Patent Publication Number: US-10766577-B2

Title: System and method of operating a subsea module

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 U.S.C. § 371 National Phase of PCT Application No. PCT/NO2016/050240 filed Nov. 25, 2016, which claims priority to Norwegian Application No. NO 20160328 filed Feb. 26, 2016. The disclosures of these prior applications are hereby incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The invention concerns the field of unmanned underwater vehicles. In particular, the invention concerns a system as set out by the preamble of claim  1 , and a method of operating the system, as set out by the preamble of claim  13 . 
     BACKGROUND OF THE INVENTION 
     Unmanned vehicles are widely used in underwater (also referred to as subsea) operations. Autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs) are used for military operations, monitoring marine life, surveying seabed geology and archeology, salvage operations, as well as a multitude of tasks in connection with the extraction of hydrocarbons from subsea wells. 
     An AUV is generally a pre-programmed robot which is capable of operating under water without any real-time input from an operator. 
     An ROV is generally an unmanned, highly maneuverable, subsea mobile vehicle, having propulsion devices (e.g. thrusters) and equipment such as torque tools, manipulator arms (including cutters and grippers), cameras (video and stills), lights, sampling devices, etc. An ROV is normally connected to a device often referred to as a tether management system (TMS) via a neutrally buoyant tether. The tether containing electrical conductors and fiber optics for communicating electrical power, video signals, and data signals. The TMS typically comprises a cage holding a reel for storing and paying out tether, and may also comprise means for temporarily securing the ROV. 
     In use, the TMS is normally suspended (from e.g. a ship&#39;s crane) by a load-bearing umbilical cable which also contains power and communication means. The umbilical cable extends between the TMS and a control room aboard a surface ship, from where the ROV is controlled. The TMS is normally suspended in the water during ROV operations, below the splash zone. 
     Subsea operations in general also rely on extensive use of tools, units and equipment, many of which are remotely operated (e.g. by ROV&#39;s). Examples of such operations are BOP intervention, wellhead maintenance, and well intervention. 
     Such subsea operations, including the operation of the TMS and ROV, require considerable equipment and ancillary systems; for example a Power Distribution Unit (PDU), Hydraulic Power Unit (HPU), Instrumentation Power Assembly (IPA) and a Launch-and-Recovery System (LARS), a control room and various instruments and control interfaces. These systems and equipment are normally installed at the location of operation (e.g. on a vessel, a platform or a drilling rig), often in containers or on skids. This equipment, in addition to the ROV and the TMS, requires extensive logistics and often takes several days or weeks to mobilize to the intended location. It occupies a significant area and (in the case of a floating vessel) allowable variable deck load. 
     It is therefore a need for an improved system and method of performing these subsea operations. 
     The prior art includes WO 01/21476 A1, which discloses an AUV which is releasably connected to a flying latch vehicle. The vehicle is connected via a tether to a subsea tether management system (TMS). The TMS is connected via a load-bearing umbilical cable to a topside launch and recovery device. 
     SUMMARY OF THE INVENTION 
     The invention is set forth and characterized in the main claim, while the dependent claims describe other characteristics of the invention. 
     It is thus provided a system for managing and controlling a subsea module, characterized by a deployment module configured for releasably receiving and accommodating the subsea module, and further comprising a load-bearing cable, one end of which is connected to the subsea module, and the other end of which is connected to a cable control device on the deployment module, whereby the subsea module may be lowered out of and retracted into the deployment module. In one embodiment, the load-bearing cable is a load-bearing umbilical cable. 
     In one embodiment, the deployment module comprises power distribution and control means, communication means, configured for communication with a control facility. The deployment module may comprise a power and signal cable, configured for connection to a power and signal interface unit on a carrier structure. The deployment module may comprise lifting means, configured for suspending the deployment module. 
     In one embodiment, the subsea module is configured for holding a subsea vehicle. In one embodiment, the vehicle comprises a remotely operated vehicle (ROV). The subsea module may further comprise a tether management system (TMS) and a tether connected between the ROV and the TMS. 
     In one embodiment, the vehicle comprises an autonomous underwater vehicle (AUV). 
     In one embodiment, the subsea module comprises a remotely operated tool (ROT). The remotely operated tool may comprise utilities-and-power means to perform work on subsea or downhole equipment or installations. The remotely operated tool may comprise a signal cable, hydraulic hose or other elongate flexible element configured for connection to the subsea or downhole equipment or installation ( 22 ). 
     It is also provided a method of operating the invented system, characterized by the steps of:
         a) arranging the deployment module above a body of water and providing power and signals to the deployment module;   b) lowering the subsea module from the deployment module, via a load-bearing umbilical or wire, to a resident subsea location;   c) operating the subsea module for a desired duration; and   d) retrieving the subsea module to the deployment unit.       

     In the method, the deployment module may be placed on a carrier structure following step b). The deployment module is preferably arranged above the body of water prior to step d). 
     The resident subsea location may be on the seabed or a structure on the seabed. 
     In one embodiment of the invented method, the subsea module is controlled from a distal location, via the umbilical and the deployment module. 
     In one embodiment, the vehicle is controlled from a distal location, via the tether, the subsea module, the umbilical and the deployment module. 
     The invented system makes mobilization of an ROY, AUV and ROT more efficient, in terms of both cost and time, compared to the prior art systems. The invented system improves logistics operations, allows for more rapid mobilization, and occupies less space that prior art systems. 
     The invention may be used by any installation, facility, vessel or rig at sea, as well as on shoreline facilities, such as a quay or dock. The invention is self-contained, and requires only electrical power and signals, and lifting equipment, such that the seabed module may be lowered from the deployment module. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other characteristics of the invention will become clear from the following description of an embodiment, given as a non-restrictive example, with reference to the attached schematic side-view drawings, wherein: 
         FIG. 1  shows an embodiment of the invented system, in an inactive state aboard a carrier structure, such as an offshore platform or ship, and connected to a crane; 
         FIG. 2  shows the deployment module being suspended by the crane, above the water; 
         FIG. 3  shows a subsea module having been lowered to the seabed via an umbilical, from the deployment module; 
         FIG. 4  shows the deployment module having been moved back to, and placed on, the carrier structure and the subsea module is resting on the seabed, and an umbilical extends between the deployment module and the subsea module; 
         FIG. 5  shows the deployment module in place on the carrier structure and the subsea module resting on the seabed, and an ROV is moving in the water, connected to the TMS in the subsea module via a tether; 
         FIG. 6  is an enlarged drawing of the area marked “A 1 ” in  FIG. 5 ; 
         FIG. 7  shows the deployment module suspended above the water by the carrier structure crane, and the subsea module suspended underneath the deployment module by the umbilical; 
         FIG. 8  is an enlarged drawing of the area marked “A 2 ” in  FIG. 7 ; 
         FIG. 9  corresponds to  FIG. 3 , but illustrates an alternative embodiment of the subsea module; and 
         FIG. 10  shows the deployment module in place on the carrier structure and the alternative embodiment of the subsea module resting on the seabed, and a cable, hose or similar is connected to a subsea installation. 
     
    
    
     DETAILED DESCRIPTION OF AN EMBODIMENT 
     The following description will use terms such as “horizontal”, “vertical”, “lateral”, “back and forth”, “up and down”, “upper”, “lower”, “inner”, “outer”, “forward”, “rear”, 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&#39;s convenience only and shall not be limiting. 
       FIG. 1  shows an embodiment of the invented system, placed on the deck of a carrier structure  1 . The carrier structure may for example be a ship, a floating platform, a fixed offshore, inshore or atshore installation, or a quay. The invented system comprises a deployment module  4 , which is designated and configured for launching and recovering a subsea module, as will be described in the following. The term “deployment module” shall therefore not be limited to use only in a deployment operation, but also in a retrieval operation. The deployment module  4  is designed such that it is easily movable from one location to another. The deployment module may for example be mobilized from an onshore base on short notice, and transported by a supply vessel to an offshore rig. The deployment module  4  comprises lifting lugs  6 , by means of which it may be lifted (e.g. by a crane  2  and associated lifting gear  5 ). The crane may, for example, be a regular deck crane, which is well known in the art. When placed on the carrier structure  1 , the deployment module  4  is connected to an electrical power and signal interface unit  9  (e.g. a utility station) on the carrier structure. 
     Referring additionally to  FIG. 2  and  FIG. 8 , the deployment module  4  comprises a chassis on which an umbilical winch  10  is arranged. The deployment module  4  also comprises interface means (e.g. a cage or housing) for a subsea module  12 . The subsea module  12  is a device which is releasably connected to the deployment module  4  (by devices that are known per se) and is shown as being suspended by a load-bearing umbilical  11  which is being stored on the umbilical winch  10 . Such umbilical cable is a well-known device for communicating power, control signals, etc., and needs therefore not be described in further detail here. It should be understood that the load-bearing umbilical cable may be replaced by a load-bearing wire or rope, or similar, in combination with a piggy-back control cable. In an inactive state for example during transportation and storage the subsea module  12  may be locked to the deployment module  4 . The deployment module  4  may be formed with a designated bay or hold, into which the subsea module  12  will fit. 
     The deployment module  4  also comprises Power Distribution Units (PDU)  16 , transformers  17  and a control and communications module  18 . The deployment module is therefore a self-contained unit, only requiring power, signals and lifting means. 
     Referring additionally to  FIG. 6 , the subsea module  12  comprises in the illustrated embodiment interface means (e.g. a cage or housing) for supporting a remotely operated vehicle (ROV)  13  and a tether management system (TMS)  15 . The physical interfaces between the ROV, the TMS, and the subsea module utilize known devices, and need therefore not be described further here. The subsea module may comprise one or more holding stations for various ROV tools. 
     The ROV may be any suitable ROV known in the art, and need therefore not be described further here. Likewise, the TMS may be any suitable TMS known in the art and need therefore not be described further here. A tether  14  extends between the ROV  13  and TMS  12 , in a manner which is well known in the art. It should be understood, however, that the invention is also applicable for wireless communication with the ROV 
     A power and signal cable  8  is connected between the deployment module  4  and the power and signal interface unit  9  on the carrier structure  1 , thus providing electrical power to the umbilical winch and equipment such as the PDU  16 , transformers  17  and the control and communications module  18 . 
     A method of using the invented system in the illustrated embodiment will now be described:
         Referring to  FIG. 1 , the self-contained deployment module  4  has been placed on the deck of a carrier structure  1  (e.g. an offshore rig, a floating platform, a fixed installation, a quay), and lifting gear  5  has been attached to the crane  2 . The power-and-signal cable  8  has been connected to a utility station  9 .   Referring to  FIG. 2 , the crane  1  has lifted the deployment module  4 , via the lifting gear  5  and crane wire  7 , and is suspending the deployment module  4  above the water surface S. The cable  8  supplies electrical power and signals to the deployment module  4  and its onboard equipment, including the umbilical winch  10 . The cable is placed in a chute  3 . The subsea module may be operated by an operator located on the carrier structure, either via the cable  8  or by wireless connection, which per se is known in the art.   Referring to  FIG. 3 , the subsea module  12  has been lowered from the deployment module  4 , by means of the winch  10  and via the load-bearing umbilical  11 , to the seabed B.   Referring to  FIG. 4 , the deployment module  4  has been hoisted back onto the rig  1 , and the umbilical  11  has been placed in the chute. The deployment module  4  is connected to the power and signal interface unit  9  via the cable  8 , whereby signals to and from the subsea module may be communicated to and from the signal interface unit  9 , and hence to control stations and monitoring equipment on the carrier stricture. The subsea module  12  is now resident Oil the seabed, and ready to commence operation. The subsea module may be resident for long or short durations, depending on the requirements of the operation.   Referring to  FIG. 5  and  FIG. 6 , the ROY  13  is moving in the water W, connected to the TMS  15  on the subsea module  12  via a tether  14 , The ROY is thus operated and controlled by signals through the umbilical  11  to the subsea module  12  and TMS  15 , and the tether  14 . The ROY may thus be controlled, monitored or operated from a distal location, fix example a control room on the rig  1 , or on a different vessel or on an onshore location.       

     The communication between the deployment module  4  and a control room may be via the cable  8  (discussed above), or by wireless means L (e.g. 4G telephone or satellite network). Such wireless communication may be useful if the control room  19  is at a distal location (e.g. an onshore site), but may also be used to communicate with nearby facilities (e.g. a vessel or rig). Such means of wireless communication are well known in the art and need therefore not be described in further detain here.
         Referring to  FIG. 7  and  FIG. 8 , the subsea module  12  is being retrieved (recovered) in a manner similar to its deployment (launch), only in reverse order. The winch  10  is hauling the subsea module  12  (holding the ROV  13  and the TMS  15 ) via the umbilical  11 , into the deployment module  4 , whereupon the deployment module  4  is placed on the rig deck, corresponding to the situation illustrated in  FIG. 1 .       

     Although the invention has been described with the use of a crane  2  and lifting gear  5 ,  6 , it should be understood that the invention is not limited to an overboarding device. In an alternative embodiment (not illustrated), the deployment module  4  may be placed on a balcony or above a moon-pool or other deck opening and remain there during the ROV operations, whereby the subsea module  12  may be lowered into the sea without a preceding crane operation. 
     Although the invention has been described with the subsea module  12  resting on the seabed when the ROV  13  is in operation, it should be understood that the invention is not limited to the subsea module being in such position. The subsea module may rest on (or be connected to) other structures, and/or it may be equipped with buoyancy modules (not shown), whereby is may be made neutrally buoyant. The connection to other structures may be by mechanical devices and/or by magnetic devices (e.g. electromagnets). 
     Although the invention has been described with reference to a subsea module carrying an ROV and a TMS, it should be understood that the invention is equally applicable for a subsea module carrying any unmanned undersea vehicle, such as an AUV or a non-tethered ROV. 
     Referring to  FIGS. 9 and 10 , the subsea module  12  as described above may be replaced by an alternative embodiment of a subsea module  20 . This subsea module  20  may be any remotely operated tool (ROT), for example a BOP intervention tool or a wellhead tool. The ROT  20  is deployed from, and retrieved back into, the deployment module  4  in a manner similar to what is described above with reference to the subsea module  12 , and also operated via similar means. Only the differences between the two embodiments of the subsea module are therefore described in the following. 
       FIG. 9  illustrates the ROT  20  having been placed on the seabed, in the vicinity of a seabed installation  22 , for example a BOP. In  FIG. 10 , the deployment module  4  has been moved back onto the carrier  1 , and a cable  21  has been extended between the seabed installation  22  and the ROT  20 . In should be understood that the cable  21  in fact may be any elongate element, such as a control cable, power cable, umbilical, hydraulic hose, or similar, depending on the actual requirement for the case at hand. Reference number  23  schematically indicates utilities-and-power means, which may comprise e.g. electrical motors, hydraulic accumulators, control devices, pumps, or other mechanical or hydraulic power means.