DK3083451T3

DK3083451T3 - Method for injecting fluids into an underwater installation

Info

Publication number: DK3083451T3
Application number: DK14830844.8T
Authority: DK
Inventors: Luc Riviere; Vincent Peyrony; Gabriel Beaudonnet; William Hudson
Original assignee: Total Sa
Priority date: 2013-12-19
Filing date: 2014-12-19
Publication date: 2018-09-03
Also published as: AU2014369554A1; AR099370A1; EP3083451A1; WO2015092331A1; FR3015446A1; AU2014369554B2; UY35897A; FR3015446B1; EP3083451B1

Description

DESCRIPTION

TECHNICAL FIELD

The invention relates to techniques for storing and injecting functional fluids into an underwater facility.

TECHNOLOGICAL BACKGROUND

These techniques are in particular usable for injecting chemical products, like for example demulsifiers, biocides, corrosion inhibitors, hydrate formation inhibitors, deposit inhibitors or again hydraulic control fluids on offshore sites for exploiting hydrocarbon deposits.

In the case of an underwater mining operation of hydrocarbon deposits, chemical products are transported as far as the wellheads and other underwater equipment by umbilical ducts from a platform, a vessel located on the surface or a facility located on land.

Because of the great depth of certain underwater deposits, capable of reaching beyond 3000 metres, and insofar as these facilities sometimes comprise satellite sites distributed over a wide area, transport of the functional fluids using umbilical ducts can lead to considerable costs of manufacture and maintenance because of the lengths and cross-sections of the umbilicals. Indeed, an umbilical duct generally comprises both a cabling system for supplying electricity to the underwater facility, ducts carrying hydraulic control fluids, ducts conveying chemical products, and cables for communication, control and power supply of the devices located in deep water.

Apart from a high cost of manufacture and maintenance, such umbilical ducts are subject to the environmental stresses of the sea bottoms, for example thermal stresses and pressure stresses, requiring regular surveillance.

Umbilical ducts also have to be connected to the facility, and require the presence of a platform or a vessel on the surface to ensure the injection and reception of the fluids. Furthermore, the storage, on a vessel, of chemical products like methanol, demulsifiers, biocides or products for preventing corrosion or the formation of deposits in the ducts of the facility, present a significant environmental risk.

Thus alternatives are sought to the umbilical ducts for conveying fluids, in particular chemical products, to an underwater facility.

Devices and methods of extraction and storage of hydrocarbons from underwater facilities have been proposed. For example, FR 2 776 274 Al and DE 25 38 419 Al propose underwater storage vessels comprising a deformable elastomer reservoir located at the bottom of the water, connected to an underwater facility on the one hand, and to a vessel located on the surface using an umbilical on the other hand. The document US 2012/0085276 Al also proposes an underwater storage vessel with deformable walls located on the seabed. However these documents do not propose any method for avoiding an umbilical duct connected to the surface to convey the functional fluids to the underwater facility, and propose no solution for the safe storage of these fluids at the bottom of the water for a duration of mining operation of several months. No method for the safe and controlled injection of these fluids is proposed.

Consequently, a method is sought for the efficient and safe storage and injection of functional fluids, such as chemical products, in underwater facilities from tanks located at the bottom of the water.

DESCRIPTION OF THE INVENTION

In order to respond to the problems described above, the present invention proposes a method for injecting fluid into an underwater facility having the characteristics of the Claim 1. The method comprises: - lowering a fluid-storage system to the bottom of the water, the fluid-storage system comprising at least one storage vessel with rigid walls containing a functional fluid; and - injecting at least a portion of the functional fluid into the underwater facility; and - raising at least one portion of the fluid-storage system back up to the surface, the portion comprising the storage vessel.

In particular this method has the advantage of not requiring an umbilical duct and platform or vessel on the surface to inject a functional fluid. This functional fluid is stored near the facility in a vessel with rigid walls held at the bottom of the water throughout the duration of fluid injection. The method is particularly advantageous for exploiting facilities having numerous satellite fields, in which the lengths of umbilical ducts required to connect the different wellheads can reach several tens of km, considerably increasing the mining operation costs.

The method also allows a fluid-storage vessel to be maintained throughout a duration of several months at the bottom of the water, the fluid-storage system comprising vessels with rigid walls, better resisting the stresses of the sea bottoms and the stresses of chemical compatibility with the functional fluids than elastomer vessels.

The invention can also comprise a plurality of fluid-storage vessels containing the same functional fluid. The use of at least two storage vessels containing the same functional fluid, i.e. a first vessel and a second vessel, allows continuous operation of the facility. Indeed, by only injecting the functional fluid from one fluid-storage vessel at a time, when the functional fluid from the first vessel is spent, the additional vessel can constitute a reserve of functional fluid ensuring continuous injection of the fluid in the facility while the first vessel is replenished.

The lowering and raising of the storage system can advantageously be carried out using a crane or any other lifting device from a platform or a vessel located on the surface.

The expression "functional fluid" can designate a gas as well as a liquid, for example hydrocarbons or a chemical product such as a demulsifier, biocide, corrosion inhibitor, hydrate formation inhibitor, deposits inhibitor or again a hydraulic control fluid.

Advantageously, the storage vessel can comprise a partition forming a mobile piston separating the functional fluid from the sea environment, and injection of the functional fluid can comprise a translation of the partition.

By only maintaining a single mobile partition between the sea environment and the functional fluid, the method as object of the invention can have the advantage of being capable of being produced in a hydrostatic configuration. Indeed, when the mobile partition is stopped, the pressure in the portion of the vessel containing the functional fluid can equal the pressure acting in the sea environment. In this way, it is possible to manufacture a fluid-storage vessel comprising lighter rigid walls, not requiring any resistance to pressure differences more than a few thousand hPa.

According to the invention, the storage system comprises a pump connected to the storage vessel by a first duct and to said underwater facility by a second duct, and injection of the functional fluid can comprise operation of the pump.

The use of a pump to cause the displacement of the mobile partition of the storage vessel can mean doing away with a mechanical actuator exerting pressure on the mobile partition of the fluid-storage vessel. The pump causes the displacement of the mobile partition and circulation of the functional fluid by creating a pressure difference between the sea environment and the functional fluid.

The use of a pump allows the vessel to be separated from the element actuating the displacement of the piston of the fluid-storage vessel. In particular, it is possible to provide on the storage system for several separate modules connected one to another. Thus, one module can comprise the pumps, while another module can comprise the fluid-storage vessels. The pumps have a duration of operation more than that of the use cycle of the fluid-storage vessels. They can remain at the bottom of the water for more than one year, while the fluid-storage vessels are advantageously raised to the surface when all the functional fluid they contain has been spent, for example after a few months.

The use of pumps calls for an additional refinement of implementation of the method. In particular, the storage system comprises an accumulation vessel connected to the pump and to the underwater facility, and comprises at least one valve over a portion of the third duct connecting the accumulation vessel to the underwater facility. The injection of the functional fluid comprises: - filling the accumulation vessel with a volume of functional fluid; and - injecting a portion of the volume into the underwater facility by opening the valve.

In this way, it is possible to control more finely the amount of functional fluid injected into the underwater facility, especially when the amounts to be injected are less than the volumes injected by actuation of the pumps. In this embodiment, the accumulation vessel can act as intermediate reservoir, maintained at a slightly higher pressure, typically more than one millibar to some ten bar, than the pressure of the underwater facility, and of which the contents can be injected into the underwater facility using precise control of the opening and closing of a valve.

According to one embodiment of the invention, the injection of the functional fluid can take place over a duration between one month and one year before raising said portion of the storage system back to the surface. A duration of more than one month has a considerable advantage in terms of the costs of maintenance and replacement of used vessels. Indeed, if the fluid-storage system and the vessels it contains are capable of resisting the stresses acting at the bottom of the water, the intervention of a platform or a vessel on the surface to raise the fluid-storage vessels or other modules of the system can be carried out less often.

The injection of functional fluid can be carried out continuously at a rate of some tens of litres per hour, for chemical products such as for example demulsifiers, corrosion inhibitors, hydrate formation inhibitors, deposit inhibitors. However, certain other products may not be injected continuously, like biocides that can be injected sporadically at a rate, for example, of around two hundred litres per hour, five hours per week.

Advantageously, a measuring system of the functional fluid contained in the storage vessel can be included.

In this way, it is possible to know the volume of functional fluid present in the fluid-storage vessel which allows its replacement or refilling to be anticipated. Thus it is also possible to ensure a control of the amount of functional fluid injected into the underwater facility.

According to one embodiment of the invention, the fluid-storage system can comprise at least one replenishing duct of the storage vessel, and the method can moreover comprise: - lower a replenishing vessel containing the functional fluid at the level of the replenishing duct, and - filling the storage vessel with the functional fluid from the replenishing vessel, and - raising the replenishing vessel back up to the surface.

In this way, it may no longer be necessary to raise the fluid-storage vessels back up to the surface. The use of a replenishing vessel lightens the structure to be handled from a platform or a vessel to refill the fluid-storage vessel.

According to one embodiment, the fluid-storage system can comprise at least one replenishing umbilical connected to the storage vessel on the one hand, and to a reservoir of functional fluid on the surface on the other hand, the replenishing umbilical performing a refilling of the storage vessel.

This embodiment makes it possible to maintain permanent control on the amount of functional fluid contained in the storage vessel. Refilling the storage vessel from the surface makes it possible to maintain the latter longer at the bottom of the water, and only to raise it to the surface for maintenance operations.

DESCRIPTION OF THE FIGURES

The method as object of the invention will be better understood on reading the following description of the embodiments presented for illustrative purposes, with no limitations, and by observing the drawing below wherein: - FIG. 1 is a schematic perspective representation of an underwater storage system near to a hydrocarbon production well in deep water; and - FIG. 2 is a top view schematic representation of a system of fluid storage and injection according to one embodiment; and - FIG. 3 is a top view schematic representation of a module comprising a fluid storage and injection vessel; and - FIG. 4 is a cross-section schematic representation of a fluid storage and injection vessel; and - FIG. 5 is a front view schematic representation of a portion of system of fluid storage and injection according to one embodiment; and

For reasons 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 of injecting fluid into an underwater facility comprises a first step, consisting in lowering a system of fluid-storage and injection to the bottom of the water. The objective of the method being to inject a functional fluid, the system of storage and injection comprises at least one storage vessel filled, initially, with a functional fluid. This fluid-storage vessel is connected by means of a duct to a facility. Typically, this facility consists of a hydrocarbon mining wellhead. However other facilities can benefit from the invention presented herewith.

Once the system is lowered and installed at the bottom of the water, a phase of mining operation can take place, during which the functional fluid contained in the storage vessel is injected, continuously or intermittently, into the facility. Different means can be implemented to inject the functional fluid. In particular it can be planned to use a pump, connecting the fluid-storage vessel to the facility. FIG. 1 represents one example of an underwater storage system near to a hydrocarbon production well in deep water. A wellhead 100 located at the bottom of the water is supplied by ducts 6 with functional fluid coming from a system of fluid storage and injection 1. This system of fluid storage and injection 1 is comprised among other things with storage vessels 21. The extracted hydrocarbons can typically be conveyed to the surface from the wellhead 100 by a duct 106.

Once the injection of functional fluid has been carried out, the injection is no longer required or when the fluid-storage vessel has been emptied of its contents, a final step consists in raising the system of storage or a portion of it including at least the fluid-storage vessel up to the surface

Now to be described in more detail are the different elements contributing to implementation of this method of injection of functional fluid.

In one particular embodiment of the invention represented in FIG. 2, the system of fluid storage and injection 1 comprises several modules 11. In this example, eight modules 11 can be seen each comprising a fluid-storage vessel 21-24 and four modules each comprising two pumps 5.

The arrangement of these different modules 11 can differ from that represented in FIG. 2, especially in order to approach the pumps 5 of the fluid-storage vessels 21-24, or to adapt to the configuration of the sea bottom near the facility 100. It can also happen that a module 11 only contains a single pump 5.

One example of module 11 is represented in FIG. 3, representing a storage vessel 21 provided with a connection element 70 to a duct. The module 11 comprises means of hitching 14 to a lifting device. These hitching means 14 can for example have the form of openings made in a metal armature, intended to receive a hook, a shackle or any other hitching system, for example to the cable of a crane or a winch.

Advantageously, the system of storage and injection 1 comprises at least two fluid-storage vessels for the same type of functional fluid 30, so as to be able to replace an empty storage vessel without having to interrupt the injection of said fluid into the facility 100.

The first ducts 7 connecting the fluid-storage vessels 21-24 to the pumps 5 are planned. The connection of these first ducts 7 is carried out using well known techniques, and can for example entail the intervention of a remotely controlled robot.

The second ducts 6 are provided to connect the pumps 5 to the underwater facility 100. The lengths of the first 7 and second 6 ducts are reduced in order to reduce the risks of damage to these ducts 6, 7. These ducts 6 and 7 can either be rigid type, or flexible type.

As represented in FIG. 2, one module 11 containing two pumps 5 comprises a collector 260 provided on an armature of the system of storage 1. The second duct 6 extends from the collector 260 as far as the underwater facility 100. The connection between the pump 5 and the collector 260 is made using an intermediate duct 60. This intermediate duct 60 can either be rigid type, or flexible type.

In this way, the system of storage 1 enables direct interaction with the elements of the underwater facility 100 to be reduced. The use of an intermediate duct 60 coupled with a collector 260 allows the raising to the surface for maintenance of a defective pump 5 without having to disconnect the second duct 6 of the facility 100. As represented in FIG. 2, an accumulation vessel 8 is provided, connected to the second duct 6 on the one hand, and to a third duct 16 on the other hand, with smaller cross-section, connecting the accumulation vessel 8 to the facility 100. A valve 9, for example a solenoid valve, is placed on the third duct 16.

In this way, the valve 9 being closed, the pump 5 is used initially to fill the accumulation vessel 8. This accumulation vessel 8 is capable of resisting a high external pressure, for example a pressure exceeding one hundred thousand hPa. Then, control of the flow rate of functional fluid 30 injected into the facility 100 is carried out by controlling the opening of the valve 9.

Injection of the functional fluid 30 is carried out normally by actuating a pump 5, thus creating a depression in the functional fluid 30 of the fluid-storage vessel 21-24 to which the pump 5 is connected. However, the flow rate of the functional fluid 30 injected is difficult to control and essentially depends on the capacity and operating mode of the pump 5. For applications requiring greater fineness in the control of the flow rate of the functional fluid 30 injected, the addition of the accumulation vessel 8 described above authorises injection of the functional fluid 30 with a low flow rate.

When the level of functional fluid 30 contained in a fluid-storage vessel 21-24 reaches a critical level or when the fluid is spent, three options are planned to replace the functional fluid missing from the storage vessel in question. A first option consists in raising the empty fluid-storage vessel 21-24 up to the surface using a crane or any other lifting device provided on a platform or a vessel. To do this, hitching means 14 are arranged on the four corners of a removable module of the system 1 as represented in FIGS. 2 and 3.

In this way, it is possible to ensure stability of the system of storage and injection 1 during handling by the lifting device. A second option consists in using a replenishing vessel 270 lowered by a lifting device such as, for example, a crane from a platform or a vessel. For small volumes, this replenishing vessel 270 can also be attached to a remotely controlled robot. This replenishing vessel 270 can contain a volume of functional fluid less than that of a fluid-storage vessel 21-24 and can serve to refill an empty storage vessel at least partially. As represented in FIG. 2, the replenishing vessel advantageously comprises a hitching system 271 to a receptacle 211 provided on the system of storage 1. The hitching system 271 advantageously fits into the receptacle 211, and ducts, not represented, enable the contents of the replenishing vessel 270 to be transferred to the fluid-storage vessel 21-24. It is possible to provide a receptacle 211 on each module comprising a fluid-storage vessel 21-24.

Such mean for refilling a fluid-storage vessel without raising it can turn out to be advantageous when the storage vessel in question is only present in a single example in the system of storage 1. It can also have the advantage of not requiring disconnection of the first ducts 7. A third option consists in deploying, from a replenishing vessel, a replenishing umbilical connecting to the receptacle 211. Replenishing with product is then carried out by directly transferring the product from the replenishing vessel to the at least partially empty fluid-storage vessel 21-24 through the replenishing umbilical. This method allows large volumes of products to be transferred. The replenishing umbilical has either a line dedicated to each product, or a single line common to all the products. In the latter case, this line can be emptied and cleaned between the replenishing of each product. FIG. 4 represents an example of fluid-storage vessel 20 containing a functional fluid 30. Different shapes can be planned for the storage vessel 20, a cylindrical shape being particularly advantageous. As represented in FIG. 4, the fluid-storage vessel 20 has a top surface 202 having orifices 203. This top surface 202 allows the sea environment 3 to penetrate into the storage vessel 20 as far as a mobile partition 40. The presence of such a rigidly connected perforated surface 202 of the fluid-storage vessel 20 in particular facilitates its handling by limiting the movement of the mobile partition 40, and facilitates the installation of a sensor 204 intended to measure the volume of functional fluid 30 present in the fluid-storage vessel 20.

Advantageously the sensor 204 can be a sonar type device, measuring the position of the mobile partition 40 in the fluid-storage vessel 20, thus enabling calculation of the volume of functional fluid 30 remaining.

Furthermore, the surface 202 comprises means of fixing 201 to an armature of the system of storage and injection 1. These means can for example be openings or notches provided to fit with elements with complementary shape on the system of storage 1.

The mobile partition 40 advantageously has sufficient height to ensure risk-free translation of inclination of the partition 40 in the storage vessel 20. For example, a height of fifty centimetres satisfies this criterion. The height of the mobile partition 40 can be smaller. For example, when the storage vessel has a cylindrical shape, the mobile partition 40 has less risk of suffering buttressing by sliding in the vessel. A height of at least fifty centimetres for the mobile partition 40 can then be provided.

The partition 40 comprises at least a system of guiding 41. These systems of guiding 41 have a shape that fits closely with that of the cross-section of the fluid-storage vessel 20. In FIG. 4, the system of guiding 41 represented is a seal, in contact with the wall of the storage vessel 20.

The system of guiding 41 favours a rectilinear displacement of the partition 40 in the storage vessel 20.

The mobile partition 40 comprises at least one seal 42, in a material compatible with the nature of the functional fluid 30 stored in the vessel 20. This seal can play the part of the system of guiding.

This seal 42 prevents the functional fluid 30 from mixing with the sea environment 3 despite the displacement of the partition 40. Thus it ensures the tightness of the storage vessel 20, and efficiently separates the sea environment 3 from the functional fluid 30.

The fluid-storage vessel 20 represented in FIG. 4 operates in a quasi-hydrostatic configuration, i.e. the pressure in the functional fluid 30 is equal to or very close to that of the sea environment 3. The pressure difference between the two environments does not exceed, for example, a thousand hPa.

As represented in FIG. 4, the fluid-storage vessel 20 comprises, in its lower part, an opening and a connection element 70. As represented in FIG. 5, the connection 70 is intended to be connected to a duct 71. By placing such an opening in the lower part of the fluid-storage vessel 20, the functional fluid 30 can escape from the storage vessel 20 by the connection element 70 until the mobile partition 40 comes to stop against the bottom surface of the fluid-storage vessel 20. FIG. 5 represents schematically in front view an embodiment of the system of fluid storage and injection 1, in particular comprising a module 11 comprising a rigid armature fitted with means of attaching 14 to a lifting device for raising at least a part of the system 1. On this schematic representation, the system has two rows of fluid-storage vessels 20, the latter each being fitted with means of fixing 201 one to another and to the armature of the system of storage 1. The module 11 of FIG. 4 comprises two removable storage vessels 20.

The armature of the module 11 is configured to facilitate the insertion of the fluid-storage vessels 20 on a system of storage 1 and to ensure the stability of the storage vessels 20 in the module 11.

On its armature the module 11 comprises ducts 71, required for the transfers of fluid, connected to a distributor 710.

This distributor 710 allows switching between the injection of the functional fluid 30 from a replenishing vessel 270 by the receptacle 211, and the injection of the functional fluid 30 from a storage vessel 20 to the facility 100.

The invention is not limited to the embodiments presented above as examples and can comprise other equivalent embodiments.

For example, the system of storage 1 may only comprise a single fluid-storage vessel 20 for a given type of functional fluid 30. The armature 11 can also be an integral part of such a fluid-storage vessel 20.

The storage vessels can be held at the bottom of the water in the event of interruption of mining of a deposit, to then be reused rapidly when reworking the mining operation.

The shape of the fluid-storage vessels need not be cylindrical, especially in order to optimise the storage of the vessels, to optimise use of the space within a module 11 and to facilitate the installation of the storage vessels at the bottom of the water.

The guiding and sealing systems described above can have other forms than the seals. Other means can ensure the functions of guiding the mobile partition sliding in the storage vessel and maintaining tightness between the functional fluid of the storage vessel and the sea environment. For example a metal ring with diameter slightly less than the diameter of the vessel can be provided. Several wheels or pads, for example three or four wheels, distributed along the edge of the piston can also fulfil these functions.

Claims

A method of injecting fluid into an underwater installation (100), the method comprising: immersing a fluid storage system (1) on the bottom of the water, wherein the fluid storage system comprises at least a rigid wall storage tank (20-24), and which contains a utility fluid (30), wherein the storage system (1) comprises a pump (5) which is connected via a first conduit (7) to the storage container (20-24) and via a second conduit (6) to the subsea installation ( 100), wherein the storage system (1) further comprises a collection vessel (8) connected to the pump (5) and to the subsea installation (100), and at least a valve (9) on a section of a third conduit (16) which connecting the collection vessel to the underwater installation; filling the collection vessel (8), by closed valve (9), with a useful fluid (30) when the pump (5) is switched on; and injecting a portion of this volume into the subsea installation (100) upon opening the valve (9); and lifting at least a portion of the fluid storage system to the surface, said portion including the storage container.

A method according to claim 1, wherein the storage container (20-24) comprises a partition (40) forming a movable piston separating the utility fluid (30) from the marine environment (3), and wherein the injection of the utility fluid comprises a displacement of the partition (40).

A method according to any one of the preceding claims, wherein the injection of the utility fluid takes place for a period of one month and one year before the part of the storage system is brought back to the surface.

Method according to any one of the preceding claims, characterized in that the injection of the utility fluid comprises: measuring a utility fluid volume (30) contained in the storage container (20-24).

A method according to any one of the preceding claims, wherein the fluid storage system (1) comprises at least one supply conduit for the storage container (20-24), the method further comprising: immersing a supply container (270) containing the utility fluid (30), to the height of the supply line; filling the storage container (20-24) with the utility fluid from the supply container; and lifting the supply container to the surface.

A method according to any one of the preceding claims, wherein the fluid storage system (1) comprises at least one supply line, which is partly connected to the storage container (20-24) and partly to a useful fluid reservoir on the surface, the method comprising: filling the storage tank using the supply line.