OA18203A - Method for managing the heating of fluids circulating in a network of underwater pipes - Google Patents

Abstract

The invention relates to a method for managing the heating of fluids circulating in a network of subsea pipelines (2-1) providing a connection between a surface installation (6) and at least one subsea production well (4). , the method comprising removably connecting at least one heating station (14a, 14b) of fluids to an underwater pipe and controlling said heating station as a function of the operating mode of the pipe network.

Description

Title of the invention

Method for managing the heating of fluids circulating in a network of underwater pipes

Background of the invention

The present invention relates to the general field of underwater pipes resting on the seabed and providing a connection between wells for the production of underwater hydrocarbons, in particular oil and gas, and a surface installation, for example. a floating production, storage and unloading unit.

In the same offshore hydrocarbon production field, it is common to operate several wells which can be separated from each other by several kilometers, or even tens of kilometers. The fluids from these various wells must be collected by underwater pipes laid on the seabed and transferred by bottom / surface connection pipes to a surface installation, for example a ship or a land collection point, which will collect them to store them (and possibly process them).

In addition, due to their extraction at a great depth in the subsoil, the fluids (oil and gas) from subsea hydrocarbon production wells exit at a relatively high temperature at the level of the seabed ( typically of the order of 70 ° C). The sea water being generally cold, especially at great depths where it is typically 4 ° C, if no measures are taken to conserve the heat of the fluids leaving the production wells, they will gradually cool down. traveling the miles of submarine pipes. However, these fluids contain various chemical compounds for which cooling causes phenomena that are troublesome to maintain good circulation conditions.

Thus, gas molecules, in particular methane, combine with water molecules to form, under certain pressure and temperature conditions, hydrate crystals. These can stick to the walls, agglomerate there and lead to the formation of plugs capable of blocking the submarine pipe. Likewise, the solubility in petroleum of compounds with high molecular weight, such as paraffins or asphaltenes, decreases when the temperature drops, which gives rise to solid deposits which are themselves capable of blocking the underwater pipe.

One of these known solutions to attempt to remedy these problems consists in thermally insulating the underwater pipes in order to retain as much as possible the initial heat of the fluids transported. Several technologies are available for this purpose, including for example the implementation of coaxial pipes comprising an internal pipe conveying the fluids and an external pipe coaxial with the previous one in contact with the underwater environment, the annular space between these internal pipes and external being filled with a thermal insulation material or else emptied of any gas.

However, this thermal insulation solution for underwater pipes only makes it possible to slow down the inevitable cooling of the fluids transported. In particular, if the distance to be covered at the bottom of the water is too great, or if the flow of fluid is slowed down or even stopped for a certain time, the temperature of the fluids may drop below a critical threshold.

Another known solution for preventing the formation of plugs in underwater pipes consists in frequently cleaning the latter by circulating scrapers (or "pig" in English) inside them which remove any deposits from the walls. .

However, the scraping of an underwater pipe can at best only eliminate deposits of relatively small sizes to avoid any risk of the scraper getting stuck in the pipe. Also, despite the use of scraping, this solution still requires thermally insulating the pipes to limit as much as possible the formation of solid deposits inside them.

Yet another known solution consists in heating the underwater pipes over their entire length by means of one or more electric cables which are wound around the pipes in order to heat them by the Joule effect. This solution, which is called “heat tracing” (or “heat tracing” in English) makes it possible to maintain the fluids transported in the underwater pipes at a temperature above a critical threshold throughout their journey from the production well to surface installation.

The latter solution presents obvious problems associated with the installation of such electric heating cables over the entire length of the underwater pipes, with the significant costs that this represents in terms of installation. In addition, the traced heating is based on the continuity of the installation all along the underwater pipes. However, if this continuity were to be broken for one reason or another at one point in the pipes, the entire installation would be out of service. This constraint therefore makes it necessary to consider this type of heating only for the so-called preservation phases of the fluids transported, and not for the operational phases of operation.

Purpose and summary of the invention

The main aim of the present invention is therefore to propose a method for managing the heating of fluids circulating in a network of underwater pipes which does not have the aforementioned drawbacks.

This aim is achieved by means of a method for managing the heating of fluids circulating in a network of subsea pipelines providing a connection between a surface installation and at least one subsea production well, the method comprising, in accordance with invention, the removable connection of at least one fluid heating station to an underwater pipe and the control of said heating station as a function of the operating mode of the pipe network.

The method according to the invention is remarkable in that it ensures local management of the heating of the fluids transported by one or more removable heating stations which are activated only when the situation requires it. These heating stations are local and can be positioned at one or more strategic points of the underwater pipeline network in order to ensure a sufficient temperature level of the fluids transported over a very long length.

For example, on a network of underwater pipes 80 km long, and in the case of heating management which would require continuous heating of the pipes during normal operation, these heating stations could be connected all the approximately 30km along the pipes. Likewise, the method according to the invention can be used at the foot of a "riser" (that is to say a pipe used to connect the seabed with a surface installation) in the case of ultra fields. deep (depth greater than 2000m) for which the temperature of the fluids transported will sharply decrease following the Joule Thomson expansion they undergo (10 ° C every 1000m). In this application, the heating according to the invention makes it possible to supply the thermal energy which is lost during the ascent of the fluids.

In addition, the heating stations of the method according to the invention are completely removable and can therefore be easily disconnected from the underwater pipes in order to be moved to another place in the pipe network or to undergo a maintenance or repair operation. These heating stations can also be integrated into existing pipe networks because their connection to an underwater pipe does not require major network modifications. In the event of a heating station failure, the rest of the operating line will not be affected (other heating stations will not be taken out of service).

The method for managing the heating of fluids according to the invention thus presents great ease of installation on a network of pipes (these heating stations are removable and independent of each other), very great flexibility of use (they can be used in normal operation phase, in fluid preservation phase, etc.), and a low cost of installation and maintenance. The method according to the invention also makes it possible to be able to transfer the heating of the fluids which usually exists on the surface installation in order to position it under the sea, which thus makes it possible to save space on the surface installation.

According to one embodiment in which the network of underwater pipes comprises:

two main conduits interconnected at the bottom of the sea and each connected to the surface installation so as to form at least one fluid circulation loop; and a plurality of secondary conduits connecting production wells to the two secondary conduits;

the method may include connecting each main pipe to at least one fluid heating station downstream of the secondary pipes, and activating the heating stations during normal operation of the pipe network to maintain the temperature of the fluids at above a predetermined temperature threshold at any point in the network.

In this so-called “conventional loop” embodiment, the heating stations make it possible to ensure, during normal operation, a sufficient temperature level of the fluids transported over a very long length in order to avoid the formation of deposits in the fluid. underwater pipes. For example, a single heating station per main pipe is sufficient to ensure a sufficient temperature level at any point of an 80 km loop (cumulative length of the main pipes).

Still in this embodiment, in the phase of preserving the network of pipes, the method advantageously comprises closing the secondary pipes, injecting a treated fluid into the main pipes in order to purge the main pipes of the fluids they contain, and stopping the heating stations after the main pipes have been purged.

In the preservation phase, the treated fluid, typically diesel fuel, which is stored in the surface installation is injected into the loop formed by the main pipes isolated from the secondary pipes to purge the latter of all fluids coming from the production well. Unlike fluids from the production well, the treated fluid that is injected into the loop is not subject to the formation of deposits in the pipes at temperatures as low as those found on the seabed. Also, once purged of all fluids coming from the production well, the heating stations can be stopped.

During the restart phase of the pipe network following a preservation phase, the process comprises reactivating the heating stations while keeping the secondary pipes closed so as to heat the main pipes, then gradually reopening the secondary pipes to restart production.

This restart phase typically follows a phase of preserving the pipeline network. Once the heating stations have been reactivated, the secondary pipes are gradually reopened to allow production to restart.

In an alternative embodiment, in which the network of underwater pipes further comprises two connecting pipes connecting the two main pipes to one another downstream from the heating stations, the method may comprise, in the phase of preserving the network of underwater pipes. -marines:

the closing of the secondary pipes and the main pipes between the two connecting pipes with the opening of the latter, and the activation of the heating stations to maintain the temperature of the fluids above a predetermined temperature threshold at all points an upstream fluid circulation loop; and the injection of a treated fluid into the main conduits of a downstream fluid circulation loop to purge the fluids that it contains.

In this so-called “double loop” embodiment, the heating stations ensure, during normal operation, a sufficient temperature level of the fluids transported over a very long length in order to avoid the formation of deposits in the fluid. underwater pipes.

In addition, in the preservation phase, the treated fluid is injected into the downstream loop to purge the main pipes of all fluids coming from the production well and thus prevent any formation of deposits in this downstream loop. In the upstream loop, the activated heating stations continue to heat the transported fluids to prevent them from freezing when cold. Compared to the embodiment described above, only one loop is purged of the fluids that it contains, which limits the necessary quantity of treated fluid. This configuration thus makes it possible to simplify the connection to an existing surface installation for which modifications are generally difficult to achieve.

Still in this so-called double-loop embodiment, in the restart phase of the network of underwater pipes following a preservation phase, the method can comprise:

stopping the injection into the main conduits of the downstream fluid circulation loop of a treated fluid;

the reopening of the main pipes between the connecting pipes;

the closing of the two connecting conduits to merge the upstream and downstream fluid circulation loops together;

injecting methanol into at least one of the connecting lines to prevent the formation of hydrates therein; and the gradual reopening of secondary lines to restart production.

In an alternative embodiment also with a double loop, in the phase of preserving the network of underwater pipelines, the method may include stopping the heating stations and depressurizing the upstream fluid circulation loop to prevent the formation of hydrates in this upstream loop.

In another variant embodiment with a double loop, the network of underwater pipes can also comprise:

two connecting pipes connecting the two main pipes to one another downstream from the heating stations;

two additional heating stations connected to the main pipes downstream of the connecting pipes; and two additional connecting pipes connecting the two main pipes to one another downstream of the additional heating stations;

the process comprising, in the preservation phase:

the closure of secondary lines;

the closing of the main conduits between the two connecting conduits and between the two additional connecting conduits with the opening of the latter to form a double circulation loop of the transported fluids;

deactivation of heating stations and additional heating stations and depressurization of the two fluid circulation loops to prevent hydrate formation therein; and injecting a treated fluid in the main conduits into a riser loop downstream of the two fluid circulation loops to purge the fluids therein.

In this other variant, the method may comprise, in the restart phase of the network of underwater pipes following a preservation phase:

stopping the injection into the main pipes of the riser loop of a treated fluid;

the reopening of the main pipes between the connecting pipes and between the additional connecting pipes;

closing the connecting pipes and the additional connecting pipes to merge the two fluid circulation loops and the riser loop together;

injecting methanol into connecting lines and additional connecting lines to prevent hydrate formation therein; and the gradual reopening of secondary lines to restart production.

In yet another variant embodiment known as a “hybrid loop”, the network of underwater pipes comprises:

a production line connected to the surface installation / a plurality of secondary lines connecting production wells to the production line; and a service line connected to the production line downstream of the secondary lines;

the method comprising connecting the production line to at least one fluid heating station downstream of a connection with the service line, and activating the heating station during normal operation of the pipeline network to maintain the temperature of the fluids above a predetermined temperature threshold at any point in the network.

Regardless of the embodiment, the heating station can be connected directly to a submarine pipe or by means of a bypass pipe connected to the submarine pipe.

Likewise, at least one of the underwater pipes can be connected to at least one heating station. To improve the availability of the production line, it is possible to create redundancy with at least one of the subsea pipelines which is connected to at least two heating stations installed in series or in parallel. With such redundancy, a heating station is able to provide the required heating on its own. Normally only one of these

J two heating stations is used or both are used at half power.

If one of the heating stations is removed, the other station takes over.

Brief description of the drawings

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate exemplary embodiments thereof without any limiting nature. In the figures:

- Figures IA to IC are schematic views of an exemplary implementation of the method of the invention according to a first embodiment called a single loop;

FIGS. 2A to 2D are schematic views of an exemplary implementation of the method of the invention according to a second embodiment called a double loop;

FIGS. 3A to 3D are schematic views of an exemplary implementation of the method of the invention according to a third embodiment called a double loop;

FIGS. 4A to 4D are schematic views of an exemplary implementation of the method of the invention according to a fourth embodiment called a double loop;

FIG. 5 is a schematic view of an exemplary implementation of the method of the invention according to a fifth embodiment called a hybrid loop; and

- Figures 6 to 9 show different characteristics of the heating stations for the implementation of the method according to the invention.

Detailed description of the invention

The invention applies to any network of underwater pipes providing a connection between at least one well for the production of underwater hydrocarbons and a surface installation such as the network 2-1 shown in FIGS. IA to IC.

The purpose of such a network 2-1 is to transport the hydrocarbons (oil and gas) coming from one or more subsea production wells 4 in order to route them to a surface installation 6 which can be, as shown in FIG. ίο floating production, storage and offloading unit (also called FPSO for “Floating Production Storage and Offloading”).

Alternatively, the hydrocarbons coming from the production wells 4 could be conveyed directly to a coastal surface installation through very long pipes.

In the first embodiment shown in Figures IA to IC, the network 2-1 comprises two main submarine pipes 8a, 8b which are each connected to the surface installation 6 and which are interconnected at the bottom of the sea so as to form a fluid circulation loop (we speak of a conventional loop network). For example, the cumulative length of these two main pipes can reach 160 km.

The network 2-1 also comprises a plurality of secondary submarine conduits 10 (6 in number in the example illustrated) which each make it possible to connect an underwater production well 4 to the two main conduits 8a, 8b. These secondary pipes 10 are each equipped with a valve 12 controlled directly from the surface installation 6.

The method according to the invention consists in locally heating the fluids transported in the main pipes 8a, 8b of the network 2-1 thus described in order to maintain the fluids transported at a temperature above a critical threshold making it possible to avoid the formation of deposits inside said pipes.

To this end, the method provides for the removable connection of at least one fluid heating station to an underwater pipe and the control of said heating station as a function of the operating mode of the pipe network.

Thus, in the first embodiment shown in Figures IA to IC, each main pipe 8a, 8b is equipped with at least one heating station 14a, 14b for the fluids transported, these heating stations being controlled from the installation of surface 6 and optionally each coupled to a pump 16a, 16b.

The operation of the heating stations 14a, 14b is not detailed here. For example, we can use heating stations operating on the principle of electromagnetic induction thanks to a solenoid supplied with electric current from the surface installation and wound around the corresponding pipe to heat the latter by induction and consequently fluids transported by conduction. Alternatively, the heating stations can operate on the microwave principle, by chemical reactions or by any other known method for heating any type of fluid circulating in an underwater pipe.

Preferably, the heating stations 14a, 14b have a small footprint on the ground and can be easily moved on the network according to the specific heating needs. In addition, these heating stations can be easily connected to existing networks.

Furthermore, it will be noted that one of the main pipes (namely here the pipe 8a) comprises a second surface heating station 18a (coupled to a pump 20a) connected at the end of the pipe just below the surface of the sea.

In conjunction with Figures IA to IC, we will now describe the way in which the heating stations 14a, 14b and 18a of the network 2-1 are controlled according to the invention according to the various operating phases of the network.

FIG. 1A shows a normal operating phase (called "operational") of the pipe network which consists in locally heating the main pipes 8a, 8b so as to maintain at any point thereof a temperature of the fluids above a predetermined temperature threshold.

During this phase of normal operation, the heating stations 14a, 14b (and their associated pumps 16a, 16b) are activated continuously (the heating station 18a can, on the other hand, be deactivated as shown in dotted lines in the figure).

It will be noted that only two heating stations judiciously positioned on the network may be sufficient to maintain a sufficient temperature of the fluids over a very great length, for example over a cumulative length of the main pipes which can reach 160 km.

Figure IB shows a phase of preservation of the subsea pipeline network 2-1. The preservation phase is a phase during which the circulation of fluids is interrupted, for example to carry out a maintenance operation on the network.

During such a phase, the fluids located outside the influence of the heating stations 14a, 14b and 18a are no longer heated and gradually cool down, with the risk that this entails leading to the formation of deposits in the main pipes.

Also, the fluid heating management method provides, in the preservation phase, to cut off the arrival of fluids from the production wells 4 by closing the secondary conduits 10 (by closing the valves 12), to keep the stations activated. heating 14a, 14b and injecting a treated fluid which does not freeze when cold, typically gas oil.

For this purpose, the pumps 16a, 16b associated with the heating stations 14a, 14b are stopped and the treated fluid is injected from a tank of the surface installation via the main pipe 8a by actuating the pump 20a associated with the heating station on the surface 18a (which is deactivated). This treated fluid will purge all fluids from the main pipes by driving these fluids towards the surface installation via the main pipe 8b.

The treated fluid thus fills the circulation loop formed by the main pipes 8a, 8b. Once this circulation loop has been filled with the treated fluid, the heating stations 14a, 14b can be stopped (heating the treated fluid not being necessary because it does not freeze when cold).

Figure IC shows a restart phase of the subsea pipeline network 2-1. This restart phase typically follows a preservation phase as described above.

During this restart phase, the method of managing the heating of the fluids comprises the reactivation of all the heating stations 14a, 14b, 18a (including the surface heating station 18a), the secondary conduits 10 being kept closed. The heating stations thus make it possible to heat the treated fluid circulating in the circulation loop so as to heat the main pipes 8a, 8b. Once the latter have been reheated, the secondary conduits 10 are gradually opened (by opening the valves 12) so as to allow production to be restarted.

In conjunction with FIGS. 2A to 2D, a description will now be given of an architecture of a network of submarine pipes 2-2 according to a second embodiment of the invention called a “double loop”.

This network of pipes 2-2 differs from that described above in particular in that it further comprises two connecting pipes 22, 24 which allow the two main pipes 8a, 8b to be connected together downstream of the heating stations 14a, 14b (downstream and upstream are understood here in relation to the direction of circulation of the fluid in the network during normal operation of the latter).

The network of pipes 2-2 also includes valves 26a, 26b positioned on the main pipes 8a, 8b between the two connecting pipes 22, 24, as well as a service pipe 28 connecting the surface installation (not shown on the figures) to the most upstream connection pipe 22.

In the normal operating phase of the pipe network 2-2 (FIG. 2A), the method according to the invention provides for locally heating the fluids circulating in the main pipes 8a, 8b so as to maintain a temperature at all points thereof. fluids above a predetermined temperature threshold.

During this phase of normal operation, the heating stations 14a, 14b (and their associated pumps 16a, 16b) are thus activated continuously (the heating station 18a being on the other hand deactivated). Furthermore, the connection pipes 22, 24 are closed (by closing valves 30, 32 positioned on these pipes), as is the service pipe 28.

In the preservation phase of the pipe network 2-2 (figure 2B), the method provides, initially, to close the secondary pipes 10 (by closing the valves 12) and the main pipes 8a, 8b between the connecting pipes. 22, 24 (by closing the valves 26a, 26b).

In parallel, the connection pipes 22, 24 are open (by opening the valves 30, 32) and the service pipe 28 remains closed. Thus, the main pipes of the 2-2 network form a double circulation loop for the fluids transported, namely an upstream circulation loop upstream of the upstream connection pipe 22, and a downstream circulation loop downstream of the connection pipe downstream 24.

Furthermore, the heating stations 14a, 14b are kept activated so as to maintain the temperature of the fluids above a predetermined temperature threshold at any point of the upstream fluid circulation loop. The circulation of fluids in this upstream loop is achieved by actuating only one of the pumps associated with the heating stations (here the pump 16b).

Secondly, a treated fluid which does not freeze when cold (for example gas oil) is injected into the main pipes from a tank of the surface installation via the main pipe 8a by actuating the pump 20a associated with the station of surface heating 18a (which is deactivated). This treated fluid will purge the downstream fluid circulation loop of all fluids by expelling these fluids towards the surface installation via the main pipe 8b.

Thus, during this preservation phase, any risk of deposit formation in the main pipes can be eliminated; in the upstream fluid circulation loop by activating the heating stations 14a, 14b, and in the downstream loop by the presence of a treated fluid which does not freeze when cold.

FIGS. 2C and 2D illustrate the same network of pipes 2-2 during a restart phase following a preservation phase as described above.

During this restart phase, the method for managing the heating of the fluids comprises, initially (FIG. 2C), the activation of the surface heating station 18a so as to heat the treated fluid which in turn goes heat the main pipes at the level of the downstream fluid circulation loop. The fluids circulating in the upstream loop are always heated by the other heating stations 14a, 14b.

Secondly (figure 2D), when the main pipes at the level of the downstream fluid circulation loop are sufficiently hot, provision is made to stop the injection of the treated fluid into the main pipes 8a, 8b at the level of the downstream fluid circulation loop. The main pipes 8a, 8b are then reopened (by opening the valves 26a, 26b) while the connecting pipes 22, 24 are closed so as to merge the upstream and downstream fluid circulation loops. The secondary conduits 10 can then be gradually opened (by opening the valves 12) so as to allow production to be restarted.

Finally, a fluid (typically methanol) is injected through the service line 28 into the upstream connection line 22 (by opening a control valve 34) to prevent the formation of hydrates in this connection line.

In conjunction with FIGS. 3A to 3D, a description will now be given of an architecture of a network of underwater pipes 2-3 according to a third embodiment of the invention, also with a “double loop”.

This network of pipes 2-3 differs from that described above in particular in that the service pipe 28 is connected to the two connection pipes, namely to the upstream connection pipe 22 and to the downstream connection pipe 24.

The method for managing the heating of such a network of pipes 2-3 is similar to that described for the network of FIGS. 2A to 2D.

In particular, in the normal operating phase (FIG. 3A), the method according to the invention provides for locally heating the main pipes 8a, 8b so as to maintain at all points thereof a temperature of the fluids above one. predetermined temperature threshold.

During this phase of normal operation, the heating stations 14a, 14b (and their associated pumps 16a, 16b) are activated continuously and the connection pipes 22, 24 are closed, as is the service pipe 28.

During the preservation phase (FIG. 3B), the method provides for closing the secondary conduits 10 as well as the main conduits 8a, 8b between the connecting conduits 22, 24, the latter being on the other hand open (by opening the valves 30, 32 ) so that the main pipes form a double circulation loop for the transported fluids.

Compared to the operating mode described in connection with FIG. 2B, the method further comprises deactivating the heating stations 14a, 14b and depressurizing the upstream fluid circulation loop by opening the valve 34 of the service line 28. The purpose of this depressurization is to prevent the formation of hydrates in the pipes of the upstream fluid circulation loop.

In addition, a treated fluid which does not freeze when cold is injected into the main pipes from a tank of the surface installation via the main pipe 8a by actuating the pump 20a associated with the surface heating station 18a (which is deactivated. ). This treated fluid will purge the downstream fluid circulation loop of all fluids by expelling these fluids towards the surface installation via the main pipe 8b.

Thus, during this preservation phase, any risk of deposit formation in the main pipes can be eliminated; in the upstream loop for circulation of fluids by depressurization, and in the downstream loop by the presence of a treated fluid which does not freeze when cold.

The restart phase following a preservation phase is also similar to that described in connection with FIGS. 2C and 2D.

In particular, the method of managing the heating of the fluids comprises, firstly (FIG. 3C), the activation of the surface heating station 18a so as to heat the treated fluid which will in turn heat the main pipes to the surface. level of the downstream fluid circulation loop. The other heating stations 14a, 14b are also reactivated to heat the fluids circulating in the upstream loop and the depressurization of the upstream loop is stopped (by closing the valve 34 of the service line 28).

When the main pipes at the level of the downstream fluid circulation loop are hot, the injection of the treated fluid into the main pipes 8a, 8b at the level of the downstream fluid circulation loop is stopped (FIG. 3D). The main pipes 8a, 8b are then reopened, while the connecting pipes 22, 24 are closed so as to merge the upstream and downstream fluid circulation loops. The secondary conduits 10 can then be gradually opened (by opening the valves 12) so as to allow production to be restarted.

Finally, a fluid (typically methanol) is injected through the service line 28 both into the upstream connection line (by opening the control valve 34) and into the downstream connection line 24 (by opening a control valve 36) so as to avoid the formation of hydrates in these connecting pipes.

In conjunction with FIGS. 4A to 4D, a description will now be given of an architecture of a network of submarine pipes 2-4 according to a fourth embodiment of the invention, also with a “double loop”.

This network of pipes 2-4 differs from that described above in particular in that the service pipe 28 is connected to two additional connection pipes 38, 40 positioned downstream of the connection pipes 22, 24 and interconnecting the main pipes. 8a, 8b.

The network of pipes 2-4 also includes additional heating stations 42a, 42b (with their respective pumps 44a, 44b) respectively connected to the main pipes 8a, 8b between the connecting pipes 22, 24 and the additional connecting pipes 38, 40.

The network of pipes 2-4 also comprises valves 46a, 46b positioned on the main pipes 8a, 8b between the two additional connecting pipes 38, 40.

The method of managing the heating of such a network of pipes 2-4 is as follows.

In normal operation phase (FIG. 4A), the method provides for locally heating the main conduits 8a, 8b so as to maintain at any point thereof a temperature of the fluids above a predetermined temperature threshold.

During this phase of normal operation, the heating stations 14a, 14b (and their associated pumps 16a, 16b), as well as the additional heating stations 42a, 42b (with their respective pumps 44a, 44b), are activated continuously and the connection pipes 22, 24, 38, 40 are closed, as is the service pipe 28. Thus, the main pipes 8a, 8b are heated locally so as to maintain at all points thereof a temperature of the fluids at above a predetermined temperature threshold.

In the preservation phase (FIG. 4B), the method provides for closing the secondary pipes 10 (by closing the valves 12) as well as the main pipes 8a, 8b both between the connecting pipes 22, 24 (by closing the valves 26a , 26b), and between the additional connection pipes 38, 40 (by closing the valves 46a, 46b).

The connection pipes 22, 24, 38 and 40 are on the other hand open so that the main pipes form a double circulation loop for the fluids transported (an upstream loop upstream of the upstream connection pipe 22, and a downstream loop circulation between the downstream connection pipe 24 and the additional connection pipe 38).

The heating stations 14a, 14b and the additional heating stations 42a, 42b are deactivated (as well as their associated pumps) and the upstream and downstream loops are depressurized by opening the valves 34 and 36 of the service line 28. This depressurization has for the purpose of preventing the formation of hydrates in the pipes of the upstream and downstream fluid circulation loops.

A treated fluid which does not freeze when cold is also injected into the main pipes from a tank of the surface installation via the main pipe 8a by actuating the pump 20a associated with the surface heating station 18a (which is deactivated). This treated fluid will purge all fluids from the fluid circulation loop (called “riser loop”) which is located downstream of the downstream loop by expelling these fluids towards the surface installation via the main pipe 8b.

Thus, during this preservation phase, any risk of deposit formation in the main pipes can be eliminated: in the upstream and downstream loops for circulation of fluids by depressurization, and in the riser loop by the presence of a treated fluid which does not freeze when cold.

The restart phase following a preservation phase takes place as follows.

The method of managing the heating of the fluids comprises, first of all (FIG. 4C), the activation of the surface heating station 18a so as to heat the treated fluid which will in turn heat the main pipes at the level of the riser loop. The heating stations 14a, 14b and 42a, 42b are also reactivated to heat the fluids circulating in the upstream and downstream fluid circulation loops. The depressurization of the upstream and downstream loops is stopped (by closing the valves 34 and 36 of the service line 28).

When the main lines 8a, 8b are hot, the injection of the treated fluid into the riser loop is stopped (FIG. 4D). The main conduits 8a, 8b are then reopened, while the connecting conduits 22, 24 and 38, 40 are closed so as to merge between them the upstream and downstream fluid circulation loops and the riser loop. The secondary conduits 10 can then be gradually opened (by opening the valves 12) so as to allow production to be restarted.

Finally, a fluid (typically methanol) is injected through the service line 28 into the connecting lines 22, 24 and 38, 40 to prevent the formation of hydrates in these lines.

In connection with FIG. 5, a description will now be given of an architecture of a network of submarine pipes 2-5 according to a fifth embodiment of the invention called a “hybrid loop”.

In this embodiment, the network 2-5 comprises a production pipe 8c connected to the surface installation (not shown in FIG. 5), a plurality of secondary pipes 10 connecting production wells 4 to the production pipe , and a service line 47 connected to the production line 8c downstream of the secondary lines 10.

Such a 2-5 network can be used for transporting fluids over long distances. In this case, the method according to the invention is similar to those described above, namely that it comprises the connection of the production line 8c to a heating station 14c of fluids positioned downstream of a connection with the supply line. service 47.

During normal operation, this heating station 14c (and its associated pump 16c) is activated to maintain the temperature of the fluids above a predetermined temperature threshold at any point in the network (the service pipe 47 being closed by closing of a valve 49 provided thereon).

In the preservation phase, the secondary pipes 10 are closed (by closing the associated valves 12) and the service pipe 47 is open. A treated fluid (typically gas oil) is injected from the surface installation into the production line 8c in order to purge the latter of the fluids that it contains before stopping the heating station 14c once the main line has been purged.

Finally, in the restart phase, the treated fluid circulating in the service line 47 is heated by a conventional heating system 47a (located in the surface installation) so as to heat the production line 8c by transmission. When the latter is sufficiently hot, the injection of the treated fluid is stopped and the secondary conduits 10 are gradually opened (by opening the valves 12) so as to allow production to be restarted.

Alternatively, the network of underwater pipes 2-5 according to this fifth embodiment can be used for heating at the bottom of the “riser” (ie at the bottom of a pipe used to connect the seabed to the installation. surface). In this case, the heating station 14c is activated only during the normal operating phases.

Still alternatively, the network of underwater pipes 25 according to this fifth embodiment can be used for transporting fluids over shorter distances but at very great depth. In this case, the network further comprises another heating station at the bottom of the riser which is also activated in the preservation phase.

In connection with FIGS. 6 to 9, various characteristics of the heating stations will now be described for the implementation of the method according to the invention.

These heating stations correspond to those described above in the various embodiments of the networks of underwater pipes.

As shown in Figure 6, the heating station 14a, 14b may include a conduit 48 which is spirally wound inside the heating station and which is heated (eg by electromagnetic induction). The footprint of these heating stations is thus small.

In the embodiment of Figure 6, the heating station 14a, 14b is connected directly to an underwater pipe

8a, 8b, for example by means of valves 50.

In the embodiment of FIG. 7, the heating station 14a, 14b is connected to an underwater pipe 8a, 8b, by means of a bypass pipe 52 (or "bypass" pipe) connected to the corresponding submarine pipe by valves 50. In addition, the submarine pipe is equipped with a bypass valve 54.

In the embodiment of FIG. 8, the submarine pipe 8a, 8b is connected to two heating stations 14a, 14b; 14'a, 14'b installed in series on the connection principle of FIG. 7 (via bypass pipes 52, 52 'and the use of bypass valves 54, 54 ⁷ ).

This embodiment thus provides for a redundancy of the heating stations in which each heating station is capable of providing on its own the desired heating of the fluids transported. Normally only one of these two heating stations is used or both are used at half power. If one of the heating stations is removed, the other station takes over.

In the variant embodiment of FIG. 9, the submarine pipe 8a, 8b is connected to two heating stations 14a, 14b; 14'a, 14'b installed in parallel with the presence upstream and downstream of the heating stations of devices 56 making it possible to ensure a switch of a scraper intended to scrape any deposits from the walls.

Claims (10)

1. Method for managing the heating of fluids circulating in a network of underwater pipes (2-1; 2-2; 2-3; 2-4; 2-5) providing a link between a surface installation (6) and at least one subsea production well (4), characterized in that it comprises the removable connection of at least one heating station (14a, 14b) of fluids to a subsea pipe by means of 'a bypass pipe (52) connected to the submarine pipe and the control of said heating station according to the operating mode of the pipe network. 2. The method of claim 1, wherein the network of subsea pipes comprises: two main conduits (8a, 8b) interconnected at the seabed and each connected to the surface installation (6) so as to form at least one fluid circulation loop; and a plurality of secondary conduits (10) connecting production wells (4) to the two secondary conduits; the method comprising connecting each main pipe to at least one heating station for fluids downstream of the secondary pipes, and activating the heating stations during normal operation of the pipe network to keep the temperature of the fluids above a predetermined temperature threshold at any point in the network. 3. Method according to claim 2, wherein, in the phase of preserving the network of pipes, the method comprises closing the secondary pipes, injecting into the main pipes a treated fluid to purge the main pipes of the fluids that it is. they contain, and stopping the heating stations once the main pipes have been purged. 4. The method of claim 3, wherein, in the restart phase of the pipe network following a preservation phase, the method comprises reactivating the heating stations by keeping the secondary pipes closed so as to heat the main pipes, then the heating. gradual reopening of secondary pipes to restart production. 5. The method of claim 2, wherein the network of underwater pipes further comprises two connecting pipes (22, 24) connecting the two main pipes (8a, 8b) to each other downstream of the heating stations (14a, 14b), the process comprising, during the preservation phase of the underwater pipeline network: the closing of the secondary pipes and the main pipes between the two connecting pipes with the opening of the latter, and the activation of the heating stations to maintain the temperature of the fluids above a predetermined temperature threshold at all points an upstream fluid circulation loop; and the injection of a treated fluid into the main conduits of a downstream fluid circulation loop to purge the fluids that it contains. 6. The method of claim 5, wherein, in the restart phase of the network of underwater pipes following a preservation phase, the method comprises: stopping the injection into the main conduits of the downstream fluid circulation loop of a treated fluid; the reopening of the main pipes between the connecting pipes; the closing of the two connecting conduits to merge the upstream and downstream fluid circulation loops together; injecting methanol into at least one of the connecting lines to prevent the formation of hydrates therein; and the gradual reopening of secondary lines to restart production. 7. The method of claim 5, wherein, in the phase of preserving the network of underwater pipelines, the method comprises stopping the heating stations and depressurizing the upstream fluid circulation loop to prevent the formation of. hydrates in this upstream loop. 8. The method of claim 2, wherein the network of subsea pipelines further comprises: two connection pipes (22, 24) connecting the two main pipes (8a, 8b) to each other downstream of the heating stations (14a, 14b); two additional heating stations (42a, 42b) connected to the main pipes downstream of the connecting pipes; and two additional connection pipes (38, 40) connecting the two main pipes to each other downstream of the additional heating stations; the process comprising, in the preservation phase: the closure of secondary lines; the closing of the main conduits between the two connecting conduits and between the two additional connecting conduits with the opening of the latter to form a double circulation loop of the transported fluids; deactivation of heating stations and additional heating stations and depressurization of the two fluid circulation loops to prevent hydrate formation therein; and injecting a treated fluid in the main conduits into a riser loop downstream of the two fluid circulation loops to purge the fluids therein. 9. The method of claim 8, wherein the method comprises, in the restart phase of the network of submarine pipes following a preservation phase: stopping the injection into the main pipes of the riser loop of a treated fluid; the reopening of the main pipes between the connecting pipes and between the additional connecting pipes; closing the connecting pipes and the additional connecting pipes to merge the two fluid circulation loops and the riser loop together; the injection of methanol into the connecting pipes and 5 additional connecting lines to prevent hydrate formation therein; and the gradual reopening of secondary lines to restart production. 10. The method of claim 1, wherein the network of subsea pipelines (2-5) comprises: a production line (8c) connected to the surface installation (6); a plurality of branch lines (10) connecting production wells (4) to the production line; and a service line (47) connected to the production line (8c) downstream of the secondary lines (10); the method comprising connecting the production line to at least one heating station (14c) for fluids downstream of a connection with the service line, and activating the heating station during normal operation of the network of pipes to keep the temperature of the fluids above a predetermined temperature threshold at any point in the network. 11. A method according to any one of claims 1 to 10, wherein at least one of the underwater pipes (8a, 8b) is connected to at least two heating stations (14a, 14b) installed in series or in parallel.