 as circles) to the host production facility 1. Taking umbilical 5 as an example, this connects subsea wells 7, 8 and 9 to the host production facility 1 . Note that each subsea well, for example subsea well 7, could comprise several physical wells. In addition to the umbilicals, hydrocarbon-carrying pipelines are also shown as thick black lines that follow substantially the same route as the umbilicals 2, 3, 4, 5.

WO-A-201 1/147459 discloses a subsea oil and/or gas production system comprising a host production facility and a plurality of subsea wells. A fluid conveying network is provided that connects each subsea well to the host production facility. In contrast to figure 1 above, a separate electrical power and data network is provided for conveying direct current electrical power and data, operatively connected to each subsea well for providing each subsea well with data transfer and electrical power services. The use of direct current ensures that the electrical power and data network can provide power over much greater distances than currently available, and the use of separate networks for conveying fluids and for providing electrical power and data transfer allows for a much more flexible system.

Referring to Figure 2 herein, a schematic diagram of a plurality of subsea wells connected to a host production facility 15 is illustrated. Pipelines carrying hydrocarbons are illustrated as thick black lines. Subsea fluid conduits are illustrated as thick dashed lines, and a separate network carrying data and electric power is illustrated as dotted lines. The separate network provides cables for electric power and data transfer, distributed in different ways. This type of network is referred to herein as a DC/FO network, as it provides DC current via an electrical cable and data transfer using Fibre Optic (FO) cables.

The DC/FO network can typically provide a total system power of 100 kW and a total data bandwidth of 120 Gb/s, although it will be appreciated that any power and bitrates may be used within the constraints of the subsea environment. The DC/FO network in this description is served by hubs 16, 17 and 18, each with a typical output power of 10 kW and a data bandwidth of 1 Gb/s (limited by the subsea control system), although it will be appreciated that any power and bitrates may be used within the constraints of the subsea environment. The DC/FO network carries high voltage direct current from the host production platform 15 (or another source), and a function of the hub is to convert this voltage to a lower voltage usable by the subsea wells 19, 20, 21 (typically it must be converted from around 10,000V DC to below 1 ,000V DC). In the example of Figure 3, hub 16 provides electric power and data to subsea wells 19, 20 and 21 , and may also be connected to hub 17. The DC/FO network is separate from the subsea fluid conduit network and does not necessarily follow the same path as the subsea fluid conduit network.

Turning now to Figure 3, there is illustrated schematically in a block diagram an example of a subsea hub node 17. The hub 17 is provided with a unit 37 for receiving electric power and data from an external source. A processor 38 is used to control the operation of the hub 17. A computer readable medium in the form of a memory 37 is provided on which is stored a computer programme 40. When executed by the processor 38, the program 40 controls the operation of the hub 17. The memory 39 may also be used to store data such as a log of the hub’s 17 operation. A unit 41 for providing electric power in the network is provided, and a unit 42 for providing data transfer in the network is provided. It will be appreciated that these units operate most efficiently if they are physically combined and comprise a plurality of connectors, each connector having connections capable of providing both data and electric power transfer. There could be separate electric power and data transfer connection points, or a hybrid connector with connection points for electric power and connection points for data.

Referring to figure 3, the DC/FO cable carries high voltage direct current from a host production platform 15 (or another host facility), and a function of the hub 17 is to convert this voltage to a lower voltage usable by the subsea wells 19, 20, 21 (typically it must be converted from around 10,000V DC to below 1 ,000V DC). In the example of Figure 3, hub 16 provides electric power and data to subsea wells 19, 20 and 21 , and may also be connected to hub 17. The DC/FO network is separate from the subsea fluid conduit network and does not necessarily follow the same path as the subsea fluid conduit network. An advantage of using direct current is that electric power can be transmitted over longer distances than using AC. For example, using High Voltage Direct Current (FIVDC), losses can be reduced to around 20% per 1 ,000 km, which makes direct current more attractive for supplying electric power to subsea wells from a remote source. Furthermore, the use of direct current reduces capital costs, as fewer and thinner conductors can be used compared with electric power transmission using AC. This is because the root mean square (RMS) voltage measurement of an AC conductor is only around 71% of the peak voltage, which determines parameters such as the insulation thickness and minimum conductor sizing. Another advantage of using direct current rather than AC is that, in a distributed electric power network, there is no need to synchronise AC sources, further reducing capital costs. The use of direct current allows the transfer of electric power over distances greater than 150 km.

Figure 4 illustrates a cross section view of an electric power and data transfer cable 43. The cable comprises a protective sheath 44 in which optical fibres 45 are provided for data transfer, and electric power cables 46 are provided for electric power transfer. Each end of the cable 43 has one or two connectors, one end for connecting to the hub 17 (see figure 1 ) and another end for connecting to a subsea well (typically via a subsea control module) or another subsea asset that requires data and electric power. Figure 5 is shown schematically by way of example only to illustrate the functional components of an electric power and data transfer cable. A typical cable will have multiple cores for data and one or two electric power cores, and various layers of shielding.

Each power cable can deliver high voltage direct current up to 100kW with a maximum operational voltage of 10 kV and a maximum current rating of 10 A. The power cable has a low conductor resistance for each path to minimize power losses. Receiving DC/FO subsea nodes can convert the high voltage direct current distributed by the DC/FO cable towards four low voltage DC interfaces through DC/DC converters. A DC/FO subsea node may be provided with the option to supply a low voltage alternating current (AC) interface from any one of the low voltage DC interfaces by using a DC/AC inverter module.

Fibre optic communications are preferred for data transfer as there will be no electromagnetic interference from the DC power part of the cable, and they have a higher bandwidth than electrical transmission and can transmit data over longer distances than electrical transmission owing to very low losses.

SUMMARY The invention provides a subsea node for connecting an associated subsea system to a host facility for provision of electrical power and data, the subsea node comprising, a termination for connecting the subsea node to a cable carrying power and data from the host facility, a platform, provided by a surface of the subsea node, for landing an underwater intervention drone, and a subsea node inductive coupler associated with the platform and connected to the termination for receiving power and data; whereby an underwater intervention drone landed on the platform and having a corresponding inductive coupler can receive power and data via the subsea node inductive coupler.

The subsea node may comprise a landing frame terminating an end of a power and data cable, wherein the landing frame is used to land said end on the seafloor.

The subsea node may be configured to be landed outside of the subsea system and to be connectable thereto by jumpers.

The subsea node may comprise one of, a subsea manifold template, a manifold cluster, a well head tree, or a PLEM.

The subsea node inductive coupler may be located on the surface providing the platform and protrudes therefrom.

The platform may have a length of at least 2m and a width or at least 1 m.

The subsea node inductive coupler may be retrofitted to the subsea node.

The invention also provides a system comprising the subsea node of the invention and an underwater intervention drone configured to be landed on the platform and including a corresponding inductive coupler for receiving power and data via the subsea node inductive coupler.

The platform and the underwater intervention drone may have inductive couplers having cooperating male and female housings.

DRAWINGS The invention will now be described in more detail and with reference to the accompanying drawings, in which:

Figure 1 illustrates schematically a plurality of subsea wells connected to a host production facility;

Figure 2 illustrates schematically a plurality of subsea wells connected to a host production facility using a DC/FO system;

Figure 3 illustrates schematically in a block diagram a subsea node; and Figure 4 illustrates schematically a DC/FO cable;

Figure 5, shows an example of a DC/FO subsea node with a schematic representation of the location of an inductive coupler and a UID according to an embodiment;

Figure 6 shows schematically the DC/FO node, inductive coupler and UID according to an embodiment;

Figure 7 shows schematically another embodiment of a system according to an embodiment.

DETAILED DESCRIPTION

In an embodiment as shown in figure 5, a subsea well structure 100 having one or more well structures servicing a wellhead, is supplied with power and data by connecting a DC/FO subsea node 50 landed on the seabed near to but outside the well structure 100. In this case the DC/FO node is connected to the well structure 100, such as an xmas tree type structure, via flying leads 51. The DC/FO subsea node 50 includes a landing frame 52 which integrates the cable head 53 terminating the DC/FO cable 54 into the DC/FO subsea node 50. The purpose of the landing frame 52 is provide DC/FO subsea node 50 with a landing interface outside of the well structure plus dropped object protection. The cable 54 is connected at its distal end (not shown) to a host facility (15) or production system topside, such as an onshore production facility, a platform, or a vessel. The landing frame 52 includes a substantially flat top surface 56 forming a convenient platform for landing a UID. Clearly in use, when landed on the seafloor, the surface 56 and hence the platform will be substantially parallel with the seafloor, which is to say, substantially horizontal.

The DC/FO subsea node 50 is additionally provided in an embodiment with an inductive coupler 55 connected for both power and data to landing frame 52. The landing frame 52 may be provided with various connectors 57 for multiple power and data outlets. In this case the inductive coupler 55 is connected to one electric connector and one optical wet mate connector for power and data respectively.

The inductive coupler 55 is located in this embodiment on top of the platform constituted by the substantially flat surface 56 provided by the landing frame 52 of the node 50. It is convenient to land a UID 60, provided with a cooperating inductive coupler 61 on the platform (surface 56) of the landing frame 52.

Typically a UID 60 may have dimensions of 2.5m length, 1.0m width, and 0.5m width approximately. Since the landing frame 52 typically provides a top surface having dimensions in the region of 3.5m length, 1 .2m width, a UID 60 of these sort of dimensions can be accommodated by readily available landing frames attached for power and data to a host facility by, for example, a DC/FO cable. The size of the UID 60 is not limited and can be larger than the landing area provided by the flat surface 56 of the landing frame 52. For stability the UID 60 should be approximately the same size as the landing frame surface or smaller. The dimensions of the landing frame 52 are exemplary and many different landing frame designs are known. In order to provide a docking platform for a UID 60 the landing frame 52 requires an appropriate available surface for landing that cooperates with a surface of the UID 60 - in this case a flat surface with co-operating male and female inductive couplers 55, 61. Whilst the inductive couplers are all shown as male (protruding from the flat surface) the male coupler could be located on the drone and the female coupler could be provided in the platform of the subsea structure of landing frame.

In figure 5 the inductive coupler 55 has been provided as a retrofit to a known landing frame 52, conveniently assembled on a vessel or before loading on the vessel and before landing on the seafloor. However, the inductive coupler 55 could also be added to landing frames 52 that have already been used to land the power and data cable 54 in a retrofit fashion to provide a system according to the invention. Additionally, instead of a known landing frame 52 a new landing frame including one or more inductive couplers 55 and one or more surfaces for landing a UID 60 could be designed for future projects.

In an embodiment as shown in figure 6, a subsea node, for example a well structure 100 having one or more well structures servicing a wellhead, is supplied with power and data by connecting a DC/FO subsea node 50 landed inside the well structure 100. The DC/FO node may be any subsea node, such as a subsea manifold template, a manifold cluster, a well head tree, or a PLEM. In this case, the DC/FO node may be connected to the well structure 100, such as an xmas tree type structure, via flying leads 51 .

The DC/FO subsea node 50 comprises a housing 62 inside which the DC/FO cable 54 is terminated. Trawl protection and/or dropped object protection is provided by the well structure and a separate landing frame is not required. In this case the cable head 53 is optional since the cable 54 can be terminated directly into the housing 62. The cable 54 is connected at its distal end (not shown) to a host facility (15) or production system topside, such as an onshore production facility, a platform, or a vessel.

In the embodiment of figure 6 the UID 60 can be more accurately positioned relative to the well structure. In accordance with the embodiment of figure 5, the inductive coupler 55 could be added to a known well structure, or the well structure could be designed bespoke to have the inductive coupler 55 provided on a platform provided for a particular design of UID 60.

In figure 6, power and data leads 58, 59 from the cable head 53 are shown schematically connecting the inductive coupler for power and data. In this embodiment as for figure 5 it is envisaged that the inductive coupler 55 in fact is provided with power and data via connectors 57 in the DC/FO node 50, that is, via wet mate connectors on the housing 62 which are connected to the cable head 53. The location of the transformer and any other required hardware is not limited but is conveniently provided either in the housing of the DC/FO node 50 or in the retrofitted inductive coupler 55. In figure 6 the landing surface 56 for the UID 60 is shown as part of the housing 62 of the DC/FO node, but in this case the surface 56 could appropriately be formed on the subsea structure where the housing 62 of the DC/FO node has been landed and which forms the trawl and / or dropped object protection.

In the embodiments of the invention, whilst the DC/FO cable provides data in optical fibre cables separate to the power cables, these may be combined in the subsea node so that power and data can be transferred through a single inductive coupler analogous to a USB connection. Alternatively the inductive coupler itself is provided with the hardware necessary to provide an AC signal modulated for data transmission using the DC power and optical data signal provided from the DC/FO cable.

Wireless power and data is described in, for example, WO-A-201 1014608, which discloses a subsea data and power transmission apparatus including primary and secondary open magnetic circuits with coils for wireless data and power transfer between a drilling tool and a drilling rig. The primary magnetic circuit is U-shaped and the secondary is O-shaped. Both magnetic systems are electrically insulated. The electrical signal and power are transferred from one magnetic circuit to another through an air or water gap between the magnetic circuits. The U-shaped and O-shaped magnetic circuits allow communication and power transfer remotely with no mechanical or electrical connectors.

Another embodiment is shown in figure 7. In the embodiments of figures 5 and 6 it is envisaged that the inductive couplers on the subsea node are retrofitted either on the landing frame outside well structure (figure 5) or on the DC/FO node within the subsea structure (figure 6) using the provided wet mate connectors, for example as a retrofit to existing systems or provided to extant but not yet installed systems.

In figure 7, a bespoke or integrated system is shown with the subsea node 50 being provided with a plurality, in this case 4, inductive couplers 55, 71 , 72, 73. The inductive coupler 55 being dedicated for use by the UID 60 and located in a suitable position on a surface 56 of the landing frame 52 or well structure 100. The surface 56 being specifically provided for landing the UID 60. In this case, two of the remaining inductive couplers 71 , 72 may be used for providing power and / or data to subsea production systems (SPS) and one inductive coupler 73 may be a spare to provide redundancy.

Similarly to figure 5, the DC/FO node 50 has a housing 62, and the surface 56 may be provided by the housing or a frame surrounding and protecting the housing.

Illustrative embodiments of the invention have been described. Modification may be made without departing from the scope of the invention as defined by the claims.