SUB-SEA FACILITY AND METHOD FOR HEATING A MULTI-PHASE EFFLUENT FLOWING INSIDE A SUBSEA CASING

Abstract

A subsea installation for heating a multiphase effluent circulating inside a subsea shell, includes at least one pipeline section disposed along a vertical direction and has an inner tube, an outer tube disposed around the inner tube while being coaxial therewith, a thermal insulation layer, and a system for heating by induction the outer tube. The outer tube has at a lower end an intake aperture to allow circulation of the multiphase effluent from bottom to top in an annular space delimited between the outer tube and the inner tube. The inner tube opening is at an upper end inside the outer tube and emerges at a lower end towards a discharge outlet for the multiphase effluent to allow counter-current circulation of the multiphase effluent from top to bottom inside the inner tube.

Claims

1-15. (canceled).

16. A subsea installation for heating a multiphase effluent circulating inside a subsea shell, comprising at least one pipeline section disposed along a substantially vertical direction, the pipeline section comprising an inner tube, an outer tube disposed around the inner tube while being coaxial therewith, a thermal insulation layer disposed around the outer tube, and a system for heating by induction the outer tube disposed around the thermal insulation layer, the outer tube comprising at a lower end an intake aperture in order to allow circulation of the multiphase effluent from bottom to top in an annular space delimited between the outer tube and the inner tube, and the inner tube opening at an upper end inside the outer tube and emerging at a lower end towards a discharge outlet for the multiphase effluent in order to allow counter-current circulation of the multiphase effluent from top to bottom inside the inner tube.

17. The installation according to claim 16, wherein the inner tube of the pipeline section opens at an upper end inside the outer tube at an end segment thereof which is devoid of induction heating.

18. The installation according to claim 17, wherein the end segment of the outer tube of the pipeline section has at its upper end a curved shape outwards so as to limit the pressure drops of the flow of the multiphase effluent during its passage from the annular space towards the inner tube.

19. The installation according to claim 17, wherein the end segment of the outer tube of the pipeline section contains a conical part which is curved inwards so as to improve the guiding of the effluent from the annular space towards the inner tube.

20. The installation according to claim 16, wherein the passage section of the annular space is substantially equal to the passage section of the inner tube.

21. The installation according to claim 16, wherein the pipeline section comprises a plurality of centralizers which are positioned in the annular space between the outer tube and the inner tube.

22. The installation according to claim 16, wherein the system for heating by induction the pipeline section comprises at least one induction coil wound around the thermal insulation layer and supplied with alternating electric current so as to generate an induced current in the outer tube to heat it.

23. The installation according to claim 22, wherein the pipeline section further comprises a flexible shell disposed around the induction coil of the heating system in order to form a hermetic enclosure, said enclosure being filled with a liquid at equal pressure with the external environment.

24. The installation according to claim 16, wherein the inner tube of the pipeline section is made of a corrosion-resistant alloy.

25. The installation according to claim 16, comprising a plurality of pipeline sections) which are supplied with multiphase effluent via a common distributor into which the intake aperture of the outer tube of each pipeline section emerges.

26. The installation according to claim 25, comprising at least two bundles of pipeline sections, each bundle comprising a plurality of pipeline sections, the pipeline sections of the one of the bundles being supplied with multiphase effluent via a common distributor and supplying in series or in cascade multiphase effluent to the pipeline sections of another bundle whose discharge outlets emerge towards a common manifold.

27. The installation according to claim 26, comprising two bundles of pipeline sections each comprising nine pipeline sections.

28. The installation according to claim 26, comprising three bundles of pipeline sections each comprising six pipeline sections.

29. The installation according to claim 27, wherein the pipeline sections of all the bundles are arranged inside the same parallelepiped volume in several distinct groups of pipeline sections corresponding to the different bundles or in an interlocked disposition of the pipeline sections of the different bundles.

30. A method for the subsea heating of a multiphase effluent circulating inside a subsea shell, comprising the circulation, along a vertical direction from bottom to top, of the multiphase effluent inside of an annular space delimited between coaxial outer and an inner tubes of a vertical pipeline section, followed by counter-current circulation, along a vertical direction from top to bottom, of the multiphase effluent inside the inner tube of the pipeline section, with the application of an induction heating of the outer tube of the pipeline section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 is a schematic view of a subsea installation for heating a multiphase effluent according to the invention.

[0030] FIG. 2 is a magnification of FIG. 1 showing the lower portion of a pipeline section of the installation of FIG. 1.

[0031] FIG. 3 is a magnification of FIG. 1 showing the upper portion of a pipeline section of the installation of FIG. 1.

[0032] FIG. 4 is a sectional view along IV-IV of FIG. 3.

[0033] FIG. 5 shows an example of arrangements of the pipeline sections of the installation according to the invention.

[0034] FIG. 6 shows an example of the electrical connections of the system for heating the installation of FIG. 5.

DESCRIPTION OF THE EMBODIMENTS

[0035] The invention applies to any network of subsea pipelines ensuring a connection between at least a subsea hydrocarbon production well and a surface installation.

[0036] Such a subsea pipeline network aims to transport the hydrocarbon effluents (multiphase mixture of oil, gas, water and solid particles) coming from one or more subsea production wells in order to convey them to a surface installation, for example a floating production, storage and offloading unit (also called FPSO).

[0037] These networks generally comprise several subsea pipelines which are laid on the seabed and in which the multiphase effluents coming from the production wells circulate.

[0038] To maintain the effluents transported in these subsea pipelines at a temperature above a critical threshold making it possible to avoid the formation of deposits inside said pipelines, the invention provides for connecting the pipelines to one or more removable subsea heating installations such as the one represented in FIG. 1.

[0039] The heating installation 2 represented in this figure is removably connected to a subsea pipeline (not represented). It is controlled from the surface installation (not represented in the figure) depending in particular on the operating mode of the network (typically: normal operating phase, preservation phase or production restart phase).

[0040] In general, the heating installation 2 according to the invention comprises a plurality of pipeline sections 4 which are connected to each other and which are disposed in a substantially vertical direction. The pipeline sections 4 are arranged inside a parallelepiped-shaped frame 6.

[0041] Each pipeline section 4 is disposed vertically, that is to say it extends along a mainly vertical direction, that is to say parallel to the direction of gravity.

[0042] Furthermore, each pipeline section 4 comprises an inner tube 8 centered on a vertical axis X-X and an outer tube 10 disposed around the inner tube while being coaxial therewith.

[0043] At its lower vertical end, the outer tube 10 comprises an intake aperture 12 which allows vertical circulation of the multiphase effluent from bottom to top in the annular space 14 which is delimited between the outer tube and the inner tube.

[0044] At its upper vertical end, the inner tube 8 opens inside an upper vertical end of the outer tube 10. Finally, at its lower vertical end, the inner tube 8 emerges towards a discharge outlet 16 for the multiphase effluent.

[0045] Thus, the multiphase effluent coming from the subsea pipeline penetrates inside the pipeline section 4 of the heating installation according to the invention from the bottom by entering the annular space 14 delimited between the outer tube and the inner tube through the intake aperture 12. The effluent flows vertically in this annular space 14 from bottom to top then, at the upper end of the pipeline section, reverses to be directed towards the inner tube 8 inside which it flows vertically from top to bottom. The effluent is then discharged from the bottom of the pipeline section via the discharge outlet 16.

[0046] It will be noted that the passage section of the annular space 14 delimited between the outer tube and the inner tube can be equal to the passage section of the inner tube 8 so that the flow speeds of the effluent are identical in the upward direction and downward direction. Ideally, the passage section of the annular space 14 is minimized in order to obtain the highest possible flow velocity, which promotes heat transfer. Similarly, it is preferable to have an inner tube with a small passage section so as to reduce the diameter of the outer tube, and therefore the overall weight of the pipeline section.

[0047] It will also be noted that the pressure difference between the interior of the inner tube 8 and the interior of the annular space 14 delimited between the outer tube and the inner tube is very low, so that it is possible and advantageous to give a very small thickness (of the order of a few millimeters) to the inner tube. For example, the latter can be made of a corrosion-resistant alloy.

[0048] Each pipeline section 4 of the heating installation according to the invention further comprises a thermal insulation layer 18 which is disposed around the outer tube 10, as well as a system 20 for heating by induction the outer tube which is disposed around the thermal insulation layer 18.

[0049] The induction heating system 20 consists of one or more induction coils 22 which are wound in superimposed rows around the thermal insulation layer 18. These induction coils 22 are supplied with alternating electric current so as to generate an induced current in the outer tube 10 to heat it.

[0050] The induction heating system also comprises a flexible shell 24 which is disposed around the induction coils 22 in order to form a hermetic enclosure, the latter being filled with a liquid which is at equal pressure with the external environment (namely the surrounding sea water).

[0051] The induction coils 22 of the heating system extend over the entire height of the pipeline section, except for an upper end portion P which is not surrounded by the induction coils, and therefore which is not subjected to the induction heating.

[0052] This unheated upper end segment P which is visible in particular in FIG. 3 encompasses in particular the upper end area of the outer tube 10 in which the inner tube 8 opens (area in which the multiphase effluent reverses to be directed inside the inner tube).

[0053] This upper end area of the outer tube 10 is the location in which a gas pocket of the multiphase effluent circulating in the pipeline section is likely to stagnate. As this area is not subjected to the induction heating, there is therefore no risk of heating stagnant gas in this high portion which could lead to destructive overheating of the thermal insulation layer 18.

[0054] According to one advantageous disposition visible in particular in FIG. 3, the end segment of the outer tube 10 of the pipeline section has at its upper end a shape l0a which is curved outwards. This curved shape l0a makes it possible to increase the resistance to the internal/external pressure differential and to limit the pressure drops of the flow of the multiphase effluent during its passage from the annular space 14 towards the inside of the inner tube 8.

[0055] According to another advantageous disposition not represented in the figures, the end segment of the outer tube 10 of the pipeline section can contain a conical part which is curved inwards so as to improve the guiding of the effluent from the annular space 14 towards the inside of the inner tube 8.

[0056] According to yet another advantageous disposition not represented in the figures, the pipeline section also comprises a plurality of centralizers which are positioned in the annular space 14 between the outer tube and the inner tube. These centralizers ensure centering and maintenance of the inner tube inside the outer tube.

[0057] For example, the centralizers can take the form of rings which are perforated to disturb as little as possible the flow of the multiphase effluent in the annular space between the outer tube and the inner tube.

[0058] In relation to FIGS. 5 and 6, an example of arrangement of the pipeline sections of the heating installation according to the invention will now be described.

[0059] In this exemplary embodiment, the pipeline sections 4 of the heating installation are arranged in two distinct bundles F1, F2 each of nine pipeline sections.

[0060] Each bundle F1, F2 thus comprises nine pipeline sections, respectively 4-1 and 4-2, the pipeline sections 4-1 of one of the bundles (here the bundle Fl) being supplied with multiphase effluent via a common distributor 26. This distributor 26 is positioned at the center of the pipeline sections 4-1 and is connected by fittings 28 (see FIG. 2) to the intake aperture 12 of the outer tube of each pipeline section.

[0061] Furthermore, each of the pipeline sections 4-1 of the bundle Fl supplies multiphase effluent to the pipeline sections 4-2 of the other bundle F2. This supply of the pipeline sections of the second bundle can occur in series or in cascade (that is to say in parallel).

[0062] In the exemplary embodiment of FIGS. 2 and 5, this supply is in series and carried out by means of fittings 30 connecting the discharge outlet 16 of the inner tube of each pipeline section 4-1 of the bundle Fl to the intake aperture 12 of the outer tube of each pipeline section 4-2 of the other bundle F2.

[0063] In addition, the discharge outlets 16 of the inner tube of each pipeline section 4-2 of the bundle F2 emerge towards a common outlet manifold 32.

[0064] FIG. 6 represents the electrical supply diagram of the heating installation according to the arrangement described in relation to FIG. 5.

[0065] More specifically, this FIG. 6 shows the different electrical connections of the induction coils of the system for heating each pipeline section 4-1, 4-2 of the two bundles F1, F2 to the three phases of a three-phase electrical power network.

[0066] The power supply occurs via a three-phase electric current, each phase L1, L2 and L3 of which is connected to a group of six pipeline sections 4-1, 4-2. More specifically, the phase L1 is connected to a group of six pipeline sections 4-1 of the bundle F1, the phase L2 is connected to a group of six pipeline sections comprising three pipeline sections 4-1 of the bundle F1 and three pipeline sections 4-2 of the bundle F2, and L3 is connected to a group of six pipeline sections 4-2 of the bundle F2.

[0067] Other arrangements than those described in relation to FIGS. 5 and 6 can be of course envisaged.

[0068] For example, the pipeline sections of the two bundles can be arranged in an interlocked disposition, rather than a disposition in two distinct groups.

[0069] Similarly, the heating installation can alternatively comprise three bundles of pipeline sections each comprising six pipeline sections.