OA17374A - A containment system and a method for using said 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, and an over pressure valve (23) for extracting fluid out from the cavity to the environment if pressure inside the cavity is too high.

Description

A containment System and a method for using said containment System.

FIELD OF THE INVENTION

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 like 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 SUMMARÏ 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 intended to be sealed to the seafloor around the leaking device and 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 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.

Thanks to these features, the fluids contained inside the dôme volume around the leaking device is heated by the hydrocarbon fluid outputting from the leaking device, and is not cooled by the sea water.

The dôme is substantially sealed, and the leaking device can not suck cold sea water from the environment.

The pressure inside the cavity is limited by the over pressure valve.

As the thermal exchanges between the sea water and the hydrocarbon fluid are cancelled and as the pressure inside the cavity can not increase above a predetermined value, the hydrates formation is prevented inside the cavity of the containment System of présent invention.

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 dôme further comprises an injection device that inputs a warm fluid into the cavity.

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

According to an aspect of the containment system, the containment system further comprises a pipe having an inner tube forming an inner channel, and an outer tube surrounding said inner tube and forming an annular channel, and wherein the inner channel is used to extract the hydrocarbon fluid from the upper output opening and the annular channel is used to feed the dôme with at least a warm fluid, or inversely.

According to an	aspect	of	the	containment system,
the dôme comprises a material that	is a	thermally isolating
material.
According to an	aspect	of	the	containment system,
the thermally isolating	material	has a	thermal conductivity
lower than 0.1 W.irT1. K-1.
According to an	aspect	of	the	containment System,

the containment system further comprises at least one sensor for measuring an interface level of a fluid interface between sea water and hydrocarbon fluid inside the dôme, at least one output valve connected to the upper output opening for outputting hydrocarbon fluid from the cavity, and a control unit for controlling said interface level on the bases of the interface level measured by the sensor.

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

- a first output opening for extracting a first phase from the cavity, said first output opening being positioned on the dôme at a level proximal to the first level, said first phase being for example an oil phase of the hydrocarbon fluid, and

- a second output opening for extracting a second phase from the cavity , said second output opening being positioned on the dôme at a level proximal to a highest level of the dôme, said second phase being lighter than the first phase, and being for example a gas phase of the hydrocarbon fluid.

According to an aspect of the containment system, the over pressure valve is a bail check valve.

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 at least:

- a dôme intended to be sealed to the seafloor around the leaking device and 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.

The dôme comprises

- at least one upper output opening adapted to extract hydrocarbon fluid for recovering,

- an over pressure valve adapted to extract fluid out from the cavity to the environment if a pressure différence between the cavity and the environment exceeds a predetermined pressure limit, and

- an injection device that injects a warm fluid into the cavity.

The method of the invention comprises the following successive steps:

a) injecting the warm fluid inside the cavity by the injection device and making the containment System to go down towards the leaking device,

b) installing the dôme around the leaking device on the seafloor, so as the base level corresponds to the seafloor.

Thanks to the above method, the dôme can be installed above the leaking device without hydrates formation inside the cavity.

In preferred embodiments of the method proposed by the invention, one and/or the other of the following features may optionally be incorporated.

According to an aspect of the method, after step b) the method comprises a step of sealing the dôme to the seafloor.

According to an aspect of the method, after step b) , the method comprises a step of stopping the injection of warm fluid if hydrates formation is not detected inside the cavity.

According to an aspect of the method, the containment System further comprises at least one sensor, at least one output valve connected to the upper output opening, and a control unit, and the method further comprises the following steps:

- the at least one sensor measures an interface level of a fluid interface between sea water and hydrocarbon fluid inside the dôme,

- the control unit calculâtes a control value of the at least one output valve on the bases of said measured interface level, and controls said at least one output valve for outputting hydrocarbon fluid from the cavity.

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.

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 <a/

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, natural gas, or a mix of them.

The leaking device 2 is leaking a hydrocarbon fluid from an 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 clogged 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 defined 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 intended to be sealed on the seafloor and forming a cavity 21 under said dôme 20, said cavity accumulating the hydrocarbon fluid,

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

- 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 sealing 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 an diameter D20. This outer diameter corresponds to a maximum distance between two internai points of the dôme, taken in an horizontal plane at a level near the base level 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 level. 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 volume is isolated (not in communication) with the environment sea water. The thermal exchange between the cold sea water and the hydrocarbon fluid is cancelled. This first effect cancels the hydrate formation.

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.

» y

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.

The containment system 1 advantageously comprises at least one sensor 60 for measuring the interface level IL of the fluid interface between sea water and the hydrocarbon fluid inside the dôme 20.

The sensor 60 may give a first measurement of a liquid level correspondîng to the interface level IL between the liquid component of the hydrocarbon fluid (e.g. oil) and the sea water, and a second measurement of a gas level correspondîng to an interface between the liquid component and a gas component (e.g. natural gas ) of the hydrocarbon fluid.

The containment system 1 additionally comprise an output valve 62 connected to the upper output opening 22 and/or pipe 50 for outputting the recovered hydrocarbon fluid to the recovery boat 6.

Then, a control unit 61 calculâtes a control value on the bases of a measured value of the interface level IL, and opérâtes the output valve on the bases of the control value for outputting hydrocarbon fluid from the cavity. The control unit 61 may calculate the control value to keep the interface level at a constant level inside the cavity 21.

The containment System 1 may also comprise an injection device 30 that injects a warm fluid WF into the cavity 21. Therefore, the hydrocarbon fluid can be heated, and prevented to form hydrates.

The injection device 30 may comprise a plurality of output ports spread inside the volume of the cavity, so as to ensure a constant warming of the hydrocarbon fluid inside the cavity 21.

The injection device 30 may inject warm fluid WF from the upper portion 24, the latéral portion 25 or from both portions 24, 25 of the dôme 20.

The warm fluid WF 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 additîonal means.

The warm fluid may be water, oil, gas oil, or crude oil or any heat transfer fluid. The warm fluid may be additionally heated or not.

The pipe 50 is advantageously a two concentric tubes pipe, having an inner pipe 51 forming an inner channel, and an outer tube 52 surrounding said inner pipe 51 and forming an annular channel between the inner tube and the outer tube. The inner channel may be connected to the upper output opening 22 and used to extract the hydrocarbon fluid from the cavity 21. The annular channel may be therefore connected to the injection System 30, and 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 containment System 1 may comprise other output openings and/or pipes for feeding additionally fluids, or for extracting other fluids, liquid or gases from the cavity.

For example, 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).

Advantageously, the cavity 21 can be used as a phase separator for separating the water and the hydrocarbon fluid, and for separating each phase of the hydrocarbon fluid (oil, gas) so as to extract them separately.

To this end, the dôme 20 may comprise:

- a first output opening for extracting a first phase from the cavity, said first output opening being positioned on the dôme at a level proximal to the first level Ll, said first phase being for example an oil phase of the hydrocarbon fluid, and

- a second output opening for extracting a second phase from the cavity , said second output opening being positioned on the dôme at a level proximal to a highest level of the dôme, said second phase being lighter than the first phase, and being for example a gas phase of the hydrocarbon fluid.

Thanks to the above first and second output opening, quantifies of each phase (oil, gas) can be limited inside the cavity 21 to predetermined values. An Archimedes force maximum that applies on the containment System 1 can be predetermined, and the weights of the foot 20c can therefore be predetermined for maintaining the containment System 1 landed at the seafloor 5.

The upper portion 24 of the dôme 20 may comprise output openings, called vents, for evacuating large quantifies of fluid inside the cavity 21. These vents are helpful to facilitate the installation of the containment System 1 above the leaking device 2. The vents are opened during the first transient steps of installation, noticeably when the containment system 1 is made to go down to the seafloor 5 around the leaking device 2. During these steps ail the hydrocarbon fluid may be evacuated to cancel its Archimedes force on the containment system and to prevent hydrates formation problem.

Moreover, the dôme 20 may comprises upper and latéral portions 24, 25 that comprise thermal isolating material, so as to thermally isolate the cavity 21 from the cold environment of sea water. Ideally, the dôme 20 may be manufactured with at least a thermally isolating material, said thermally isolating material preferably having a thermal conductivity lower than 0.1 W.m¹.K¹.

The following thermal isolation 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 isolation 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 isolation. Between the layers, isolation materials may be included, or heating devices (electric, hydraulic or of any kind) to improve again the thermal isolation of the dôme.

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

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

The dôme 20 comprises an over pressure valve 23 that extract fluid out of the cavity and into 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 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 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 limit.

Advantageously, the dôme 20 of présent embodiment is fed with warm fluid before and during the sealing and fixing step of the dôme 20 above the seafloor, so as hydrates formation is prevented.

The cavity 21 is closed, and the fluid inside the cavity is rapidly heated by the hydrocarbon fluid itself outputting from the leaking device 2.

The over pressure valve 23 insures that the pressure inside the cavity is not increasing, and then insuring that the containment System is not destroyed.

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

The method for using or installing the containment System 1 according to the invention is now explained.

The dôme of the containment System 1 comprises:

- at least one upper output opening 22 adapted to extract the hydrocarbon fluid for recovering,

- an over pressure valve 23 adapted to extract fluid out from the cavity to the environment if a pressure différence between the cavity and the environment exceeds a predetermined pressure limit, and

- an injection device 30 that injects a warm fluid into the cavity.

The method comprises the following successive steps:

a) injecting the warm fluid inside the cavity 21 by the injection device 30 and making the containment System to go down towards the leaking device 2, __

b) installing the dôme 20 around the leaking device 2 on the seafloor, so as the base level corresponds to the seafloor 5.

Thanks to the above method, the volume of the cavity 21 is continuously heated before the dôme is installed above the leaking device 2. After installation, the volume of the cavity 21 is heated by the warm fluid and by the hydrocarbon fluid itself.

The	fluids	inside	the cavity 21 are	then
continuously	heated,	and	the hydrates	formation	is
prevented.
Then,	the dôme	20 can	be sealed to the seafloor	5 by

any means.

Then if the hydraulic and thermal conditions are steady inside the cavity 21 around the leaking device 2, the injection of warm fluid by the injection device 30 can be stopped. The fluid inside the cavity will be heated only by the hydrocarbon fluid exiting from the leaking device 2.

If the flow of hydrocarbon fluid is fluctuating, and if the pressure inside the cavity 21 is increasing too much, the over pressure valve 23 will open to limit the pressure.

Thanks to the above pressure limitation, hydrates are also prevented.

The containment system 1 may also further comprises a sensor 60, an output valve 62 connected to the upper output opening 22, and a control unit 61.

The sensor measures an interface level IL of a fluid interface between sea water and hydrocarbon fluid inside the dôme 20. The control unit calculâtes a control value of the at least one output valve on the bases of said measured interface level, and it controls the output valve for outputting hydrocarbon fluid from the cavity 21.

Thanks to the above method, hydrocarbon fluid can be efficiently recovered from the leaking device 2, even at a great depth, and without hydrates formation.

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) intended to be sealed to the seafloor around the leaking device and 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 the dôme (20) further 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.

2. The containment System according to claim 1, wherein the dôme (20) further comprises an injection device (30) that inputs a warm fluid (WF) into the cavity.

3. The containment System according to claim 2, wherein the injection device (30) comprises a plurality of output ports spread inside the cavity, said output ports being fed with the first warm fluid.

4. The containment System according to claim 2, further comprising a pipe (50) having an inner tube (51) forming an inner channel, and an outer tube (52) surrounding said inner tube and forming an annular channel, and wherein the inner channel is used to extract the hydrocarbon fluid from the _K____ upper output opening (22) and the annular channel is used to feed the dôme (20) with at least a warm fluid (WF), or inversely.

5. The containment System according to any one of the daims 1 to 4, wherein the dôme (20) comprises a material that is a thermally isolating material.

6. The containment System according to claim 5, wherein the thermally isolating material has a thermal conductivity lower than 0.1 W.m^_1.K¹.

7. The containment System according to any one of the daims 1 to 6, further comprising at least one sensor for measuring an interface level (IL) of a fluid interface between sea water and hydrocarbon fluid inside the dôme (20), at least one output valve connected to the upper output opening (22) for outputting hydrocarbon fluid from the cavity (21) , and a control unit for controlling said interface level (IL) on the bases of the interface level measured by the sensor.

8. The containment System according to any one of the daims 1 to 7, wherein the dôme (20) comprises:

- a first output opening for extracting a first phase from the cavity, said first output opening being positioned on the dôme at a level proximal to the first level, said first phase being for example an oil phase of the hydrocarbon fluid, and

- a second output opening for extracting a second phase from the cavity , said second output opening being positioned on the dôme at a level proximal to a highest level of the dôme, said second phase being lighter than the first phase, and being for example a gas phase of the hydrocarbon fluid.

9. The containment System according to any one of the claims 1 to 8, wherein the over pressure valve (23) is a bail check valve.

10. A method for using the 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 at least a dôme (20) intended to be sealed to the seafloor around the leaking device and 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, and wherein said dôme comprises:

- at least one upper output opening (22) adapted to extract the hydrocarbon fluid for recovering,

- an over pressure valve (23) adapted to extract fluid out from the cavity to the environment if a pressure différence between the cavity and the environment exceeds a predetermined pressure limit, and

- an injection device (30) that injects a warm fluid into the cavity, and wherein the method comprises the following successive steps:

a) injecting the warm fluid inside the cavity by the injection device (30) and making the containment System to go down towards the leaking device,

b) installing the dôme (20) around the leaking device on the seafloor, so as the base level corresponds to the seafloor.

11. The method according to claim 10, wherein after step b) the method comprises a step of sealing the dôme to the seafloor.

12.

The method according to claim 10 or claim 11 wherein after step b), the method comprises a step of stopping the injection of warm fluid if hydrates formation is not detected inside the cavity.

5 13. The method according to any one of the claims 10 to 12, wherein the containment system (1) further comprises at least one sensor (60), at least one output valve (62) connected to the upper output opening (22), and a control unit (61), and

10 wherein the method further comprises the following steps:

- the at least one sensor measures an interface level (IL) of a fluid interface between sea water and hydrocarbon fluid inside the dôme (20),

- the control unit calculâtes a control value of the

15 at least one output valve on the bases of said measured interface level, and controls said at least one output valve for outputting hydrocarbon fluid from the cavity (21).