Abstract:
A system for seafloor mining comprising a vertical riser anchored to the seafloor; a mining machine to deliver seafloor ore to the vertical riser; a lifting system to pass the ore through the vertical riser; and a transport vessel removably connected to the vertical riser to receive ore from the vertical riser.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a method and associated system for seafloor mining. In particular, the invention relates to a method and associated system for deepwater seafloor mining in areas which are exposed to non-benign seastates and/or cyclonic (or similar) weather events. However, it should be appreciated that the method and system for seafloor mining may be used in sheltered waters or benign seastate locations. 
       BACKGROUND OF THE INVENTION 
       [0002]    The deep sea contains many different resources available for extraction, including silver, gold, copper, manganese, cobalt, and zinc. These raw materials are found in various forms on the sea floor, usually in higher concentrations than terrestrial mines. However, most of these deposits are found in water having a, depth of between 1,000 and 6,000 meters. Therefore there are substantial technical challenges mining and transporting ore from the seafloor. 
         [0003]    In order to mine the ore from the deposits, the applicant has developed a method and system for seafloor mining. The system includes a dynamically suspended subsea pump located at the bottom of a vertical riser that extends to a surface vessel. A combination of seafloor production tools excavate and deliver the mineralised ore in slurry form to the pump via a horizontal transport pipe. In use, the ore travels through the horizontal transport pipe, up through the riser and into the surface vessel. The ore is then dewatered and transferred to a barge. 
         [0004]    The above method and system for seafloor mining is primarily for use in relatively calm ocean water. That is, the above method and system for seafloor mining is impractical or unfeasible in areas that are disposed to large wave height fluctuations especially evident in cyclone (or typhoon) prone, locations. This is largely due to riser sensitivity and to high riser dynamic loading and the seastate limitations associated with the transfer of ore from the mining support vessel to an adjacent barge. 
         [0005]    The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge in Australia. 
       OBJECT OF THE INVENTION 
       [0006]    It is an object of the invention to overcome or alleviate one or more of the disclosures or provide the consumer with the useful or commercial choice. 
       SUMMARY OF THE INVENTION 
       [0007]    In one form, although not necessarily the only or broadest form, the invention relates to a system for seafloor mining comprising: 
         [0008]    a vertical riser anchored to the seafloor; 
         [0009]    a mining machine to deliver seafloor ore to the vertical riser; 
         [0010]    a lifting system to pass the ore through the vertical riser; and 
         [0011]    a transport vessel removably connected to the vertical riser to receive ore from the vertical riser. 
         [0012]    The vertical riser is preferable in the form of a rigid riser. However, it is possible that the vertical riser is a flexible riser. It is also envisaged that the vertical riser may be formed from a rigid section and a flexible section. 
         [0013]    At least one buoyancy device may be used to support the vertical riser. The buoyancy device may be in the form of a buoyancy tank. The buoyancy of the buoyancy tank may be varied. 
         [0014]    The lifting system may be of any suitable form. The lifting system may be in the form of a subsea pump. The subsea pump is normally located adjacent a bottom of the vertical riser. 
         [0015]    An alternative lifting system may use air to lift the ore through the vertical riser. The air may be pumped into the vertical riser. Sufficient air may be pumped into the vertical riser at a position to lift the ore. This position may be varied according to design. An air supply line may extend down the vertical riser to deliver air into the vertical riser. A compressor may be attached to the air supply line to enable air to travel through the air supply line. 
         [0016]    The transport vessel may include a cargo hold for storage of the ore. The transport vessel may include a processing plant for de-aerating and/or dewatering the ore. 
         [0017]    A jumper may be used to connect the mining machine to the vertical riser. The jumper may be connected to adjacent the bottom of the riser. A quick coupling may be used to connect the jumper to the mining machine. 
         [0018]    A flexible link hose may be used to connect the vertical riser to the transport vessel. A quick coupling may be used to connect the jumper to the mining machine. 
         [0019]    A support vessel may be used to control the operation of the mining machine. The support vessel may be linked to the mining machine via an umbilical. 
         [0020]    The mining machine may be used to excavate ore to supply to the vertical riser. Alternatively, the mining machine may be used to retrieve already excavated ore and supply them to the vertical riser. It should be appreciated that more than one mining machine may be connected to the vertical riser. 
         [0021]    In another form, the invention resides in a method for seafloor mining including the steps of: 
         [0022]    connecting a mining machine from a vertical riser which is anchored to the seafloor; and 
         [0023]    connecting a transport vessel from the vertical riser. 
         [0024]    The method may further include one or more of the steps of: 
         [0025]    commencing operation of a lifting system; 
         [0026]    lowering a mining machine from the seafloor. 
         [0027]    disconnecting a mining machine from a vertical riser which is anchored to the seafloor; 
         [0028]    disconnecting a transport vessel from the vertical riser; 
         [0029]    discontinuing operation of a lifting system; and 
         [0030]    retrieving a mining machine from the seafloor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    Embodiments of the invention, by way of example only, will now be described with reference to the accompanying figures in which: 
           [0032]      FIG. 1  is a schematic view of an operational system for seafloor mining according to a first embodiment of the invention; 
           [0033]      FIG. 2  is a schematic view of a non-operational system for seafloor mining; and 
           [0034]      FIG. 3  is a schematic view of a system for seafloor mining according to a second embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0035]      FIG. 1  shows a system for seafloor mining  10  for use in areas which have large wave height fluctuations and/or are located in cyclone prone areas. However, it should be appreciated that the system  10  for seafloor mining may be used in low wave height areas. The system  10  includes a vertical riser  20 , a subsea pump  30 , a mining machine  40 , a transport vessel  50  and a support vessel  60 . 
         [0036]    The vertical riser  20  is used to transport ore received from the mining machine  40  to the transport vessel  50 . The vertical riser  20  is constructed from a rigid pipe which is anchored to the seafloor via an anchor  21 . The anchor  21  can be in the form of a clump weight, piled foundation structure or an alternate vertically loaded foundation apparatus. A chain  26  or other suitable tether is normally used to attach the vertical riser  20  to the anchor  21 . The type and size of the vertical riser  20  and would readily be chosen by a person skilled in the art depending on design requirements. 
         [0037]    A dump valve  24  is located adjacent a bottom of the vertical riser  20 . The dump valve  24  is used to ensure the vertical riser  20  does not become blocked during an uncontrolled shut down. In an uncontrolled shut down, the dump valve  24  is opened thereby releasing ore from vertical riser  20  through an outlet  25  located below the dump valve  24 . It would be appreciated by a person skilled in the art that there are numerous ways in which the dump valve  24  is activated at an appropriate time. 
         [0038]    A buoyancy tank  23  is attached to adjacent the top of the vertical riser  20 . The buoyancy tank  23  is used to assist in maintaining the tension in the vertical riser  20 . The positioning of the buoyancy device  23  is at a depth where the waves do not cause unacceptable loading or movement on the riser  20 . Accordingly, the size and form of the buoyancy tank  23  would be evident to a person skilled in the art. The vertical riser  20  passes through buoyancy tank  23 . 
         [0039]    The buoyancy of the buoyancy tank  23  can be varied to allow relocation of the vertical riser  20 . The buoyancy of the buoyancy tank  23  can be varied by varying the amount of water that is located within the buoyancy tank  23 . Once mining at a site is completed, the buoyancy tank  23  is partially flooded to reduce the tension of the chain  26  between the vertical riser  20  and anchor  21 . For such an operation, the riser  20  can be supported from surface by the transport vessel  50  or the support vessel  60  whilst the chain  26  at the base of the vertical riser  26  is disconnected from the anchor  21 . Once the chain  26  has been removed, the vertical riser  20  can be relocated and connected to another anchor  21  at the next location. Air can then be added to the buoyancy tank to remove the water and allow the buoyancy tank to support the vertical riser  20 . 
         [0040]    The subsea pump  30  is used to pump the ore from the seafloor to the transport vessel  50 . The subsea pump  30  is located adjacent the end of the vertical riser  20 . The size and type of the subsea pump  30  will be dependant on design requirements which would be readily be assessed by a person skilled in the art. It should be appreciated that the means that is used to operate the pump could be varied. For example, the pump may be powered electrically or hydraulically, 
         [0041]    The mining machine  40  is used to mine the ore from the seafloor. The typical size of the seafloor which contains the ore is approximately 500 meters wide by 1000 meters long by about 10 to 40 meters deep. The seafloor terrain is generally very rugged. The water depth also ranges from 1,000 meters to 2,500 meters. The mining machine  40  may work on the rugged terrain with slopes as high as 25 degrees. Therefore, the mining machine  40  ideally would be designed to perform under these rugged deep sea conditions. The mining machine  40  could be designed to mine the ore by performing any combination of the following steps, including, but not limited to, (1) excavating the ore from the fields located on the seabed floor, (2) breaking down the ore into chunk sizes using a cutter mounted on the mining machine  40 , and (3) forcing the ore into a crusher located on the mining machine to crush the ore into manageable sizes to ensure the ore passes through the vertical riser  20 . It should be appreciated that the mining machine  40  may be used to simply collect ore that has been previously stockpiled so that the ore can be transferred to the transport vessel  50 . Many variations and embodiments are envisioned for the mining machine  40 . 
         [0042]    It should be appreciated the system for mining may use a number of mining machines. These mining machines may have varying operations such as excavating ore, stockpiling ore and/or collecting ore from the stockpile. Further, there may be a number of different mining machines performing the same operation. 
         [0043]    A jumper  70  is used to connect the mining machine  40  to the vertical riser  70  via the subsea pump  30 . The jumper  70  may also be referred to as the horizontal transport pipe or a riser transfer pipe. The jumper  70  may be configured in an arced shape. This may reduce the force exerted by the subsea pump  30  on the mining machine  40 . The other function of the arc shaped jumper  70  is to provide flexibility and range of movement of mining machine  40  relative to the vertical riser  20 . 
         [0044]    A large radius of the jumper  70  may lower the centrifugal force and wear. Jumper buoyancy devices  71 , such as buoys are used to maintain the jumper in its arced state. A quick release coupling  72  may be located on one or more ends of the jumper to enable quick release of the jumper from the subsea pump  30  and/or mining machine  40 . A remotely operated vehicle (ROV) (not shown) may be associated with the jumper  70  to enable the quick release (or connection) of the jumper  70  with the pump and/or mining machine  40 . 
         [0045]    The transport vessel  50  is used to store and transport ore that are removed from the seafloor. Accordingly, the transport vessel  50  includes a cargo hold  51  for placement of the ore. The transport vessel  50  also includes a processing plant  52  to both dewater and dewater the ore prior to their placement in the cargo hold  51 . The wastewater from the processing plant  52  is pumped into the sea via a dewatering pipe  54  at a depth that does not have an unacceptable environmental impact. Alternatively, the wastewater is pumped into water injection lines (not shown) which may be piggy backed onto the vertical riser  20  to power a compression chamber of the pump  30  to lift the ore to the surface vessel. 
         [0046]    The transport vessel  50  is attached to the vertical riser  20  via a flexible link hose  80 . A quick release coupling  81  is located at the end of the hose to join the flexible link hose  80  to the transport vessel  50 . A swivel  83  is located on the transport vessel  50 , adjacent to the quick coupling  81 , in order to allow rotation or “weathervaning” of the transport vessel  50 . Hose buoys  82  are connected around the link hose  80  to enable surface retrieval of the flexible link hose  80 . It should be appreciated that the buoy  82  may be used with other types of floating devices to enable retrieval of the flexible link hose  80  such as a floating rope. 
         [0047]    The support vessel  60  is used to transport and support the mining machine  40 . An umbilical  61  extends from the support vessel  60  to the mining machine  40  in order to control the operation of the mining machine  40  from the support vessel  60 . The support vessel  60  includes deployment and retrieval equipment  61  to both place and retrieve the transport vessel  50  as is required. 
         [0048]    The system  10  commences operation by running the subsea pump  30 . Operation of the pump enables the mining machine  40  to excavate ore from the seafloor. It should be appreciated that movement of the mining machine  40  is controlled by an operator located within the support vessel  60 . Once the ore passes through the mining machine  40 , the ore then pass through the jumper  70 , through the subsea pump  30  and into the vertical riser  20 . The ore then pass through the flexible link hose  80  and into the onboard processing plant  81  located on the transport vessel  50 . Once the water is removed from the ore, the ore is placed within the cargo hold  51 . 
         [0049]    In the event that the system for seafloor mining  10  is unable to continue operation due to wave height implications or simply the transport vessel  50  is full, then the flexible link hose  80  is de-coupled from the transport vessel  50  allow the transport vessel  50  to leave the location of the mine. The jumper  70  is also de-coupled from the mining machine  40  via the ROV. The placement and retrieval equipment  61  located on the support vessel  60  is utilised to remove the mining machine  40  from the seafloor. Once the mining machine  40  is removed from the seafloor, the support vessel  60  is able to travel to a safe location. 
         [0050]    During any large wave activity, the buoyancy device  23  and vertical riser  20  are positioned below any wave activity. Therefore, the vertical riser  20 , buoyancy device  23 , subsea pump  30  and jumper  70  can remain at the mining site during a storm as shown in  FIG. 2 . 
         [0051]    In order to commence mining operations after an unacceptable storm event or seastate condition or simply to continue mining operations, both the support vessel and transport vessel  50  return to the site of the subsea mine. The transport vessel  50  retrieves the flexible link hose  80  and couples the flexible link hose  80  using the transport vessel  60  and the quick coupling  81 . The support vessel deploys the mining machine  40  to the seafloor. The ROV is used to connect the jumper  70  to the mining machine  40 . The mining operation can then commence. 
         [0052]    It should also be appreciated that the advantages provided by the system  10  when wave heights implications become an issue also provide advantages in normal use. The quick disconnection of the transport vehicle  50  allows the transport vessel  50  to transport and/or discharge the ore in a reduced timeframe. That is, once its cargo hold is full, the transport vessel  50  disconnects from the flexible link hose  80  and transports the ore to an onshore stockpile or transfers the ore to a separate transportation vessel in sheltered waters. A further transport vessel  50  is then able to connect to vertical riser  20  via the link hose  80  to allow the continuation of mining operations. 
         [0053]    The system  10  for mining the seafloor enables the quick removal of the mining machine  40 , the transport vessel  50  and support vessel  60  when required. Further, the system  10  allows for increased production seastate limits and hence increased production time. Still further, the support provided for the vertical riser  20  reduces dynamic and fatigue loading. Lastly, the systems provides for no offshore transfer of ore between vessels. 
         [0054]      FIG. 3  shows an alternative embodiment of the system  10  for seafloor mining. In this embodiment the pump  30  has been replaced with an air lift system  90 . The air lift system  90  includes a compressor  91  which is mounted on the transport vessel  50 . An air supply line  92  extends from the compressor  91 , along the flexible link hose  80  and passes toward a bottom of the vertical riser  20 . The air supply hose  92  extends through the vertical riser  20  via a nipple  93  to supply air within the vertical riser  20  in order to lift ore from seafloor. It should be appreciated that the placement of the supply line  92  within the vertical riser  20  and the size of the compressor  91  is dependant on design and would be able to be determined by a person skilled in the art. 
         [0055]    In this specification, the terms “comprise”, “comprises”, “comprising” or similar terms are intended to mean a non-exclusive inclusion, such that a system, method or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed. 
         [0056]    It will also be appreciated that various other changes and modifications may be made to the invention described without departing from the spirit and scope of the invention.