OA17260A - A containment system and a method for using such containment system. - Google Patents

Abstract

A containment system (1) for recovering hydrocarbon fluid from a leaking device (2) comprising a dome (20) sealed to the seafloor around the leaking device and forming a cavity (21) for accumulating hydrocarbon fluid. The dome comprises an upper output opening (22) for extracting the hydrocarbon fluid. The containment system comprises a sensor (60) for measuring an interface level (IL) of a fluid interface between hydrocarbon fluid and any other fluid inside the dome (20), and an output valve (62) connected to the upper output opening (22) for outputting hydrocarbon fluid, and controlled on the bases of the interface level (IL) measured by the sensor.

Description

The présent invention concerns a containment system for recovering spilled oil that is leaking under water.

BACKGROUND OF THE INVENTION

The présent invention concerns more precisely a containment system for recovering a hydrocarbon fluid from a leaking device that is situated at the seafloor and that is leaking the hydrocarbon fluid from a well.

Recovering oil that is leaking from an under water oil device is a great problem, especially for oil device that are installed at deep sea floor.

The explosion on the Deepwater Horizon platform in the Gulf of Mexico demonstrated how much such a containment system is difficult to control.

One of the main problems was the formation of hydrates that clogged the used containment system.

For example, at a depth of around 1500 meters, the sea water is cold (for example around only 5°C) and at a high pressure. These environment conditions may transform the sea water and hydrocarbon fluid into hydrates having a quasi-solid phase and which can fill and clogged any cavity.

Hydrates inhibitors Iike methanol could be injected to avoid hydrate formation. But, the needed quantity of such chemical is huge and inhibitors are also pollution for the environment.

OBJECTS AND SUMMARY OF THE INVENTION

One object of the présent invention is to provide a containment system that avoids the formation of hydrates inside the dôme.

To this effect, the containment system of présent invention is adapted to be landed at the seafloor corresponding to a base level of the containment system. It comprises a dôme forming a cavity under said dôme, said cavity being adapted to completely surround and include the leaking device, and to accumulate hydrocarbon fluid coming upwardly from the leaking device, said dôme comprising at least one upper output opening adapted to extract the hydrocarbon fluid for recovering.

The dôme further comprises:

- a sensor for measuring an interface level of a fluid interface between hydrocarbon fluid and any other fluid inside the dôme,

- an output valve connected to the upper output opening for outputting hydrocarbon fluid from the cavity, said output valve being controlled on. the bases of the interface level measured by the sensor.

Thanks to these features, the level of hydrocarbon fluid contained inside the dôme volume around the leaking device can be maintained at a predetermined level.

The hydrocarbon fluid outputting from the leaking device is usually hot compared to the cold sea water.

A large portion of hydrocarbon fluid can be maintained to keep the dôme volume at a high température, heated by the hydrocarbon fluid itself.

Therefore, hydrates formation is prevented inside the cavity of the containment system of présent invention.

Hydrates inhibitors that are usually used can be cancelled or their used quantity can be largely reduced.

In various embodiments of the containment system, one and/or other of the following features may optionally be incorporated.

According to an aspect of the containment system, the output valve is controlled so as to keep the interface level lower or equal to a level of output of the hydrocarbon fluid from the leaking device.

The jet of hydrocarbon fluid at the output of the leaking device is above the interface level, i.e. inside the hydrocarbon fluid accumulated bellow the dôme. Said jet is not cooled by the sea water. The cold sea water is not sucked by the jet inside the hydrocarbon fluid accumulated bellow the dôme. Hydrates formation is prevented.

According to an aspect of the containment system, it further comprises a control unit that implements a level control law so as to keep the interface level lower or equal to a level of output of the hydrocarbon fluid from the leaking device.

According to an aspect of the containment system, the dôme comprises:

- a first valve for extracting a gas component from the cavity, said first valve being positioned on the dôme at a level proximal to a highest level of the dôme, and

- a second valve for extracting a liquid component from the cavity , said second valve being positioned on the dôme at an intermediate level intermediate between the base level and the highest level of the dôme.

According to an aspect of the containment system, it further comprises a control unit that implements a séparation control law that controls the first valve so as a gas interface level is lower than the highest level of the dôme, and so as a liquid interface level is lower than the intermediate level.

Eventually, there is only one first valve for extracting the gas component and the liquid component of the hydrocarbon fluid.

According to an aspect of the containment system, the dôme comprises an over pressure valve that extract fluid out from the cavity to the environment if a pressure différence between the cavity and the environment exceeds a predetermined pressure limit.

According to an aspect of the containment system, the dôme comprises an injection device that inputs an injection fluid into the cavity.

According to an aspect of the containment system, the injection device comprises a plurality of output ports inside the cavity, said output ports being fed with the injection fluid.

According to an aspect of the containment system, the injection fluid comprises one or a combination of the fluid components chosen in the list of an alcohol, an éthanol, a methanol, a glycol, an ethylene glycol, a diethylene glycol, and a low-dosage hydrate inhibitor (LDHI).

Another object of the invention is to provide a method for using a containment system for recovering hydrocarbon fluid from a leaking device that is situated at the seafloor and that is leaking hydrocarbon fluid from a well. The containment system comprises:

- a dôme forming a cavity, said cavity being adapted to completely surround and include the leaking device, and to accumulate hydrocarbon fluid coming upwardly from the leaking device, said dôme comprising at least one upper output opening,

- a sensor, and

- an output valve connected to the upper output opening.

The method comprises the following successive steps:

al) measuring by the sensor an interface level of a fluid interface between hydrocarbon fluid and any other fluid inside the dôme, bl) controlling the output valve on the bases of the interface level measured by the sensor for outputting hydrocarbon fluid from the cavity.

In various embodiments of the method, one and/or other of the following features may optionally be incorporated.

According to an aspect of the method, at step bl), the output valve is controlled so as to keep the interface level lower or equal to a level of output of the hydrocarbon fluid from the leaking device.

According to an aspect of the method, the dôme further comprises an injection device that is able to input an injection fluid into the cavity, and before landing the containment system at the seafloor and surrounding the leaking device, the method comprises the following steps:

a2) measuring by the sensor a first interface level (IL1) of a fluid interface between hydrocarbon fluid and injection fluid inside the dôme, b2) controlling the output valve on the bases of the first interface level measured by the sensor for outputting hydrocarbon fluid from the cavity, c2) measuring by the sensor a second interface level of a fluid interface between injection fluid and water inside the dôme, and d2) controlling the injection device on the bases of the second interface level measured by the sensor for adding injection fluid inside the cavity.

According to an aspect of the method, at step b2) the upper output opening is controlled so as to keep the first interface level at a level higher than a first predetermined level, said first predetermined level being preferably proximal to the upper output opening.

According to an aspect of the method, at step d2) the injection device is controlled so as to keep the second interface level at a level lower than a second predetermined level, said second predetermined level being preferably proximal to the base level.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be apparent from the following detailed description of at least one of its embodiments given by way of non-limiting example, with reference to the accompanying drawings. In the drawings:

- Figure 1 is a schematic view of a vertical eut of a containment system according to the invention;

- Figure 2a, 2b, and 2c are showing an example of method for installing the containment system of figure 1;

- Figure 3 is a vertical eut of a variant of the containment system of figure 1.

MORE DETAILLED DESCRIPTION

In the various figures, the same reference numbers indicate identical or similar éléments. The direction Z is a vertical direction. A direction X or Y is a horizontal or latéral direction. These are indications for the understanding of the invention.

As shown on figure 1, the containment system 1 of présent invention is adapted for recovering hydrocarbon fluid from a leaking device 2 that is situated at a seafloor 5 of a deep offshore installation. The leaking device 2 is for example the well itself, a pipeline, a blow out preventer device, a wellhead or any device connected to the wellhead. The seafloor 5 is for example at more than 1500 meters deep below the sea surface 4. At this depth, the sea water is cold, for example around only 5°C and at high pressure.

The hydrocarbon fluid may be liquid oil, naturai gas, or a mix of them.

The leaking device 2 is leaking a hydrocarbon fluid from a subsea well 3. The hydrocarbon fluid exiting from the subsea may be rather hot, for example above 50 °C. However, the environment cold température and high pressure may transform the sea water and hydrocarbon fluid into hydrates having a quasi-solid or solid phase. These hydrates can fill and clog any cavity.

The containment system 1 of présent invention is landed and fixed to the seafloor by any means, such as anchoring or heavy weights 29 for compensating the upward

Archimedes force applied on the containment system 1 by the hydrocarbon fluid that is lighter than the sea water (lower mass density). The seafloor corresponds in the présent description to a base level of the containment system 1.

The other levels are defîned going upwards, in the vertical direction Z towards the sea surface 4.

The containment system 1 of présent invention comprises at least:

- a dôme 20 forming a cavity 21 under said dôme 20, said cavity accumulating the hydrocarbon fluid, and

- an upper output opening 22 to extract the hydrocarbon fluid for recovering.

The dôme 20 can be sealed on the seafloor.

The containment system 1 may additionally comprise an over pressure valve 23 to extract fluid from the cavity to the environment if a pressure différence between the cavity and the environment exceeds a pressure limit.

The dôme 20 is preferably fixed to the seafloor.

For example, the dôme 20 comprises foot 20c having heavy weights for maintaining and securing the dôme 20 to the seafloor.

The dôme 20 completely surrounds the leaking device 2. In a horizontal plane (XY) , the dôme 20 has a closed loop shape encompassing the leaking device 2. Said shape may be for example a circle shape, a square shape or any polygonal shape.

The dôme 20 has a diameter D20. This outer diameter corresponds to a maximum distance between two internai points of the dôme, taken in a horizontal plane at a Ievel near the base Ievel BL. The diameter D20 is for example of 6 meters or more.

The dôme 20 is higher than a total height of the leaking device 2. It has a height H20 of approximately 3 meters or more. It completely includes the leaking device 2 (i.e. the part above the base Ievel. Ail that is under the seafloor is not taken into account as the dôme is sealed to the seafloor).

The dôme 20 defines an inner dôme volume, called the cavity 21. This cavity volume communicates with the environment sea water via lower opening 26 near the seafloor 5. Pressure between inside and outside of the cavity 21 is then balanced (equalised).

The dôme 20 is a hollow structure having:

- an upper portion 24 extending in a radial direction to an outer peripheral end 24a, said radial direction being perpendicular to the vertical direction AX (equal to direction Z on the figure), and

- a latéral portion 25 extending from the upper portion 24 downwardly between an upper end 25a and a lower end 25b, said lower end 25b comprising for example the foot 20c.

The latéral portion 25 has said diameter D20.

The latéral portion 25 of the dôme is downwardly opened so as to surround the leaking device 2.

The dôme 20 comprises an upper output opening 22 having of small diameter compared to the dôme diameter. Said upper output opening is adapted to be connected to a pipe 50 for extracting the hydrocarbon fluid from the containment system 1 to a recovery boat 6 at the sea surface 4, so as the hydrocarbon fluid is recovered.

In a vertical plane (XZ), the upper portion 24 of the dôme 20 may hâve a convergent shape from the latéral portion 25 up to the upper output opening 22. The dôme 20 is a cover that can hâve advantageously an inverted funnel shape.

The hollow structure of the dôme 20 forms a largely opened cavity 21 in the direction to the seafloor. It is positioned above and around the leaking device 2 so as to accumulate the light hydrocarbon fluid.

The cavity 21 accumulâtes hydrocarbon fluid coming upwardly from the leaking device 2, i.e. oil and/or natural gas. The hydrocarbon fluid fills the upper volume of the cavity, down to an interface level IL.

Moreover, the dôme 20 may comprises upper and latéral portions 24, 25 that comprise thermal insulating material, so as to thermaily insulate the cavity 21 from the cold environment of sea water. Ideally, the dôme 20 may be manufactured with at least a thermaily insulating material, said thermally insulating material preferably having a thermal conductivity lower than 0.1 W.m^_1.K^_1.

The following thermal insulation materials may be used: synthetic material such as Polyuréthane (PU) or polystyrène material, or a fibre textile with Polyvinyl chloride (PVC) coating or PU coating, or Alcryn ®. The thermal insulation material may be foam, or a gel contained inside a double wall structure.

The dôme 20 may comprise a plurality of walls, layers or envelopes for improving the thermal insulation. Between the layers, insulation materials may be included, or heating devices (electric, hydraulic or of any kind) to improve again the thermal insulation of the dôme.

The thermal insulation of the dôme 20 passively insulates the cavity 21, while the first injection device 30 actively insulates the cavity 21. Both effects prevent the formation of hydrates inside the cavity 21.

The cavity 21 is a volume storing a quantity of hydrocarbon fluid and absorbing the fluctuations of hydrocarbon fluid flows.

The containment system 1 of présent invention comprises :

- a sensor 60 for measuring the interface level IL of the fluid interface between the hydrocarbon fluid and any other fluid (e.g. sea water) inside the dôme 20,

- an output valve 62 connected to the upper output

opening 22	for	extracting the	hydrocarbon fluid from	the
cavity 21.
The	output	valve 62 is	operated	or controlled	on
the bases	of	the	interface	level IL	measured by	the
sensor 60.
The	control	of the output valve	may be manuai	or
automatic.
In	a manuai	control, a	user reads	the value of	the
interface level	and	détermines	to open or	close the output

valve 62.

In an automatic control, the containment system further comprises a control unit 61 that implements a level control law that calculâtes a control value on the bases of a measured value of the interface level IL, and that opérâtes the output valve 62 on the bases of the control value. The control unit 61 closes or opens the output valve 62 for outputting hydrocarbon fluid from the cavity.

Additionally, the output valve 62 may be controlled so as to keep the interface level IL at a level inside the cavity 21, said level being constant.

Advantageously, the level is lower or equal to a leaking level LL, said leaking level being a level of output of hydrocarbon fluid from the leaking device (see figure 1).

The jet of hydrocarbon fluid outputting from the leaking device 2 is therefore going directly inside the hydrocarbon fluid accumulated inside the cavity 21. The jet is not in contact with sea water at its output from the leaking device. The cold sea water is not suck by the jet. Hydrates formation is then prevented.

Advantageously, the level is higher than the leaking level LL, but at a predetermined small distance, said distance being lower than 50 cm, or preferably lower than 1 m. The jet of hydrocarbon fluid does not suck lost of sea water, and the sucked sea water is going back downwardly inside the dôme by gravity effect.

This case may happen when the jet of hydrocarbon fluid is at a leaking level LL lower than the level of the lower opening 26, and particulariy when the jet is directed in a horizontal direction.

Advantageously, the level is higher or equal to the level of the lower opening 26. No hydrocarbon fluid is leaking from the cavity to the environment into the sea water.

The containment System 1 may also comprise an injection device 30 that injects an injection fluid IF into the cavity 21.

The injection device 30 may comprise a plurality of output ports spread inside the volume of the cavity, so as to ensure a uniform mixing of the injection fluid into the

hydrocarbon fluid inside the cavity 21.	inject	injection
The injection	device	30	may
fluid IF from the upper	portion	24,	the	latéral	portion 25
or from both portions 24	, 25 of	the	dôme	20.
Thank to the	control	of	the	fluid	interface

Ievel IL inside the dôme, the various flow of injection fluid to each portion of the dôme can be determined, and the injection system 30 is itself more efficient to prevent hydrates formation.

The injection fluid IF may be sea water pumped near the sea surface 4 via a pump 63. The pumped sea water may be used as it, i.e. at the température of sea water at the sea surface 4, or heated by additional means. Its température is therefore much higher than the température of sea water at the seafloor depth.

The injection fluid may be an alcohol, an éthanol, a methanol, a glycol, an ethylene glycol, a diethylene glycol, and a low-dosage hydrate inhibitor (LDHI). The LDHI are fluids that inciude a mix of at a kinetic inhibitor fluid and an anti-agglomerant fluid. A kinetics inhibitor fluid is a fluid that delays the formation of hydrates. An anti-agglomerant fluid is a fluid hydrates to agglomérâtes into large that prevents the solids; only small hydrates are formed.

injection

The fluid may be additionally heated or

The tubes pipe, pipe 50 having is an channel, and an outer pipe 51 and forming an tube and the outer tube.

advantageously a two concentric inner pipe 51 forming tube 52 surrounding said annular channel between the

The inner channel an inner inner inner may be connected to the upper output opening 22 and used hydrocarbon fluid from the cavity 21. The to extract the annular channel

used to feed it with the warm fluid from the surface. However, it is apparent that the two channel of such pipe can be connected to the dôme according to the other inverse possibility without any change.

The sensor 60 may provide the interface level via a direct or indirect measurement. For example, the sensor 60 may be composed of a plurality of température or pressure sensors positioned along a vertical direction Z inside the cavity 21. The évolution of the measured température or pressure indicates the position of the interface level IL. The sea water is cold and the hydrocarbon fluid is hot or warm. The discontinuity in the measured température or pressure indicates the position of the interface level IL inside the cavity 21.

The sensor 60 may also provide measurements concerning other interface levels.

For example, the sensor 60 may provide a gas interface level corresponding to a level of an interface between a gas component and a Iiquid component of the hydrocarbon fluid contained inside the cavity 21.

Additionally, the dôme 20 may comprise a first output valve 71 for extracting the gas component from the cavity. The first output valve is positioned at a highest level of the dôme, i.e, on the upper portion 24 of the dôme (the cover).

The first output valve 71 is then controlled on the bases of the gas interface level measurement provided by the sensor 60.

The gas component of the hydrocarbon fluid extracted from the first output valve 71 may be recovered by a pipe to the recovery boat 6.

Moreover, the dôme 20 may comprise a second output valve 72 for extracting the Iiquid component from the hydrocarbon fluid inside the cavity 21. The second output valve 72 is positioned at an intermediate level between the base level and the highest level of the dôme.

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then controlled on

The second output valve 72 is level IL, interface the bases of the interface the interface level between hydrocarbon fluid.

any other second output valve 72 is being the level of a fluid fluid (liquid component) and

Advantageously, the controlled so as to keep the interface level IL lower or equal to the intermediate level of valve 72.

The liquid component of the extracted from the second output valve by a pipe to the recovery boat 6.

the above first

Thanks to valves 71, 72, gas hydrocarbon fluid cavity 21. The dôme 20 separator.

Thanks valves fluid value.

to said second output hydrocarbon fluid may be recovered and second output component and liquid component of the extracted from the can the

71, 72 inside and the their be directly is used as above first dôme 20 control, has of phase or components and second output the quantity of light a determined and measured

Knowing the nature quantity inside the dôme, determined. Additionally, these as the buoyancy is lower or buoyancy limit. Taking into containment System components, buoyancy can be determined, and can be kept stable at

The control the fluids components and their buoyancy of valves can the dôme can be be controlled so equal to account the the the seafloor 5.

of the first predetermined weights of containment System containment System 1 the manual (e.g. operated by automatic by implementing the control valves 71, 72 can be operated vehicle) or law according the above rules inside be and second output a remotely a control unit

61.

The control unit 61 may that controls ail the valves, plurality of units that are independent to each other one of a single control may be composed either interconnected or said plurality.

unit of or

The output valve 62 or the first output valve may be used as a vent valve, for evacuating large quantifies of hydrocarbon fluid inside the cavity 21 during the installation of the containment system 1 above the leaking device 2. The vent valve can be opened or controlled during the first steps of installation before landing at seafloor. During these steps most of the hydrocarbon fluid may be evacuated to reduce or cancei its buoyancy Archimedes force and to prevent hydrates formation.

The dôme 20 may also comprises an over pressure valve 23 that extract fluid out of the cavity 21 to the environment if a pressure différence between the cavity 21 and the environment exceeds a predetermined pressure limit.

The predetermined pressure limit is for example of 10 bars, 20 bars, or 50 bars. This limit has to be determined accordingly with the cavity size and the leaking device flow.

The over pressure valve 23 is for example a bail check valve. The bail check valve comprises a support element, a bail, and a spring that loads the bail to the support element so as to close an opening. The tuning of the spring load is adapted to the predetermined pressure 1imit.

The predetermined pressure limit may insure that hydrates formation is prevented.

Moreover, the containment system 1 may comprise a drain valve for purging or limiting the quantity of water inside the cavity 21. Said drain valve might be positioned proximal to the base level BL (seafloor) .

Figure 3 is presenting a variant of the containment system of figure 1. In said variant, the containment system 1 further comprises a wall 10 installed around the leaking device 2. This wall 10 is extending from a lower end at the base level at the seafloor 5 to a first level above the leaking level LL and the level of the output opening 26. The wall 10 is for example a cylinder.

Advantageously, the wall 10 is sealed or quasi-sealed to the seafloor 5 around the leaking device.

The wall 10 further comprises a one way valve 13 that allows the water inside the wall cavity to exit from it.

Thanks to this variant, the interface between hydrocarbon fluid HF and water W is divided into an inner interface and an outer interface. The inner interface is inside the wall cavity and it has a level, denoted interface level IL. The outer interface is outside the wall 10, i.e. between the wall 10 and the dôme 20. It has a level denoted outer interface level IL3.

The sensor 60 may measure the inner interface level IL and/or the outer interface level IL3 instead of the interface level IL.

The measurement of the outer interface level permit to indirectly control the inner interface level IL. The wall 10 of présent variant allows controlling a lower level of hydrocarbon fluid interface around the leaking device 2. Thanks, to such variant, a leaking device 2 having a leaking level LL near seafloor 5 and/or having an horizontal jet can be treated efficiently. The volume inside the wall 10 (wall cavity) is rapidly warmed by the hydrocarbon fluid itself, while the cold sea water is expulsed outside from this wall 10 by the one way valve 13. Hydrates formation is therefore prevented.

The output vale 62 is then controlled on the bases of the outer interface level IL3. It keeps the inner interface level IL at a level lower or equal to the leaking level LL of output of the hydrocarbon fluid, even if the outer interface level IL3 is higher than this level LL.

An exampie of method for installing and using the containment system 1 according to the invention is now explained in view of figures 2a, 2b and 2c corresponding to three successive states during installation. Figures 2a and 2b are states before the containment system 1 is landed at the seafloor and surrounding the leaking device 2. Figure 2c is a state after the landing of the containment system 1 above the leaking device 2. On these figures, the base level corresponds to the lowest level of the containment system 1, i.e. the surface that will be in contact with the seafloor when it is landed.

On figure 2a, the containment system is not installed above the leaking device 2. It is near the seafloor 5, but positioned laterally aside the leaking device 2.

The dôme 20 is firstly filled by the injection device 30 of an injection fluid IF. The used injection fluid is one of those listed, and is preferably heated.

The output valve 62 is now a valve situated just above the dôme 20, preferably directly at the output of the upper output opening 22. In présent case, this valve is not combined to a pump as it was on figure 1. However, any valve situated above the dôme 20 can be used.

Then, the containment system 1 is laterally moved so to be positioned above the leaking device 2 (figure 2b), its dôme 20 being substantially coaxial to the vertical direction AX defined by a vertical direction corresponding

to the output of device 2.	hydrocarbon fluid from the leaking
Hydrocarbon	fluid HF has a density lower than

injection fluid IF, and is accumulated inside the dôme 20 in the upper portion of the cavity 21, the injection fluid IF being below said hydrocarbon fluid.

Therefore, there are a fluid interface between hydrocarbon fluid HF and injection fluid IF at a first

interface	level IL1,	and	a fluid	interface	between
injection	fluid IF and sea	water W at	a	second	interface
level IL2.
To	stabilise	(keep	constant)	the	first	interface

level IL1, the output valve 62 is opened (controlled) to evacuate a quantity of hydrocarbon fluid HF. The quantity of hydrocarbon is for example extracted via the pipe 50 or extracted to the sea for example via a chock valve.

The upper output opening 22 may be controlled on the bases of the first interface level IL1, said first interface level being measured by the sensor 60.

The upper output opening 22 may be controlled so as the first interface level IL1 is equal or higher than a first predetermined level. The first predetermined level may be relatively high and proximal to the upper output opening 22. The quantity of hydrocarbon fluid stored inside the cavity 21 is therefore small during this state, and the risk of hydrates accumulation and clogging the cavity is very low.

To stabilize the second interface level IL2, the injection device 30 is controlled to add a quantity of injection fluid IF inside the cavity 21.

The injection device 30 may be controlled on the bases of the second interface level IL2, said second interface level being measured by the sensor 60.

Advantageously, injection device 30 may be controlled so as the second interface level IL2 is equal or lower than a second predetermined level. The second predetermined level may be relatively low and proximal to the base level BL. The quantity of injection fluid stored inside the cavity 21 is therefore high during this state, and the risk of hydrates formation is reduced.

Thanks to the above method, the containment system 1 can be installed above the leaking device 2 without forming any hydrates. These transient states and steps are important for avoiding the hydrates formation.

Then, the containment system 1 is landed above the seafloor 5 and the dôme 20 is surrounding the leaking device 2 and enclosed it (figure 2c).

The output valve 62 of the containment system 1 is controlled so as to substantially fill it with the hydrocarbon fluid outputting from the leaking device 2.

This reduces the quantity of sea water inside the cavity 21 and therefore reduces the possibility of hydrates formation. The hydrocarbon fluid is relatively hot, and therefore storing a huge quantity of hydrocarbon fluid inside the cavity heats the entire cavity 21 and reduces the risk of hydrates formation inside said cavity.

During this state, the fluid interface between hydrocarbon fluid and any other fluid (sea water or injection fluid) is at an interface level IL.

The output valve 62 is controlled on the bases of 10 the interface level IL, said interface level being measured by the sensor 60.

Advantageously, the output valve 62 is controlled so as to keep such interface level lower or equal to a level LL of output of the hydrocarbon fluid from the 15 leaking device 2.

Thanks to the above method, the containment system 1 can be used permanently above the leaking device 2 without forming any hydrates.

Claims (13)

1. A containment system (1) for recovering hydrocarbon fluid from a leaking device that is situated at the seafloor and that is leaking hydrocarbon fluid from a well, wherein the containment system (1) is adapted to be landed at the seafloor corresponding to a base level of the containment System, and wherein the containment system comprises a dôme (20) forming a cavity (21) under said dôme, said cavity being adapted to completely surround and include the leaking device, and to accumulate hydrocarbon fluid coming upwardly from the leaking device, said dôme comprising at least one upper output opening (22) adapted to extract the hydrocarbon fluid for recovering, and wherein the containment system is characterised in that it further comprises:

- a sensor (60) for measuring an interface level (IL) of a fluid interface between hydrocarbon fluid and any other fluid inside the dôme (20), and

- an output valve (62) connected to the upper output opening (22) for outputting hydrocarbon fluid from the cavity (21), said output valve being controlled on the bases of the interface level (IL) measured by the sensor (60).

2. The containment system according to claim 1, wherein the output valve (62) is controlled so as to keep the interface level (IL) lower or equal to a level (LL) of output of the hydrocarbon fluid from the leaking device.

3. The containment system according to claim 1 or claim 2, further comprising a control unit (61) that implements a level control law so as to keep the interface level (IL) lower or equal to a level (LL) of output of the hydrocarbon fluid from the leaking device.

4. The containment system according to any one of the daims 1 to 3, wherein the dôme (20) comprises:

- a first valve (71) for extracting a gas component from the cavity, said first valve being positioned on the dôme at a level proximal to a highest level of the dôme, and

- a second valve (72) for extracting a liquid component from the cavity , said second valve being positioned on the dôme at an intermediate level intermediate between the base level and the highest level of the dôme.

5. The containment system according to claim 4, further comprising a control unit (61) that implements a séparation control law that controls the first valve (71) so as a gas interface level is Iower than the highest level of the dôme, and so as a liquid interface level is Iower than the intermediate level.

6. The containment system according to any one of the daims 1 to 5, wherein the dôme (20) comprises an over pressure valve (23) that extract fluid out from the cavity to the environment if a pressure différence between the cavity and the environment exceeds a predetermined pressure limit.

7. The containment system according to any one of the daims 1 to 6, wherein the dôme (20) comprises an injection device (30) that inputs an injection fluid into the cavity.

8. The containment system according to claim 7, wherein the injection device (30) comprises a plurality of output ports inside the cavity, said output ports being fed with the injection fluid.

9. The containment System according to claim 7 or daim 8, wherein the injection fluid comprises one or a combination of the fluid components chosen in the list of an alcohol, an éthanol, a methanol, a glycol, an ethylene glycol, a diethylene glycol, and a low-dosage hydrate inhibitor (LDHI).

10. A method for using a containment system (1) for recovering hydrocarbon fluid from a leaking device that is situated at the seafloor and that is leaking hydrocarbon fluid from a well, and wherein the containment system (1) comprises:

- a dôme (20) forming a cavity (21) under said dôme, said cavity being adapted to completely surround and include the leaking device, and to accumulate hydrocarbon fluid coming upwardly from the leaking device, said dôme comprising at least one upper output opening (22),

- a sensor (60), and - an output valve (62) connected to the upper output opening (22), and wherein the method comprises the following successive steps: a) measuring by the sensor (60) an interface

Ievel (IL) of a fluid interface between hydrocarbon fluid and any other fluid inside the dôme,

b) controlling the output valve (62) on the bases of the interface Ievel (IL) measured by the sensor (60) for outputting hydrocarbon fluid from the cavity (21).

11. The method according to claim 10, wherein at step bl), the output valve (62) is controlled so as to keep the interface Ievel (IL) lower or equal to a Ievel (LL) of output of the hydrocarbon fluid from the leaking device.

12. The method according to claim 10 or claim 11, wherein the dôme (20) further comprises an injection device (30) that is able to input an injection fluid into the cavity, and wherein, before landing the containment system at the seafloor and surrounding the leaking device (2), the method comprises the following steps:

a2) measuring by the sensor (60) a first interface level (IL1) of a fluid interface between hydrocarbon fluid and injection fluid inside the dôme, b2) controlling the output valve (62) on the bases of the first interface level (IL1) measured by the sensor (60) for outputting hydrocarbon fluid from the cavity (21), c2) measuring by the sensor (60) a second interface level (IL2) of a fluid interface between injection fluid and water inside the dôme, and

d2) controlling the injection device (30) on the bases of the second interface level (IL2) measured by the sensor (60) for adding injection fluid inside the cavity (21) • 13. The method according to claim 12, wherein at

step b2) the upper output opening (22) is controlled so as to keep the first interface level (IL1) at a level higher than a first predetermined level, said first predetermined level being preferably proximal to the upper output opening (22).

14. The method according to claim 12, wherein at step d2) the injection device (30) is controlled so as to keep the second interface level (IL2) at a level lower than a second predetermined level, said second predetermined level being preferably proximal to the base level (BL).