An injection buoy, a system, and a method for preventing formation of an ice plug in an injection hose

Abstract

An injection buoy (1), a system, and a method for preventing formation of an ice plug in an injection hose (30) in an emergency disconnect of the injection buoy (1) from a floating vessel (FV) The injection buoy (1) comprises a chamber (10) for holding an anti-freezing agent prior to injecting the anti-freezing agent into the injection hose (30) when an emer- gency valve (14) of the injection buoy (1) is activated to an open position.

Description

[0001] AN INJECTION BUOY, A SYSTEM, AND A METHOD FOR PREVENTING FORMATION OF AN

[0002] ICE PLUG IN AN INJECTION HOSE

[0003] The invention relates to a buoy for connecting to a floating vessel, such as a ship, for injecting a fluid into a subsea reservoir. More specifically, the invention is related to an injection buoy for use in a buoy turret system wherein the injection buoy in operation is connected to a turret arranged within a moonpool of a floating vessel for injecting a fluid into a subsea reservoir. The injection buoy is anchored to the seabed via multiple mooring lines configured for allowing weathervaning of the floating vessel when connected to the injection buoy.

[0004] The floating vessel may be a ship for bringing liquified gas, such as liquified carbon dioxide (CO2), from an onshore loading terminal across a sea to a subsurface permanent storage reservoir. The ship may for example be a ship as disclosed in Norwegian patent publication NO346899 Bl, wherein the ship comprises a loading line for communicating liquified gas received from the onshore terminal into at least one vessel onboard the ship, and a processing plant. The processing plant disclosed in NO346899 Bl comprises:

[0005] - an injection processing module comprising an injection pump configured for injecting liquified gas into the subsurface permanent storage reservoir; wherein the injection processing module is operatively connected to the at least one vessel and a gas injection line provided with a connector for connecting to a flexible injection hose extending from a subsea connection point being connected to a well of the subsurface permanent storage reservoir. The processing plant of the ship disclosed in NO346899 Bl further comprises a liquifying processing module configured for liquifying gas, wherein the at least one vessel is in loop communication with the liquifying processing module so that gas evaporated from the liquified gas within the at least one vessel is liquified in the liquifying processing module and communicated back into the at least one vessel. When connected to a buoy, such as an injection buoy, the floating vessel, typically a ship, must be kept at a relatively exact position. In shallow water, for example less than 200 m, the ship may be kept in position by means of a free weathervaning anchoring system. However, in deeper water, for example more than 200 m, keeping a ship in position by means of an anchoring system, may be impractical or even impossible. It is therefore common to keep a ship at a relatively exact position by means of a Dynamic Positioning System (DPS). A DPS is a computer-controlled system to automatically maintain a ship's position and heading by using its own propellers and thrusters. Position reference sensors, combined with wind sensors, motion sensors and gyrocompasses provide information to the computer pertaining to the ship's position and the magnitude and direction of environmental forces affecting its position. A ship may also be kept at a desired position by means of a combination of Dynamic Positioning System DPS and an anchoring system allowing for free weathervaning.

[0006] In operation, a DPS relies on power to the propellers and thrusters, and on operating sensors for providing information to the computer pertaining to the ship's position and the magnitude and direction of environmental forces affecting its position.

[0007] In a completion phase of an injection operation of for example a liquified carbon dioxide, measures should be taken to prevent ice formation, a so-called ice plug, due to pressure drop within the riser. One common measure for preventing ice formation is to pressurize the riser filled with CO2 prior to disconnecting the injection buoy from the ship. An alternative, or additional measure, may be to stabilise the CO2 filled riser with an anti-freezing agent to prevent formation of an ice plug. The anti-freezing agent may for example be methanol or glycol that is pumped from a reservoir in the ship and into the riser.

[0008] In an emergency wherein the ship loses its engine power or in any other way cannot operate the propellers and thrusters, the ship is subject to a so-called drift off wherein the desired position of the ship is negatively affected by environmental forces from for example wind, waves, and ocean current. In such an emergency, the injection buoy must be disconnected from the ship to avoid damaging the injection buoy and equipment operatively connected thereto. In an event of a drift off when the ship is subject no minor envi- ronmental forces, a disconnect may be performed in a controlled manner. However, in harsh conditions, an emergency disconnect may be required.

[0009] An even more serious emergency than a drift off, is a situation known as drive off. A drive off may occur if required information to the computer of a DPS suddenly disappears or are erroneous. A typical drive off situation may arise if for example the DPS loses its contact with satellites providing position reference for the DPS. In a drive off emergency, the ship may suddenly and with great power start moving in an uncontrolled manner. To avoid damaging the injection buoy and equipment operatively connected thereto, an immediate disconnect is required.

[0010] In an emergency as discussed above, and especially in a drive off emergency, maintaining the pressure in the riser is still necessary to avoid the risk of formation of an ice-plug. However, in such an emergency an immediate disconnect of the injection buoy is required. Due to the immediate disconnect required, increasing a pressure within the riser and / or pumping an anti-freezing agent from the reservoir in the ship may not be possible.

[0011] Any ice-plug in a riser may be thawed by means of a heating cable running along the riser from the injection buoy to a template at the wellhead. Thawing an ice plug in a riser will require large amount of energy to be generated by the ship. Generating the large amount of power may be costly. However, the highest cost is related to non-productive time spent for thawing an ice-plug since a day rate for operating an injection vessel may be very high.

[0012] An alternative to actively thawing an ice plug by means of actively heating the riser is to allow the ice plug to be thawed by the surrounding sea water. However, this alternative will prevent access to the injection well during a thawing period and may therefore also represent high costs for any floating vessel, typically a ship, waiting for connection to the injection buoy.

[0013] According to prior art, an anti-freezing agent may in an emergency be injected into the riser by means of for example a pump operatively connected to a reservoir of antifreezing agent arranged at the template of the injection well. Providing a reservoir and pump on the template will require additional maintenance and costs but more importantly will represent a release of large amounts of for example COzto the atmosphere.

[0014] Publication WO2022 / 184752 discloses a buoy configured to accomplish a fluid connection, via at least one riser, from a vessel on a water surface to a subsea template located on a seabed, so as to enable transport of fluid from the vessel to the subsea template for injection of the fluid into a subterranean void via a drill hole from the subsea template to the subterranean void. The injection buoy contains at least one valve configured to allow or shut off a passage of fluid from the vessel to the at least one riser. The injection buoy also contains a primary communication interface configured to be connected to an external site and receive commands from the external site, for example in the form of optical signals transmitted via a fiber optic cable. In response to the received commands, the injection buoy is configured to control the at least one valve to either allow or shut off the passage of fluid from the vessel to the at least one riser.

[0015] Publication WO20180192346 Al discloses a flexible pipe system comprises an unbonded flexible pipe connected to a floating vessel and a sensor system with an optical fibre integrated in the unbonded flexible pipe. Interrogating equipment transmits optical signals into the fibre, receives optical signals reflected from the fibre and detects a parameter of the unbonded flexible pipe. A turret connects the flexible pipe rotationally to the floating vessel via a swivel device that provides a fluid transfer passage between the turret and the vessel. The interrogating equipment is arranged on the turret and is further configured to transfer signals indicative of the detected parameter to receiving equipment on the floating vessel. In this way, optical signals reflected from the fibre can reach the interrogating equipment without distortion in the swivel, so that parameters can be detected with sufficient quality also for floating vessels equipped with a turret mooring system.

[0016] Publication N020210292 Al discloses an injection buoy for connecting to a moonpool of a floating vessel and for providing fluid communication between the floating vessel and injection hose(s) extending to a template at a wellhead. The injection buoy comprises a fluid transfer passage for, in an operation state of the injection buoy, communicating fluid from the floating vessel to the injection hose(s). The fluid transfer passage is provided with inlet valve configured for opening and closing fluid communication through the fluid transfer passage.

[0017] Publication AU2010251212 B2 discloses a method and an apparatus protecting one or more flexible risers in a sub-sea environment.

[0018] The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art. The object is achieved through features, which are specified in the description below and in the claims that follow. The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

[0019] In what follow, the fluid connection between the buoy and a template on a seabed is denoted injection hose instead of the somewhat misleading term riser.

[0020] In a first aspect the invention there is provided an injection buoy for connecting to a moonpool of a floating vessel and for providing fluid communication between the floating vessel and an injection hose extending to a template operatively connected to a wellhead. The injection buoy comprises a fluid transfer passage for, in an operation state of the injection buoy, communicating fluid from the floating vessel to the injection hose. The fluid transfer passage is provided with an inlet valve configured for opening and closing fluid communication through the fluid transfer passage.

[0021] The injection buoy further comprises a chamber for holding a fluid comprising an antifreezing agent, a discharge conduit for providing fluid communication between the chamber and the fluid transfer passage, and an emergency valve operable between a closed position wherein the fluid from the chamber is prevented from passing through the discharge conduit and into the fluid transfer passage, and an open position providing fluid communication between the chamber and the fluid transfer passage.

[0022] The injection buoy according to the invention is primarily designed for use for injecting a so-called greenhouse gas into a subsea reservoir, as a final stage of for example a CCS- process (CCS: Carbon Capture and Storage). The fluid communicated from the floating vessel, via the injection buoy and further into a subsea reservoir may therefore be liqui- tied CO2. Other fluids that may be communicated from the floating vessel, via the injection buoy and further into a subsea reservoir are for example liquified gases such as nitrogen oxide (NOX), ozone (03), methane (CH4), fluorinated gases including halogens, petroleum gases (LPG) and noble gases.

[0023] A suitable anti-freezing agent within the chamber of the injection buoy may therefore be glycol, methanol, or a combination thereof. A volume of the anti-freezing agent communicated into the discharge conduit is preferably adapted to the volume of the injection hose so that an optimal volume of the anti-freezing agent can be communicated into the injection hose. The optimal volume may be controlled by filling the chamber of the injection buoy with the desired volume, or by controlling a time during which the emergency valve is in the open position, or a combination thereof.

[0024] Preferably, the emergency valve is operatively connected to an actuator responsive to a signal initiated from a remote location. In an operating state of the injection buoy, the remote location may be a floating vessel connected to the injection buoy. In one embodiment of the invention, the signal initiated from the remote location may activate a control unit provided in the injection buoy. In such an embodiment the control unit may be configured for issuing an activation signal to at least the actuator for the emergency valve. The control unit may further be configured for issuing further control signals to one or more valves arranged at a subsea well template forming part of a system according to an aspect of the invention that is discussed below.

[0025] To at least facilitate communication of the anti-freezing agent from the chamber via the fluid transfer passage and into the injection hose, the chamber holding the anti-freezing agent may be at least partly pressurized.

[0026] The injection pressure of the injection hose is adapted to a pressure of the injection reservoir, which may be specific for each injection reservoir.

[0027] In one embodiment, the chamber is pressurized with a fluid pressure being higher than an injection pressure of the injection hose.

[0028] In one embodiment, the chamber may be non-pressurized or pressurized with a pressure being lower than a pressure of the injection hose. To be able in an emergency disconnect to urge the anti-freezing agent from the chamber and into the fluid transfer passage when the emergency valve is open, and further into the injection hose, such a non- or partly pressurized chamber of the injection buoy, may further comprise a pressure source configured for being controllably set in fluid communication with the chamber. The pressure source may typically be an accumulator bank of a pressurized gas, such as air. A communication between the pressure source and the chamber may be controlled by means of a control unit forming part of the injection buoy.

[0029] The buoy may further comprise an injection pump configured to pump the anti-freezing agent from the chamber and into the fluid transfer passage. The pump may be activated in response to a signal from a control unit forming part of the injection buoy. An effect of such a pump is that the fluid within the chamber can be non-pressurized or partly pressurized in a standby position.

[0030] The injection buoy may be provided with a closable supply conduit for, when the injection buoy is at least partly connected to the floating vessel, connecting to a fluid supply line operatively connected to at least one fluid source of the floating vessel. One of the at least one fluid source may be a reservoir of anti-freezing agent in the floating vessel, so that the fluid supply conduit allows filling the chamber of the injection buoy with at least one fluid comprising a desired volume of anti-freezing agent. Said filling may take place for example during a connection operation of the injection buoy to floating vessel. The fluid supply line is in one embodiment further configured to communicate a pressurized gas from a source on the floating vessel and into the chamber of the injection buoy to provide a desired pressure within the chamber of the injection buoy. In an embodiment wherein the injection buoy is provided with a pressure source, this may be pressurized in the same way as for the chamber, as discussed above.

[0031] In a second aspect of the invention, there is provided a system comprising the injection buoy according to the first aspect of the invention, an injection hose, and a subsea template operatively connected to a wellhead of an injection well, the injection hose having a first end portion operatively connected to the injection buoy and a second end portion operatively connected to the template.

[0032] The system may further comprise a control line for communicating control signals from the injection buoy, and at least to an actuator for operating a flow control valve of the template. The control signal from the injection buoy may typically be in response to a control signal from a control unit of the injection buoy of the system.

[0033] The control signal from the control unit of the injection buoy to the actuator for operating the flow control valve of the template at the well head, may be in response to a control signal for operating the emergency valve of the injection buoy to an open position. In one embodiment the flow control valve of the template at the well head may be operated to a closed position once the anti-freezing agent is injected into the injection hose. By the term once is meant simultaneously or within a few seconds, for example within 1-10 seconds, after opening the emergency valve of the injection buoy. By closing the flow control valve of the template at the well head, a mix of injection fluid and the anti-freezing agent will be locked or confined within the injection hose downstream of the injection buoy when the injection buoy is disconnected from the floating vessel, as will be disclosed below.

[0034] Once the emergency valve is opened, typically in response to an emergency, such as for example when the floating vessel connected to the injection buoy is subject to a drive off, the injection buoy is disconnected from the turret of the floating vessel, and the antifreezing agent is injected into the fluid transfer passage, and further into the injection hose in a top-down direction. When being disconnected from the floating vessel, a fluid communication into an inlet of the fluid transfer passage of injection buoy is prevented by means of a valve known per se. Injecting the anti-freezing agent in a top down direction makes it possible to avoid release of any fluid within the injection hose to the atmosphere.

[0035] In a third aspect of the invention, there is provided a method for emergency disconnection of the system according to the second aspect of the invention from a floating vessel, wherein the floating vessel is provided with at least one injection pump for injecting a liquified gas into a subsea reservoir. The method comprises the steps of: a) activating an emergency signal configured to, in sequence:

[0036] - stopping the at least one fluid injection pump arranged on the floating vessel;

[0037] - closing the inlet valve of the fluid transfer passage; and

[0038] - releasing the injection buoy from the moonpool of the floating vessel; b) closing a flow control valve at the template to prevent the anti-freezing agent from passing the template; c) opening the emergency valve in the injection buoy to allow anti-freezing agent to communicate from the chamber into the fluid transfer passage and thereby into the injection hose; and d) closing the emergency valve when a predetermined pressure is achieved in the fluid transfer passage and thereby the injection hose.

[0039] In step b) the internal volume of the injection hose comprising the mix of anti-freezing agent and the liquified gas, is defined in a top portion by the inlet valve of the fluid transfer passage and in a bottom portion by the flow control valve of the well template.

[0040] Steps b) and c) may be initiated by means of signals issued from a control unit of the injection buoy. Thus, steps b) and c) may be executed immediately after the injection buoy has been released from the turret of the moonpool of the floating vessel.

[0041] In step d) a pressure may be measured by means of a sensor arranged downstream of the discharge conduit, so that a pressure within the fluid transfer channel, and thus the injection hose can be measured. The sensor may be operatively connected to the control unit that controls the actuator of the emergency valve. The control unit is configured for sending a signal to the actuator of the emergency valve to close the emergency valve when a predetermined pressure within the fluid transfer channel and the injection hose, has been achieved. The predetermined pressure is achieved by communicating a volume of antifreezing agent into the fluid transfer channel of the injection buoy.

[0042] The method may further comprise in a step e) reconnecting a floating vessel to the injection buoy to prepare injection restart and, if required, refill the chamber with fluid comprising anti-freezing agent; f) opening the inlet valve of the injection buoy to communicate fluid through the injection buoy, and start pumping the fluid from the floating vessel; and g) providing a signal to activate the flow control valve at the template to an open position to inject fluid into the reservoir.

[0043] Thus, the mix of liquified gas and anti-freezing agent is injected into the subsea reservoir, and substantially no gas within the injection hose is released to the environment.

[0044] In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein:

[0045] Fig. 1 shows an implement of an injection buoy according to an embodiment of the invention;

[0046] Fig. 2 shows a system according to the invention wherein the system comprises the injection buoy in fig. 1, an injection hose connected to a template at an injection wellhead, wherein the system is connected to a floating vessel; and

[0047] Fig. 3 shows in larger scale a detail of an upper part of the system in fig. 2.

[0048] Any positional indications refer to the position shown in the figures.

[0049] In the figures, same or corresponding elements are indicated by same reference numerals. For clarity reasons, some elements may in some of the figures be without reference numerals.

[0050] A person skilled in the art will understand that the figures are just principal drawings. The relative proportions of individual elements may also be distorted.

[0051] Any positional indications refer to the positions in the figures.

[0052] In the figures, the reference numeral 1 denotes an injection buoy according to the invention. The injection buoy 1 is configured for releasably connecting to a turret of a moonpool MP of a floating vessel FV. In the figures, the floating vessel FV is in the form of a ship, for example of the type disclosed in publication NO3446899 Bl. The injection buoy 1 is provided with a swivel arrangement and is configured for being connected / disconnected to / from the floating vessel FV in a manner known per se from a so-called loading buoy. When installed offshore, the injection buoy 1 is anchored to the seabed SB via multiple mooring lines 2 (only two shown in figures 2 and 3) and configured for allowing weathervaning of the floating vessel FV when connected to the injection buoy 1.

[0053] In fig. 1, the injection buoy 1 comprises a fluid transfer passage 3 for communicating fluid from the floating vessel FV to an injection hose 30 (see figures 2 and 3) that forms part of a system according to the invention.

[0054] The fluid transfer passage 3 is provided with an inlet valve 5 configured for opening and closing fluid communication through the fluid transfer passage 3. The inlet valve 5 is arranged in the injection buoy 1 downstream or below a lower swivel part 7 (shown in fig. 1 only) configured for connecting to a turret in the moonpool MP of the floating vessel FV, as known per se. The inlet valve 5 is configured for being automatically closed during a disconnect of the discharge buoy from the floating vessel FV, in the same way as an ordinary disconnect operation known from an offshore loading or injection operation.

[0055] The injection buoy 1 further comprises a chamber 10 for holding a fluid, typically an antifreezing agent such as for example glycol and / or methanol. A discharge conduit 12 extends between the chamber 10 and the fluid transfer passage 3 so that the anti-freezing agent can be communicated into the fluid transfer passage 3, and thus further into the injection hose 30.

[0056] A fluid communication from the chamber 10 and the fluid transfer passage 3 is controlled by means of an emergency valve 14 operable between a closed position wherein fluid from the chamber 10 is prevented from passing through the discharge conduit 12 and into the fluid transfer passage 3, and an open position providing fluid communication between the chamber 10 and the fluid transfer passage 3.

[0057] In fig. 1, the emergency valve 14 is operatively connected to an actuator 16. The actuator

[0058] 16 is responsive to a signal from a control unit 20. The signal is preferably transmitted from the control unit to the actuator via a control cable (not shown). The emergency valve 14 may for example be a solenoid valve configured for opening when receiving a signal in the form of an electric current provided by the control unit 20. However, other types of valves that can be remotely controlled may also be used.

[0059] The control unit 20 is configured for being activated by means of an emergency signal issued in response to an emergency wherein there is an urgent need for disconnecting the injection buoy 1 from the floating vessel or ship FV, as will be discussed below. An urgent need typically arises in an event of a drift off, and particularly in an event of the even more serious drive off, as discussed above.

[0060] In figures 2 and 3, the injection buoy 1 according to the invention forms part of a system comprising an injection hose 30 having a first end portion operatively connected to an outlet of the fluid transfer passage 3 of the injection buoy 1, and a second end operatively connected to a subsea template 50 (see fig. 2). The subsea template 50 is operatively connected to an injection well head 70 in a manner know per se.

[0061] The subsea template 50 comprises a flow control valve 52 configured for being remotely operated between an open position wherein injection fluid is communicated to the well head 70 and into a subsea reservoir, and a closed position preventing fluid communication to the well head 70.

[0062] In an emergency wherein a disconnect of the system from the floating vessel FV is urgently needed, an emergency signal for activating the disconnect may typically be initiated manually, for example from a bridge or pilothouse of the ship FV as mentioned above. In one embodiment, the emergency signal is sent both to control units (not shown) onboard the ship FV, and to the control unit 20 arranged within the injection buoy 1.

[0063] The control units onboard the ship FV are configured for, in a manner known per se, controlling operation of on board injection pumps for urging a fluid such as liquified CO2 through the injection buoy 1 and into a subsea reservoir, controlling a locking mechanism for securing the injection buoy 1 to the turret of the moonpool MP of the ship FV, and, in one embodiment, closing the inlet valve 5 of the fluid transfer passage 3 of the injection buoy 1. In an alternative embodiment, the inlet valve 5 of the fluid transfer passage 3 of the injection buoy 1 is configured for being controlled by the control unit 20 of the injection buoy 1.

[0064] In an emergency, the emergency signal is communicated to the control unit 20 within the injection buoy 1. The control unit 20 comprises a programmable logical controller programmed to control at least the emergency control valve 14 of the discharge conduit 12, and the flow control valve 52 of the template 50.

[0065] Thus, when an emergency disconnection is required, an emergency signal is issued. The emergency signal is configured to, in sequence:

[0066] - stopping fluid injection pump(s) arranged on the floating vessel FV;

[0067] - closing the inlet valve 5 of the fluid transfer passage 3 of the injection buoy 1, and

[0068] - releasing the injection buoy 1 from the moonpool MP of the floating vessel FV; wherein the control unit 20 of the injection buoy 1 is configured to issue signals to:

[0069] - closing the flow control valve 52 of the template 50;

[0070] - activating the actuator 16 to open the emergency valve 14 to allow fluid communication from the a chamber 10, via the discharge conduit 12 and the fluid transfer passage 3, into a volume comprising the injection hose 30 and the fluid transfer passage 3. The volume is defined by the closed inlet valve 5 of the injection buoy 1 and the flow control valve 52 of the template 50.

[0071] To urge the fluid within the chamber 10 into said volume, a fluid pressure within the chamber 10 is higher than a pressure within the injection hose 30, which in turn is higher than a reservoir pressure. A reservoir pressure may be specific for each injection reservoir. Alternatively, or additionally, the fluid within the chamber 10 may be urged into said volume by means of a pump (not shown). However, a pressurized chamber 10 is generally preferred over a pump, i.a. since a pump may represent a more complicated injection buoy.

[0072] The fluid pressure within the chamber 10 may be provided during the connection of the injection buoy 1 to the ship FV. In such an implement, pressurized gas is provided from a pressure source (not shown) onboard the ship FV and is communicated via a closable conduit 18 extending from the chamber 10 to a top portion of the injection buoy 1. In one embodiment, the closable conduit 18 comprises a one-way valve (not shown).

[0073] A connection of the conduit 18 to the pressure source of the ship FV is typically a manual operation controlled by operators within the control room R above the moonpool MP of the floating vessel FV.

[0074] Pressurizing the chamber 10 typically takes place after a desired volume of anti-freezing agent has been communicated into the chamber 10 from a source of anti-freezing agent arranged within the floating vessel FV. The anti-freezing agent from the source onboard the floating vessel FV is communicated into the chamber 10 via the conduit 18, i.e., the same conduit as used for communicating the pressurized gas into the chamber.

[0075] As an alternative to or additional to pressurizing the chamber 10 from a source in the floating vessel FV, the injection buoy 1 may comprisea pressure source 19 arranged in the injection buoy 1. The pressure source 19 in the injection buoy 1 are configured for being controllably set in fluid communication with the chamber 10. The pressure source 19 may typically be an accumulator bank of a pressurized gas, such as air. A communication between the pressure source 19 and the chamber 10 may be controlled by means of the control unit 20 forming part of the injection buoy l. The pressure source 19 may be refilled from the floating vessel in a similar way as discussed above for filling the chamber 10 via the conduit 18. A conduit for filling the pressure source 19 from the floating vessel FV is not shown.

[0076] A volume of anti-freezing agent required for preventing formation of an ice-plug in an emergency disconnect may be less than an internal volume of the compartment 10.

[0077] In one embodiment, the volume of anti-freezing agent filled into the compartment 10 of the injection buoy 1 is limited to the volume needed to prevent formation of an ice-plug in the volume defined by the injection hose 30 and the fluid transfer passage 3 of the injection buoy 1. Alternatively, the compartment 10 may be filled with a larger volume than needed for the volume of the injection hose 30 and the fluid transfer passage 3 of the system. To avoid injecting more anti-freezing agent than required, the discharge conduit 12 may in such a case be provided with a flow meter (not shown) being in communication with the control unit 20, so that the injection of the anti-freezing agent is stopped by closing the emergency valve 14 once a predetermined volume has been communicated into the injection hose 30 and the fluid transfer passage 3.

[0078] To prevent formation of an ice-plug, a volume of anti-freezing agent injected is typically around 2-5 % of the volume defined by the closed inlet valve 5 of the injection buoy l and the flow control valve 52 of the template 50.

[0079] From the above, it will be clear that formation of an ice plug in the system can be prevented in an emergency disconnect, such as in an event of drive off. A drive off-situation may be remedied after a short period of time, for example within one hour, whereupon a reconnect procedure of the ship FV may start immediately. This is contrary to a prior art reconnect procedures where an ice plug must be thawed, either by means of a heating cable powered from energy from the floating vessel FV, and / or waiting for the ice-plug to be thawed by the surrounding sea water as mentioned above.

[0080] During a reconnect of the injection buoy 1 to the floating vessel FV, the chamber 10 is, if required, refilled with anti-freezing agent and re-pressurized as discussed above, i.e., any refilling of the chamber 10 may typically be a manual operation carried out by operators being within the control room R. The re-pressurising of the chamber 10 or the accumulator bank 19 is not necessary in an embodiment wherein the injection buoy 1 is provided with a pump for urging the anti-freezing agent from the chamber 10 into the fluid transfer conduit 3 and the injection hose 30. After any refilling of fluid into the chamber 10, the chamber 10 of the injection buoy 1 is in a standby mode. When the chamber 10 is in a standby mode, the injection of the liquified gas may commence. Due to the pressure within the injection reservoir, the pressure within the injection hose 30 is raised to at least balance a differential pressure across the flow control valve 52. The inlet valve 5 of the fluid transfer passage 3 of the injection buoy 1 is opened, and the injection pump of the floating vessel FV is activated. When the fluid pressure within the injection hose 30 has reached a predetermined level, a signal is provided to activate the flow control valve 52 of the template 50 to an open position. Thereafter, injection of the liquified fluid from the floating vessel FV, is commenced. Thus, the anti-freezing agent within the injection hose 30 is also injected into the reservoir.

[0081] From the above, it will be appreciated that the present invention may solve formation of an ice plug in an emergency disconnect during an injection operation. Preventing for- mation of an ice plug will reduce downtime for at least the floating vessel FV that underwent an emergency disconnect, but also for any floating vessel(s) that may have to queue to connect to the injection buoy.

[0082] Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

C l a i m s1. An injection buoy (1) for connecting to a moonpool (MP) of a floating vessel (FV) and for providing fluid communication between the floating vessel (FV) and an injection hose (30) extending to a template (50) operatively connected to a wellhead (70), the injection buoy (1) comprises:- a fluid transfer passage (3) for, in an operation state of the injection buoy (1), communicating fluid from the floating vessel (FV) to the injection hose (30), the fluid transfer passage (3) provided with an inlet valve (5) configured for opening and closing fluid communication through the fluid transfer passage (3), c h a r a c t e r i s e d i n that the injection buoy (1) further comprises:- a chamber (10) for holding a fluid comprising an anti-freezing agent;-a discharge conduit (12) for providing fluid communication between the chamber (10) and the fluid transfer passage (3); and-an emergency valve (14) operable between a closed position wherein the fluid from the chamber (10) is prevented from passing through the discharge conduit (12) and into the fluid transfer passage (3), and an open position providing fluid communication between the chamber (10) and the fluid transfer passage (3).

2. The injection buoy (1) according to claim 1, wherein the emergency valve (14) is operatively connected to an actuator (16) responsive to a signal initiated from a remote location.

3. The injection buoy (1) according to claim 2, wherein, in an operating state of the injection buoy (1), the remote location is a floating vessel (FV) connected to the injection buoy (1).

4. The injection buoy (1) according to any of claims 2 and 3, wherein the signal initiated from the remote location is configured to activate a control unit (20) provided in the injection buoy (1), the control unit (20) configured for issuing an activation signal at least to the actuator (16) for the emergency valve (14).

5. The injection buoy (1) according to any of the preceding claims, wherein the chamber (10) is at least partly pressurized.

6. The injection buoy (1) according to claim 5, further comprising a pressure source (19) configured for being controllably set in fluid communication with the chamber (10) to increase a pressure within the chamber (10) to urge the fluid into the fluid transfer passage (3) when the emergency valve (14) is open.

7. The injection buoy (1) according to any of the preceding claims, wherein the injection buoy (1) is provided with a closable supply conduit (18) for, when the injection buoy (1) is at least partly connected to the floating vessel (FV), connecting to a fluid supply line operatively connected to a fluid reservoir in the floating vessel (FV).

8. A system comprising the injection buoy (1) according to any of the preceding claims, an injection hose (30), and a subsea template (50) operatively connected to a wellhead (70) of an injection well, the injection hose (30) having a first end portion operatively connected to the injection buoy (1) and a second end portion operatively connected to the template (50).

9. The system according to claim 8, further comprising a control line for communicating control signals from the injection buoy (1) and at least to an actuator for operating a flow control valve (52) of the template (50).

10. A method for emergency disconnection of the system according to claim 8 or 9 from a floating vessel (FV) provided with at least one injection pump for injecting a liquified gas into a subsea reservoir, c h a r a c t e r i s e d i n that the method comprising: a) activating an emergency signal configured to, in sequence:- stopping the at least one fluid injection pump arranged on the floating vessel (FV);- closing the inlet valve (5) of the fluid transfer passage (3); and- releasing the injection buoy (1) from the moonpool (MP) of the floating vessel(FV); b) closing a flow control valve (52) at the template (50) to prevent the antifreezing agent from passing the template (50); c) opening the emergency valve (14) in the injection buoy (1) to allow anti- freezing agent to communicate from the chamber (10) into the fluid transfer passage (3) and thereby into the injection hose (30); and d) closing the emergency valve (14) when a predetermined pressure is achieved in the fluid transfer passage (3) and thereby the injection hose (30).

11. The method according to claim 10, further comprising: e) reconnecting a floating vessel (FV) to the injection buoy (1) to prepare injection restart, and, if required, refill the chamber (10) with fluid comprising at least the anti-freezing agent; f) opening the inlet valve (5) of the injection buoy (1) to communicate fluid through the injection buoy (1), and start pumping the fluid from the floating ves- sei (FV); and g) providing a signal to activate the flow control valve (52) at the template (50) to an open position to inject fluid into the reservoir.

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