WO2020038703A1

WO2020038703A1 - A method of supplying injection fluid to a subsea facility

Info

Publication number: WO2020038703A1
Application number: PCT/EP2019/070864
Authority: WO
Inventors: Julie LUND; Marius BJØRN
Original assignee: National Oilwell Varco Denmark I/S
Priority date: 2018-08-20
Filing date: 2019-08-02
Publication date: 2020-02-27
Also published as: EP3841270A1; BR112021003148A2; EP3841270B1; CA3107074A1; AU2019324447A1; BR112021003148A8; US20210310324A1

Abstract

The present invention relates to a method of supplying injection fluid to a subsea facility, the method comprises the step of arranging a storage container (12) at a first subsea location, supplying the storage container with injection fluid from a surface facility (14), moving the storage container to a second subsea location and supplying the injection fluid from the storage container at said second subsea location to the subsea facility, wherein the second subsea location is closer to the seabed (3) than the first subsea location. Preferably the storage container at the second subsea location is supported by the seabed.

Description

A METHOD OF SUPPLYING INJECTION FLUID TO A SUBSEA FACILITY

TECHNICAL FIELD

The present invention generally relates to subsea supplying of injection fluids and specifically comprises a method of supplying an injection fluid to a subsea facility, such as a petroleum production subsea facility or a drilling facility.

BACKGROUND Subsea drilling and petroleum production activity often require the use of injection fluids, such as mud or chemicals at or near the seabed. Historically, such injection fluid has been supplied to the point of injection via hoses, tubes or pipes bundled into "umbilicals" to supply the injection fluid from nearby surface facilities e.g. from a vessel to the respective points of injection. Longer offsets, remote locations and deep-water subsea facilities contribute to make this umbilical solution undesirable, difficult and expensive.

It has been suggested to install storage container with injection fluid at the seabed nearby the point of injection. Thereby much shorter injection pipes are required for the injection fluid injection. Subsea installed storage containers offer great potential benefits both for continuous and intermittent injection.

However, the cost of filling the containers may offset these benefits, thus the cost and risk associated with filling should be minimized in order to optimise the benefit.

Currently three approaches are pursued for filling of flexible reservoirs: Filling approach A: A filling pipe is lowered from a surface vessel to the subsea- installed container to be filled. On large water depths, this requires a long and expensive feed pipe, which may be complicated to operate. The large dead volume in the pipe is generally undesired and may in particular be difficult when smaller container for e.g. descaler or biocides are to be filled due to increased risk of overfilling. Filling approach B: The storage container is recovered to the deck of the surface vessel, where the storage container is replenished. The main problems related to this approach are that the crane and storage container should be dimensioned to the lifting operation and that the transition of the storage container through the turbulent water zone i.e. the splash zone may be difficult in particular where the storage container in not completely filled and/or where the storage container is large. This method in particular limits the size of the storage unit, i.e. volume and weight per tank is limited by crane and moonpool capacity. Moreover, many small tanks may increase the number or lifting operations, which will make the method more complicated and increase the cost. Filling approach C: The storage container can be connected to a host by a trickle line. This method requires no cranes and is suitable for larger volumes. Flowever, the method may also require long lines and there is a risk of not having the storage volume required to ensure a continuing production. The host may be a floating or rigid facility comprising one or more tanks with injection fluid. This filling approach could be combined with Filling approach A and/or B.

WO2014/165765 discloses a method of transporting payloads between a sea surface and a seafloor that includes providing a structure having at least one buoyancy tank, and changing a volume of buoyancy material within the at least one buoyancy tank. An arrangement of buoyancy tanks may be incorporated into the barge-like structure, such that when the buoyancy tank is empty (air filled), the entire structure and the payload is able to float on the surface of the water similar to a barge. DISCLOSURE OF THE INVENTION

An object of the invention is to provide a method of supplying an injection fluid to a subsea facility, which at least partially alleviate at least one of the above-discussed problems. In an embodiment, it is an object of the invention is to provide method of supplying an injection fluid to a subsea facility, which mitigates the problems related to large dead volumes in the hose.

In an embodiment, it is an object of the invention is to provide method of supplying an injection fluid to a subsea facility, which enables relatively simple refilling of storage containers, and preferably even large storage containers.

In an embodiment, it is an object of the invention is to provide method of supplying an injection fluid to a subsea facility, which is highly suitable for fluid injection at relative deep water, and where the filling and/or refilling of the storage container(s) is relatively simple and cost effective. In an embodiment, it is an object of the invention is to provide method of supplying an injection fluid to a subsea facility, where the filling and/or refilling of the storage container(s) is relatively simple with low risk of damaging equipment even where the storage container is relatively large.

These and other objects have been solved by the invention as defined in the claims and as described herein below.

In one aspect the invention relates to a method of supplying injection fluid to a subsea facility, the method comprises the step of arranging a storage container at a first subsea location, supplying the storage container with injection fluid from a surface facility, moving the storage container to a second subsea location and supplying the injection fluid from the storage container at said second subsea location to the subsea facility, wherein the second subsea location is closer to the seabed than the first subsea location. Preferably the storage container at the second subsea location is supported by the seabed.

The invention relates to subsea filing and/or refilling of a storage container with injection fluid. Due to the subsea use of the storage container it is designed as a closed container to which the admission to the interior parts is operated by valves and the like.

The term "subsea" means a location below the sea surface, which is the interface between the seawater and the atmosphere. The storage container is filled and/or refilled with injection fluid at a subsea location referred to as the first subsea location. After the filling/refilling the storage container is moved to a second subsea location where the injection fluid is utilized. The second subsea location is typically near the seabed or at the seabed. At the second subsea location the injection fluid typically is injected into wells for oil and gas production. When the storage container is emptied for injection fluid it can be moved to the first subsea location to be refilled with injection fluid. The movement of the storage container between the second subsea location and the first subsea location can e.g. be carried out by means of a crane mounted on a floating facility.

It should be emphasized that the term "comprises/comprising" when used herein is to be interpreted as an open term, i.e. it should be taken to specify the presence of specifically stated feature(s), such as element(s), unit(s), integer(s), step(s) component(s) and combination(s) thereof, but does not preclude the presence or addition of one or more other stated features.

The term "substantially" should herein be taken to mean that ordinary product variances and tolerances are comprised. The term "seabed" is generally used to denote the subsea floor.

The term "about" is generally used to include what is within measurement uncertainties. When used in ranges the term "about" should herein be taken to mean that what is within measurement uncertainties is included in the range. All features of the invention and embodiments of the invention as described herein, including ranges and preferred ranges, may be combined in various ways within the scope of the invention, unless there are specific reasons not to combine such features. Throughout the description or claims, the singular encompasses the plural unless otherwise specified or required by the context.

To obtain a relatively calm environment in the first subsea location where the storage container is filled or refilled with injection fluid it has been found that the first subsea location should be located below the splash zone. The splash is a zone between the sea surface to a distance below the sea surface where waves, tidal movements and other movements in the sea causes a relatively uneasily

environment. The splash zone is defined in the British Standard and European Norm BS EN 61400-3 2009, terms and definitions 3.43. Thus, in an embodiment of the method the first subsea location is a subsea location below the splash zone, such as at least about 2.5 m below the splash zone, such as at least about 5 m below the splash zone, such as at least about 20 m below the splash zone, such as at least about 50 m below the splash zone.

As it is desirably to have a relatively calm environment in the first subsea location where the storage container is filled with injection fluid and it turns out

experiencefully that the sea environment turns more calm if you go to a certain depth beyond the sea surface, such as about 10 m or more. In an embodiment of the method the first subsea location is a subsea location from about 10 m to about 100 m below the water surface, such as from about 20 m to about 75 m below the water surface. Depending on the actual sea depth at the location where the method is applied the distance between the first subsea location and the second subsea location may vary significant. The distance between first subsea location and the second subsea location in substantially vertical direction may in fact vary in a rather large span between from about 100 m and up to about 3000 m, and in an embodiment the second subsea location is at least about 100 m below the first subsea location, such as at least about 500 m below the first subsea location, such as at least about 1000 m below the first subsea location, such as at least about 2000 m below the first subsea location, such as at least about 2500 m below the first subsea location.

The storage container is adapted for the injection fluid, which is stored in the container. The storage container may be a rigid container or a flexible container or a combination of a rigid and a flexible container. The storage container may also be encased in a preferably rigid protective structure. The storage container comprises an inlet and an outlet for injection fluid allowing the container to receive and deliver injection fluid. The inlet and outlet are controlled by valves and may be combined as one unit, i.e. the same pipe and coupling serves as inlet and outlet for the injection fluid. In an embodiment the storage container is a rigid container, a flexible container or a combination thereof, preferably the container is a flexible container optionally encased in a rigid protective structure.

In an embodiment the container comprises a flexible container where the storage container in the second subsea location is at least partly enclosed in a mechanical protection structure, preferably the storage container in the first subsea location is not enclosed in the mechanical protection structure. Thus, the storage container can be filled with injection fluid in the first subsea location and then moved to the second subsea location where it can be stored in the mechanical protective structure. The mechanical protection structure can e.g. be a frame, such as a metal frame or it can be a more box-like structure. Both a frame and a box are capable of serving as a mechanical protective structure.

Consequently, the method according to the invention includes an embodiment comprising moving the flexible storage container from the first location to the second location, comprising encasing the flexible storage container in the

mechanical protection structure at the second subsea location.

The mechanical protection structure should be able to protect the storage container from any impact which may appear in the second subsea location, and in an embodiment the mechanical protection structure is a rigid mechanical protection structure, such as a rigid external container. The rigid external container can e.g. be made from metal or polymer material.

For the purpose of being as close as possible to the location where the injection fluid is used, the method also provides an embodiment where the storage container, optionally encased in the mechanical protection structure, in the second position is arranged directly on the seabed.

According to the method, the storage container can be arranged in a foundation rack preferably with other storage containers such that several storage containers can be arranged in the foundation rack. The foundation rack may, thus, hold several storage containers and serve to keep track of several storage containers. Thus, the method also includes an embodiment where the storage container, optionally encased in the mechanical protection structure, in the second position is arranged at a foundation structure, such as a foundation and rack structure, preferably the foundation and rack structure is adapted for holding two or more storage

containers. The foundation and rack structure are preferably made from metal, such as stainless steel. The foundation and rack structure may comprise one or more locking mechanisms which can lock and secure the storage containers to the foundation and rack structure. In an embodiment the entire rack structure comprising several storage containers is adapted to be moved between the first subsea location and the second subsea location and visa versa. Thus, it is possible to fill several storage containers in the first subsea location at substantially the same time.

Depending of the use and nature of the injection fluid, the storage container may have desired size and storage capacity, such as a storage capacity from 1 or 2 m³, such as about 35 m³ or about 40 m³, and up to several cubic meters. However, the method according to the invention is also suitable for filling containers with large capacity and in an embodiment of the method the storage container has a storage capacity of at least about 500 m³, such as at least about 1000 m³, such as at least about 2000 m³, such as at least about 4000 m³, such as at least about 6000 m³, such as at least about 8000 m³.

In an embodiment the storage container has a capacity to contain injection fluid for about half a year's consumption of injection fluid. Thus, the storage container can be replenished every six months.

When the storage container is in the first subsea location the storage container can be held in the location by lines connected to a surface facility, such as a platform or ship. One or more cranes on the surface facility may serve to keep the storage container in the first subsea location. A tube or hose for filling injection fluid into the storage container can be led from the surface facility to the storage container where it can be coupled to the inlet of the container e.g. by a use of a ROV (remote operated vehicle). The ROV may also be used to operate valves in connection with the storage container and inlet, and to decouple the tube or hose from the storage container when the supplying of injection fluid has been completed, such that the storage container can be moved from the first subsea position to the second subsea position. Thus, the method does also include an embodiment wherein the storage container is maintained substantially at the first location during the supplying of the storage container with injection fluid from the surface facility, the storage container is preferably maintained at the first location using one or more lines, such as one or more hoist lines; one or more buoyancy arrangements and/or one or more ballast arrangements.

The filling of the storage container with injection fluid also have the advantage that large dead volume in the tubes or hoses used for filling the storage container can be avoided. Moreover, the present invention reduces the mechanical demands to the tubes or hoses and the spooling systems for the tubes or hoses.

The second subsea facility may comprise a drilling facility or a production facility, referred to as a subsea facility, located at the seabed. Both a drilling facility or a production facility requires injection fluid during operation. Preferably the injection fluid is supplied from the storage container at said second subsea location to an injection point of the subsea facility, such as, an injection point comprising a downhole with injection point, a manifold with injection point, a flowline with injection point or a x-mas tree with injection point. The injection point is preferably close to the seabed such as from the seabed to about 50 m above or below the seabed in vertical direction.

In an embodiment of the method according to the invention, the surface facility comprises a floating unit such as a platform or a vessel. The surface facility may be a floating production storage and offloading (FPSO) or a floating production vessel.

Before the storage container is located in the subsea locations it is transported to the place of operation and a surface facility and in an embodiment the method comprises launching the storage container from the surface facility prior to arranging the storage container at the first subsea location, wherein the storage container is preferably substantially empty at the launching, preferably the storage container is passing through a splash zone to reach the first location, the storage container preferably being substantially empty during the passage through the splash zone. Thus, the storage container is transported to the place of operation by a vessel or ship. This vessel or ship may also be the surface facility from which the storage container is launched. Alternative, the storage container can be transferred from the vessel or ship to e.g. a production platform or FPSO, which then serves as the surface facility. Preferably, the storage container when launched passes a splash zone before reaching the first subsea location below the splash zone. When the storage container has reached the first subsea location, it can be kept here for the desired time by means of e.g. cranes and lines as previously described. When the storage container has been filled with injection fluid as described it can be moved to the second subsea location.

As previously mentioned the storage container may also be moved from the second subsea location to the first subsea location for replenishment of injection fluid and in an embodiment the method comprises lifting the storage container from its second location prior to arranging the storage container at the first subsea location, where the storage container is preferably substantially empty prior to lifting it from the second location and where the supplying of the injection fluid to the storage container at the first location is a replenishment of injection fluid and where the method comprises the further step of washing and/or flushing the storage container before replenishment of injection fluid. Thus, in this embodiment the storage container is subjected to a cleaning operation before the replenishment.

In an embodiment, the method comprises decoupling an injection pipe from the storage container prior to lifting the storage container from the second location. The decoupling can be accomplished by use of a ROV. The storage container and the injection pipe is preferably equipped with valve means, which can be operated by the ROV or by other remote controlled devices. The decoupling can also be performed as a fully automated process controlled from e.g. the surface facility.

In an embodiment the method comprises coupling an injection pipe to the storage container for supplying the injection fluid from the storage container to the subsea facility after having located the storage container at the second location. This operation may also be accomplished by using a ROV. Again, this coupling can also be performed as a fully automated process controlled from e.g. the surface facility.

In an embodiment the method comprises coupling a supply pipe to the storage container for supplying the storage container with injection fluid from the surface facility and decoupling the supply pipe from the storage container prior to moving the storage container from the first location to the second container, wherein the coupling of the supply pipe to the storage container preferably is performed at the first location.

The coupling and decoupling of pipes can also be achieved by mounting coupling devices (such as inlets and outlets) on the underside, i.e. the side facing the seabed, of the storage container. Such a solution may enable automated coupling of the reservoir to the injection pipes in the second seabed location. Thus, in one embodiment the outlet for injection fluid is mounted on the underside of the storage container. The inlet for injection fluid may also be mounted on the underside of the storage container or on the upper side, i.e. the side facing the sea surface, of the storage container. In an embodiment the inlet and the outlet is provided in the same pipe and coupling.

The injection fluid may be any fluid suitable for use in extracting carbonouos fluid, such as oil and gas from a well and for drilling in a well and an embodiment the injection fluid is selected from inhibitors, dispensing agents, descalers, biocides, demulsifiers, buoyant and non-buoyant chemicals, MEG, methanol or any combinations comprising one or more of these.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in further details with reference to

embodiments shown in the drawing in which: Figure 1 shows installation of a rack with storage containers;

Figure 2 shows filling of a storage container according to the invention;

Figure 3 shows a foundation and rack structure;

Figure 4 shows a storage container with buoyant fluid; and

Figure 5 shows a storage container with non-buoyant fluid. The figures are not accurate in every detail but only sketches intended to the show the principles of the invention. Details which are not a part of the invention may have been omitted. In the figures the same reference numbers may be used for the same parts. Figure 1 shows the installation of a rack 1 containing a number of storage

containers 2. The rack 1 is installed on the seabed 3 near a (not shown) subsea facility.

The installation of the rack 1 comprises two vessels 4, 5 floating on the sea surface 6. Each vessel is connected to the rack 1 via lines. By means of the lines shown as 7a and 7b (there may several more lines connecting the rack and the vessels), the rack 1 is lowered from the sea surface 6 to the seabed 3. At the seabed 3 the storage containers 2 are coupled with injection pipes which can deliver injection fluid to the subsea facility.

The opposite procedure may take place in a similar manner. The storage containers are decoupled from the injection pipes, e.g. by means of a ROV, and the rack 1 is connected to lines illustrated by 7a and 7b, which connect the rack 1 with the vessels 4, 5. When the rack 1 and the vessels are safely connected the rack 1 can be lifted upwards towards the sea surface 6 from the seabed 3 by means of the lines 7a, 7b co-acting with a crane or other lifting means. When the rack 1 has reached the sea surface 6 it can loaded aboard one of the vessels 4, 5 for replenishing the storage containers 2 with injection fluid. Alternative the rack may be replaced with another rack with filled storage containers and the rack retrieved from the seabed can be brought ashore for replenishment of the storage containers.

Figure 1 illustrates the technique which have been used for several years, and, although, the procedures may look quite simple, the procedures are in fact rather complicated as they are performed offshore where wind and wave movements cannot be controlled and the operation normally requires carefully balancing with buoyancy modules and ballast modules and excellent coordination between the two vessels which are required to operate the rack.

Figure 2 illustrates how a storage container 12 can replenished with injection fluid in a first subsea location near the sea surface and then moved to a second subsea location at the seabed 3 to deliver injection fluid to a subsea facility (which is not shown in the figure).

The method requires only one vessel 14. In this particular embodiment the vessel 14 is equipped with cranes which can hoist the storage container 12 from the second subsea position in the rack 11 at the seabed 3 to a first subsea location near the sea surface where the storage container 12 can be replenished with injection fluid. As it is seen in figure 2, in this particular embodiment the storage container 12 is mounted in a rack 11 which are shown in more details the inserted figure - the rack 11 will be described in further details in the following figures.

The storage container 12 is located in the first subsea location near the sea surface 6 but below the splash zone 19 (indicated by shaded field). The storage container 12 is kept in fluid connection with an injection fluid tank on the vessel 14 via the refill hose 18, which supply the injection fluid from the injection fluid tank on the vessel 14 to the storage container 12.

When the storage container 12 has been filled with injection fluid, the refill hose 18 is decoupled from the storage container 12. The storage container is also connected with the vessel 14 by one or more not shown lines. The lines interact with a crane on the vessel 14 and the storage container filled with injection fluid is lowered down to the second subsea location at seabed 3 by means of lines and the crane. The movement of the storage container 12 is indicated by the arrow in the figure. In the second subsea position at the seabed the storage container 12 is mounted in the rack 11 a coupled to an injection fluid supply pipe which deliver injection fluid to the subsea facility (the injection pipe and the subsea facility are not shown in the figure). A not shown ROV may assist in mounting the storage container 12 in the rack 11 and the coupling of the storage tank to the injection fluid supply pipe.

Consequently, Figure 2 shows an embodiment of the invention where the storage container 12 is moved to a first subsea location below the splash zone 19, but near the sea surface 6 and the vessel 14 where the storage container 12 is brought in fluid connection with an injection fluid tank on the vessel to refill the storage container 12. During the refilling the storage container 12 is kept in in the first subsea location below the splash zone 19 where the water is calm and not affected by wind and waves. Thus, the storage container is in a location where it is not subjected to large forces and the connection between the storage container 12 and the vessel 14 is not subjected to the same amount of forces as if the storage container 12 was in the splash zone 19.

Figure 3 shows the rack 11 in more details. The rack comprise a frame 21 which divide the rack 11 into five compartments 22a, 22b, 22c, 22d, and 22e. In the first compartment 22a is mounted four storage containers 12a. The three following compartments 22b, 22c and 22d houses a storage container 12b each. The fifth compartment 22e houses two storage containers 12a.

The rack 11 is made from stainless steel and the storage containers 12 and 12b are made from polymer material.

The storage containers 12a and 12b have different capacities and contains different volumes of injection fluid. The storage containers 12a and 12b are selected depending on the consumption of the specific injection fluid. The storage containers 12a are selected for injection fluids, which are consumed in less amounts and the storage containers 12b are selected for injection fluid which are consumed in larger amounts.

The injection fluids may also differ in density, thus, some injection fluids may be buoyant injection fluids and some injection fluids may be non-buoyant injection fluids. This is illustrated in figure 4 and 5.

Figure 4 illustrates a storage container 12 storing buoyant injection fluid 31. The storage container 12 comprises an outer rigid shell comprising sidewalls 33, a bottom part 34 and a top part 35. The bottom part 34 comprises an opening 36 which allows fluid communication with the environment. The top part 35 comprises and opening 37 in which a coupling device 38 is mounted. A tube 39 is mounted to the coupling device and extends into the storage container 12 towards the bottom part 34. A perforated tube 40 is also mounted to the coupling device 38 and extends down in the storage container 12 towards the bottom part 34. A flexible container 41 is also attached to the coupling device 38 and enclosing the tube 39 and the perforated tube 40.

The buoyant injection fluid 31 is stored inside the flexible container 41 and in fluid communication with the tube 39 and the perforated tube 40. The coupling device 38 can be coupled to an injection pipe or a refilling hose respectively. When the coupling device is coupled to a refilling hose injection fluid can enter the flexible container 41 via the tube 39 and fill the flexible container 41 so it substantially fill out the interior of the rigid shell.

When the buoyant injection fluid 31 is to be retrieved for use for e.g. injection into a well an injection pipe is coupled to the coupling device 38 and the injection fluid can be retrieved via the tube 39. As the flexible container 41 is emptied it will be compressed by sea water entering via the opening 36. Due to the fact, that the injection fluid is buoyant it will seek towards the top part 35 of the storage container 12 and the flexible container 41 will be compressed around the pipe 39 towards the top part 35. However, the perforated tube 40 surrounding the tube 39 will ensure that there always is fluid communication between the injection fluid 31 in the flexible container 41 and the lower inlet 42 of the tube 39. Thus the external pressure serves to facilitate emptying the flexible container 41.

Figure 5 illustrates the situation when a storage container 12 is storing non-buoyant injection fluid 32. The storage container 12 also comprises an outer rigid shell comprising sidewalls 33, a bottom part 34 and a top part 35. The bottom part 34 comprises an opening 36, which allows the interior of the rigid shell to be in fluid communication with the environment, i.e. the seawater. The top part 35 comprises and opening 37 in which a coupling device 38 is mounted. A tube 39 is mounted to the coupling device and extends into the storage container 12 towards the bottom part 34. A perforated tube 40 is mounted to the coupling device 38 and extends down in the storage container 12 towards the bottom part 34 outside the tube 39. A flexible container 41 is also attached to the coupling device 38 and enclosing the tube 39 and the perforated tube 40. The flexible container 41 may or may not be attached to the bottom part 34 of the rigid shell.

The non-buoyant injection fluid 32 is stored inside the flexible container 41 and in fluid communication with the tube 39 and the perforated tube 40. The coupling device 38 can be coupled to an injection pipe or a refilling hose respectively. When the coupling device is coupled to a refilling hose non-buoyant injection fluid can enter the flexible container 41 via the tube 39 and fill the flexible container 41 so it substantially fill out the interior of the rigid shell.

The non-buoyant injection fluid 32 can also be retrieved from the storage container 12 and injected into e.g. a well. When the non-buoyant injection fluid 32 is to be retrieved for use an injection pipe is coupled to the coupling device 38 and the injection fluid can be retrieved via the tube 39. As the flexible container 41 is emptied it will be compressed by sea water entering via the opening 36 and optionally other not shown openings. As the injection fluid is non-buoyant and heavier than the surrounding seawater it will sink towards the bottom part 34 of the storage container 12 and the flexible container 41 will be compressed around the pipe 39 towards the top part 35. However, as in the case with buoyant fluid the perforated tube 40 surrounding the tube 39 will ensure that there is always fluid communication between the non-buoyant injection fluid 32 in the flexible container 41 and the lower inlet 42 of the tube 39.

According to the invention the storage container 12 is brought in the first subsea position when the storage container needs to be replenished. When the injection fluid is retrieved from the storage container 12 for use in e.g. a well the storage container is in the second subsea position.

The storage containers for storing buoyant and non-buoyant injection fluid shown in figure 4 and 5 are only examples and other configurations may be used. The tube 39 need not be mounted in the central part of the container. The tube may be mounted closer to the sidewalls. In other embodiments the tube may be mounted in the sidewall or in the bottom part of the storage container. In some embodiments the perforated tube 40 may be omitted.

Claims

PATENT CLAIMS

1. A method of supplying injection fluid to a subsea facility, the method comprising

• arranging a storage container at a first subsea location,

· supplying the storage container with injection fluid from a surface facility,

• moving the storage container to a second subsea location and

• supplying the injection fluid from the storage container at said second subsea location to the subsea facility, wherein the second subsea location is closer to the seabed than the first subsea location, preferably the storage container at the second subsea location is supported by the seabed.

2. The method of claim 1, wherein the first subsea location is a subsea location below the splash zone, such as at least about 2.5 m below the splash zone, such as at least about 5 m below the splash zone, such as at least about 20 m below the splash zone, such as at least about 50 m below the splash zone.

3. The method of claim 1 or claim 2, wherein the first subsea location is a subsea location from about 10 m to about 100 m below the water surface, such as from about 20 m to about 75 m below the water surface

4. The method of any one of the preceding claims, wherein the second subsea location is at least about 100 m below the first subsea location, such as at least about 500 m below the first subsea location, such as at least about 1000 m below the first subsea location, such as at least about 2000 m below the first subsea location, such as at least about 2500 m below the first subsea location.

5. The method of any one of the preceding claims, wherein the storage container is a rigid container, a flexible container or a combination thereof, preferably the container is a flexible container optionally encased in a rigid protective structure.

6. The method of claim 5, wherein the container comprises a flexible container and where the storage container in the second subsea location is at least partly enclosed in a mechanical protection structure, preferably the storage container in the first subsea location is not enclosed in said mechanical protection structure.

7. The method of claim 6, wherein the method comprises moving the flexible storage container from the first location to the second location, comprising encasing said flexible storage container in said mechanical protection structure at said second subsea location.

8. The method of claim 5 or claim 6, wherein the mechanical protection structure is a rigid mechanical protection structure, such as a rigid external container.

9. The method of any one of the preceding claims, wherein the storage container optionally encased in the mechanical protection structure in the second position is arranged directly at the seabed.

10 The method of any one of the preceding claims 1-8, wherein the storage container optionally encased in the mechanical protection structure in the second position is arranged at a foundation structure, such as a foundation and rack structure, preferably the foundation and rack structure is adapted for holding two or more storage containers.

11. The method of any one of the preceding claims, wherein the storage container has a storage capacity of at least about 500 m³, such as at least about 1000 m³, such as at least about 2000 m³, such as at least about 4000 m³, such as at least about 6000 m³, such as at least about 8000 m³.

12. The method of any one of the preceding claims, wherein the storage container is maintained substantially at the first location during the supplying of the storage container with injection fluid from the surface facility, the storage container is preferably maintained at the first location using one or more lines, such as one or more hoist lines; one or more buoyancy arrangements and/or one or more ballast arrangements.

13. The method of any one of the preceding claims, wherein the subsea facility comprises a subsea facility such as a drilling facility or a production facility, preferably the injection fluid is supplied from the storage container at said second subsea location to an injection point of the subsea facility, such as, an injection point comprising a downhole with injection point, a manifold with injection point, a flowline with injection point or a x-mas tree with injection point, the injection point is preferably close to the seabed such as from the seabed to about 50 m above or below the seabed in vertical direction.

14. The method of any one of the preceding claims, wherein the surface facility comprises a floating unit such as a platform or a vessel.

15. The method of any one of the preceding claims, wherein the method comprises launching the storage container from the surface facility prior to arranging the storage container at the first subsea location, wherein the storage container is preferably substantially empty at the launching, preferably the storage container is passing through a splash zone to reach the first location, the storage container preferably being substantially empty during the passage through the splash zone.

16. The method of any one of the preceding claims 1-14, wherein the method comprises lifting the storage container from its second location prior to arranging the storage container at the first subsea location, wherein the storage container is preferably substantially empty prior to lifting it from the second location and wherein the supplying of the injection fluid to the storage container at the first location is a replenishment of injection fluid, wherein the method comprises the further step of washing and/or flushing the storage container before replenishment of injection fluid.

17. The method of any one of claim 16, wherein the method comprises decoupling an injection pipe from the storage container prior to lifting the storage container from the second location.

18. The method of any one of the preceding claims, wherein the method comprises coupling an injection pipe to the storage container for supplying the injection fluid from the storage container to the subsea facility after having located the storage container at the second location.

19. The method of any one of the preceding claims, wherein the method comprises coupling a supply pipe to the storage container for supplying the storage container with injection fluid from the surface facility and decoupling the supply pipe from the storage container prior to moving the storage container from the first location to the second location, wherein the coupling of the supply pipe to the storage container preferably is performed at at the first location.

20. The method of any one of the preceding claims, wherein the injection fluid is selected from inhibitors, dispensing agents, descalers, biocides, demulsifiers, buoyant and non-buoyant chemicals, MEG, methanol or any combinations comprising one or more of these.