Method for transferring fluid between an offshore first assembly located in a body of water and an assembly floating on the body of water, associated assembly and installation

Abstract

The method comprises the following steps: - installation and mechanical tensioning of a plurality of mooring lines (70) between the offshore assembly (12) and the floating assembly (16), each mooring line (70) having an active length (76) under mechanical tension between a first point and a second point; - fluid connection between a first capacity (22) and a second capacity (44) via a fluid transfer system (64), and fluid transfer between the first capacity (22) and the second capacity (44); - continuous measurement of the mechanical tension applied over the active length (76) of at least one mooring line (70); - control, by a control system (62) of the active length (76) of at least one mooring line (70), to maintain the mechanical tension applied over the at least one mooring line (70) within a predefined mechanical tension range.

Description

[0001] La présente The invention relates to a method for transferring fluid between an offshore assembly located in a body of water, the offshore assembly having a first fluid storage capacity, and an assembly floating on the body of water having a second fluid storage capacity, the method comprising the following steps: arrangement of a side face of the floating assembly opposite a side face of the offshore assembly to place the floating assembly side by side with the offshore assembly; installation and mechanical tensioning of a plurality of mooring lines between the offshore assembly and the floating assembly, each mooring line having a first attachment point on the offshore assembly, a second attachment point on the floating assembly, and an active length under mechanical tension between the first point and the second point; fluid connection between the first fluid storage capacity and the second fluid storage capacity via a fluid transfer system, and fluid transfer between the first fluid storage capacity and the second fluid storage capacity.

[0002] The process is particularly applicable to the transfer of cryogenic petroleum fluids such as liquefied natural gas or liquefied petroleum gases. The process is also applicable to the transfer of treated liquefied gases obtained by processing oil or natural gas extracted offshore, or more generally from liquefied gases produced or recovered offshore.

[0003] The offshore structure is, for example, a floating liquefied natural gas (FLNG) unit, a floating storage and regasification unit (FSRU) unit, or a floating liquefied petroleum gas (LPG) export unit. In another variation, the offshore structure is designed for the storage and transport of liquefied gases such as carbon dioxide or ammonia.

[0004] A floating assembly is, for example, a ship or barge used to transport liquefied gas to the coast. Specifically, a floating assembly is an LNG carrier or, more generally, a vessel transporting liquefied gas.

[0005] Offshore liquefied gas production terminals must regularly unload the fluid they produce or process. In this context, when no pipeline suitable for transporting cryogenic fluid exists between the production terminal and the coast, it is known to recover the fluid stored offshore using transport vessels or barges that bring the fluid back to the coast.

[0006] In benign maritime conditions, i.e. with a calm body of water or in sheltered areas, it is known to carry out a side-by-side fluid transfer by mooring the floating assembly to the offshore assembly parallel to each other along their lateral faces, and placing between them discharge arms or flexible pipes to transfer the fluid.

[0007] This transfer method, while effective, has limitations as soon as the weather deteriorates. In particular, mooring cannot be achieved beyond a certain amplitude of relative movement between the floating assembly and the offshore assembly, otherwise the mooring lines are likely to break. Furthermore, when unloading arms are used, their specifications are limited in their ability to absorb relative displacements.

[0008] In more complicated environments, it is known to discharge the fluid by placing the floating assembly in tandem with the offshore assembly, or even by placing a discharge buoy between the two, connected respectively to the floating assembly and the offshore assembly by flexible pipes.

[0009] Such a solution exists for oil unloading, but it remains far less suitable for transferring cryogenic fluids. In particular, the flexible pipelines frequently used for oil transfer have no industrial application for unloading cryogenic fluids over long distances. Furthermore, a fleet of transport barges specifically adapted for this type of unloading is required.

[0010] One aim of the invention is therefore to obtain a method of fluid transfer between an offshore assembly located in a body of water and a floating assembly, which can be used in less favorable weather conditions than those generally used for side-by-side transfer, the transfer method being simple to implement with floating assemblies not dedicated to tandem transfer.

[0011] To this end, the invention relates to a fluid transfer method of the aforementioned type, characterized by the following steps: continuous measurement of the mechanical tension applied over the active length of at least one mooring line; control, by a control system, of the active length of at least one mooring line, to maintain the mechanical tension applied over at least one mooring line within a predefined mechanical tension range.

[0012] The method according to the invention may comprise one or more of the following features, taken individually or in any technically feasible combination: It includes the following steps: continuous measurement of the mechanical tension applied over the active length of a plurality of mooring lines, in particular all mooring lines connecting the offshore assembly and the floating assembly; checking the active length of each mooring line to maintain the mechanical tension applied over each mooring line within a predefined mechanical tension range; at least one mooring line is connected on one of the first and second points to a reel, checking the active length of at least one mooring line by winding and / or unwinding at least one mooring line on the reel; it includes connecting the other of the first and second points of at least one mooring line to a fixed mooring point;the reel includes a kinetic energy recovery system, the method comprising the recovery of electrical energy during the unwinding of at least one mooring line and the winding of at least one mooring line using at least a part of the electrical power recovered by the kinetic energy recovery system; it includes the measurement of a relative movement between the offshore assembly and the floating assembly, the method comprising the control by the control system of the active length of at least one mooring line to maintain an amplitude of relative movement between the offshore assembly and the floating assembly within a predefined range of movement amplitude;The side-by-side arrangement of the lateral face of the offshore assembly and the lateral face of the floating assembly includes the wedging between the lateral face of the offshore assembly and the lateral face of the floating assembly of at least one fender, preferably a plurality of longitudinally spaced fenders; the wedging of the fender(s) includes positioning the fender(s) on a spacing frame configured to increase the distance between the lateral face of the offshore assembly and the lateral face of the floating assembly when the lateral face of the offshore assembly and the lateral face of the floating assembly are arranged side-by-side; fluid transfer is carried out through an articulated discharge arm and / or through a flexible conduit.

[0013] The invention also relates to a fluid transfer system between an offshore unit located in a body of water, the offshore unit having a first fluid storage capacity, and a unit floating on the body of water, having a second fluid storage capacity, the fluid transfer system comprising: a mooring system comprising a plurality of mooring lines between the offshore assembly and the floating assembly, configured to be installed and mechanically tensioned such that each mooring line has a first attachment point on the offshore assembly, a second attachment point on the floating assembly, and an active length under mechanical tension between the first point and the second point; a fluid transfer system configured to establish a fluid connection between the first fluid storage capacity and the second fluid storage capacity and a fluid transfer between the first fluid storage capacity and the second fluid storage capacity; characterized by a mooring system control system comprising at least one sensor for continuous measurement of the mechanical tension applied over the active length of at least one mooring line, the control system comprising a control unit configured to control the active length of at least one mooring line, to maintain the mechanical tension applied over at least one mooring line within a predefined mechanical tension range.

[0014] The fluid transfer system according to the invention may comprise one or more of the following features, taken individually or in any technically feasible combination: the mooring system includes at least one reel, at least one mooring line being connected to one of the first and second points to at least one reel, the control system controlling the active length of at least one mooring line by winding and / or unwinding at least one mooring line on the reel; the control system includes at least one sensor for continuously measuring a relative positioning between the offshore assembly and the floating assembly to determine a relative movement between the offshore assembly and the floating assembly, the method including the control by the control system of the active length of at least one mooring line to maintain an amplitude of relative movement between the offshore assembly and the floating assembly within a predefined range of movement amplitude;The reel includes a kinetic energy recovery system configured to recover electrical energy during the unwinding of at least one mooring line and to provide at least part of the recovered electrical power to wind up the at least one mooring line.

[0015] The invention also relates to a fluid handling installation, comprising: an offshore assembly intended to be placed in a body of water, the offshore assembly having a first fluid storage capacity; a floating assembly, having a second fluid storage capacity, and a fluid transfer assembly as defined above, configured to be mounted between the offshore assembly and the floating assembly.

[0016] The installation according to the invention may include the following feature: the offshore assembly is a platform, for example floating or fixed, a floating liquefied natural gas unit, a floating storage and regasification unit, a floating liquefied petroleum gas export unit, the floating assembly advantageously being a fluid transport vessel or barge.

[0017] The invention will be better understood upon reading the following description, given solely by way of example, and made with reference to the attached drawings, in which: [ Fig. 1 ] there figure 1 is a schematic top view of a fluid handling installation comprising a fluid transfer system between an offshore assembly and a floating assembly for implementing a transfer process according to the invention; [ Fig. 2 ] there figure 2 is a flowchart illustrating the main steps of a fluid transfer process according to the invention. Fig. 3 ] there figure 3 is a view of the mechanical tension applied over time on a mooring line deployed between the offshore assembly and the floating assembly during the implementation of the fluid transfer process according to the invention, and in comparison, without implementing the fluid transfer process according to the invention.

[0018] A first fluid transfer method according to the invention is implemented in a fluid handling installation 10, schematically represented on the figure 1 .

[0019] As illustrated on the figure 1 The installation 10 comprises an offshore assembly 12, located in a body of water 14, and a floating assembly 16 movable relative to the offshore assembly 12 on the body of water 14, between a fluid transfer configuration shown on the figure 1 , in which it is moored to the offshore assembly 12 and a fluid transport configuration away from the offshore assembly 12, in which it navigates over the body of water 14 to an unloading facility advantageously on the coast.

[0020] The installation 10 further includes a fluid transfer assembly 18 according to the invention, configured to moor the floating assembly 16 on the offshore assembly 12 by arranging them side by side, and to allow the transfer of fluid between the offshore assembly 12 and the floating assembly 16.

[0021] The body of water 14 is, for example, an ocean, a sea, a lake, or a river. The depth of the body of water 14 with respect to the installation 10 is, for example, between 15 m and 4000 m.

[0022] The offshore complex 12 is, for example, an offshore cryogenic fluid production and / or processing terminal. The offshore complex 12 is notably a floating liquefied natural gas unit (FLNG), a floating storage and regasification unit (FSRU), or a floating liquefied petroleum gas (LPG) export unit.

[0023] The offshore assembly 12 includes a hull 20 which is here floating on the body of water 14. Alternatively, the offshore assembly 12 is a fixed platform on the body of water 14.

[0024] The assembly offshore 12 further includes a first storage capacity 22 for fluid, in particular cryogenic fluid, disposed in and / or on the hull 20.

[0025] A cryogenic fluid is a substance used or stored at low temperatures, often below -150 °C (-238 °F). These fluids have special properties due to their low temperatures and are often gases at room temperature that become liquid when cooled. Common examples of cryogenic fluids include liquefied natural gas (LNG), liquefied petroleum gases (LPG), liquid nitrogen, liquid helium, liquid oxygen, and others.

[0026] The hull 20 extends here along a first longitudinal axis AA' between a first longitudinal end 24 and a second longitudinal end 26.

[0027] The hull 20 is advantageously closed horizontally by at least one upper deck 24 on which utilities are located, including fluid transfer pumps and / or fluid treatment systems and possibly surface infrastructure. The hull 20 defines lateral faces 30A, 30B, one of which, 30A, is intended for the mooring of the floating assembly 16.

[0028] The floating assembly 16 is, for example, a barge or a ship. It comprises a floating hull 40 enclosed by at least one upper deck 42.

[0029] The floating assembly 16 further includes a second fluid storage capacity 44, in particular cryogenic fluid, disposed in and / or on the hull 40, the second fluid storage capacity 44 being intended to be connected to the first fluid storage capacity 22 to effect a fluid transfer between the offshore assembly 12 and the floating assembly 16 via the fluid transfer assembly 18.

[0030] The floating assembly 16 further comprises at least one autonomous propulsion system 46, such as at least one motor associated with at least one propeller or at least one thruster, enabling the movement of the floating assembly 16 relative to the offshore assembly 12 between the fluid transport configuration, away from the offshore assembly 12, and the fluid transfer configuration visible on the figure 2 , moored on the whole offshore 12.

[0031] The hull 40 extends between a stern 50 and a bow 48 along a second longitudinal axis B-B'. It has lateral faces 52A, 52B, of which face 52A is intended to be placed opposite lateral face 30A in the mooring configuration.

[0032] With reference to the figure 1 , the fluid transfer assembly 18 includes a dynamic mooring system 60, intended to be placed between the offshore assembly 12 and the floating assembly 16, a control system 62 for the dynamic mooring system 60 and a fluid transfer system 64, configured to fluidly connect the first storage capacity 22 to the second storage capacity 44 when the dynamic mooring system 60 is put in place.

[0033] The fluid transfer assembly 18 further includes a system 66 for maintaining a minimum spacing between the offshore assembly 12 and the floating assembly 16 in the fluid transfer configuration.

[0034] In this example, the dynamic mooring system 60 comprises a plurality of mooring lines 70 configured to be mechanically tensioned. For each mooring line 70, the dynamic mooring system 60 includes a reel 72 disposed on one of the offshore assembly 12 and the floating assembly 16 to control an active length 76 of the mooring line 70 and a mooring point 74 disposed on the other of the offshore assembly 12 and the floating assembly 16.

[0035] In this example, the mooring system 60 comprises a plurality of mooring lines 70, each associated with a reel 72 on one of the offshore assembly 12 and the floating assembly 16, and with a mooring point 74 on the other of the offshore assembly 12 and the floating assembly 16.

[0036] In particular, the mooring system 60 comprises a plurality of mooring lines 70 extending from a region of deck 28 of the offshore assembly 12 located in the vicinity of the first longitudinal end 24 to a region of deck 42 of the floating assembly 16, located in the vicinity of the stern 50.

[0037] The mooring system 60 further includes a plurality of mooring lines 70 extending from a region of deck 28 of the offshore assembly 12 located in the vicinity of the second longitudinal end 26 to a region of deck 42 of the floating assembly 16 located in the vicinity of the bow 48 on deck 42.

[0038] In this example again, all the furlers 72 are arranged on the offshore assembly 12, while all the mooring points 74 are located on the floating assembly 16.

[0039] Alternatively, at least one furler 72 is located on the floating assembly 16, and at least one mooring point 74 is located on the offshore assembly 12. Alternatively again, all the furlers 72 are located on the floating assembly 16 and all the mooring points 74 are located on the offshore assembly 12.

[0040] Thus, each mooring line 70 includes an active length 76 intended to be put under mechanical tension, extending between a first point located on a reel 72 and a second point constituted by the mooring point 74.

[0041] Each mooring line 70 is for example formed of a cable or a chain, in particular a cable made of non-metallic material, such as a polymer material in particular nylon.

[0042] Each reel 72 includes a rotating drum 80 for increasing or decreasing the active length 76 of the mooring line 70, a motor 82 for driving the rotation of the drum 80 selectively in both directions of rotation, a brake 84 for locking the drum 80 and fixing a determined active length 76, and advantageously, a kinetic energy storage system 86, configured to store the kinetic energy related to the rotation of the drum 80 when unwinding the mooring line 70 to increase its active length 76.

[0043] The kinetic energy storage system 86 includes, for example, an electric generator whose rotor is linked to the drum 80, a stator, and at least one storage battery and / or a flywheel.

[0044] The energy storage system 86 is connected to the motor 82 to provide electrical power enabling the rotation of the motor 82 when winding the mooring line 70.

[0045] The control system 62 includes, for each mooring line 70, a sensor 90 for measuring the mechanical tension applied to the mooring line 70. It also includes sensors 92A, 92B for determining the relative positioning of the offshore assembly 12 and the floating assembly 16.

[0046] The control system 62 further includes a central control unit 94, configured to receive data from sensors 90, 92A, 92B, and to control the mechanical tension applied to each mooring line 70 to maintain it within a predefined mechanical tension range, and advantageously to determine the amplitude of movement of the floating assembly 16 relative to the offshore assembly 12 and to control the length of the mooring line 70 to maintain the amplitude of movement within a predefined amplitude range.

[0047] The mechanical tension measuring sensor 90 on each mooring line 70 is, for example, located in the reel 72.

[0048] Each positioning sensor 92A, 92B is for example a geographic positioning sensor positioned respectively on the offshore assembly 12 and on the floating assembly 16.

[0049] The central control unit 94 includes, for example, a computer comprising at least one processor 96, and at least one memory 98 containing software modules to be executed by the processor 96 to perform functions. Alternatively, the control unit 94 may be at least partially in the form of one or more programmable circuits, for example, of the FPGA (Field-Programmable Gate Array) type, or as an electronic circuit dedicated to an application, of the ASIC (Application-Specific Integrated Circuit) type.

[0050] The central control unit 94 advantageously includes a module 100 for determining the mechanical tension applied to each mooring line 70 from the data received from each mechanical tension measuring sensor 90, a module 102 for determining an amplitude of relative movement between the offshore assembly 12 and the floating assembly 16, from the data received from the positioning sensors 92A, 92B, for example by difference between the geographical data obtained from each positioning sensor 92A, 92B.

[0051] The central control unit 94 further includes a module 104 for developing a command of the active length 76 of each mooring line 70, configured to drive each motor 82 and the associated drum 80 in order to wind or unwind the mooring line 70, to maintain the mechanical tension applied to the mooring line 70, as determined by the mechanical tension determination module 100 in a predefined mechanical tension range between a minimum mechanical tension and a maximum mechanical tension, and advantageously, to simultaneously maintain an amplitude of movement, for example a horizontal amplitude of movement between the floating assembly 16 and the offshore assembly 12, as determined by the amplitude determination module 102, in a predefined amplitude of movement range.

[0052] The predefined range of mechanical tension is for example between 5 tonnes and 30 tonnes, in particular between 5 tonnes and 10 tonnes.

[0053] The predefined range of movement amplitude is for example between -10 m and +10 m, specifically between -2 m and +2 m.

[0054] In particular, the command development module 104 is configured to reduce the active length 76 of each mooring line 70 when the mechanical tension applied to the mooring line 70 determined by the mechanical tension determination module 100 approaches the lower bound of the predefined mechanical tension range, and / or when the amplitude of movement determined by the amplitude determination module 102 approaches the upper bound of the predefined amplitude of movement range.

[0055] The command development module 104 is also configured to increase the active length 76 of the mooring line 70 when the mechanical tension applied to the mooring line 70 determined by the mechanical tension determination module 100 approaches the upper bound of the predefined mechanical tension range and / or when the movement amplitude determined by the amplitude determination module 102 approaches the lower bound of the predefined movement amplitude range.

[0056] Preferably, if the two requirements of maintaining mechanical tension and amplitude of movement cannot be met, the control development module 104 is configured to control the active length 76 of the mooring line 70 within the predefined mechanical tension range without simultaneously maintaining the amplitude of movement within the predefined amplitude of movement range.

[0057] The fluid transfer system 64 in this example comprises at least one articulated discharge arm 110, preferably several articulated discharge arms 110 mounted on one of the offshore assembly 12 and the floating assembly 16, being connected to the capacity 22, 44 of this assembly 12, 16 and at least one connecting flange 112, mounted on the other of the offshore assembly 12 and the floating assembly 16 being connected to the capacity 22, 44 of this assembly.

[0058] In the example shown on the figure 1 , the articulated unloading arms 110 are mounted on deck 28 of the offshore assembly 12 by being connected to the first fluid storage capacity 22 while the connection flanges 112 are mounted on deck 42 of the floating assembly 16, by being connected to the second fluid storage capacity 44.

[0059] Each articulated unloading arm 110is thus mobile towards the connection flange 112 in the fluid transfer configuration to connect to the connection flange 112 and fluidly connect the first fluid storage capacity 22 to the second fluid storage capacity 44.

[0060] The support system 66 includes at least one fender 120 intended to be inserted between the respective lateral faces 30A, 52A of the respective hulls 20, 40 and advantageously, in this example, a spacing frame 122 for each fender 120 to define, between the opposing lateral faces 30A, 52A, an intermediate spacing greater than the spacing defined by the fenders 120, taken perpendicular to the longitudinal axes A-A', B-B', and to reduce the hydrodynamic interactions between the offshore assembly 12 and the floating assembly 16.

[0061] The defenses 120 and the reinforcements 122 define an intermediate spacing between the lateral faces 30A, 52A which is greater than 0.5 m, in particular between 2 m and 8 m.

[0062] In this example, the spacing frames 122 are mounted integrally to the hull 20, preferably from the lateral face 30A, projecting transversely from the longitudinal axis A-A'. The fenders 120 are advantageously deployable from the deck 28 to be inserted between the spacing frame 122 and the lateral face 52A.

[0063] Alternatively, at least one fender 120 and possibly a frame 122 supporting the fender 120 are mounted as a unit to the hull 40, extending transversely from the lateral face 52A.

[0064] The 120 defense, for example, is a floating defense made from a block of elastomeric material.

[0065] A fluid transfer process within the operating installation 10 between the offshore assembly 12 and the floating assembly 16 will now be described, with reference to figures 1 And 2 .

[0066] Initially, when the first storage capacity 22 of the offshore assembly 12 needs to be unloaded, the floating assembly 16 moves in the vicinity of the offshore assembly 12.

[0067] At step 150, the floating assembly 16 is positioned side by side with the offshore assembly 12, the respective longitudinal axes A-A', BB' of the offshore assembly 12 and the floating assembly 16 being arranged parallel.

[0068] The first lateral face of the floating assembly 52A is then located opposite and away from the first lateral face 30A of the offshore assembly 12 with interposition of the distance-keeping system 66, in particular of each fender 120 possibly mounted on a frame 122. This keeps at a distance the elements located on the respective decks 24, 42, in particular the infrastructure present on each of the decks 24, 42.

[0069] Then, in step 152, a plurality of mooring lines 70 are installed, each from a reel 72 to a mooring point 74, and are mechanically tensioned.

[0070] Thus, each mooring line 70 has an active length 76 under mechanical tension between a first point defined on a reel 72 and a second point defined by a mooring point 74.

[0071] The mechanical tension of the active length 76 is set to be equal to a value within the predefined mechanical tension range.

[0072] Then, in step 154, the fluid transfer system 64 is mounted to fluidly connect the first storage capacity 22 to the second storage capacity 44.

[0073] In the example shown on the figure 1 , the articulated unloading arms 110 are moved to the 112 connection flanges and are each connected to a 112 connection flange.

[0074] Fluid transfer is then activated in this example from the first storage capacity 22 to the second storage capacity 44.

[0075] At step 156, during the fluid transfer, a continuous measurement (e.g. at a frequency greater than 1 Hz) is carried out using each mechanical tension measuring sensor 90 connected to a mooring line 70 and continuous measurements (e.g. at a frequency greater than 1 Hz) are carried out using the positioning sensors 92A, 92B, respectively on the offshore assembly 12 and on the floating assembly 16. The measurements are received by the control system 62, in particular by the central control unit 94.

[0076] The mechanical tension determination module 100 then calculates the mechanical tension applied to each mooring line 70 and determines whether the mechanical tension is within the predefined mechanical tension range. The amplitude determination module 102 determines a measure of the relative motion between the offshore assembly 12 and the floating assembly 16, for example, a measurement of the horizontal motion amplitude between these assemblies 12 and 16.

[0077] At step 158, the control unit 94 then controls the active length 76 of each mooring line 70 to maintain in the first place the mechanical tension applied to the mooring line 70 within the predefined mechanical tension range.

[0078] To this end, the command development module 100 develops a winding or unwinding command for the mooring line 70 based on the value of the mechanical tension applied to the mooring line 70.

[0079] For example, if the mechanical tension on the mooring line 70 approaches or exceeds the upper bound of the predefined mechanical tension range, the command development module 104 establishes a mooring line 70 unwinding command to reduce the mechanical tension on the mooring line 70.

[0080] Conversely, if the mechanical tension applied to the mooring line 70 decreases towards the lower limit of the predefined mechanical tension range or exceeds it, the command development module 104 develops a winding command for the mooring line 70.

[0081] Advantageously, the command development module 104 also takes into account the range of motion of the floating assembly 16 relative to the offshore assembly 12.

[0082] If the movement amplitude decreases and approaches or exceeds the lower bound of the predefined movement amplitude range, the command development module 104 establishes or corrects the mooring line unwinding command 70.

[0083] Conversely, if the amplitude of movement increases and approaches the upper limit of the predefined amplitude of movement range, then the command development module 104 develops a command or corrects a mooring line winding command 70.

[0084] The command intended to be applied to each mooring line 70 is then transmitted to the winder 72 to carry out, with the help of the motor 82, a winding or unwinding corresponding to the command, which is possibly followed by a locking with the help of the brake 84.

[0085] When an unwinding command is executed, the kinetic energy storage system 86 is activated to convert mechanical rotational energy of the drum 80 into electrical power stored in the battery.

[0086] Conversely, the battery of the kinetic energy storage system 86 delivers electrical power to drive the rotation of the drum to the motor 80 in the case of winding.

[0087] At step 160, steps 156 and 158 are repeated as long as the floating assembly 16 is moored on the offshore assembly 12 side by side with it.

[0088] At the end of the fluid transfer, in step 162, the mooring lines 70 are released from their mooring point 74 and are wound onto the reels 72. The floating assembly 16 is then released from the offshore assembly 12 and transports the fluid it contains in the second capacity 44 to a destination, for example located on the coast.

[0089] On the figure 3 , curve 170 illustrates the temporal variations of the mechanical tension of a mooring line 70 between the floating assembly 16 and the offshore assembly 12 during a side-by-side mooring of the prior art not including continuous measurement of the mechanical tension applied to the mooring line 70, nor control of the mechanical tension.

[0090] As seen on the figure 2 , curve 170 has intervals in which the mooring line 70 is relaxed and its mechanical tension is zero, followed by intervals of high mechanical tension on the mooring line 70, which implies many dynamic fatigue stresses on the mooring line 70.

[0091] Curve 172, on the contrary, illustrates the mechanical tension applied to the mooring line 70 in the case of using the transfer method according to the invention, with a mechanical tension control applied to the mooring line 70. Curve 172 does not include intervals in which the mooring line 70 is relaxed and its mechanical tension is zero, nor excursions into high mechanical tensions.

[0092] Curves 170, 172 were obtained by simulation with a turbulent environment of the water body 14 limit to carry out a traditional side-to-side transfer operation including 1.5 m amplitude due to sea and wind and 2.5 m amplitude due to swell.

[0093] The maximum mechanical tension applied to the most mechanically stressed mooring lines 70 is thus reduced from approximately 47 tonnes to approximately 20 tonnes.

[0094] This allows, for example, operation with wave heights that can increase from 0.5 m to 1.5 m depending on the periods and directions.

[0095] The annual operability rate is therefore increased, for example by 10 to 15%, using conventional equipment. Furthermore, the relative movement envelope between the offshore assembly 12 and the floating assembly 16 is maintained within acceptable ranges.

[0096] Thanks to the invention just described, it is therefore possible to control the mechanical stresses applied to the mooring lines 70 in a coordinated manner according to the agitation of the body of water 14, by limiting the peaks of mechanical stress in the mooring lines 70 at the level of the active length 76, and by maintaining an acceptable envelope of relative movement between the offshore assembly 12 and the floating assembly 16.

[0097] This command is carried out without direct measurement of wave height, nor of the high-frequency component of ship movements.

[0098] The method according to the invention very effectively smooths out the peaks of mechanical stress in the mooring lines 70, thus allowing operation in more severe environments where mechanical stresses in the mooring lines generally limit the use of side-by-side transfer.

[0099] Thus, offshore assemblies that produce cryogenic fluids in much more turbulent areas can be designed with a smaller fluid storage capacity, limiting their size and saving investment costs, particularly in the case of floating natural gas liquefaction units.

Claims

1. Method for transferring fluid between an offshore assembly (12) located in a body of water (14), the offshore assembly (12) having a first fluid storage capacity (22) and a floating assembly (16) on the body of water (14), having a second fluid storage capacity (44), the method comprising the following steps: - arranging a lateral face (52A) of the floating assembly (16) opposite a lateral face (30A) of the offshore assembly (12) to place the floating assembly (16) side by side with the offshore assembly (12); - installation and mechanical tensioning of a plurality of mooring lines (70) between the offshore assembly (12) and the floating assembly (16), each mooring line (70) having a first attachment point on the offshore assembly (12), a second attachment point on the floating assembly (16), and an active length (76) under mechanical tension between the first point and the second point;- fluid connection between the first fluid storage capacity (22) and the second fluid storage capacity (44) via a fluid transfer system (64), and fluid transfer between the first fluid storage capacity (22) and the second fluid storage capacity (44); characterized by the following steps: - continuous measurement of the mechanical tension applied over the active length (76) of at least one mooring line (70); - control, by a control system (62), of the active length (76) of at least one mooring line (70), to maintain the mechanical tension applied over at least one mooring line (70) within a predefined mechanical tension range.

2. A method according to claim 1, comprising the following steps: - continuous measurement of the mechanical tension applied over the active length (76) of a plurality of mooring lines (70), in particular of all the mooring lines (70) connecting the offshore assembly (12) and the floating assembly (16); - control of the active length (76) of each mooring line (70) to maintain the mechanical tension applied over each mooring line (70) within a predefined mechanical tension range.

3. A method according to any one of claims 1 or 2, wherein at least one mooring line (70) is connected on one of the first and second points to a reel (72), the control of the active length (76) of at least one mooring line (70) being effected by winding and / or unwinding the at least one mooring line (70) on the reel (72).

4. Method according to claim 3, comprising connecting the other of the first point and the second point of the at least one mooring line (70) to a fixed mooring point (74).

5. A method according to any one of claims 3 or 4, wherein the reel (72) comprises a kinetic energy recovery system (86), the method comprising the recovery of electrical energy during the unwinding of at least one mooring line (70) and the winding of at least one mooring line (70) using at least a portion of the electrical power recovered by the kinetic energy recovery system (86).

6. A method according to any one of the preceding claims, comprising measuring a relative movement between the offshore assembly (12) and the floating assembly (16), the method comprising controlling by the control system (62) the active length (76) of at least one mooring line (70) to maintain an amplitude of relative movement between the offshore assembly (12) and the floating assembly (16) within a predefined range of movement amplitude.

7. A method according to any one of the preceding claims, wherein the side-by-side arrangement of the lateral face (30A) of the offshore assembly (12) and the lateral face (52A) of the floating assembly (16) comprises the wedging between the lateral face (30A) of the offshore assembly (12) and the lateral face (52A) of the floating assembly (16) of at least one fender (120), preferably of a plurality of fenders (120) spaced longitudinally.

8. Method according to claim 7, wherein the shimming of the fender or each fender (120) comprises positioning the fender or each fender (120) on a spacer frame (122) configured to increase the distance between the side face (30A) of the offshore assembly (12) and the side face (52A) of the floating assembly (16) when the side face (30A) of the offshore assembly (12) and the side face (52A) of the floating assembly (16) are arranged side by side.

9. A method according to any one of the preceding claims, wherein the fluid transfer is carried out through an articulated discharge arm (110) and / or through a flexible conduit.

10. Fluid transfer assembly (18) between an offshore assembly (12) located in a body of water (14), the offshore assembly (12) having a first fluid storage capacity (22) and a floating assembly (16) on the body of water (14), having a second fluid storage capacity (44), the fluid transfer assembly (18) comprising: - a mooring system (60) comprising a plurality of mooring lines (70) between the offshore assembly (12) and the floating assembly (16), configured to be installed and mechanically tensioned such that each mooring line (70) has a first attachment point on the offshore assembly (12), a second attachment point on the floating assembly (16), and an active length (76) under mechanical tension between the first point and the second point;- a fluid transfer system (64) configured to establish a fluid connection between the first fluid storage capacity (22) and the second fluid storage capacity (44) and a fluid transfer between the first fluid storage capacity (22) and the second fluid storage capacity (44); characterized by a control system (62) of the mooring system (60) comprising at least one sensor (90) for continuous measurement of the mechanical tension applied to the active length (76) of at least one mooring line (70), the control system (62) comprising a control unit (94) configured to control the active length (76) of the at least one mooring line (70), to maintain the mechanical tension applied to the at least one mooring line (70) within a predefined mechanical tension range.

11. Fluid transfer assembly (18) according to claim 10, wherein the mooring system (60) comprises at least one reel (72), the at least one mooring line (70) being connected on one of the first and second points to the at least one reel (72), the control system (62) controlling the active length (76) of the at least one mooring line (70) by winding and / or unwinding the at least one mooring line (70) on the reel (72).

12. Fluid transfer assembly (18) according to any one of claims 10 or 11, wherein the control system (62) comprises at least one sensor (92A, 92B) for continuously measuring a relative positioning between the offshore assembly (12) and the floating assembly (16) to determine a relative movement between the offshore assembly (12) and the floating assembly (16), the method comprising the control by the control system (62) of the active length (76) of at least one mooring line (70) to maintain an amplitude of relative movement between the offshore assembly (12) and the floating assembly (16) within a predefined range of movement amplitude.

13. Fluid transfer assembly (18) according to any one of claims 10 to 12, wherein the reel (72) comprises a kinetic energy recovery system (86) configured to recover electrical energy during the unwinding of at least one mooring line (70) and to provide at least a portion of the recovered electrical power to wind the at least one mooring line (70).

14. Fluid handling installation (10), comprising: - an offshore assembly (12) intended to be disposed in a body of water (14), the offshore assembly (12) having a first fluid storage capacity (22); - a floating assembly (16), having a second fluid storage capacity (44), and a fluid transfer assembly (18) according to any one of claims 10 to 13, configured to be mounted between the offshore assembly (12) and the floating assembly (16).

15. Installation according to claim 14, wherein the offshore assembly (12) is a platform, for example floating or fixed, a floating liquefied natural gas unit, a floating storage and regasification unit, a floating liquefied petroleum gas export unit, the floating assembly (16) advantageously being a fluid transport vessel or barge.

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