Patent Description:
Structures such as pipes or other structures which may contain fluid in their interiors are increasingly installed for long-term use subsea, e.g., on the seabed. Such structures may for example be employed in the hydrocarbon exploration and production industry for containing, processing, or transporting fluids which may for instance include hydrocarbons obtained from subsurface hydrocarbon reservoir or other fluids. These structures can suffer from deposits of scale, dirt, or other material that may build up over time and may eventually interrupt or block the interior space and/or adversely affect proper performance of the structure. When this happens, it may be necessary to clean the interior of the structure to remove the deposits, etc. Pipes known as subsea manifolds can be particularly susceptible to such problems because these provide the connection points for multiple flow lines connecting to the manifold, and they are generally of a structure which includes tight bends and corners e.g., where the lines connect.

An existing method of deposit removal in subsea structures includes mechanical removal using a pig. However, pigs can be inconvenient, time consuming and costly to operate, and may not be suitable in various deployment scenarios, such as in manifolds or tanks or the like.

In general, there has been a lack of versatile solutions for cleaning subsea structures, and doing so efficiently and effectively, such as in those structures mentioned above. In this light, the inventors have identified a need for improvements, and an aim of the present invention is to obviate or at least mitigate various drawbacks associated with the prior art. <CIT> discloses an ` intervention system for subsea completed wellbores. <CIT> discloses a cleaning unit comprising a fluid delivery hose and a hose reel rotatable around two perpendicular axis.

According to a first aspect of the invention, there is provided a subsea unit for cleaning an interior of a subsea structure, the subsea unit comprising: a hose for delivering fluid from an inlet into an interior of the subsea structure to be cleaned for cleaning the interior; a hose reel being rotatable around a first axis and a second axis, wherein the rotation of the hose reel around the first axis is for feeding the hose into or retracting the hose from the subsea structure and rotation of the hose reel around the second axis is for rotating the hose around its longitudinal axis and a feeder for controlling strain in the hose during feeding and/or retraction of the hose, in accordance with claim <NUM>.

According to a second aspect of the invention, there is provided a system for cleaning an interior of a subsea structure, the system comprising a subsea unit according to the first aspect of the invention, the subsea unit further comprising: a fluids inlet and a hydraulics inlet.

The subsea unit may further comprises an entry connector, e.g. a pipe entry connector, for connecting to the subsea structure to be cleaned, through which entry connector the hose may be fed to enter the interior of the subsea structure.

The hose may comprise a nozzle or an opening in a portion of the hose to be inserted into the interior of the subsea structure, for letting fluid out of the hose for flushing the interior of the subsea structure. The fluid may be or may comprise water. The fluid may include a cleaning additive. The hose may be a water hose. The fluids inlet may be a water inlet.

The hose reel may allow the hose to be rotated around its longitudinal axis while being fed into a pipe in a subsea manifold. This configuration may reduce problems related to feeding of the hose into the structure to be cleaned, reducing pigtail effects, thereby making it easier to reach far into the structure even through sharp bends. Rotation of the hose around its longitudinal axis may also be beneficial with regards to the cleaning process, both as it may reduce pigtail effects and as the rotation may allow the fluid stream from the nozzle of the hose to more efficiently reach all areas inside the structure as the hose rotates.

The first and second axes may typically be perpendicular to each other. The rotation of the hose reel may be powered by hydraulics and/or by pressurised water. Thus, the hose reel may be driven so as to rotate by hydraulic fluid from the hydraulics inlet or water from a water inlet. The subsea unit may include a hydraulic power unit mounted on a frame of the subsea unit.

The subsea structure may comprise a pipe, which may be a pipe of a subsea manifold. The subsea structure may comprise a subsea manifold.

The subsea unit may comprise one or more levers. The levers may control the direction of the hose reel, and whether the hose reel feeds or retracts the hose. The levers may be controlled by use of an ROV (Remotely Operated Vehicle). The feeder may be passive, configured with a load to control the strain. The purpose of the feeder may be mainly to avoid a pigtail effect in the hose during feeding and/or retraction.

The subsea unit may further comprise at least one guide funnel. This guide funnel may allow for mounting the subsea unit securely on a subsea manifold, as each one of the at least one guide funnel may be configured to fit onto a guidepost of the manifold.

The at least one guide funnel may be adjustable in length, e.g., to help to allow the subsea unit to fit manifolds or other structures of different sizes.

The subsea unit may further comprise a stiff hose guide. Such a hose guide may be useful and may be preferable for avoiding a pigtail effect on the hose during operations, as the hose guide may aid in constraining the movement of the hose.

Furthermore, the subsea unit may comprise a subsea dredge socket for connecting to a subsea dredge. Using a subsea dredge with the subsea unit during cleaning operations can aid in removal of deposits as they are being flushed from the inside of the subsea structure.

The subsea unit may further comprise a lifting lug. The lifting lug may be arranged to be connected to a wire by use of a hook, to allow for a crane or other lifting equipment to carry the subsea unit as it is being lowered to or lifted from the subsea structure, or to or from a location on the seabed at or near the subsea structure.

The subsea unit may comprise a guide wheel or a set of guide wheels, for guiding the water hose between the hose reel and the feeder.

The system may further comprise a fluids supply for providing fluid for cleaning the interior of the subsea structure, e.g. a pipe in the subsea manifold.

In embodiments where the fluid comprises water and the fluids supply is a water supply, the water supply may be arranged to deliver water with a pressure of between <NUM> and <NUM> bar (60MPa-120MPa). More preferably, the water pressure may be between <NUM> and <NUM> bar (70MPa-115MPa). Even more preferably, the water pressure may be between <NUM> and <NUM> bar (80MPa-110MPa). Even more preferably, the water pressure may be between <NUM> and <NUM> bar (90MPa-105MPa). High water pressure will allow for more efficient cleaning.

The fluids supply may be placed topside, such as on a vessel or a platform.

Furthermore, the system may comprise a further hose, for connecting the fluids supply to the fluids inlet of the subsea unit.

The system may further comprise a hydraulics source. Hydraulics may be used e.g. for rotating the hose reel. Furthermore, the system may further comprise a hydraulics hose which may be arranged to extend from the hydraulics source to the hydraulics inlet of the subsea unit.

The system may be configured to be operated at least partly by use of an ROV. The ROV may be used to operate one or more levers for controlling the direction of the rotations of the hose reel. An ROV may be used to connect the hydraulics hose to the hydraulics inlet and to connect the further hose to the fluids inlet. Furthermore, an ROV may be used to connect the entry connector to the subsea structure, e.g., to an entrance thereof. The subsea structure may for instance be a pipe in the subsea manifold to be cleaned. The system may include the ROV.

The ROV may comprise the hydraulics source. Otherwise, the hydraulics source may be a HPU (Hydraulic Power Unit) to be placed subsea near the subsea unit, or on a frame of the subsea unit, or a topside unit may comprise the HPU. Using a subsea HPU placed near the subsea unit may be preferable, as it may then not require a hydraulics hose to extend all the way from topside to the subsea unit. Using an ROV with an HPU as the hydraulics source can be even more preferable if an ROV is used for operating the cleaning system, as a separate unit simply for supplying hydraulics may then be avoidable.

The system may further comprise one or more hot stabs. Hot stabs may be used to connect the hydraulics hose and/or the further water hose to the hydraulics inlet and/or the water inlet respectively, e.g., to minimize the chance of any leakage to the surrounding environment.

According to a third aspect of the invention, there is provided a method of using the system according to the second aspect of the invention for cleaning the interior of the subsea structure.

The method may further comprise any one or more of the steps of:.

The subsea structure may be a subsea manifold, and the moving step may comprise moving the subsea unit to the subsea manifold to be cleaned. The subsea structure may comprise a pipe of a subsea manifold.

The fluid may be or may comprise water. Using water to flush out deposits from a pipe may be beneficial, as it may be cheaply available, efficient in use, non-abrasive, and/or of low contamination risk to the environment.

The method may comprise the step of deploying the subsea unit into a sea through a moon pool. A moon pool may be an opening in the floor or base of a hull, platform or chamber, e.g. of a sea-surface vessel, for providing sheltered access to a sea. Deploying the subsea unit through a moon pool can make the operation safer.

Furthermore, the method may involve guiding the subsea unit while being lowered to the subsea structure, or lowered into location at, near, or onto a subsea structure, by use of template guide lines. Using such guide lines may make it easier to hit the correct landing spot.

The method may further comprise the step of landing a guide funnel of the subsea unit on a designated guide post on the subsea structure. Having a guide funnel placed onto a guide post may aid in securing the subsea unit in place on the subsea structure, or in place at, near or adjacent to the subsea structure to be cleaned.

Furthermore, the method may comprise the step of rotating the hose around its longitudinal axis while feeding the hose into the interior of the subsea structure, e.g. a pipe in the subsea manifold. The method may include operating a hydraulic motor to drive the hose reel to rotate the hose around its longitudinal axis. Rotating the hose around its longitudinal axis while feeding it into the pipe can aid in avoiding an unwanted pigtail effect of the hose, and may increase the efficiency of the feed e.g. by making it easier to pass the hose through bends in the subsea structure e.g. pipe.

The method may further comprise the step of rotating the hose around its longitudinal axis while flushing the inside of the pipe. This may improve the cleaning efficiency, as a nozzle or an outlet in the inserted portion of the pipe, by being rotated can result in altering the direction of the fluid stream and thus increase or otherwise change the area of inside of the structure or pipe that can be directly hit by the fluid stream.

Furthermore, the method may comprise removal of flushed-off deposits by use of a subsea dredge. Removal of flushed-off deposits can be an important part in the cleaning process, since a subsea dredge can be capable of removing flushed-off deposits efficiently.

The guiding of the hose into the interior of the subsea structure, e.g. a pipe in the subsea manifold, may involve guiding the hose through a stiff hose guide of the subsea unit ahead of feeding the hose into the subsea structure. Guiding the hose through the stiff guide can constrain the hose from moving in an unwanted way, which can help prevent a pigtail effect in the hose on its way towards the subsea structure.

The method may further comprise filling the further hose with fluid prior to lowering a second end portion of the further hose down to the subsea unit. This may be done to avoid a collapse in the further hose due to the increasing water pressure of the sea as it is lowered towards the subsea unit.

The cleaning may be performed to remove a deposit in the interior of the structure to be cleaned. The deposit may be as described anywhere else herein.

Any of the first to third aspects of the invention may include one or more further features as described in relation to any other aspect, wherever described herein.

There will now be described, by way of example only, embodiments of the invention, with reference to the accompanying drawings, in which:.

In <FIG>, there is shown a subsea unit <NUM> for use in a cleaning system for cleaning an interior of a subsea structure. The subsea unit <NUM> in this example has a hydraulics inlet <NUM>, a water inlet <NUM>, a hose reel <NUM>, two guide funnels <NUM>, a lifting lug <NUM>, and a water hose <NUM>. The hose reel <NUM> is configured to rotate around a first axis <NUM> and a second axis <NUM>. The rotation around the first axis <NUM> is for feeding and retracting the water hose <NUM> and the rotation around the second axis <NUM> is for rotating the water hose <NUM> around its longitudinal axis <NUM>, which in this example is coincident with the second axis <NUM>. The hose <NUM> is wound on the reel <NUM> in multiple single-width layers.

The present example is given with reference to cleaning by way of water. In other variants however, other fluids are employed instead of water. Such other fluids may comprise liquid or gas or combinations thereof and may comprise solvents or other substances to facilitate cleaning. The other fluid may comprise a liquid or gas or combination thereof which is provided with a cleaning additive for facilitating cleaning. The choice of fluid could in general depend upon the type of subsea structure that is to be cleaned. Subsea structures may include pipes or internal bores or conduits, e.g. a pipe manifold where flow lines from different areas of the seabed are tied in to the pipe manifold. However, the subsea unit <NUM> and cleaning system may likewise be employed to clean the interior cavities in any other kind of subsea equipment. By spooling out the hose from the hose reel <NUM>, the end of the hose may be pushed far into the interior space of the subsea equipment, into difficult to reach regions, and advantageously around tight corners or bends. This may be facilitated particularly by the ability of the hose to be rotated about its own long axis.

Surfaces of the interior to be cleaned may have deposits of particles, films, or scale or other material which may need to be removed. The cleaning fluid delivered from the hose <NUM> into the space may work mechanically on such deposits, films, scale, or the like, which may be sought to be removed.

Referring again to <FIG>, the portion of the hose <NUM> which is to be spooled out from the hose reel <NUM> is provided with a nozzle <NUM>, typically at or near the spooled out end of the hose <NUM>. In order to clean the interior of the subsea structure, water passes through the hose <NUM> and is directed out of the nozzle <NUM> into the interior of the pipe. Water is supplied under pressure from a water source through the water inlet <NUM> and into the hose <NUM> stored on the reel <NUM>. In other variants, the hose can have other kinds of opening from the spooled out end for letting out water from the hose <NUM> into the interior of the structure to be cleaned.

The pressure of the water is typically supplied from above sea surface such that it counters and exceeds the subsea pressure to deliver successfully into the interior of the subsea structure. The water in such a case may be supplied through a connecting water line (not shown), e.g. a fluid line in an umbilical connecting the subsea unit <NUM> with sea surface facility.

The subsea unit <NUM> has a rigid support frame <NUM> for supporting the various components of the unit <NUM> upon a seabed. The rigid frame <NUM> may be formed of steel uprights and cross members joined together as required, so that it sinks and comes to rest on the seabed when lowering under gravity.

The hose reel <NUM> is mounted on an axle <NUM> by way of which the hose reel rotates about the axis <NUM> to spool the hose <NUM> out or in, as indicated by arrows A, B. The water from the water inlet <NUM> is supplied through an inside of the axle <NUM> to connect with an end of an innermost section of the hose on the base of reel <NUM>. For this purpose, an appropriate connecting line (not shown) between the water inlet <NUM> and the hose <NUM> can be used.

The hose reel <NUM> and axle <NUM> is further mounted on a rotatable cradle <NUM> so as to be supported by the frame <NUM>. The cradle <NUM> can rotate relative to the frame <NUM> about the axis <NUM>. The axes <NUM> and <NUM> are perpendicular to one another. The cradle <NUM> is coupled to the frame <NUM> through interconnecting planetary gears <NUM> which are driven by a motor <NUM> to rotate the cradle <NUM>, and hence the hose reel <NUM> about the second axis <NUM>. The motor <NUM> is operated by hydraulics, i.e., via hydraulic power fluid e.g. oil, supplied to the subsea unit <NUM> through the hydraulics inlet <NUM>. In this way, the rotation of hose reel <NUM> about the axis <NUM> can be carried out so as to turn and rotate the hose <NUM> that is being fed into the subsea structure from the subsea unit about its longitudinal axis <NUM>.

The rotation of the hose reel <NUM> is driven by a motor <NUM> which is also hydraulically powered by the hydraulics supplied through the hydraulics inlet to the motor <NUM>. The motor <NUM> can then be controlled to spool the hose <NUM> in or out as required.

The hydraulics, e.g., hydraulic fluid e.g., oil, is supplied typically from a hydraulics power unit (HPU) through a connecting hydraulics line to the hydraulics inlet.

The HPU may be located above sea surface or on an ROV which may be employed to facilitate operating the subsea unit <NUM>. Alternatively, the subsea unit <NUM> includes a hydraulic power unit mounted on the frame <NUM>. Electrical power for operating the HPU may then be supplied from surface via an electrical umbilical (not shown).

It can be appreciated that the unit <NUM> is further arranged so that the direction in which the hose <NUM> is fed out of the subsea unit <NUM> into the interior of the subsea structure is controlled. More particularly, the unit <NUM> is arranged to provide a track along which the hose <NUM> is moved and guided. It can be noted that the subsea unit <NUM> includes a feeder <NUM> and a set of guide wheels <NUM> for the water hose <NUM>. In the example shown, the hose <NUM> passes through the guide wheels <NUM> and through the feeder <NUM> so as to determine the direction and orientation of the hose <NUM>. The portion of the hose <NUM> leaving the feeder <NUM> is supported with its longitudinal axis <NUM> horizontal, and moves axially away from the subsea unit <NUM> for insertion into the interior of the structure to be cleaned.

In other embodiments, the subsea unit <NUM> may be arranged to leave the subsea unit <NUM> with the long axis <NUM> of the hose <NUM> in a different orientation, e.g. to align appropriately with an opening to an interior of the structure to be cleaned.

The feeder <NUM> assists with the directional positioning of the hose <NUM> as it leaves the subsea unit <NUM> and is fed into the structure to be cleaned. In addition, it is arranged to help control the tension in the hose <NUM> when spooling out or in from the hose reel <NUM>. For instance, if the spool in is too aggressive such that a predetermined tension limit is exceeded, this may be detected in the feeder such that an adjustment force can be applied to the hose <NUM> accordingly.

The subsea unit <NUM> exemplified in <FIG> has two guide funnels <NUM>. The guide funnels <NUM> are arranged to fit around corresponding guide posts to facilitate locating the subsea unit <NUM> in correct, predetermined location on the seabed. A subsea template, e.g. at the location of a manifold to be cleaned, may have upright guide posts, and by lowering the unit <NUM> so that the top of the guide posts enter and received through the guide funnels <NUM>, the subsea unit <NUM> is brought into correct position.

The subsea unit includes a lifting lug <NUM>, for lifting and lowering e.g. suspended on a hook from a wire. In addition, the subsea unit <NUM> includes two levers <NUM> for controlling the directions of rotation for the hose reel <NUM>. The levers <NUM> may for example be switched by an ROV manipulator to change the rotation direction.

The subsea unit <NUM> also typically includes a controller for controlling the motors <NUM>, <NUM> and delivery of hydraulics for rotating hose reel <NUM> appropriately for feeding the hose <NUM> in or out from the structure to be cleaned. The system provides communication with the controller to operate the hose according to instructions. Control signals or instructions for the controller for controlling the motors <NUM>, <NUM> and/or the HPU and/or other data may be communicated between the subsea unit <NUM> and above surface control computer through a communication line, for instance an electrical or optical line in an umbilical extending from the subsea unit <NUM> to above sea surface.

Turning now to <FIG>, a system <NUM> includes the subsea unit <NUM> in use for cleaning the interior <NUM> of a subsea structure <NUM>. The hose <NUM> is spooled out from the hose reel <NUM> and fed from the subsea unit <NUM> into the interior <NUM> of the structure <NUM>. The unit <NUM> includes the HPU <NUM>, a controller <NUM>, and an umbilical <NUM> connecting to the surface with the subsea end of the umbilical <NUM> connected at the subsea unit <NUM> for providing electrical power and signals for the HPU for driving the motors <NUM>, <NUM>. The controller <NUM> receives data from the feeder <NUM>.

In order to position the subsea unit <NUM> in place, the unit is lowered from a vessel onto the seabed <NUM>. An entry connector <NUM> of the subsea unit <NUM> is connected to an entrance <NUM> to the interior <NUM> of the subsea structure <NUM>. The entry connector <NUM> is in the form of tubing which extends between the frame <NUM> of the subsea unit <NUM> and the structure <NUM>, and the hose <NUM> is fed through the tubing of the entry connector <NUM> into the interior <NUM> of the structure <NUM> by spooling out the hose reel <NUM> by operating the motors <NUM>, <NUM> appropriately. The entry connector <NUM> may thus provide protection around the hose <NUM> as it passes into the structure <NUM> to be cleaned such as from effects of currents or the like. It also helps to guide the hose <NUM> to the entrance of the structure <NUM> from the feeder <NUM>. An ROV may be utilised to make the connection of the entry connector <NUM> to the entrance to the interior of the subsea structure <NUM>.

When inserted, in order to clean the interior <NUM>, water is supplied and allowed to exit the hose from the nozzle <NUM> into the interior <NUM>. The water may jet out of the nozzle to clean and wash away deposits on the inside walls of the interior of the structure <NUM>. As cleaning progresses, the hose <NUM> is fed further into the interior <NUM> by spooling out the reel <NUM> by operating the motors <NUM>, <NUM> appropriately. The hose <NUM> is rotated about its own axis to facilitate negotiation of bends or corners in the interior <NUM>. The inserted end of the hose <NUM> may therefore be controlled to facilitate positioning the end, e.g. into difficult to reach corners or bends in the interior structure. When the cleaning operation is concluded, the hose <NUM> is reeled in by reversing the direction of the motor <NUM>. The hose <NUM> is brought back out of the structure <NUM> through the entry connector <NUM> and onto the subsea unit1. The dashed lines in <FIG> signify data communication lines.

The term 'subsea' is used herein to refer to seas which include for example open oceans, inland seas, lakes, rivers and other waterways, which may comprise freshwater or salt water.

Claim 1:
A subsea unit (<NUM>) for cleaning an interior (<NUM>) of a subsea structure (<NUM>), the subsea unit (<NUM>) comprising:
a hose (<NUM>) for delivering fluid from an inlet into an interior (<NUM>) of the subsea structure (<NUM>) to be cleaned for cleaning the interior;
a hose reel (<NUM>) being rotatable around a first axis (<NUM>) and a second axis (<NUM>), wherein the rotation of the hose reel around the first axis (<NUM>) is for feeding the hose into or retracting the hose (<NUM>) from the subsea structure (<NUM>) and rotation of the hose reel around the second axis (<NUM>) is for rotating the hose (<NUM>) around its longitudinal axis (<NUM>); and,
a feeder (<NUM>) for controlling strain in the hose during feeding and/or retraction of the hose.