FR3015446A1 - METHOD FOR INJECTING FLUIDS IN AN UNDERWATER INSTALLATION - Google Patents

Abstract

The invention relates to a method for injecting fluid into an underwater installation. A fluid storage system comprising at least one rigid walled storage vessel containing a utility fluid is lowered to the bottom of the water. At least a portion of the utility fluid is injected into the subsea installation. After a period of operation, the fluid storage system, or a part thereof, including the storage tank, is raised to the surface.

Description

FIELD OF THE INVENTION The invention relates to techniques for storing and injecting utility fluids in subsea installations. BACKGROUND ART These techniques can be used in particular for injecting chemicals, such as, for example, demulsifiers, biocides, corrosion inhibitors, hydrate-formation inhibitors, deposit inhibitors or control hydraulic fluids on offshore sites for the exploitation of hydrocarbon deposits. In the case of underwater exploitation of a hydrocarbon pool, chemicals are transported to wellheads and other subsea equipment by umbilical conduits from a platform, surface vessel or well an installation located on the ground. Due to the considerable depth of certain submarine deposits, which can go beyond 3000 meters, and to the extent that these installations sometimes include satellite sites spread over a large area, the transport of utilitarian fluids by means of umbilical conduits can cause significant manufacturing and maintenance costs because of the lengths and sections of the umbilicals. Indeed, an umbilical duct generally comprises both a wiring system for the power supply of the subsea installation, control hydraulic fluid flow conduits, chemical delivery ducts, and also communication, control and power supply cables for deepwater equipment. In addition to a cost of manufacture and important maintenance, such umbilical ducts are subject to the environmental constraints of the seabed, for example thermal stresses and pressure constraints, calling for regular monitoring. The umbilical ducts must also be connected to the installation, and require the presence of a platform or a ship on the surface to ensure the injection and reception of fluids. In addition, the storage on a ship of chemicals such as methanol, demulsifiers, biocides or products preventing corrosion or the formation of deposits in the ducts of the installation, presents a significant environmental risk.

Therefore, alternatives to umbilical ducts are being sought to carry fluids, including chemicals, into an underwater installation. Devices and methods for extracting and storing hydrocarbons from subsea installations have been proposed. For example, FR 2 776 274 A1 and DE 25 38 419 A1 propose submarine storage tanks comprising a deformable elastomer reservoir located at the bottom of the water, connected to an underwater installation on the one hand, and to a ship located on the surface using an umbilical on the other hand. However, these documents do not propose any method to dispense with a umbilical duct connected to the surface to convey utilitarian fluids to the underwater installation, and do not propose any solution allowing safe storage of these fluids at the bottom of the tank. water for an operating period of several months. No method for safe and controlled injection of these fluids is proposed. Therefore, a method is sought for the efficient and safe storage and injection of utility fluids, such as chemicals, into subsea installations from trays at the bottom of the water.

SUMMARY OF THE INVENTION In order to meet the problems described above, the present invention proposes a method for injecting fluid into an underwater installation, the method comprising: - lowering a fluid storage system to the bottom of the water the fluid storage system comprising at least one rigid-walled storage bin containing a utility fluid; and injecting at least a portion of the utility fluid into the subsea installation; and - going up on the surface of at least a part of the fluid storage system, the part comprising the storage tank.

This method has the particular advantage of not requiring umbilical conduit and platform or ship surface to inject a utility fluid. This utility fluid is stored near the plant in a rigid-walled tank maintained at the bottom of the water for the duration of the fluid injection. The method is particularly advantageous for the operation of installations having many satellite fields, in which the lengths of umbilical ducts necessary for connecting the different wellheads can reach several tens of km, considerably increasing the operating costs. The method also maintains a fluid storage tank for a period of several months at the bottom of the water, the fluid storage system comprising rigid walled tanks, better resistant to seabed stresses and compatibility constraints. chemical with utilitarian fluids as elastomer bins. The invention may also include a plurality of fluid storage bins containing the same utility fluid. The use of at least two storage bins containing the same utility fluid, namely a first bin and a second bin, allows continuous operation of the installation. Indeed, by injecting the fluid utility of only one fluid storage tank at a time, when the utilitarian fluid of the first tank is exhausted, the additional tray can be a reserve of utility fluid ensuring the continuous injection of fluid in the installation while the first bin is refilled. The descent and the ascent of the storage system can advantageously be carried out by means of a crane or any other lifting device from a platform or a ship located on the surface. The term "utility fluid" can mean both a gas and a liquid, for example hydrocarbons or a chemical such as a demulsifier, a biocide, a corrosion inhibitor, a hydrate-formation inhibitor, a deposition inhibitor or hydraulic control fluid. Advantageously, the storage tank may comprise a movable piston partition separating the utility fluid from the marine environment, and the injection of the utility fluid may comprise a translation of the partition.

By maintaining only a simple movable partition between the marine environment and the utilitarian fluid, the method which is the subject of the invention can have the advantage of being able to be carried out in a hydrostatic configuration. Indeed, when the moving partition is stopped, the pressure in the portion of the tray containing the utility fluid may be equal to the pressure prevailing in the marine environment. In this way, it is possible to manufacture a fluid storage tank comprising lighter rigid walls, not requiring resistance to pressure differences greater than a few thousand hPa. According to an advantageous embodiment, the storage system may comprise a pump connected to the storage tank by a first conduit and to said subsea installation by a second conduit, and the injection of the commercial fluid may comprise the operation of the pump. The use of a pump to cause the displacement of the moving partition of the storage tank can overcome a mechanical actuator exerting pressure on the movable partition of the fluid storage tank. The pump causes displacement of the movable partition and the circulation of the utility fluid by creating a pressure difference between the marine environment and the utility fluid. The use of a pump makes it possible to separate from the tank the element actuating the movement of the piston of the fluid storage tank. In particular, it is possible to provide on the storage system several independent modules connected to each other. Thus, one module may include the pumps, while another module may include the fluid storage bins. The pumps have a longer operating life than the cycle of use of the fluid storage bins. They can remain at the bottom of the water for more than a year, while the fluid storage tanks are advantageously raised to the surface when all the utilitarian fluid they contain has been exhausted, for example after a few months . The use of pumps may call for further refinement of the implementation of the process. In particular, the storage system may comprise an accumulation tank connected to the pump and to the subsea installation, and may comprise at least one valve on a portion of the third conduit connecting the accumulation tank to the installation under -Marine. The injection of the utility fluid may include: - filling the accumulation tank with a volume of utility fluid; and - inject a part of the volume into the underwater installation by opening the valve. In this way, it is possible to control more finely the amount of utility fluid injected into the subsea installation, especially when the quantities to be injected are lower than the volumes injected by the actuation of the pumps. In this embodiment, the accumulation tank can serve as an intermediate reservoir, maintained at a slightly higher pressure, typically greater than one millibar to ten bars, at the pressure of the underwater installation, and whose contents can be injected into the underwater installation by means of precise control of the opening and closing of a valve.

According to one embodiment of the invention, the injection of the utility fluid can take place over a period of between one month and one year before the surface rise of said portion of the storage system. More than a month is a significant advantage in terms of maintenance costs and replacement of used bins. Indeed, if the fluid storage system and the bins it contains are able to withstand the stresses on the bottom of the water, the intervention of a platform or a ship on the surface to go upstream. fluid storage bins or other system modules, can be done with less frequency. The injection of utility fluid can be carried out continuously at a rate of a few tens of liters per hour, for chemicals such as, for example demulsifiers, corrosion inhibitors, hydrate formation inhibitors, inhibitors of deposits. On the other hand, some other products may not be injected continuously, such as biocides that may be sporadically injected at, for example, about two hundred liters per hour, five hours per week.

Advantageously, a system for measuring the utility fluid contained in the storage bin may be included. In this way, it is possible to know the volume of utility fluid present in the fluid storage tank which allows to anticipate a replacement or filling of the latter. It is also possible to ensure control of the amount of utility fluid injected into the subsea installation.

According to one embodiment of the invention, the fluid storage system may comprise at least one refueling pipe of the storage tank, and the method may furthermore comprise: - lowering a refueling tank containing utility fluid at the level of refueling line, and - fill the storage tank with the commercial fluid from the refueling tank, and - go up to the surface of the refueling tank. In this way, it may no longer be necessary to raise the fluid storage bins to the surface. The use of a refueling tank makes it possible to lighten the structure to be handled from a platform or a ship to fill the fluid storage tank. According to one embodiment, the fluid storage system may comprise at least one refueling umbilical connected to the storage tank on the one hand, and a surface utility fluid reservoir on the other hand, the refueling umbilical carrying out a filling of the storage bin. This embodiment makes it possible to maintain permanent control over the quantity of utility fluid contained in the storage bin. A filling of the storage tank from the surface keeps the latter longer for the bottom of the water, and up to the surface only for maintenance operations.

DESCRIPTION OF THE FIGURES The method which is the subject of the invention will be better understood on reading the following description of exemplary embodiments presented for illustrative purposes, in no way limiting, and on the observation of the following drawings in which: Figure 1 is a schematic perspective representation of a submarine storage system near a deep water hydrocarbon production well; and FIG. 2 is a diagrammatic representation, seen from above, of a fluid storage and injection system according to one embodiment; and - Figure 3 is a schematic representation in top view of a module comprising a storage tank and fluid injection; and - Figure 4 is a schematic sectional representation of a storage tank and fluid injection; and FIG. 5 is a schematic front view of a portion of a fluid storage and injection system according to one embodiment. For the sake of clarity, the dimensions of the various elements shown in these figures are not necessarily in proportion to their actual dimensions. In the figures, identical references correspond to identical elements.

DETAILED DESCRIPTION According to the invention, a method for injecting fluid into an underwater installation comprises a first step, consisting in lowering a system for storing and injecting fluid at the bottom of the water. The objective of the method being to inject a utility fluid, the storage and injection system comprises at least one storage tank filled initially with a utility fluid. This fluid storage tank is connected via a conduit to an installation. Typically, this installation consists of a hydrocarbon exploitation well head. However other facilities can benefit from the invention presented here.

Once the system is lowered and installed at the bottom of the water, an operating phase can take place, during which the utility fluid contained in the storage tank is injected, continuously or intermittently, into the installation. Various means can be implemented for injecting the utility fluid. It may in particular be envisaged to use a pump, connecting the fluid storage tank to the installation.

Figure 1 shows an example of a submarine storage system near a deep water hydrocarbon production well. A well head 100 located at the bottom of the water is supplied by conduits 6 of utility fluid from a fluid storage and injection system 1. This fluid storage and injection system 1 comprises, among other things, storage tanks. storage 21. The extracted hydrocarbons can typically be conveyed to the surface from the wellhead 100 via a conduit 106. Once the injection of the utility fluid has been achieved, that the injection is no longer necessary or when the tray fluid storage has been emptied of its contents, a final step is to go up to the surface of the storage system or a part thereof including at least the fluid storage tank. It will now be described in more detail the various elements involved in the implementation of this utility fluid injection method. In a particular embodiment of the invention shown in FIG. 2, the fluid storage and injection system 1 comprises several modules 11. In this example, there are eight modules 11 each comprising a fluid storage tank 21-24. , and four modules each comprising two pumps 5. The arrangement of these different modules 11 may differ from that shown in FIG. 2, particularly with a view to bringing the pumps 5 closer to the fluid storage tanks 21-24, or to adapt to the configuration of the seabed near the installation 100. It is also possible that a module 11 contains only one pump 5. An example of module 11 is shown in Figure 3, showing a storage tank 21 provided with a connecting member 70 to a conduit. The module 11 comprises attachment means 14 to a lifting device. These attachment means 14 may for example be in the form of openings made in a metal frame, intended to receive a hook, a carabiner or other attachment system, for example the cable of a crane or a winch. Advantageously, the storage and injection system 1 comprises at least two fluid storage tanks for the same type of utility fluid 30, so as to be able to replace an empty storage tank without having to interrupt the injection of said fluid into the storage tank. 100. First conduits 7 connecting the fluid storage tanks 21-24 to the pumps 5 are provided. The connection of these first conduits 7 is carried out by well-known techniques, and may for example involve a remote-controlled robot.

Second ducts 6 are provided for connecting the pumps 5 to the subsea installation 100. The lengths of the first 7 and second 6 ducts are reduced so as to reduce the risk of damage to these ducts 6, 7. and 7 can be either rigid type or flexible type.

As shown in FIG. 2, a module 11 containing two pumps 5 comprises a collector 260 provided on an armature of the storage system 1. The second duct 6 extends from the collector 260 to the subsea installation 100. The connection between the pump 5 and the manifold 260 is effected by means of an intermediate duct 60. This intermediate duct 60 can be either of rigid type or of flexible type.

In this way, the storage system 1 makes it possible to reduce the direct interaction with the elements of the subsea installation 100. The use of an intermediate duct 60 coupled to a collector 260 makes it possible to go up to the surface for maintenance a pump 5 defective without having to disconnect the second conduit 6 of the installation 100. As shown in Figure 2, it is possible to provide an accumulation tank 8, connected to the second conduit 6 on the one hand, and a third led 16 on the other hand, of smaller section, connecting the accumulation tank 8 to the installation 100. A valve 9, for example a solenoid valve, is placed on the third conduit 16. In this way, the valve 9 being closed, the pump 5 can initially fill the accumulation tank 8. This accumulation tank 8 is able to withstand a high external pressure, for example a pressure exceeding one hundred thousand hPa. Then, the control of the flow of utility fluid 30 injected into the installation 100 can be carried out by controlling the opening of the valve 9. The injection of the utility fluid 30 is usually carried out by actuating a pump 5 , thereby creating a depression in the utility fluid 30 of the fluid storage tank 21-24 to which the pump 5 is connected. However, the injected utility fluid flow 30 is difficult to control and depends essentially on the power and operating mode of the pump 5. For applications requiring greater finesse in the control of the injected utility fluid flow 30, the addition accumulation tank 8 described above allows the injection of utility fluid 30 with a low flow rate.

When the level of utility fluid 30 in a fluid storage tank 21-24 reaches a critical level or when the fluid is exhausted, three options are considered to replace the missing utility fluid in the storage bin in question.

A first possibility is to raise the empty fluid storage tank 21-24 to the surface using a crane or other lifting device provided on a platform or a ship. To do this, the attachment means 14 are arranged on the four corners of a removable module of the system 1 as shown in Figures 2 and 3. In this way, it is possible to ensure stability of the storage system and injection 1 during handling by the lifting device. A second possibility is to use a refueling tank 270 lowered by a lifting device such as, for example, a crane from a platform or a ship. For small volumes, this refueling tank 270 can also be attached to a remote controlled robot. This refueling tank 270 may contain a volume of utility fluid less than that of a fluid storage tank 21-24, and may be used to at least partially fill an empty storage bin. As shown in FIG. 2, the refueling tank advantageously comprises an attachment system 271 to a receptacle 211 provided on the storage system 1. The attachment system 271 advantageously fits into the receptacle 211, and ducts, not shown, allow to transfer the contents of the tank 270 to the fluid storage tank 21-24. It is possible to provide a receptacle 211 on each module comprising a fluid storage tank 21-24. Such a means for filling a fluid storage tank without reassembly can be advantageous when the storage tank in question is present in a single copy in the storage system 1. It can also have the advantage not to require a disconnection of the first ducts 7. A third possibility is to deploy, from a supply ship, a supply umbilical connecting to the receptacle 211. The supply of product is then achieved by directly transferring the product from the ship of refueling to the at least partially empty fluid storage tank 21-24 via the supply umbilical. This method allows the transfer of large volumes of products. The supply umbilical has either a line dedicated to each product, or a single line common to all products. In the latter case, this line can be emptied and cleaned between the refueling of each product.

FIG. 4 represents an example of a fluid storage tank 20 containing a utility fluid 30. Various forms can be envisaged for the storage tank 20, a cylindrical shape being particularly advantageous. As shown in FIG. 4, the fluid storage tank 20 has an upper surface 202 having orifices 203.This upper surface 202 allows the marine medium 3 to enter the storage tank 20 to a moving partition 40. The presence of such a perforated surface 202 integral with the fluid storage tank 20 makes it possible in particular to facilitate its handling by limiting the movement of the movable partition 40, and facilitates the installation of a sensor 204 intended to measure the volume of fluid utility 30 present in the fluid storage bin 20.

The sensor 204 may advantageously be a sonar-type device, measuring the position of the moving partition 40 in the fluid storage tank 20, thus making it possible to deduce the volume of the remaining utility fluid 30. Furthermore, the surface 202 comprises fastening means 201 to an armature of the storage and injection system 1. These means may for example be openings 20 or notches provided to fit onto elements of complementary shape on the system of storage. storage 1. The movable partition 40 advantageously has a height sufficient to ensure a translation without risk of inclination of the partition 40 in the storage bin 20. For example, a height of fifty centimeters meets this criterion. The height of the movable partition 40 may be smaller. For example, when the storage bin has a cylindrical shape, the movable partition 40 is less likely to be arched by sliding in the tray. A height of less than forty centimeters for the movable partition 40 can then be provided. The partition 40 comprises at least one guide system 41. These guide systems 41 have a shape that matches that of the cross section of the fluid storage tank 20. In FIG. 4, the guide system 41 shown is a seal in contact with the wall of the storage tank 20. The guide system 41 facilitates a rectilinear movement of the partition 40 in the storage bin 20.

The movable partition 40 comprises at least one seal 42, a material compatible with the nature of the utility fluid 30 stored in the tray 20. This seal can act as a guide system. This seal 42 prevents the utility fluid 30 from mixing with the marine environment 3 despite the displacement of the partition 40. It thus seals the storage tank 20, and effectively separates the marine medium 3 from the commercial fluid 30 The fluid storage tank 20 shown in FIG. 4 operates in a quasi-hydrostatic configuration, i.e. the pressure in the utility fluid 30 is equal to or close to that of the marine environment 3. The difference pressure between the two media does not exceed, for example, the thousand hPa.

As shown in FIG. 4, the fluid storage tank 20 comprises, in its lower part, an opening and a connecting element 70. As shown in FIG. 5, the connection 70 is intended to be connected to a conduit 71 By placing such an opening in the lower portion of the fluid storage tank 20, the utility fluid 30 can escape from the storage bin 20 through the connecting member 70 until the movable partition 40 abuts. against the lower surface of the fluid storage tank 20. FIG. 5 is a schematic front view of an exemplary embodiment of the fluid storage and injection system 1, in particular comprising a module 11 comprising a rigid reinforcement provided with means for dispensing fluid. 14 attaches to a lifting device for lifting at least a portion of the system 1. In this schematic representation, the system comprises two rows of fluid storage tanks 20, the latter being mu each of fastening means 201 between them and the frame 11 of the storage system 1. The module 11 of Figure 4 thus comprises two removable storage bins 20.

The armature of the module 11 is configured to facilitate the insertion of the fluid storage tanks 20 on the storage system 1 and ensure the stability of the storage bins 20 in the module 11. The module 11 comprises on its frame the ducts 71 , required for fluid transfers, connected to a distributor 710. This distributor 710 is used to switch between the injection of the utility fluid 30 from a refueling tank 270 through the receptacle 211, and the injection of the utility fluid 30 from a tank The invention is not limited to the embodiments exemplified above by way of example and may comprise other equivalent embodiments. For example, the storage system 1 may include only one fluid storage bin 20 for a given type of utility fluid. The armature 11 can also be an integral part of such a fluid storage tank 20. Although they have been described as providing a function of utility fluid injection 30, the fluid storage tanks 20 can also be envisaged. for fluid recovery purposes in order to store it and then return it to the surface. Alternatively, the storage bins can be kept at the bottom of the water in case of interruption of the exploitation of a deposit, and then be reused quickly during a resumption of operation.

The shape of the fluid storage tanks may not be cylindrical, in particular with a view to optimizing the storage of the bins, to optimize the use of space within a module 11 and to facilitate the installation of the bins. storage at the bottom of the water. The guiding and sealing systems described above may be in other forms than joints. Other means can provide the functions of guiding the sliding mobile partition in the storage tank and maintain a seal between the utility fluid of the storage tank and the marine environment. For example a metal ring diameter slightly smaller than the diameter of the tray can be provided. Several rollers or pads, for example three or four wheels, distributed along the edge of the piston can also fulfill these functions.

Claims (8)

REVENDICATIONS1. A method of injecting fluid into an underwater installation (100), the method comprising: - lowering a fluid storage system (1) to the bottom of the water, the fluid storage system comprising at least one tank of rigid wall storage (20-24) containing a utility fluid (30); and injecting at least a portion of the utility fluid into the subsea installation (100); and - surfacing at least a portion of the fluid storage system, said portion comprising the storage tank. The method of claim 1, wherein the storage bin (20-24) comprises a movable piston partition (40) separating the utility fluid (30) from the marine environment (3), and wherein the injection of the fluid utility includes a translation of said partition (40). 3. Method according to one of claims 1 or 2, wherein the storage system (1) comprises a pump (5) connected to the storage tank (20-24) by a first conduit (7) and said installation under -marine (100) by a second conduit (6), and wherein the injection of the utility fluid comprises the operation of said pump (5). 4. Method according to one of the preceding claims, wherein the fluid storage system (1) comprises an accumulation tank (8) connected to the pump (5) and the underwater installation (100), and comprises at least one valve (9) on a portion of third conduit (16) connecting the accumulation tank to the underwater installation, and wherein the injection of the utility fluid comprises: - filling the accumulation tank (8) with a volume of utility fluid (30); and injecting a portion of said volume into the underwater installation (100) by opening said valve (9). 5. Method according to any one of the preceding claims, wherein the injection of the utilitarian fluid takes place over a period of between one month and one year before raising the surface of said portion of the storage system. 6. Method according to any one of the preceding claims, characterized in that the injection of the utility fluid comprises: - measuring a volume of utility fluid (30) contained in the storage tank (20-24). 7. A method according to any one of the preceding claims, wherein the fluid storage system (1) comprises at least one supply line of the storage tank (20-24), the method further comprising: - lowering a tank refueling device (270) containing utility fluid (30) at the refueling line; - Fill the storage tank (20-24) with the utility fluid from the refill tray; and - go back to the surface of the refueling tank. A method according to any one of the preceding claims, wherein the fluid storage system (1) comprises at least one supply umbilical connected to the storage bin (20-24) on the one hand, and a storage tank utility fluid on the other hand, the supply umbilical filling the storage bin.