WO2017025689A1

WO2017025689A1 - Underwater method and facility for gas/liquid separation

Info

Publication number: WO2017025689A1
Application number: PCT/FR2016/052058
Authority: WO
Inventors: Thibault DE SORBIER
Original assignee: Technip France
Priority date: 2015-08-10
Filing date: 2016-08-09
Publication date: 2017-02-16
Also published as: FR3040067B1; FR3040067A1

Abstract

The invention concerns a method and a facility for gas/liquid separation, in an underwater environment, of a multiphase hydrocarbon mixture. Said method comprises the following steps: a) installing a separation chamber (32) in a substantially vertical direction, said separation chamber (32) having a lower end (33) and an opposing upper end (35); b) extracting, from the seabed (10), a multiphase hydrocarbon mixture comprising at least one gas phase and at least one liquid phase; and, c) injecting said multiphase hydrocarbon mixture according to a tangential component into said separation chamber (32) in order to allow said at least one gas phase to flow towards said upper end (35), while said at least one liquid phase drains towards said lower end (33).

Description

Underwater gas / liquid separation method and installation

The present invention relates to a method and an underwater installation for gas / liquid separation of a multiphase mixture of hydrocarbons and water.

One area of application envisaged is the extraction of hydrocarbons located in the seabed.

Some types of hydrocarbon deposits contain both liquid hydrocarbons and gaseous hydrocarbons, and when they are extracted from the seabed, they contain in addition water. Therefore, it is necessary to separate the gaseous and liquid phases of this mixture of fluids in order to be able to separately exploit and treat the different hydrocarbons.

In addition, this mixture of fluids, when it rises from the seabed to the surface, undergoes a detrimental pressure drop. In addition, the higher the water height, and the greater the hydrostatic back pressure of the weight of the fluid column to go back to the surface installation is important, and therefore, less production is easy. As a result, the oil recovery potential of the deposit is limited. Several devices make it easier to put into production, for example, gas injection or underwater multiphase pumping, or even the underwater gas / liquid separation of the fluid mixture.

Thus, it has been imagined to separate by gravity gas phase containing gaseous hydrocarbons from the liquid phase containing liquid hydrocarbons and water, in the underwater environment before going back to the surface. Thus, the installation comprises on the one hand a submarine feed pipe of the multiphase mixture of hydrocarbons and water, from the hydrocarbon deposit, and on the other hand, a longitudinal separation chamber installed substantially vertically. in the seabed on a supporting structure firmly anchored in said seabed. To do this, the floor of the seabed must be prepared before installing the supporting structure by means of a specific laying boat, dedicated to this type of work. The separation chamber is then installed on the support structure by means of this same specific laying boat. The separation chamber has a lower end and an opposite upper end, and the subsea feed duct is connected to the separation chamber between the two lower and upper ends. Since the diameter of the separation chamber is much greater than that of the submarine feed ducts and the internal architecture of the chamber is complex, it is impossible to clean this type of installation by scraping devices. conventionally by means of a "PIG", acronym for "Pipeline Intervention Gadget" in English.

Also, the fluid mixture optionally contains solid impurities and in particular sand. The gas phase of the multiphase mixture of hydrocarbons and water then escapes towards the upper end of the separation chamber, while the liquid phase, possibly containing sand, is evacuated towards the lower end. Also, the liquid phase is generally biphasic since it is an immiscible mixture of hydrocarbons and water. The lower end of the separation chamber is preferably connected to a pipe for recovering the two liquid phases via a pump usually referred to as a lifting pump; the recovery pipe then extending to the surface. As for the upper end of the separation chamber, it is connected to an exhaust pipe which also extends to the surface to be able to recover the gaseous phase of the mixture.

The lifting pump is slaved to the flow rate of the multiphase mixture of hydrocarbons and water in the subsea supply duct so as to optimize the separation of the gaseous and liquid phases, hereinafter gas / liquid separation, in the separation chamber. In particular, it adjusts the level of the interface between the gas phase and the liquid phases relative to the injection pipe of the mixture inside the separation chamber, by controlling the operating flow of the lifting pump. Several lift pumps can be implemented.

Nevertheless, the gas / liquid separation is not perfect and the liquid phases carry with them a certain amount of gas. Also, a problem that arises and that aims to solve the present invention is to be able to improve the efficiency of the gas / liquid separation inside the separation chamber. The invention also aims to provide an easily installable installation by conventional means and whose cleaning by conventional scraping devices is facilitated.

For this purpose, the present invention proposes, according to a first object, a gas / liquid separation method in a submarine environment, of a multiphasic mixture of hydrocarbons, said method being of the type comprising the following steps: a) one installs a longitudinal separation chamber in line with a seabed, and said separation chamber is oriented in a direction opposite to said seabed, said separation chamber having a lower end and an opposite upper end; b) extracting from said seabed a multiphase hydrocarbon mixture comprising a gaseous phase and at least one liquid phase; and, c) injecting said multiphase hydrocarbon mixture into said separation chamber to allow said at least one gas phase to escape to said upper end, while said at least one liquid phase is evacuated to said lower end. And, in step c), said multiphase mixture of hydrocarbons is injected in a tangential component of said separation chamber, so as to cause rotation of said multiphase hydrocarbon mixture within said separation chamber.

Thus, a feature of the invention lies in the setting in motion of the multiphase hydrocarbon mixture, inside the separation chamber, so as to promote gas exchange at the interface between the gas phase and the liquid phases . Indeed, causing the formation of a vortex inside the separation chamber not only increases the dimensions of the interface between the gas phase and the liquid phases, but moreover, increase the convection to the interior of the multiphase hydrocarbon mixture, and therefore the diffusion of the gas phase to the gas / liquid interface. The multiphase hydrocarbon mixture also contains water. Preferably, the separation chamber has a cylindrical symmetry of revolution, so as to promote the rotation of the multiphase mixture of hydrocarbons and water.

Advantageously, said at least one gaseous phase is recovered at said upper end. This gasy year can then be brought to the surface to be treated.

In addition, according to a particularly advantageous feature of the invention, said at least one liquid phase is drawn through said lower end. Thus, thanks to the suction, which can be controlled, the vertical position of the gas / liquid interface within the separation chamber is adjusted with respect to the relative position of the injection of the multiphasic mixture. of hydrocarbons and the separation chamber.

Preferably, said multiphase mixture of hydrocarbons is injected according to, in addition, an axial component of said separation chamber. Thanks to this characteristic, the transfers of the gaseous phase through the gas / liquid interface are further promoted.

According to yet another advantageous characteristic, said separation chamber is suspended in the underwater environment. This simplifies its installation, since it frees itself from a bearing structure at the seabed and thereby the preparation work of said seabed to receive said carrier structure and the installation time of said supporting structure.

According to another aspect, the present invention provides an underwater gas / liquid separation plant of a multiphase hydrocarbon mixture, said multiphase hydrocarbon mixture comprising at least one gaseous phase and at least one liquid phase, said installation comprising on the one hand, an underwater supply duct of said multiphase hydrocarbon mixture, and, on the other hand, a longitudinal separation chamber intended to be installed substantially vertically, said separation chamber having a lower end and an upper end. opposite, said submarine feed duct opening into said separation chamber so as to allow said at least one gaseous phase to escape towards said upper end of said separation chamber, while said at least one liquid phase is evacuated towards said lower end. Said submarine feed duct opens into said separation chamber in a tangential component of said separation chamber so as to cause said multiphase hydrocarbon mixture to rotate within said separation chamber.

The installation thus defined makes it possible to implement the separation method that is the subject of the invention and described above. It thus promotes gas exchange through the gas / liquid interface of the separation chamber.

Preferably, the installation comprises an exhaust pipe of said at least one gaseous phase extending in the extension of said upper end. The exhaust pipe joins for example a surface installation to be able to treat the gas phase, which generally contains several types of hydrocarbons.

According to a particularly advantageous embodiment of the invention, said separation chamber and said exhaust pipe form a single pipe. Thus, the separation chamber can be formed inside a conventional underwater riser, for example a flexible pipe or a rigid pipe, generally for transporting hydrocarbons between the seabed and the surface. Also, it considerably simplifies the implementation of the installation, since the exhaust pipe, defining the separation chamber, can be installed via a conventional laying boat, and in particular be reeled through the well central of some conventional laying boats. In addition, and more generally, the compact dimensions of the separation chamber, integrated into the exhaust pipe, allow said exhaust pipe to pass through the tensioners and clamps of a conventional laying boat and any other laying device traditionally used for the installation of a rigid or flexible conduit of the submarine feed duct type, "flowline" in the English language, or of the underwater riser type, "riser" in the English language. Installation costs are therefore much lower than the implementation of an underwater installation anchored in the seabed, according to the prior art.

According to a particular embodiment, the installation comprises a pipe for recovering said at least one liquid phase extending in the extension of said lower end. Thus, the recovery line, connected to the lower end, for example joins the surface installation so as to process and store the mixture of liquid phases. Preferably, said separation chamber and said pipe for recovering said at least one liquid phase form a single pipe. It is thus possible to install the exhaust pipe assembly and recovery pipe, in the same way as a conventional underwater pipe, thanks to the usual submarine pipe installation means described above. More preferably, the exhaust pipe, the separation chamber and the recovery pipe together form a single U-shaped pipe extending into the seabed, the separation chamber being formed near the seabed. Such an arrangement considerably reduces the costs of implementation of the underwater installation according to the invention.

According to another embodiment, the installation further comprises a pump for lifting said at least one liquid phase connected to said lower end of the separation chamber. In this way, said at least one liquid phase of the separated multiphase hydrocarbon mixture is sucked by said at least one lift pump so as to be able to drive said at least one liquid phase to the surface installation. Said at least one liquid phase is entrained via the recovery line, without said at least one liquid phase accumulating at an injection orifice of the dispensing element. In the opposite case, by accumulating at the injection orifice of the dispensing element, said at least one liquid phase could reduce the flow rate of the multiphase hydrocarbon mixture projected by said opening and therefore by the Similarly, it may reduce the flow rate of the multiphase hydrocarbon mixture flowing in the subsea feed line. At Moreover, the lift pump or pumps can better regulate the vertical position of the gas / liquid interface in the separation chamber.

In addition, and advantageously, said submarine feed duct opens inside said separation chamber according to, in addition, an axial component of said separation chamber. In this way, it promotes the vortex effect inside the separation chamber and thus the potential for gas exchange at the interface between liquid phases and gas phase.

Preferably, said separation chamber comprises deflection members of said multiphase hydrocarbon mixture to promote gas / liquid separation. Such bodies are for example formed of propellers.

Other features and advantages of the invention will emerge on reading the following description of a particular embodiment of the invention, given by way of indication but not limitation, with reference to the accompanying drawings in which:

- Figure 1 is a schematic view illustrating the underwater installation according to the invention in a first configuration;

- Figure 2 is a schematic view illustrating the underwater installation according to the invention in a second configuration;

Figure 3 is a schematic view of first details of the installation as shown in Figure 1;

- Figure 4 is a schematic view showing second detail elements illustrated in Figure 1 and 2, according to a first embodiment;

Figure 5 is a diagrammatic cross-sectional detail view along the plane A-A shown in Figure 4;

- Figure 6 is a schematic view showing second detail elements illustrated in Figures 1 and 2, according to a second embodiment;

Figure 7 is a schematic detail view of Figure 2; and,

- Figure 8 is a schematic cross-sectional view along the EE plane shown in Figure 7. Identical references will be used from one figure to another to designate identical or similar elements.

Figures 1 and 2 illustrate a marine environment extending vertically from a seabed 10 to a marine surface 12. At the marine surface 12 floats a surface installation 14, while extends on the seabed 10, substantially up to the plumb of said surface installation, a submarine feed duct 16 connected upstream to a hydrocarbon deposit, not shown, located in the subsoil of the seabed 10.

The hydrocarbon deposit may be an oil deposit or a natural gas deposit, or a mixture of both. The surface installation 14 can in particular be of the FPSO type (for "Floating Production Storage and Offloading" in English, or a floating unit for production, storage and unloading), FLNG (for "Floating Liquefied Natural Gas" in French). English, a floating unit dedicated to liquefied natural gas), SPAR (for Single Point Anchor Tank), Semi-Submersibles, etc. Of course, in certain circumstances, the wells in the hydrocarbon deposits can be moved away from the surface installation 14, and thus the underwater supply duct 16 as well, or at the very least the submarine feed duct 16 may have an end close to the plumb of the surface installation 14 from which said subsea feed duct extends so as to move away from the steady to reach the hydrocarbon deposit.

The hydrocarbon deposit contains a multiphase hydrocarbon mixture comprising at least one gaseous phase and at least one carbonaceous liquid phase.

The surface installation 14 may also be a fixed platform connected to the seabed 10, or a platform located on the ground, the hydrocarbon deposits lying in the sea near the coast. The submarine feed duct 16 is placed on the seabed 10 or is buried, and it can extend over several tens of kilometers.

Also, may be added to the carbonaceous liquid phase, an aqueous phase. A mixture of gaseous phase and liquid phases, hereinafter referred to as a mixture This multiphase hydrocarbon circulates inside the subsea feed duct 16. Impurities such as sediment and sand can also be suspended in the multiphase hydrocarbon mixture.

In addition, Figures 1 and 2 illustrate an underwater installation 18 gas / liquid separation, intended precisely to come separate the gas phase of the liquid phases. The subsea installation 18 has an exhaust pipe 20 to which the underwater supply duct 16 is connected. It also comprises a recovery pipe 22.

The exhaust pipe 20 may be rigid and therefore be made of metal and for example steel. The exhaust pipe 20 may be in the form of a single-wall pipe or a double pipe pipe called "pipe in pipe" in English. The exhaust pipe 20 may then comprise a metal liner or a polymer material. The exhaust pipe 20 may also be flexible. By flexible pipe means a pipe consisting of a plurality of layers of armor son made of metal, for example steel, and one or more sheaths of polymeric material. In any case, the exhaust pipe 20 may comprise an insulation and / or an external protection. The length of the exhaust pipe 20 is essentially limited by the depth of the seabed 10. In practice, the exhaust pipe 20 has for example a diameter of 10 inches, or 24.5 cm. The exhaust pipe 20 also has a length greater than 500 m and up to 5000 m or more. The upper end 15 of the exhaust pipe 20 may or may not extend above the marine surface 12. In particular, the upper end 15 of the exhaust pipe 20 may extend from 1 m to 200 m beyond the marine surface 12 so as to be connected to the surface installation 14. The exhaust pipe 20 can be installed in several configurations:

a string-like high rise configuration known as SCR for Steel Catenary Riser in English shown in FIG. 2,

a Hybrid Catenary Riser hybrid configuration in English, not shown, a tense rising hybrid configuration called FSHR for Free Standing Hybrid Riser, represented in FIG.

It will be observed that the recovery pipe 22 can also be installed according to the aforementioned configurations. Also, the exhaust duct 20 may be installed in a tautly mounted hybrid configuration, while the recovery duct 22 is installed in a chain-mounted hybrid configuration or a chain-mounted rigid configuration, or any other combination of configurations.

In a rigid chain-mounted configuration (SCR), shown in FIG. 2, the exhaust pipe 20 is suspended by its upper end 15. The lower end 17 of the exhaust pipe 20 rests at the level of the seabed 10 In a rigid chain-mounted configuration (SCR), the exhaust pipe 20 is subjected to significant vertical movements induced by the heave movement of the surface installation 14 under the effect of the swell when said surface installation is floating. These vertical movements of the exhaust pipe 20, which in practice have an amplitude of a few centimeters to several meters, induce severe and complex mechanical stresses in said exhaust pipe, in particular at the level of the curved portion and at the level of the zone of contact between said exhaust pipe and the seabed 10. Thus, the mechanical characteristics and the mass of the exhaust pipe 20 must be distributed in the most homogeneous manner possible and as uniformly as possible along said pipe exhaust. Since the exhaust pipe 20 is suspended at the surface installation 14, the mass of said exhaust pipe 20 tends to oppose the buoyancy of said surface installation and to pull it towards the bottom. As a result, a rigid configuration ascending in chain (SCR) will be poorly suited to great depths greater than about 3000 m. The recovery pipe 22 may be connected in a U-shape to the seafloor 10 to the exhaust pipe 20. The lift pump 24 may be arranged directly between the exhaust pipe 20 and the recovery pipe 22, or may be arranged on a branch circuit. In the case where the lifting pump 24 is directly arranged between the exhaust pipe 20 and the recovery pipe 22, the lifting pump 24 is in practice first fixed to the seabed via a battery anchoring, then the exhaust pipe 20 and the recovery pipe 22 are laid one after the other and connected to the lift pump by flanges, connectors, flexible or rigid connectors, or any other means conventional fitting.

In the case where the lifting pump 24 is arranged on a bypass circuit, the latter is connected to the exhaust pipe 20 and to the recovery pipe 22 via T-fittings mounted on said exhaust pipes. and recovery. A valve mounted between the exhaust pipe 20 and the recovery pipe 22 makes it possible to obstruct the direct path connecting said exhaust pipe to said recovery pipe so as to force the passage of the fluid in the bypass circuit. The exhaust pipe 20 and the recovery pipe 22 can then be connected so as to form together a single pipe and thus be installed in one piece in the seabed, from a conventional laying boat. The assembly can, for example, be unwound through the tensioners of conventional laying towers, clamps, a central well or any laying device of a conventional laying boat. The lifting pump 24 is in practice fixed on the seabed by means of an anchoring stack. Therefore, the implementation of the separation plant according to the invention can be achieved by usual means and therefore at advantageous costs. In Figure 2, the exhaust pipe 20 and in parallel the recovery pipe 22 joined together forming a U 26.

In a tense rising hybrid configuration (FSHR), as shown in FIG. 1, the exhaust pipe 20 is suspended by its upper end 15 by a tension buoy 19 and is connected to the surface installation 14 via a pipe upper flexible 21. The lower end 17 of the exhaust pipe 20 is arranged mobile in rotation on a foundation 23 fixed on the seabed 10 and connected to the end of the submarine feed pipe 16 via an injection pipe 34. flexible or rigid. Thus, the exhaust pipe 20, initially oriented vertically, is rotatable at its lower end 17 and can therefore tilt under the effect of the marine current. When the exhaust pipe 20 tilts, the tension buoy 19, exerting a vertical force on the upper end 15 of said exhaust pipe, tends to bring said exhaust pipe back to the vertical position. Thus, the exhaust pipe 20 slightly tilting with the changes in the sea current undergoes stresses much lower than those it would suffer if its orientation was fixed. This tilting capacity minimizing the stresses makes it possible to provide an exhaust pipe 20 whose outside diameter may vary along its length, in particular at the level of the separation chamber 32 which may comprise a diameter greater than that of the rest of said pipe. Exhaust 20. Also, the greater the inner diameter of the upper portion 27 of the exhaust pipe 20 above the separation chamber 32 has a reduced diameter, the more the separated gas phase tends to escape quickly to the Thus, the less the separated gaseous phase remains in the exhaust pipe 20, the less the gaseous phase has time to cool by heat exchange with the marine environment, and therefore the risk of formation of water. hydrate decreases. It must nevertheless be taken into consideration that the internal diameter of the upper part 27 of the exhaust pipe 20 must not be excessively reduced to the point that it generates too much frictional pressure drop and therefore a natural temperature drop of the gas phase by the effect of Joule-Thomson. Also, when using a heating device of the exhaust pipe 20, as described below:

the reduced dimensions of said exhaust duct make it possible to provide a heating device comprising elements with equally reduced dimensions,

- The reduced volume and the surface to be heated make it possible to limit the energy costs.

This tighter rising hybrid configuration (FSHR) also has the advantage of providing a substantially vertical and straight exhaust duct 20 contrary to a rigid chain-mounted configuration (SCR). wherein the exhaust pipe 20 is curved. In such a tighter rising hybrid configuration (FSHR), the separated liquid phase (s) falling after projection through the injection orifice (29) of the distribution element (28) flow in a balanced manner around the periphery of the inner wall. the separation chamber 32 located below the injection port 29. This balanced flow can further optimize the gas / liquid separation. The exhaust duct 20 oriented substantially vertically, for example less than 5 ° of inclination with respect to the vertical, induces the regularity of the flow of the liquid phases, and thus maximizes the efficiency of the internal deflection members, which will be described below.

Yet another advantage of this tense rising hybrid configuration (FSHR) is that the weight is fully supported by the foundation and the buoy, and therefore does not constrain the surface installation 14. This tense rising hybrid configuration (FSHR) is therefore adapted to regardless of the depth of the seabed 10.

In a hybrid chain-mounted (HCR) configuration, not shown, the exhaust pipe 20 is suspended by its upper end 15 via a first flexible or rigid pipe connected to the surface installation 14. The lower end 17 of the exhaust pipe 20 is connected to the end of the submarine supply pipe 16 via a second flexible pipe. This configuration makes it possible to provide, as for a tense rising hybrid configuration (FSHR), a substantially straight exhaust pipe 20, and therefore has all the advantages that result therefrom.

According to the variant embodiment illustrated in FIG. 1, the exhaust pipe 20 and the recovery pipe 22 meet substantially parallel to the surface installation 14, while the variant embodiment illustrated in FIG. 2 shows the exhaust pipe 20 and the recovery line 22 which meet in a double-walled pipe, which joins the surface installation 14.

Figure 7 illustrates in more detail the exhaust pipe 20 and the recovery pipe 22 which extends annularly around the exhaust pipe 20. They thus constitute a pipe with double walls, called "pipe in pipe" in English language, and who joins directly the surface installation. As shown in FIG. 8, one or more centering shims 38, or spacers, can extend into the annular space of the double-walled pipe so as to hold the exhaust pipe 20 in position at the center of the pipe 22. The centering or shim (s) 38 comprise one or more orifices 39 for the circulation of the liquid phase (s) along the annular space. This implementation mode simplifies the installation. It is also contemplated, in another variant embodiment, that the gaseous phase passes through the ring, while the liquid phase flows into the central part.

Referring again to FIGS. 1 and 2, the subsea feed duct 16 is connected to a dispensing element 28 via an injection conduit 34. The dispensing element 28, shown in FIG. detail in Figures 4 to 6, opens into a lower portion 30 of the exhaust pipe 20 via an injection port 29; the lower portion 30 forming a separation chamber 32. In practice, the subsea feed duct 16 and the injection duct 34 are interconnected via an FLET, acronym for "Flow Line End Termination" In the English language. The subsea feed duct 16 and the injection duct 34 may be fixed to the FLET via male-female connectors, by means of flanges or welds. In addition, the flow rate in the subsea feed duct 16 may for example vary between 1000 m ³ / hour and 1500 m ³ / hour.

The exhaust pipe 20, as illustrated in FIGS. 1, 2 and 4 to 6, therefore defines a separation chamber 32. The separation chamber 32 may extend over part or the entire length of the said exhaust pipe 20. As long as the length of the exhaust pipe 20 is essentially limited by the depth of the seabed 10, it is possible to take advantage of this available dimension to extend the separation chamber 32 on a great length. Indeed, the design of the separation chamber 32 is made so as to promote a particularly long length-to-diameter ratio, for example a length to diameter ratio greater than fifty. In particular the separation chamber 32 may have a length of a hundred meters to several hundred meters. In addition, the maximum diameter of the exhaust pipe 20, in particular at the level of the separation chamber 32, is dimensioned to allow the installation of the exhaust pipe 20 in a conventional manner, that is to say that said diameter is dimensioned so that said exhaust pipe can pass to through laying equipment available on conventional laying boats, in particular through installation towers, tensioners, installation wells, in the same way as a conventional underwater riser would English language).

The separation chamber 32 thus has a lower end 33 connected to the lifting pump 24 and an opposite upper end 35. The lower 33 and upper 35 ends of the separation chamber 32 are located on either side of the the injection port 29 of the dispensing element 28. A pipe section can connect the lower end 33 of the separation chamber 32 to the lifting pump 24. This section of pipe is either a pipe connection flexible, the extension of the exhaust pipe 20, or the extension of the recovery pipe 22.

It will be observed that the lower portion 30 is of cylindrical geometry with circular direction, defects near manufacture. The distribution element 28 makes it possible to connect, in accordance with the embodiment presented here, the injection duct 34 to the lower portion 30 of the exhaust pipe

20 in a substantially perpendicular direction.

According to an essential characteristic of the invention, and as is more particularly illustrated in FIGS. 4 to 6, the dispensing element 28 opens into said separation chamber 32 in a tangential component of the separation chamber 32 In other words, the injection is carried out in a direction away from the central axis of the separation chamber 32.

Also, according to an exemplary implementation of the invention, the connection between the injection pipe 34 and the separation chamber 32 is made by means of a distribution element 28 made of one or more molded parts or well machined, for example metal. The dispensing element 28 has a cylindrical body whose internal diameter is substantially equal to that of the internal diameter of the lower portion 30 of the exhaust pipe 20. The distribution element 28 also has a tangential inlet sleeve 31 opening tangentially inside the cylindrical body of the dispensing element 28. The sleeve tangential inlet 31 preferably has a diameter less than half the diameter of the cylindrical body of the dispensing element 28. The tangential inlet sleeve 31 may extend in a direction substantially perpendicular to the axis of the cylindrical body of the distribution member 28, or at an angle that can vary between 0 ° and 80 ° relative to said perpendicular to the axis of said cylindrical body. The lower portion 30 of the exhaust pipe 20 is then divided into two half-portions, the distribution element 28 being arranged between the two half-portions so as to connect the inside of the two said half-portions between them and ensure the continuity of the lower portion 30 exhaust pipe 20. The half-portions are fixed on the distribution member 28 by welding, mechanical fastening type connectors, flanges or other.

The tangential inlet sleeve 31 protrudes from the dispensing element 28.

The dispensing element 28 may comprise an inner surface coating ("liner" in English) preferably made of inconel but may be made of stainless steel or other. The inner surface coating is configured to resist corrosion but also erosion generated by the sand particles and impurities present in the multiphase hydrocarbon mixture. The dispensing element 28 may also comprise a liner and an insulation layer and optionally an outer protection and heating and control elements.

Also, the dispensing element 28 can be pre-installed on the exhaust pipe 20 at the surface, and then connected to the subsea feed duct 16 by means of the injection pipe 34. The supply duct under -marine 16, from a hydrocarbon deposit is installed independently and it is then connected to the exhaust pipe 20 and more precisely to its lower portion 30, when the exhaust pipes and recovery 20, 22 are unwound towards the seabed. It will be observed that in certain situations, for example when the seabed is The U-shaped portion 26 joining the exhaust pipe 20 and the recovery pipe 22 can be held suspended at the surface installation 14 above the seabed.

With regard to the technical advantages resulting from the subsea installation 18 according to the invention, and in particular from the relative position of the distribution element 28 and the lower portion 30 of the exhaust pipe 20, they are several orders. As illustrated in FIGS. 4 to 6, the multiphasic mixture of hydrocarbons flows in the injection duct 34 along the arrow F towards the lower portion 30 and opens out tangentially inside the separation chamber 32. In this way, the multiphase hydrocarbon mixture is rotated within the separation chamber 32. Such movement of the multiphase hydrocarbon mixture increases the gas / liquid separation; the gaseous phase escaping vertically in the exhaust duct 20 to join the surface installation 14, and the liquid phases being sucked by the lifting pump 24 and then discharged through the recovery pipe 22 to join the installation of surface 14 also.

We can then distinguish two zones of separation; a primary separation zone 36, and a secondary separation zone 37.

The primary separation zone 36 extends from the injection port 29 to the gas / liquid interface. In the primary separation zone 36, there is a first separation combining:

a separation by gravity, the liquid phases being denser than the gaseous phase flowing downwards under the effect of gravity, whereas the gaseous phases tend to escape upwards towards the upper end of the the separation chamber 32; and,

a separation by centrifugal force, the liquid phases being denser than the gaseous phase, being pressed against the inner wall of the separation chamber 32, whereas the less dense gaseous phase will be expelled from the liquid phase or phases to end up in a central area. In addition, by pressing against the inner wall of the separation chamber 32, the multiphasic mixture of hydrocarbons takes the form of a downward helical blade providing a large exchange interface with the central zone. exhaust gas phase. Thus, the larger the exchange interface, the more likely the gaseous phase will be separated from the liquid phases. This exchange interface increases especially when the distance _d between the gas / liquid interface and the injection port 29 increases.

In addition, provision is made to implement propeller deflection members inside the separation chamber 32 to further improve the separation gas phase / liquid phase.

According to a particular embodiment shown in FIG. 6, the deflection member may be a helical deflection member 25 in the form of a blade arranged in a helix inside the primary separation zone 36 of the separation chamber 32. In practice, in falling, the liquid phase (s) will flow on the upper face of the blade. At the same time, the remainder of the gaseous phase still mixed with the liquid phase or phases in the multiphase mixture of hydrocarbons firstly separated, while separating from the said liquid phase or phases, tends to rise until it comes into contact with the lower face of the blade. Thus, creating a gaseous phase plate under the lower face of the blade creating a preferential path of passage to go up the separate gaseous phase to the upper end of the separation chamber 32 while minimizing the risk of re-training of said gas phase separated by the liquid phase (s) descending to the secondary separation zone 37. The helical deflection member 25 is configured to:

limiting the drop height of the liquid phase or phases projected by the injection orifice 29 and thus limiting the risk of foaming;

maximizing the free surface of the liquid phase (s) flowing along the blade arranged in a helix, the gas / liquid separation taking place at the level of the said free surface, the effectiveness of the said gas / liquid separation increasing with the dimensions of said free surface;

- Increase the efficiency of the gas / liquid separation by centrifugation of the multiphase hydrocarbon mixture.

The blade of the helical deflection member 25 may be arranged orthogonally, or in an inclined manner, with respect to the internal surface of the separation chamber 32, and preferably inclined so that the periphery of the blade is positioned below the inner part. The blade may extend half the width of the primary separation zone 36 or only a portion of this half width. The blade may extend only into the primary separation zone 36, only into the secondary separation zone 37, or may extend into both said primary and secondary separation zones. The pitch of the helical deflection member 25 may be continuous or variable and for example decrease as one moves towards the lower end 33 of the separation chamber 32. The pitch of the helix has a dimension configured to allow the formation of the gaseous phase plate and thus allow the recovery of the separate gaseous phase countercurrent to the liquid phase or phases.

Preferably, the helical deflection member 25 may have a helix pitch of at least 1 m. The helical deflection member 25 may comprise a plurality of helical blades arranged in parallel or may comprise several blades arranged in series and thus forming several sections of propellers.

According to an alternative embodiment of the invention, illustrated in Figures 4 and 5, where there is a portion of the separation chamber 32 located in the secondary separation zone 37, the deflection member may be in the form of one or more helical grooves 42 formed in the thickness of the wall of the separation chamber 32.

Such deflection members allow the passage of a scraping device ("PIG" for "Pipeline Intervention Gadget" in English) inside the separation chamber 32. The pitch of each helical groove 42 can be continuous or variable and for example decrease as one moves towards the lower end 33 of the separation chamber 32. Preferably, the helical grooves 42 may have a helical pitch of at least 1 m . The helical grooves 42 may extend only into the primary separation zone 36, only into the secondary separation zone 37, or extend into both said primary and secondary separation zones.

It is also possible to improve this separation, by tilting the tangential inlet sleeve 31 of the dispensing element 28, according to an axial component relative to the separation chamber 32, and directed towards In practice, the angle of inclination may vary from 0 ° to 80 °, and will preferably be 30 °. In this way, the multiphase mixture of hydrocarbons, entering the separation chamber 32, takes a tangential path in an osculating circle having a greater radius of curvature than if it were projected without axial component. This looser curvature makes it possible to facilitate the rotation of the multiphase hydrocarbon mixture and to reduce the mechanical stresses exerted by said multiphase hydrocarbon mixture on the wall of the separation chamber 32.

The first gas / liquid separation may be partial. Thus, after the first gas / liquid separation, it is possible that part of the gas phase has remained trapped in the liquid phase or phases. Therefore, the secondary separation zone 37 may not contain only the liquid phase or phases, but a multiphase mixture of hydrocarbons resulting from the first gas / liquid separation, hereinafter referred to as a first-phase multiphase hydrocarbon mixture.

The secondary separation zone 37, lower than the primary separation zone 36, is located at the gas / liquid interface.

A second gas / liquid separation is then performed in the secondary separation zone 37, by decantation of the multiphase mixture of hydrocarbons firstly separated. The evacuation of the gas phase is favored by the central exhaust zone formed by the tangential movement of the multiphase hydrocarbon mixture in the primary separation zone 36. The second gas / liquid separation may be partial. Thus, at the end of the second gas / liquid separation, it is possible that part of the gas phase has remained trapped in the liquid phase or phases. Therefore, at the outlet of the secondary separation zone, the fluid may not contain only the liquid phase or phases, but a multiphase mixture of hydrocarbons resulting from the second gas / liquid separation, hereinafter referred to as a multiphase hydrocarbon mixture. secondly separated.

In practice, the distance between the nominal level of the gas / liquid interface 41 and the lower end 33 of the separation chamber 32 is configured from so as to allow a residence time of the multiphase hydrocarbon mixture firstly separated sufficiently large for the coalescence of the gas phase bubbles to be optimal. This distance between the nominal level of the gas / liquid interface 41 and the lower end 33 of the separation chamber 32 is preferably greater than 10 m.

Similarly, the distance between the injection port 29 and the upper end 35 of the separation chamber 32 is configured to allow condensates and fine liquid phase droplets to be entrained with the separate gas phase. , to be deposited on the inner wall of the separation chamber 32, and fall by gravity to be finally discharged with the liquid phases. The quality of the gas phase produced is thus improved. Similarly, condensates and fine droplets of liquid phases can be deposited on the inner wall of the upper portion 27 of the exhaust pipe 20 and fall by gravity.

The diameter of the upper portion 27 of the exhaust pipe 20 may be smaller than the diameter of the separation chamber 32 so that the separated gas phase undergoes acceleration. An upper deflection member, not shown, can be arranged at the upper end 35 of the separation chamber 32. The upper deflection member is configured to impose the separate gas phase an indirect path, preferably in a baffle. The upper deflection member may, in addition, be configured to also allow the fallout, in the separation chamber 32, potential thin droplets of liquid phases that would have been entrained in the upper part 27 of the exhaust duct 20 but which would have condensed on the walls of said exhaust duct before reaching the surface installation 14.

The nominal level of the gas / liquid interface 41, that is to say the desired level of the gas / liquid interface in nominal operation is between the injection orifice 29 of the distribution element 28, and a low point located between the lower end 33 of the separation chamber 32 and said injection port 29. Since the length of the separation chamber 32, may be important, as explained above, the length of the zone secondary partition 37 can be dimensioned so as to arrange a buffer zone between the injection port 29 of the distribution element 28 and the nominal level of the gas / liquid interface 41 in the separation chamber 32 in nominal operation. The buffer zone is configured to store the momentary surpluses of liquid phases during the flow regime by jerk (or "slug flow" in English). In any case, the length of the separation chamber 32 is preferably dimensioned so that, in the most unfavorable flow-through cases, the liquid phases can not leave said separation chamber by its upper end 35.

It will be observed that the position of the interface between the gaseous phase and the liquid phases is adjusted by means of the lifting pump 24, the flow rate of which can be varied. Sensors can thus be installed inside the separation chamber 32 to be able to control the lifting pump 24.

Also, thanks to the lifting pump or pumps 24, it is easy to adjust the level of the actual gas / liquid interface 40 illustrated in FIGS. 4 and 6, between the gaseous phase and the liquid phase or phases at the same time. The vertical position of this actual gas / liquid interface 40 vis-à-vis the injection port 29 is indeed decisive for optimizing the gas / liquid separation. In addition, sensors connected to the electrical and / or optical cables are implemented in order to be able to slave the lifting pump or pumps 24. These sensors make it possible to determine either the actual level of the gas / liquid interface 40, or the pressure at the lift pump or pumps 24, which indicates the height of the column of liquid phases.

In nominal operation, the gas / liquid interface is positioned at a predetermined distance d from the injection orifice 29 of the dispensing element 28. The predetermined distance d is preferably dimensioned so that the buffer volume of the buffer zone is between 5 m ³ and 20 m ³ . In practice, the predetermined distance d is generally greater than 50 m. Controlling the flow rate of the lift pump (s) 24 makes it possible to regulate the position of the actual level of the gas / liquid interface 40 in the separation chamber 32 so that it coincides with the nominal level of the gas / liquid interface. 41 desired. One or more sensors, not shown, arranged inside or outside the subsea installation 18, are configured to measure in real time, or at regular intervals, the actual level of the gas / liquid interface 40 in the separation chamber 32. This or these sensors may, for example, be pressure sensors, arranged under the nominal level of the gas / liquid interface 41 and configured to determine the actual level of said gas / liquid interface 40 to from the measured pressure exerted by the liquid column located between said gas / liquid interface and said pressure sensor. A control unit is configured to:

increasing the flow rate of the lifting pump or pumps 24 when the actual level of the gas / liquid interface 40 is above the nominal level of the desired gas / liquid interface 41,

- Decrease the flow rate of the lift pump or pumps 24 when the actual level of the gas / liquid interface 40 is below the nominal level of the desired gas / liquid interface 41.

One or more pressure sensors are preferably located at the lower end 33 of the separation chamber 32, and / or upstream of the lifting pump or pumps 24. In particular, the pressure sensors installed in series with the pumps of in conventional installation diagrams can in particular be used for measuring the actual level of the gas / liquid interface 40 in addition to their normal use so as to avoid the installation of an additional pressure sensor on the underwater installation 18.

The use of a pressure sensor has the advantage, compared to optical sensors, that its operation remains unchanged in a dirty environment such as that of hydrocarbons, unlike optical sensors that are subject to fouling and for which the measurement may be disturbed in the presence of turbulent flows or foam.

The use of one or more secondary pressure sensors, arranged in the upper part of the separation chamber 32, preferably at the level of the upper end 35, can make it possible to complete the pressure measurement by calculating the pressure differential between this or these secondary pressure sensors and the pressure sensor or sensors arranged under the level nominal of the gas / liquid interface 41. The greater the measured pressure differential, the more accurately the actual level of the gas / liquid interface 40 can be determined. Therefore, the higher the height of the liquid phase column, located upstream of the pressure sensor arranged below the nominal level of the gas / liquid interface 41, is large plus the pressure differential will be large. Thus, the length of the separation chamber 32 is thus determined so as to allow, in nominal operation, to have a column height of liquid phases at least equal to 1 m.

In particular, the pressure sensors installed in series with the inlet valve of the exhaust pipe 20, and arranged at the level of the surface installation 14 in the conventional installation diagrams, can be used for the measurement of the actual level of the gas / liquid interface 40 in addition to their normal use so as to avoid the installation of an additional pressure sensor on the underwater installation 18.

In particular, the addition of additional sensors generally requires for their fixation, to drill locally the pipes. However, these holes tend to create points of weakness on the pipes which induce major security risks with regard to the exposure of said pipes to operating pressures, to torsion and bending movements, as well as vibrations, very important.

In addition, the large height of the column of liquid phases generates a high pressure at the suction of the lift pump or pumps 24. This significant pressure induces a phenomenon of retro-condensation of the gas bubbles entrained with the liquid phases. . Retro-condensation means that the gas is re-liquefied under the effect of the high pressure. Thus, the bulk volume fraction of gas mixed within the liquid phase (s) at the suction of the lift pump (s) 24 is significantly reduced. In addition, the higher the bulk volume fraction of gas decreases the more the efficiency of the lift pump (s) 24 increases. Indeed, more gas is mixed with the liquid phase or phases, plus the multiphase hydrocarbon mixture is compressible, and the efficiency of the lifting pump or pumps 24 decreases. Also, the column of liquid phases tends, under the effect of gravity, to flow through the or lifting pumps 24 and increases the effectiveness of said one or more lift pumps. Thus, a wide range of conventional underwater lifting pumps is selectable.

Also, when foam forms at the level of the secondary separation zone 37, the distance separating the upper part of the foam and the lifting pump or pumps 24 is such that if a foam column of this size were to form foam would decompose into liquid under its own weight. Thus, it is impossible for the foam to reach the lifting pump or pumps 24 and be sucked by the latter, thus avoiding the risk of defusing, damaging or even destruction of said lifting pump or pumps.

In an advantageous embodiment of the invention, an upstream pressure sensor is installed upstream or at the injection orifice 29. This upstream pressure sensor makes it possible to detect a potential temporary congestion of the buffer zone. In such a case of temporary waterlogging, the actual level of the gas / liquid interface 40 would be above the injection port 29. Such a case of clogging is undesirable and induces the degradation of the performance of the gas / liquid separation. Therefore, when the upstream pressure sensor detects a case of clogging of the buffer zone, the control unit can:

- either control the increase of the flow rate of the lifting pumps 24 accordingly,

or, in certain cases where there is a risk of damaging the underwater installation 18, controlling the shutdown of devices located upstream or downstream of said underwater installation and the shutdown of the lifting pumps 24.

In order to avoid the accumulation and adhesion of solidified condensates, for example paraffins, gel, ice, or hydrates which would adhere to the internal walls of the separation chamber 32, it is intended to implement heating elements along the separation chamber 32. Thus, the warming of these solidified condensates causes them to melt. The heating elements can then be powered by a power supply extending along the separation chamber 32 and controlled and controlled, for example by means of extended optical fibers also along the separation chamber 32.

According to a particular embodiment of the invention, especially when the water depths are large and therefore the environment of the subsea installation 18 is cold, the exhaust pipes 20 and recovery 22 have a coating external insulation so as to avoid heat transfer from the inside to the outside of said exhaust pipes 20 and recovery 22 and thus to limit the temperature decrease of the gas phase and the liquid phases flowing in said ducts d exhaust and recovery. Where appropriate, and identically to the separation chamber 32, the exhaust pipe 20, the recovery pipe 22 and any other equipment of the invention may be equipped, in part or in whole, with active heating, direct or indirect. This active heating means may comprise heating electric cables arranged around the exhaust pipe 20, and / or the recovery pipe 22 and / or any other equipment, and configured to heat the liquid or gaseous phase (s) at inside said pipes or said equipment. According to an alternative embodiment, the active heating means may comprise a device for induction of a current in the metal body of the exhaust pipe 20, and / or the recovery pipe 22 and / or any other equipment. so as to create at the level of said pipe or said equipment a joule heat release and thus heat the liquid or gaseous phase or phases within said pipes or said equipment. The active heating means may also comprise means for measuring the temperature of the liquid and gaseous phases. These measuring means may, for example, be in the form of optical fibers arranged around the exhaust pipe 20, and / or the recovery pipe 22 and / or any other equipment. A temperature control unit can then be configured to control the temperature of the liquid and gaseous phases to a desired value. Maintaining the liquid and gaseous phases at a temperature desired avoids the formation of solid hydrates, ice, wax, or other, especially during production stop phases.

This possibility of heating can make it possible to avoid the formation of solid hydrates or wax deposits, especially during the production stop phase, but can also be used continuously during normal production operations.

As represented in FIGS. 1 to 4, the underwater installation 18 is equipped with a bypass duct 11 equipped with a shut-off valve 13 and which connects the submarine supply duct 16 and the duct 22. In the normal operating phase, the stop valve 13 is in the closed position and opposes the passage of the multiphase hydrocarbon mixture through the bypass duct January 1. On the other hand, during the maintenance and scraping operations of the recovery line 22 in particular, or when the multiphase hydrocarbon mixture no longer contains enough gas, the shut-off valve 13 is brought to the open position in such a way that allowing the passage of the maintenance and / or scraping devices, and / or the passage of the multiphase hydrocarbon mixture through the bypass duct 1 1 so as to divert said multiphase hydrocarbon mixture directly into the recovery line 22 without prior gas / liquid separation. In addition, another valve not shown can be installed at the junction between the subsea feed duct 16 and the injection pipe 34 to prevent upwelling, or the scraper device ("PIG For "Pipeline Intervention Gadget" in English) inside when the shutoff valve is in the open position.

According to a particular embodiment of the invention, not shown, one or more line dividers can be installed at the recovery line 22, most generally upstream of the lifting pump or pumps 24, in order to separate the residual gas phase of the two-phase multiphase hydrocarbon mixture. The line separator is in the form of a cylinder body arranged in the axis of the recovery line 22. The in-line separator includes means for imposing rotational movement on the two-phase multiphase hydrocarbon mixture. By centrifugal effect, the liquid phase (s) more dense that the gaseous phase will be pressed on the walls of the cylindrical body, while the less dense gaseous phase will be expelled from the liquid phase or phases to end up in a central zone of said cylindrical body. The line separator then comprises a gas phase extraction duct, a first part of which extends coaxially with the cylindrical body so that the gaseous phase of the central zone of said cylindrical body penetrates inside said duct. The diameter of the extraction duct, generally less than half the diameter of the cylindrical body, is preferably dimensioned so as to extract in addition to the gas phase located in the central zone of said cylindrical body, a thin layer of liquid phase so as to ensure that the liquid phase leaving the in-line separator is at the most purified from the gas phase. The extraction duct then comprises a second portion extending orthogonally to the periphery of the cylindrical body and passing through said cylindrical body. The first and second parts of the extraction duct are connected to each other via a bend. The liquid phase (s), for their part, flow around the extraction duct towards the recovery line (22). The second part of the extraction duct is then connected to the exhaust duct (20) so as to reinject the phase gaseous newly separated, or directly to the surface installation 14. In this particular embodiment comprising an in-line separator, it is possible to minimize the dimensions of the exhaust pipe 20, including the separation chamber 32 , without degrading the overall gas / liquid separation. Indeed, the minimization of the dimensions of the exhaust pipe 20 tends to degrade the first and second gas / liquid separation which take place at the primary and secondary separation zones 36 and 37. The addition of a separator The line then allows a third gas / liquid separation to compensate for the degradation of the first and second gas / liquid separations. The use of an in-line separator arranged downstream of the lower end 33 of the separation chamber 32 is particularly advantageous insofar as the height of the column of liquid phases in the secondary separation zone of said separation chamber generates: a sufficient pressure at said on-line separator to allow a natural flow of the multiphase hydrocarbon mixture within the in-line separator.

an operating pressure at said on-line separator greater than the operating pressure at the primary separation zone of the separation chamber 32 to allow reinjecting the gas phase from the third gas / liquid separation inside. the exhaust pipe 20, and thus avoid the risk that the gas phase from the first and second gas / liquid separation escapes through the extraction duct and goes to the line separator. In such a configuration, the separation chamber 32 notably allows the absorption of any liquid phase plugs during the jerk regimes and generates at input of the on-line separator a continuous regime devoid of jerk, the system by -coup being incompatible with the proper operation of said on-line separator.

Claims

1. A gas / liquid separation method in a submarine environment, of a multiphase hydrocarbon mixture, said method being of the type comprising the following steps:

a) a longitudinal separation chamber (32) is installed in line with a seabed (10), and said separation chamber (32) is oriented in a direction opposite to said seabed, said separation chamber (32) having a lower end (33) and an opposite upper end (35);

b) extracting from said seabed (10) said multiphase hydrocarbon mixture comprising a gaseous phase and at least one liquid phase; and,

c) injecting said multiphase hydrocarbon mixture into said separation chamber (32) to allow said at least one gaseous phase to escape to said upper end (35), while said at least one liquid phase is evacuated to said lower end (33);

characterized in that in step c) said multiphase hydrocarbon mixture is injected in a tangential component of said separation chamber (32) to cause rotation of said multiphase hydrocarbon mixture within said separation chamber (32).

2. Separation method according to claim 1, characterized in that said at least one gaseous phase is recovered at said upper end (35).

3. Separation method according to claim 1 or 2, characterized in that sucks said at least one liquid phase through said lower end (33).

4. Separation method according to any one of claims 1 to 3, characterized in that suspending said separation chamber (32) in the underwater environment.

5. Separation method according to any one of claims 1 to 4, characterized in that in step c), said multiphase mixture is injected hydrocarbon further according to an axial component of said separation chamber (32).

6. Subsea gas / liquid separation installation of a multiphase mixture of hydrocarbons, said multiphase hydrocarbon mixture comprising at least one gaseous phase and at least one liquid phase, said installation comprising, on the one hand, a conduit of subsea supply (16) of said multiphase hydrocarbon mixture, and secondly, a longitudinal separation chamber (32) to be installed substantially vertically, said separation chamber (32) having a lower end (33) and an opposite upper end (35), said subsea feed duct (16) opening into said separation chamber (32) so as to allow said at least one gas phase to escape to said end upper (35) of said separation chamber, while said at least one liquid phase is evacuated to said lower end (33);

characterized in that said submarine feed duct (16) opens into said separation chamber (32) in a tangential component of said separation chamber so as to cause rotation of said multiphase hydrocarbon mixture to inside said separation chamber (32).

7. Underwater installation according to claim 6, characterized in that it comprises an exhaust pipe (20) of said at least one gaseous phase extending in the extension of said upper end (35).

8. Underwater installation according to claim 7, characterized in that said separation chamber (32) and said exhaust pipe form a single pipe.

9. Underwater installation according to any one of claims 6 to 8, characterized in that it comprises a recovery line (22) of said at least one liquid phase extending in the extension of said lower end (33). ).

10. Subsea installation according to claim 9, characterized in that said separation chamber (32) and said recovery line (22) of said at least one liquid phase form a single pipe.

1 1. Underwater installation according to any one of claims 6 to 10, characterized in that it further comprises a lifting pump

(24) of said at least one liquid phase connected to said lower end (33).

12. Underwater installation according to any one of claims 6 to 11, characterized in that said submarine feed duct (16) opens into said separation chamber (32) according to, furthermore an axial component of said separation chamber (32).

13. Underwater installation according to any one of claims 6 to 12, characterized in that said separation chamber (32) comprises deflecting members of said multiphase mixture of hydrocarbons to promote the separation of said gaseous and liquid phases.