Subsea mining

Abstract

An extraction unit (103) for a subsea mining system (100) configured to extract resources (221) from a sea floor (210), the extraction unit (103) comprising: a frame (1); a frame support (2) configured to support the frame (1) on the sea floor (210); a tool slide (3) attached to the frame (1) in a movable manner; a tool platform (16) attached to the tool slide (3) in a movable manner; and an excavation tool (6) attached to the tool platform (16) and configured to excavate resources (221) from the sea floor (210). There is also provided a method of extracting resources (221,222) comprising operating an extraction unit (103) on or adjacent a sea floor (210), and transporting extracted resources (221,222) to a short-based location.

Description

[0001] SUBSEA MINING

[0002] The present disclosure relates to subsea mining systems and methods.

[0003] BACKGROUND

[0004] Subsea mining comprises various operations for gathering resources located below the water surface. Subsea mining may comprise extraction (such as collecting) of resources, e.g. minerals, solids or mud, from the ocean (sea) floor, and may comprise excavation into layers of the sea floor to gather resources. In some cases, subsea mining may also refer to extraction of resources present in the water or mudline directly above and adjacent the sea floor.

[0005] One example of subsea mining activities currently seeing growing interest is deep-sea mining to extract minerals such as ferromanganese crusts, seafloor massive sulfide deposits and polymetallic nodules. Subsea mining may also be applicable to lakes, rivers, artificial water areas or other non-ocean bodies of water.

[0006] During the subsea mining process, the resources generally need to be extracted and transported to the surface for storage, further processing and / or transport. At locations other than those close to shore, vessels need to be used for subsea mining activities. Such vessels are often specialized for the purpose, and have high operational costs. Operational efficiency and reliability are therefore of high importance in subsea mining operations, particularly at deep waters. In addition, stringent safety requirements must usually be met, both technically (e.g., to avoid unintended impact on marine life) and for personnel involved in the different operations.

[0007] Examples of subsea mining methods and systems which may be useful for understanding the field of technology include US 9,080,309 B2; EP2863008; WO2011122942; EP3019667; GB2495287; WO 2017 / 151852 A1 ; US 10,502,348 B2; KR 10-2018-0076921 ; US 2014 / 0041262 A1 ; DE 2 008384; US 4,414,159; US 5,199,767; WO 2021 / 143491 A1 ; CN 109611097 A; CN 1344844 A; JP 2003-269070; CN 106368652 A; US 2011 / 0309668 A1 ; WO 2021 / 143490 A1 ; JP 2019-120063; and JP 2019-52491 .

[0008] In WO 2018 / 059811 A1 , methods, systems and devices are described for the extraction of methane hydrate by excavating seabed ground material containing methane hydrate, transporting the ground material to a processing facility on the sea surface and processing the ground material for methane production. There is a continuous need for improved technology to make subsea mining operations and equipment more efficient and versatile. It is an aim of the present disclosure to provide such improvements, or at least alternatives, to known technology.

[0009] SUMMARY

[0010] In an example, there is provided an extraction unit for a subsea mining system, configured to extract resources from a sea floor, the extraction unit comprising: a frame; a frame support configured to support the frame on the sea floor; a tool slide attached to the frame in a movable manner; a tool platform attached to the tool slide in a movable manner; and an excavation tool attached to the tool platform and configured to excavate resources from the sea floor. There is also provided a method of extracting resources comprising operating an extraction unit on or adjacent a sea floor, and transporting extracted resources to a shortbased location.

[0011] The detailed description below and appended claims outline further inventive aspects and embodiments.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0013] These and other characteristics will become clear from the following description of illustrative embodiments, given as non-restrictive examples, with reference to the attached drawings, in which:

[0014] Fig. 1 illustrates a schematic view of a subsea mining system according to a general example concept.

[0015] Fig. 2 depicts a schematic structure of a vertical transport system of the subsea mining system according to an example.

[0016] Fig. 3 shows a perspective side view of a riser structure of the vertical transport system according to an example.

[0017] Fig. 4 depicts a perspective view of an extraction unit for subsea mining systems according to a first example.

[0018] Fig. 5 shows a perspective view of an extraction unit for subsea mining systems according to a second example.

[0019] Fig. 6 illustrates a perspective detail view of the extraction unit depicted in Fig. 5. Fig. 7 depicts a perspective view of an extraction unit for subsea mining systems according to a third example.

[0020] Fig. 8 depicts a perspective view of an extraction unit for subsea mining systems according to a fourth example.

[0021] Fig. 9 illustrates an extraction unit according to another example.

[0022] DETAILED DESCRIPTION

[0023] The following description may use terms such as “horizontal”, “vertical”, “upwards”, “downwards”, ’’upper”, “lower”, etc. These terms generally refer to the views and orientations as shown in the drawings and that are associated with a normal use of the invention. The terms are used for the reader’s convenience only and shall not be limiting.

[0024] Fig. 1 shows a schematic illustration of a subsea mining system 100 according to a general example concept. Subsea mining may include any form of extracting resources 221 from a subsea location with an extraction unit 103. For example, subsea mining may comprise extraction of minerals, solids or mud from the sea floor 210 as illustrated in Figure 1 . Subsea mining may comprise excavation of resources 221 from the sea floor 210. Subsea mining may also comprise extraction of resources 221 from the sea water or mudline region, for example directly adjacent the sea floor 210, or extraction of resources 221 floating or moving in the sea water. In some examples, the extraction unit 103 may comprise one or multiple remotely operated vehicles (ROV) 188 for operational assistance. The extraction unit 103 may comprise processing equipment, for example a mineral cleaner or sorting unit to select sizes of minerals and / or crushing minerals to a desired size or separating minerals / resources from waste.

[0025] After extraction by the extraction unit 103, the extracted resources 222 (see Fig. 2) may be transported to a location for further processing, e.g. a surface vessel 101 being at least partially above the water line 211 , by a vertical transport system 110. The vertical transport system 110 in this example comprises a buffer storage 102 for receiving and temporarily holding the extracted resources 222. The extraction unit 103 may be connected to the vertical transport system 110 by a tubing 105. The vertical transport system 110 may optionally be directly connected to the extraction unit 103. The tubing 105 may be a flexible hose to enable the extraction unit 103 to move relative to the vertical transport system 110. In the illustrated example, the vertical transport system 110 is suspended by and carried by the vessel 101 via a riser 107. Supporting equipment, such as a remotely operated vehicle (ROV) 188 may be used to monitor subsea operations. The ROV 188 may be operated via a control line 189 (see Fig. 1 ) to the vessel 101 or, optionally, wirelessly.

[0026] The vertical transport system 110 may use an air-lift system to move mined materials from the sea floor to the surface vessel 101 through the riser 107. Also known in the state of the art is the use of submerged dredge pumps. These pumps can offer a better energy efficiency in comparison to the air-lift system.

[0027] Illustrated schematically in Fig. 2, in this example, the riser 107 comprises a first riser pipe 107a for vertical transport of the extracted resources 222 and a second riser pipe 107b to move the transport medium back towards the sea floor 10. The vertical transport system 110 thus has a “closed loop” configuration. The transport medium can be a liquid, e.g. sea water, for pumping the extracted resources 222 upwards. In other examples, the liquid may be sea water and the sea water may be discharged at the vessel 101 after transporting the extracted resources 222 upwards, making pumping to the bottom and the second riser pipe 107b obsolete. In other examples, the water may be discharged at the bottom after transporting it downwards with the second riser pipe 107b. In such so called open-loop systems it may be beneficial to clean the water or transport liquid prior to discharging it into the sea to reduce the environmental effects. Cleaning the water is to be understood to separate the water from the extracted resources, e.g. by filtering, in order to reduce the impact on the environment (e.g. fish or plants) by discharging dirty water. Additionally, dirty or muddy water may create sediment plumes, which may negatively affect sea life. In another example, the subsea mining system 100 may comprise a closed-loop system, wherein the transport medium is not discharged, but separated from the transported extracted resources 222 and (partially or fully) re-used to move the extracted resources 222 upwards. In this example, there may be a reduced impact on the environment and sea life as there is no (or minimal) discharge of transport medium to the sea. Generally, it is also conceivable to implement an air lift system or submerged dredge pump(s) as a vertical transport system 110, in which the extracted resources 222 are lifted by means of a directional gas flow or pump action. Air lift systems or submerged dredge pumps can be implemented with a single riser pipe, thus reducing complexity of the vertical transport system 110. The vertical transport system 110 depicted in Fig. 2 may thus be regarded as a non-limiting example of how the transport may be carried out.

[0028] The vertical transport system 110 in this example further comprises a buffer storage 102. The buffer storage 102 is designed to temporarily store the extracted resources 222 after they have been extracted by the extraction unit 103 and to dose the extracted resources 222 into the first riser pipe 107 for transportation to surface. The buffer storage 102 may store the extracted resources 222 when there is downtime in the riser 107 or at the vessel 101 enabling continuous extraction by the extraction unit 103 also when the vertical transport system 110 is not operating. The buffer storage 102 may comprise a dosing section 201 to selectively dose the extracted resources 222 into the riser 107 to enable a steady flow of the mixture of the extracted resources 222 and the transport medium without clogging the riser 107. The dosing section 201 may, for example, comprise a frustoconical bottom with a valve arrangement to facilitate dosing of the extracted resources 222. In some examples, another type of dosing system may be used, e.g. an Archimedean screw.

[0029] The resources 221 on the sea floor 210 are extracted by the extraction unit 103. In this example, the extracted resources 222 are transported to the buffer storage 102 by a submerged dredge pump 232. The extraction unit 103 may comprise a cleaning and sorting device 231 , for example to remove mud or sea floor.

[0030] In this example, the transport medium is pumped through the vertical transport system 110 by a charge pump 250 and positive displacement pumps 251 . The positive displacement pumps 251 may comprise a single or multiple positive displacement pumps 251 . The positive displacement pumps 251 may e.g. be based on a design similar to mud pumps or slurry pumps used for example in offshore drilling or in mining operations. The transport medium is pumped downwards through the second riser pipe 107b. The dosing section 201 is operated to dose an amount of extracted resources 222 from the buffer storage 102 into the transport medium. The transport medium with resources 222 dispensed therein continues upwards through the first riser pipe 107a and into a separation unit 270 on the vessel 101. In the separation unit 270, the extracted resources 222 and the transport medium are separated to enable reuse of the transport medium by feeding it back to the positive displacement pumps 251 and to enable storage or further processing of the extracted resources 222. The separation unit 270 may also separate valuable resources (e.g. minerals) from mud, silt or other waste material, which may have been extracted simultaneously with the extracted resources 222, storing the valuable resources in a storage 271 , such as a tank.

[0031] The subsea mining system 100 may comprise hoisting equipment 266, such as a winch, to lower and lift the subsea parts of the vertical transport system 110, such as the riser 107, the buffer storage 102 and the dosing section 201 as well as the extraction unit 103 with the tubing 105. The subsea parts are thereby retrievable to the vessel 101 after operations have completed, or e.g. for maintenance.

[0032] Fig. 3 illustrates an example of a riser 107 for a subsea mining system, for example for a subsea mining system 100 as described above. The riser 107 comprises a first riser pipe 107a and a second riser pipe 107b and is thus suitable for a “closed loop” configuration as described above. Optionally, the riser 107 may comprise only one riser pipe if, for example, gas lift or a submerged pump arrangement is used to transport extracted resources 222. In the following, advantageous extraction units 103 will be described with reference to Figs 4 to 9. Extraction units 103 for subsea mining systems, for example for a subsea mining system 100 as described above, present challenging system components regarding precise positioning, efficient handling and reliable operability on the sea floor 210. Particularly in deep waters, the extraction unit 103 is operated under demanding conditions and still required to provide a high yield of extracted resources 222 for efficiency reasons. For instance, it may be required to perform accurate and dynamic positioning of the extraction unit 103 on the sea floor 210, but at the same high stability should be provided during excavation processes which can exert high forces on the extraction unit 103. Thus, it is preferable to provide extraction units 103 with flexibility and maneuverability as well as with good stability. Furthermore, a high degree of autonomy would be desirable for extraction units 103 operating in deep waters.

[0033] Fig. 4 depicts a perspective top view of an extraction unit 103 for subsea mining systems according to a first embodiment. The illustrated extraction unit 103 is configured to extract resources 221 from a sea floor 210 and comprises a frame 1 . The frame 1 may have a substantially rectangular shape as indicated in Fig. 4. For instance, the frame 1 may have a side length of 10 to 40 m. According to alternative embodiments, the frame 1 may have a substantially circular shape. The frame 1 may comprise a grid-like frame structure with struts in order to provide a stable and low in weight frame 1 . As illustrated, a tool slide 3 is mounted to the frame 1 in a movable manner. For this, the frame 1 may comprise at least one frame guide rail 19 on which the tool slide 3 may slide in horizontal directions x along the frame 1 . The depicted example shows an implementation with a tool slide 3 extending between two parallel frame guide rails 19. As indicated, the tool slide 3 may comprise slide track rollers 20 in order to facilitate sliding on the frame guide rails 19. A drive mechanism such as e.g. a motor with a rack-and-pinion arrangement or chain drive, or a hydraulic cylinder, may be used to move the tool slide 3 relative to the frame 1 .

[0034] The tool slide 3 may extend between two opposite frame sections and may be configured to move in the horizontal directions x within the frame 1 . As depicted, a tool platform 16 is attached to the tool slide 3 in a movable manner. For this, the tool slide 3 may comprise at least one slide guide rail 21 to which the tool platform 16 may be mounted. The illustrated example shows an implementation with two parallel slide guide rails 21 . For instance, the slide guide rails 21 may allow the tool platform 16 to slide along the tool slide 3 as indicated by the horizontal directions y in Fig. 4. As shown, the tool platform 16 may comprise platform track rollers 22 (or equivalent) in order to facilitate rolling or sliding on the slide guide rails 21 . The tool platform 16 may form a substantially planar base and may be configured to move along the horizontal directions y within the tool slide 3. Optionally, a tool slide 3 may comprise more than one moveable tool platform 16. As illustrated, the tool platform 16 may comprise a tool bearing 23 such that an excavation tool 6 with an excavation tool shaft 4 may be mounted to the tool platform 16 in a movable, e.g. slidable manner. Thus, the excavation tool shaft 4 with the excavation tool 6 may be lowered and lifted relative to the frame 1 in vertical directions z. By this, axial movability of the excavation tool 6 in a vertical direction, which may be substantially perpendicular to a horizontal frame plane of the frame 1 , can be provided. According to alternative embodiments, the excavation tool 6 and / or the excavation tool shaft 4 may be fixed to the tool platform 16 in an immovable manner. The excavation tool 6 can be a drilling tool, for example, e.g. a drill bit. Other excavation tools 6, such as e.g. drum cutters, helical cutter heads, shearers, other conventional cutting tools or excavator shovels are also conceivable.

[0035] The excavation tool shaft 4 may be an elongated shaft oriented substantially vertically when in use, thus extending through a horizontal frame plane defined by the frame 1 . The excavation tool shaft 4 may comprise a cylindric shape, for instance. If according to the depicted example the excavation tool 6 is implemented as a drill bit, the excavation tool shaft 4 may enclose a drive shaft as e.g. a rotatable drilling shaft (not shown) configured to rotate about its longitudinal axis in order to rotate the excavation tool 6. According to alternative embodiments, the excavation tool 6 may be also implemented as an excavator shovel or a different excavation tool, thus it is also conceivable to perform other or additional trajectories than rotation by a driving shaft enclosed in the excavation tool shaft 4 and / or by the excavation tool 6. Generally, the excavation tool 6 is configured to excavate resources 221 from the sea floor 210 and may comprise any shape and mechanism suitable to extract material from the ground.

[0036] In the context of this application, the term “movable” may generally refer to translatory and rotatory movability. For instance, the tool slide 3, the tool platform 16 and the excavation tool shaft 4 may be slidable with a translatory trajectory according to the depicted embodiments, but it is generally also possible to provide pivot bearings e.g. between the tool slide 3 and the tool platform 16 in order to allow for a platform rotation.

[0037] The frame 1 may be attached to a frame support 2 which is configured to support the frame 1 on the sea floor 210. The frame support 2 may, for instance, comprise support legs, e.g. positioned in the corners of the rectangular frame 1 . Preferably, the frame 1 is attached to the frame support 2 in a movable manner. According to the example depicted in Fig. 4, the frame 1 is attached to the substantially vertical support legs in a slidable manner such that the frame 1 can be shifted relative to the frame support 2. It may be particularly advantageous if the support legs are individually adjustable in their individual length and / or orientation (described in further detail below), thus allowing to align the frame 1 horizontally on uneven ground structures for improved balance. The frame support 2 may for example comprise length-adjustable and / or tiltable support legs for this purpose. By means of an adjustable frame support 2, e.g. implemented by adjustable support legs, the frame 1 obtains supplementary vertical movability in the vertical directions z in addition to an optional vertical movability of the excavation tool shaft 4.

[0038] By means of the extraction unit 103 presented above, at least the horizontal movability degree of excavation equipment for extracting resources 221 is highly improved. Within the frame 1 , the excavation tool 6 may be positioned in a continuously variable location in the horizontal frame plane defined by the frame 1 . Thus, the excavation tool 6 may be easily transferred from one position to another, whether for accurate positioning, position correction, consecutive excavation processes in a target area or for test excavations in order to identify an optimum excavation position, for instance. By this, the flexibility and efficiency of the extraction unit 103 are beneficially increased. At the same time, the frame 1 provides a stable and resistant structure for underwater operations, thus ensuring the operability of the extraction unit 103. In addition to the horizontal movability of the extraction unit 103, further optional degrees of freedom may be provided by an optional vertical movability of the frame support 2 or by an optional vertical movability of the excavation tool 6 and / or excavation tool shaft 4, thus providing an even higher operational flexibility of the extraction unit 103 and its components.

[0039] In the context of this application, horizontal movability may refer to movement directions substantially parallel to the sea floor 210, while vertical movability may refer to movement directions substantially perpendicular to the sea floor 210.

[0040] The extraction unit 103 may furthermore comprise a drive unit 5 for driving the excavation tool 6, e.g. by means of a rotatable drive shaft enclosed in the excavation tool shaft 4. Thus, the excavation tool 6 may be driven directly at the level of the extraction unit 103, thus enhancing the autonomy of the extraction unit 103 and reducing the complexity of the subsea mining system 100. The drive unit 5 may comprise a motor which may be controlled and supplied with energy via a supply and processing unit 25 attached to the frame 1 , which will be described further with reference to Fig. 5.

[0041] Reference is now made to Figs. 5 and 6. With reference to Fig. 5, a perspective top view of an extraction unit 103 for subsea mining systems according to a second embodiment is provided. With reference to Fig. 6, a perspective detail view of the extraction unit 103 depicted in Fig. 5 is provided. The extraction unit 103 presented according to the second embodiment is generally based on the extraction unit 103 according to the first embodiment illustrated in Fig. 4, but provides further advantageous components and functions in order to even further optimize the extraction unit 103. For instance, the extraction unit 103 depicted in Fig. 5 comprises a frame 1 , a frame support 2, a tool slide 3, an excavation tool shaft 4, a drive unit 5 and an excavation tool 6, which are basically similar to the components explained with reference to Fig. 4.

[0042] Furthermore, the extraction unit 103 illustrated in Fig. 5 comprises a cover unit 7 configured to confine sediment plume during excavation processes. The cover unit 7 may comprise a deployable flexible blanket configured to at least partially cover the frame area. The blanket may, for instance, be stowed in the frame structure and unfolded upon a respective trigger signal. The trigger signal may, for example, be issued upon detection of a critical plume value, e.g. by means of an environmental sensor, or automatically upon the start of an excavation process or by a remote control command received by a control module 18 (see Fig. 6) of the extraction unit 103. Furthermore, the cover unit 7 may comprise a shutter 7a which may be selectively rolled out at least partially on the tool slide 3, e.g. for covering the space between the slide guide rails 21 . Thus, environmental impacts caused by sediment plume generated upon excavation processes can be mitigated and the extraction unit equipment can be efficiently protected from clogging.

[0043] Furthermore, the extraction unit 103 illustrated in Figs 5 and 6 comprises a suction unit 8 for extracting the resources 221 excavated by the excavation tool 6. By means of the suction unit 8, which may be configured to generate a suitable negative pressure, pressure differential or liquid flow for material transport, the resources 221 may be easily extracted and transported. The suction unit 8 may comprise a tube 24 for the transport of extracted resources 222, which may be implemented as a flexible hose. The tube 24 may be connected to the excavation tool shaft 4, which may enclose a lifting pipe for conveying the excavated material released from the sea floor 210 by the excavation tool 6.

[0044] Furthermore, the extraction unit 103 as illustrated in Figs 5 and 6 may comprise a preprocessing unit 9 for extracted resources 222. The resources 221 excavated from the sea floor 210 and provided as extracted resources 222 may generally be unprocessed sea floor material, e.g. a target substance mixed with floor ground containing further organic or inorganic material. By means of the pre-processing unit 9, which may for instance comprise a screen (such as a grizzly screen), a cone crusher 9a for crushing extracted resources 222 to a desired size and / or a separation stage 9b for separating extracted resources 222 from waste. In this manner, the extracted resources 222 may be prepared for intermediate storage or further transport to a target location, e.g. to the surface vessel 101 or to the buffer storage 102 via tubing 105. Thus, the transport of the extracted resources 222 may be facilitated and clogging of riser pipes 107a, 107b can be efficiently prevented by pre-processing, for example. According to alternative embodiments, the subsea mining system 100 and the extraction unit 103 may be configured to forward excavated resources 221 directly to the target location, without any intermediate storage or pre-processing.

[0045] The extraction unit 103 as illustrated in Figs 5 and 6 may further comprise a supply and processing unit 25 attached to the frame 1 . The supply and processing unit 25 comprises a power module 10 for powering the extraction unit 103. The power module 10 is configured to receive power from a remote location, for example from the surface vessel 101 via the tubing 105 or via another conduit. Furthermore, the supply and processing unit 25 comprises a control module 18 for controlling the extraction unit 103 according to a predefined controlling scheme and / or by remote control signals. For instance, the power module 10 and the control module 18 may be configured to supply energy and control signals to the drive unit 5 of the extraction unit 103. For instance, the power module 10 and the control module 18 may be configured to supply energy and control signals to a tool slide drive (not shown) and / or to a tool platform drive (not shown) and / or to an excavation tool shaft drive (not shown) and / or to a frame support drive (not shown) in order to move these components relative to the frame 1 . Furthermore indicated in Fig. 5 is instrumentation 13 which may comprise at least one sensor, e.g. an environmental sensor, a camera or other sensors which may be configured to assist in controlling the extraction unit 103.

[0046] Generally, the extraction unit 103 is configured to be connected to a vertical transport system 110, e.g. by a tubing 105. The vertical transport system 110 may for instance be configured according to the embodiment illustrated in Fig. 2. Alternatively, the extraction unit 103 may comprise a vertical transport system 110, e.g. by providing an integrally connected air lift system or other suitable vertical transport mechanisms. Optionally, the extraction unit 103 and / or the vertical transport system 110 may comprise a buffer storage 102.

[0047] Furthermore, the extraction unit 103 illustrated in Fig. 5 comprises an auxiliary handling tool 15 (also depicted in Fig. 7). The auxiliary handling tool 15 may be configured to support service processes as maintenance or repair operations, e.g. changes of excavation tools 6. Thus, the autonomy of the extraction unit 103 can be further enhanced. As illustrated, the auxiliary handling tool 15 may be implemented as a robot arm, thus providing a highly flexible, versatile and precisely controllable auxiliary handling tool 15. For instance, the robot arm may be equipped with sensoring equipment and / or with a camera for on-site and / or remote control assistance. As depicted, the auxiliary handling tool 15 may be attached to the tool platform 16. According to alternative embodiments, it may be also placed on the tool slide 3 or other suitable locations within or on the frame 1 .

[0048] Furthermore, the extraction unit 103 illustrated in Fig. 5 comprises a support platform 11 (also depicted in Fig. 7) configured to store auxiliary tool equipment. By this, the extraction unit 103 provides increased autonomy and efficiency. The support platform 11 may be stowed in the frame structure and folded out upon a respective trigger signal. For instance, the support platform 11 may provide spare parts, tool bits as e.g. drill bits, repair tools and other equipment for maintenance, repair or varying excavation conditions and tasks. According to an example, the excavation tool 6 may be attached to the excavation tool shaft 4 in a releasable manner and the auxiliary handling tool 15 or a remotely operated vehicle (ROV) for operational assistance may be configured to assist in detaching the excavation tool 6 from the excavation tool shaft 4 and attaching a different excavation tool 6 to the excavation tool shaft 4.

[0049] Furthermore, the extraction unit 103 illustrated in Fig. 5 comprises motive members 12 (also depicted in Fig. 7) which are operable to move the extraction unit 103 relative to the sea floor 210. By motive members 12, the overall maneuverability of the extraction unit 103 can be further enhanced. As illustrated, the motive members 12 may comprise thrusters operable to rotate the extraction unit 103 about a vertical axis and / or move the extraction unit 103 sideways. The motive members 12 may, for example, be used to orient the unit 103 prior to landing on the sea floor 210 for extracting resources 221 . Optionally, the thrusters may be turnable, such as to provide positioning assistance in all six degrees of freedom. According to the depicted example, one motive member 12 is mounted to each corner of the rectangular frame 1 . According to alternative examples, the extraction unit 103 may comprise more or fewer thrusters or thrusters at different positions of the extraction unit 103.

[0050] Furthermore, the extraction unit 103 illustrated in Fig. 5 comprises a wire connection means 14 for lowering, positioning and / or retrieving the extraction unit 103. Thus, easy and precise handling of the extraction unit 103 may be beneficially ensured. For instance, the wire connection means 14 may be configured for attaching a wire or a wire hook, by which the extraction unit 103 may be lowered and / or lifted underwater. The wire or wire hook may be connected to the surface vessel 101 , for instance, or to a different base location as e.g. a fixed sea-level platform or support vessel. The wire connection means 14 may comprise an eyelet, a hook or a different suitable attachment means for attaching a lifting means as a wire or a wire hook. According to an advantageous embodiment, the wire connection means 14 comprises a floating element in order to provide a floating lifting sling which can be easily caught by a lifting means, for example with the assistance of an ROV 188. Optionally, the extraction unit 103 may be connected to the surface vessel 101 via a wire during the entire operation subsea. The wire may be used to reposition the extraction unit 103 at regular intervals during the subsea mining process, optionally with the assistance of the motive members 12 and / or other equipment such as instrumentation 13.

[0051] Reference is now made to Fig. 7, which depicts a perspective top view of an extraction unit 103 for subsea mining systems according to a third embodiment. The extraction unit 103 presented according to the third embodiment is generally based on the extraction unit 103 according to the first and second embodiments illustrated in Figs. 4 to 6, but provides further advantageous components and functions in order to even further optimize the extraction unit 103. As illustrated, the extraction unit 103 further comprises an auxiliary collection tool 17 configured to extract material from the sea water surrounding the extraction unit 103. For instance, the auxiliary extraction tool 17 may comprise a suction mechanism and optionally a movable extraction arm and / or a flexible tube 24 for material extraction. The material extracted by the auxiliary extraction tool 17 may contain resources 222 which can be forwarded to a vertical transport system 110, or it may contain plume, pollutants or other harmful substances which can be extracted from the sea water in order to reduce the environmental impact caused by the excavation process. Thus, the auxiliary extraction tool 17 may also present a cleaning tool of the extraction unit 103. According to an advantageous embodiment depicted in Fig. 7, the auxiliary extraction tool 17 may be operated, e.g. guided through the sea water, by means of the auxiliary handling tool 15, thus increasing the range of the auxiliary extraction tool 17.

[0052] Fig. 8 illustrates another example of an extraction unit 103. The extraction unit 103 may comprise any combination of the features described in relation to the examples above. In addition, the extraction unit 103 shown in Fig. 8 comprises a second tool slide 3b in addition to a first tool slide 3a. Each of the tool slides 3a and 3b may be of a design equivalent to the tool slide 3, and comprise the relevant associated components as described above. The second tool slide 3b, like the first tool slide 3a, thus has a tool platform 16 attached thereto in a movable manner and an excavation tool 6 configured to excavate resources 221 from the sea floor 210.

[0053] Each excavation tool 6 can be connected via a tube 24 to transport extracted resources, similarly as described above. Equipment for processing and / or transport of extracted resources may be common (i.e., shared) between the two excavation tools.

[0054] In Fig. 8, each excavation tool 6 can be independently moveable within the frame 1 and operate in parallel, thus increasing operational flexibility and capacity.

[0055] Also illustrated in Fig. 8, but applicable to any example or embodiment described herein, the excavation tool 6 may comprise a plurality of removable weights 26. The weights 26 may be releasably fixed to the excavation tool 6, for example to the shaft 4, such as to provide a downforce on the excavation tool 6 by means of the gravity of the weights 26. The extraction unit 103 may be arranged to permit a variable number of weights 26 to be employed, whereby an appropriate number can be selected based on the operational conditions in any given case. Fig. 8 also illustrates an ROV 188 operated from the extraction unit 103, to assist the subsea mining operations.

[0056] Fig. 9 illustrates an extraction unit 103 according to another example. The extraction unit 103 may comprise any combination of the features described in relation to the examples above. In the extraction unit 103 in Fig. 9, the frame support 2 is fixed to the frame 1 in a tiltable manner. In this example, the frame support 2 comprises a plurality of support legs which are each tiltable relative to the frame 1 . In this manner, the extraction unit 103 may more easily be positioned on sections of the sea floor 210 which are inclined or uneven. Advantageously, the tiltable frame support 2 can be combined with vertically movable and / or extendible frame support 2, such as vertically movable and / or extendable support legs as described above.

[0057] Additionally, or alternatively, the excavation tool 6 may be tiltable relative to the frame 1 . For example, the tool platform 16 can be fixed to the tool slide 3 in a tiltable manner or the tool shaft 4 of the excavation tool 6 can be fixed to the tool platform 16 in a tiltable manner. Fig. 9 illustrates the excavation tool 6 in two orientations, with the tilted orientation is shown in dashed outline. In this manner, the extraction unit 103 may more easily be operated on sections of the sea floor 210 which are inclined or uneven, with the excavation tool 6 operating substantially vertically into the soil even if the frame 1 is inclined.

[0058] The described subsea mining systems and extraction tools beneficially enhance precise positioning, efficient handling and reliable operability of system components placed on the sea floor. Particularly in deep waters, accurate and dynamic positioning as well as high flexibility and maneuverability of extraction units may be provided by means of the suggested features. Furthermore, a high degree of autonomy may be provided by the presented extraction units.

Claims

CLAIMS1 . An extraction unit (103) for a subsea mining system (100) configured to extract resources (221 ,222) from a sea floor (210), the extraction unit (103) comprising: a frame (1 ); a frame support (2) configured to support the frame (1 ) on the sea floor (210); a tool slide (3) attached to the frame (1 ) in a movable manner; a tool platform (16) attached to the tool slide (3) in a movable manner; and an excavation tool (6) attached to the tool platform (16) and configured to excavate resources (221 ,222) from the sea floor (210).

2. The extraction unit (103) according to claim 1 , wherein the excavation tool (6) is attached to the tool platform (16) in a movable, such as a vertically movable, manner.

3. The extraction unit (103) according to claim 1 or 2, wherein the frame (1 ) is attached to the frame support (2) in a movable, such as a vertically movable, manner.

4. The extraction unit (103) according to any preceding claim, wherein the extraction unit (103) further comprises a suction unit (8) for extracting the resources (221 ,222) excavated by the excavation tool (6), the suction unit (8) fluidly connected to the excavation tool (6) via a tube (24).

5. The extraction unit (103) according to any preceding claim, wherein the extraction unit (103) further comprises a buffer reservoir and / or a pre-processing unit (9) for extracted resources (222).

6. The extraction unit (103) according to any preceding claim, wherein the excavation tool (6) is a drilling tool or a cutting tool.

7. The extraction unit (103) according to any preceding claim, wherein the extraction unit (103) further comprises an auxiliary handling tool (15).

8. The extraction unit (103) according to claim 7, wherein the auxiliary handling tool (15) comprises a robot arm and / or the auxiliary handling tool (15) is attached to the tool platform (16).

9. The extraction unit (103) according to any preceding claim, wherein the extraction unit (103) further comprises an auxiliary extraction tool (17) configured to extract material from the sea water surrounding the extraction unit (103).

10. The extraction unit (103) according to any preceding claim, wherein the extraction unit (103) further comprises a support platform (11 ) configured to store auxiliary tool equipment.11 . The extraction unit (103) according to any preceding claim, wherein the extraction unit (103) further comprises a drive unit (5) for driving the excavation tool (6).

12. The extraction unit (103) according to any preceding claim, wherein the extraction unit (103) further comprises at least one motive member (12), for example a thruster, operable to move the extraction unit (103) relative to the sea floor (210).

13. The extraction unit (103) according to any preceding claim, wherein the extraction unit (103) is configured to be connected to a vertical transport system (110) or wherein the extraction unit (103) comprises a vertical transport system (103).

14. The extraction unit (103) according to any preceding claim, wherein the extraction unit (103) further comprises a wire connection means (14) for suspending the extraction unit (103) from a surface vessel (101), for example for lowering, positioning and / or retrieving the extraction unit (103).

15. The extraction unit (103) according to any preceding claim, wherein the extraction unit (103) further comprises a cover unit (7) enclosing the excavation tool (6) and configured to confine sediment plume.

16. The extraction unit (103) according to any preceding claim, wherein the tool slide (3) is a first tool slide (3a) and the extraction unit (103) comprises a second tool slide (3b) having a second tool platform (16) attached to the second tool slide (3b) in a movable manner and a second excavation tool (6) attached to the second tool platform (16) and configured to excavate resources (221 ,222) from the sea floor (210).

17. The extraction unit (103) according to any preceding claim, wherein the excavation tool (6) comprises a plurality of removable weights (26).

18. The extraction unit (103) according to any preceding claim, wherein the tool slide (3) is moveable relative to the frame (1) in a first direction (x), the tool platform (16) is moveable relative to the tool slide (3) in a second direction (y), and wherein the first and second directions (x,y) are perpendicular.

19. The extraction unit (103) according to any preceding claim, wherein the frame support (2) is fixed to the frame (1 ) in a tiltable manner, for example wherein the frame support (2) comprises a plurality of support legs which are each tiltable relative to the frame (1 ).

20. The extraction unit (103) according to any preceding claim, wherein the excavation tool (6) is tiltable relative to the frame (1 ), for example wherein the tool platform (16) is fixed to the tool slide (3) in a tiltable manner or wherein a tool shaft (4) of the excavation tool (6) is fixed to the tool platform (16) in a tiltable manner.21 . A method of extracting resources (221 ,222), the method comprising: operating an extraction unit (103) according to any preceding claim on or adjacent a sea floor (210), and transporting extracted resources (221 ,222) to a short-based location.

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