EP2497578A2

EP2497578A2 - Remediation of underwater fluid storage tanks

Info

Publication number: EP2497578A2
Application number: EP12158317A
Authority: EP
Inventors: Antony Stephen Bamford; Vincent Van Lilley
Original assignee: Geoprober Drilling Ltd
Current assignee: Geoprober Drilling Ltd
Priority date: 2011-03-07
Filing date: 2012-03-06
Publication date: 2012-09-12
Also published as: GB201103751D0; EP2497578A3

Abstract

An underwater fluid storage tank remediation assembly (20) is disclosed which comprises: a flexible pipe (28) which can be inserted into an underwater fluid storage tank (24); a fluid injection device (22) coupled to the flexible pipe and arranged so that fluid flowing down the pipe passes into the fluid injection device, the fluid injection device comprising at least one fluid outlet for directing a jet (36) of fluid into the tank to agitate contaminants (8) in the tank; a pipe gripping and rotation device (30) which can be selectively actuated to grip and rotate the flexible pipe relative to the tank, to facilitate movement of the fluid injection device coupled to the pipe within the tank; a motivating arrangement (32) for generating a motive force which can be used to steer the fluid injection device around the tank when the flexible pipe is rotated by the pipe gripping and rotation device; and a contaminant withdrawal arrangement (34) for withdrawing contaminants agitated by the fluid injection device from the tank.

Description

The present invention relates to an underwater fluid storage tank remediation assembly for removing contaminants from an underwater fluid storage tank, and to a corresponding method. In particular, but not exclusively, the present invention relates to an underwater fluid storage tank remediation assembly for use in the remediation and abandonment of offshore platforms, where underwater tanks or cells have been used for the storage of fluid such as crude oil, and to a corresponding method. The present invention also relates to various devices that can be utilised in the remediation of such tanks or cells.
In the oil and gas exploration and production industry, a wide range of different types of platforms have been employed for gaining access to subsea hydrocarbon deposits in offshore environments. One particular type of platform employs a gravity based structure (GBS) of large mass. Platforms of this type are particularly prevalent in North Sea oil fields, examples including the Brent field in the UK, and the Statfjord field in Norway.
A typical platform structure employing a GBS 1 is shown in Fig. A. The GBS 1 includes a number of concrete fluid storage tanks or cells 2, which rest on a seafloor 3. A plurality of hollow concrete legs 4 rise from the GBS structure 1, to support a production platform 5. The cells 2 are used to store fluids recovered from a well or wells whose production is controlled by the platform 5. To improve the strength and rigidity of the platform structure, the legs 4 are partially filled with water. Additionally, to ensure there are no leaks from the concrete oil storage cells 2 into the marine environment, the water in the concrete legs 4 is maintained at a level which is below sea level, as indicated in Fig. A. The difference in levels between the water in the legs 4 and sea level is such that the water in the legs is at a lower pressure than external ambient water pressure. The oil storage cells 2 communicate with the legs 4, so that the oil in the cells is exposed to the pressure of the water in the legs. As a result, the fluid in the oil storage cells 2 is similarly at a lower pressure than external ambient seawater pressure. In this way, oil egress from the cells 2 would be prevented in the event of a leak. Typically, the level of fluid in the platform legs 4 is maintained at a height which results in a differential pressure of around 4 bar (58.8 psi).
One of the concrete oil storage cells 2 is shown schematically in Fig. B. The cells 2 are filled via a network of piping 6, which generally introduces oil at the top of the cells, and removes oil from the bottom 7. This pipework is often very convoluted, making access into the cells 2 very difficult. Also, a typical operating lifetime of the platform 5 will be a number of decades, during which time a large volume of oil from a producing well or wells, together with contaminants which comprise an array of hazardous materials such as Barium Sulphate scale, will pass through the cells 2. It is expected that contaminants comprising scale and other hazardous materials will have accumulated in a layer on the bottom of the cells, as indicated schematically by reference numeral 8 in Fig. B.
As the well reaches the end of production, the oil production platform 5 becomes redundant. The well is capped and abandoned, and the platform 5 can then be removed. Current proposals for the abandonment of platforms that employ a GBS are for the abandonment of the concrete cells 2 in situ. This will require that the hazardous material 8 be sampled, agitated, mobilised and removed, the platform legs 4 severed below the water line, and seawater allowed to fill the cells 2.
The first stage of the abandonment process will be to drill an access hole in the top of the concrete cell 2 underwater, and to take a sample of the material in the cell. This is illustrated in Fig. C, and can be achieved utilising a remotely operated, subsea drilling stack 9. The stack 9 includes isolation valves 10, and an upper annular sealing mechanism 11 to ensure that the required (typically 4 bar) differential pressure is maintained. An additional annular sealing mechanism 12 is also provided, so that there are two barriers against seawater leakage into the cell. A reciprocating tubing gripper assembly 13 is used to advance a drilling motor (not shown), and to react the drilling torque, so that the access hole can be drilled and the material sampled.
Remediation of the cells 2 will require the mixing and mobilisation of the contents of the cells, and removal of the volume of contaminants, which may be re-injected into a suitable wellbore. There are many tools on the market for performing such operations on land, where cleaning up the contents of oil storage tanks is a relatively routine operation. However, the clean up and remediation of a concrete cell offshore will require a device that is perhaps 40 to 60 metres in length, which can deployed through a hole drilled in the concrete caps of the cells 2, and also through an annular seal which will be required to maintain the typically 4 bar differential pressure. Currently, no such suitable devices are available.
It is amongst the objects of the present invention to obviate or mitigate at least one of the foregoing disadvantages.
According to a first aspect of the present invention, there is provided an underwater fluid storage tank remediation assembly for removing contaminants from an underwater fluid storage tank, the assembly comprising:

a flexible pipe which can be inserted into an underwater fluid storage tank;
a fluid injection device coupled to the flexible pipe and arranged so that fluid flowing down the pipe passes into the fluid injection device, the fluid injection device comprising at least one fluid outlet for directing a jet of fluid into the tank to agitate contaminants in the tank;
a pipe gripping and rotation device which can be selectively actuated to grip and rotate the flexible pipe relative to the tank, to facilitate movement of the fluid injection device coupled to the pipe within the tank;
a motivating arrangement for generating a motive force which can be used to steer the fluid injection device around the tank when the flexible pipe is rotated by the pipe gripping and rotation device; and
a contaminant withdrawal arrangement for withdrawing contaminants agitated by the fluid injection device from the tank.

The assembly of the present invention, comprising a flexible pipe which can be utilised to insert a fluid injection device into the tank, and a motivating arrangement which can be used to steer the fluid injection device, provides the ability to access an underwater fluid storage tank to remediate the tank by removing contaminants contained in the tank. In particular, the inherent flexibility of the pipe enables the pipe, carrying the fluid injection device, to be inserted through an aperture drilled in a wall of the tank. Additionally, the flexibility of the pipe enables the fluid injection device to move around within the tank when the pipe is rotated, whilst the motivating arrangement enables the position of the fluid injection device within the tank to be controlled during such rotation, so that the agitation and removal of contaminants can be optimised.
Reference is made to contaminants that are present in an underwater storage tank. The contaminants will typically be materials of the type which are found in tanks used to store fluids produced from an oil or gas well, particularly crude oil. The contaminants may comprise solids, fluids or a mixture thereof. The contaminants may be of a type that cannot be discharged into the environment without undergoing treatment, and may comprise hazardous materials such as Barium Sulphate scale. Typically, the contaminants (especially solids) will have fallen out of suspension from fluid in the tank and settled on a base of the tank, to form a layer of contaminant material which must be removed before the tank can be abandoned.
The fluid injection device may be coupled to an end of the flexible pipe, and may be directly or indirectly coupled to the pipe.
The fluid injection device may comprise a valve associated with the outlet, for controlling the flow of fluid through the outlet.
The flexible pipe may be arranged so that it adopts a curved profile or shape when the pipe is inserted into the tank. The flexible pipe may comprise a continuous length of tubing, and may be spooled on a storage reel prior to insertion into the tank. In this way, the flexible pipe may adopt a generally helical configuration when it is unspooled and unconstrained. The flexible pipe may be arranged so that it adopts a helical configuration when inserted into the tank.
The motivating arrangement may comprise a motor or turbine coupled to the fluid injection device, for rotating the fluid injection device relative to the flexible pipe. The motor or turbine may be fluid operated, and may be a positive displacement motor (PDM). At least one motivating element may be provided on the fluid injection device, and the element may be arranged so that it can contact an inner surface or wall of the tank, or materials in the tank such as contaminants, to steer the device when it is rotated by the motor. The motivating element may be a flexible abrasive element such as a brush, for agitating the contaminants. The motivating element may be provided on an external surface of the fluid injection device. The motivating element may be axially or helically oriented. The at least one fluid outlet of the device may be arranged to direct fluid on to or past the motivating element, to clean contaminants from the element. The at least one outlet may be oriented so as to promote rotation of the fluid injection device, and may be oriented such that the jet of fluid is directed generally rearwardly, relative to a direction of rotation of the device.
The fluid injection device may be secured against rotation relative to the flexible pipe. The motivating arrangement may comprise a fluid nozzle which may be positioned in, or which may define, the at least one outlet of the fluid injection device. The nozzle may be movable relative to a main body of the fluid injection device, so that the direction of the jet of fluid into the tank can be controlled, to thereby steer the device. The fluid injection device may comprise a plurality of outlets, and may comprise a plurality of corresponding nozzles.
The fluid injection device may comprise a flow control element for permitting fluid flow through a selected one or more of the plurality of outlets. The control element may comprise an outlet portion which can communicate with the selected outlet(s) to permit fluid flow therethrough. The control element may be movable e.g. rotatable from a position where the outlet portion does not communicate with the selected outlet(s), to a position where it communicates with the selected outlet(s), to permit flow. The control element may be a manifold, and may have a plurality of outlets.
The motivating arrangement may comprise a control unit for controlling the motive force, so that the position of the fluid injection device within the tank can be varied, to steer the tool.
Where the motivating arrangement comprises a fluid operated motor or turbine coupled to the fluid injection device and at least one motivating element on the device, the control unit may be arranged to control the operation of a pump which is utilised to supply fluid to the fluid injection device and to the fluid driven motor, to thereby control rotation of the device. This in turn facilitates a variation of the motive force which the motivating element imparts, so that the device can be steered. The control unit may also be arranged to control the flow of fluid through the at least one outlet of the fluid injection device, by controlling the operation of the pump.
Where the fluid injection device is secured against rotation relative to the flexible pipe, the control unit may be arranged to control the operation of a pump which is utilised to supply fluid to the fluid injection device, to thereby control the flow of fluid through the nozzle in the at least one outlet of the fluid injection device, and thus the motive force, so that the tool can be steered. The control unit may be arranged to control the position of the at least one nozzle, and thus the direction of the jet of fluid into the tank, to thereby steer the fluid injection device.
The flexible pipe may comprise an outer flexible pipe portion, and an inner flexible pipe portion located within the outer pipe portion so that an annular flow channel is defined between an inner surface of the outer pipe portion and an outer surface of the inner pipe portion. The inner pipe portion may be secured against rotation relative to the outer pipe portion. The fluid injection device may be coupled to the ends of the inner and outer pipe portions. This may serve to secure the inner pipe portion against rotation relative to the outer pipe portion, and may also facilitate isolation of a bore of the inner pipe portion from the annular flow channel. The annular flow channel may communicate with a pump, and the assembly may comprise a valve for selectively closing the annular flow channel so that the pressure of the fluid in the channel can be raised to above ambient external water pressure, to support the flexible pipe during gripping by the pipe gripping and rotation device.
The assembly may comprise pressure control equipment for maintaining a pressure of fluid in the inner flexible pipe portion at a level which is lower than a pressure of fluid in the annular flow channel. This may facilitate insertion of the flexible pipe into the tank, because a differential pressure area between the outer pipe portion and the inner pipe portion (resulting from their different dimensions) may be such that there will be net force on the inner pipe portion tending to urge the flexible pipe into the tank. The pressure control equipment may comprise pressure isolation means for isolating the fluid in the inner pipe portion from the fluid in the annular flow channel. The outlet of the fluid injection device may serve for communicating the pressure of the fluid in the tank to the fluid in the inner pipe portion, which may be at a level that is lower than ambient external water pressure. The pressure control equipment may comprise a valve which can be selectively opened to communicate ambient water pressure to the fluid in the annular flow channel. The at least one outlet of the fluid injection device may communicate with the annular flow channel, and the pressure control equipment may comprise at least one valve in the fluid injection device, for selectively closing said outlet. This may facilitate isolation of the channel from the lower pressure of the fluid in the tank, relative to ambient water pressure.
The assembly may comprise a rigid pipe section coupled to or forming an upper end of the flexible pipe. The rigid pipe section may be coupled to or may form an upper end of the outer flexible pipe portion. The provision of the rigid pipe section may facilitate gripping and rotation of the flexible pipe by the pipe gripping and rotation device. It will be understood that the rigid pipe section is of greater rigidity than the flexible pipe/a remainder of the flexible pipe, in that it has a higher resistance to deformation under the applied load of the pipe gripping and rotation device. The rigid pipe section may be of the same material as the flexible pipe/a remainder of the flexible pipe but of greater wall thickness; or may be of the same wall thickness but of a different material having a higher yield strength.
The at least one outlet of the fluid injection device may be arranged so that it is in fluid communication with the inner pipe portion, and the assembly arranged so that fluid flows down the inner pipe portion to the fluid injection device for injection into the tank. The contaminant withdrawal arrangement may comprise at least one fluid inlet formed in a wall of the outer pipe portion, or in a wall of the fluid injection device, said inlet being in fluid communication with the annular flow channel so that contaminants agitated by the fluid injection device can be withdrawn along the channel. The fluid injection device may comprise a flow port arranged to direct a jet of fluid upwardly along the annular flow channel past the inlet, to enhance withdrawal of contaminants (which may be by the stimulation of a Venturi effect).
The at least one outlet of the fluid injection device may be arranged so that it is in fluid communication with the annular flow channel, and the assembly arranged so that fluid flows down the annular flow channel to the fluid injection device for injection into the tank. The contaminant withdrawal arrangement may comprise a fluid inlet defined by the fluid injection device and which can be arranged so that it is in fluid communication with the inner pipe portion so that contaminants agitated by the fluid injection device can be withdrawn along the inner pipe portion. The contaminant withdrawal arrangement may comprise at least one secondary outlet, for generating a secondary jet of fluid. The at least one secondary outlet may open on to an external surface of the fluid injection device, for directing the secondary jet into the tank to promote the withdrawal of contaminants. The at least one secondary outlet may open on to an internal bore of the tool, for promoting the withdrawal of contaminants. The fluid inlet of the fluid injection device may comprise a tapered portion, to promote withdrawal of contaminants (which may be by the stimulation of a Venturi effect), and the at least one secondary outlet may be arranged to direct a jet of fluid into the tapered portion to promote fluid flow. The shape of the inlet may be adjustable.
The fluid injection device may comprise a plurality of fluid outlets for directing jets of fluid into the tank, and each fluid outlet may be supplied with fluid from a common fluid chamber or gallery within the device.
The pipe gripping and rotation device may comprise a plurality of pipe gripping elements which are movable between retracted positions out of contact with the flexible pipe, and deployed positions where they contact and grip the flexible pipe so that the pipe can be rotated. The gripping elements may be arranged to grip the outer flexible pipe portion and/or the rigid pipe section coupled/forming an upper end of the outer flexible pipe portion. The gripping elements may be mounted on a support which can be rotated about an axis that is parallel to an axis of the flexible pipe, to thereby rotate the gripping elements and thus the flexible pipe. The rotatable support may be mounted on a slewing bearing to facilitate the rotation. The device may comprise a drive unit such as a motor for rotating the support. The pipe gripping and rotation device may be configured for continuous rotation, or for limited angular rotation. In the latter case, this will require that the gripping elements be periodically released and the elements rotated back in an opposite direction before being redeployed to grip the pipe for a subsequent further rotation. The gripping elements may be movable axially (that is in a direction parallel to an axis of the flexible pipe) whilst gripping the pipe, for translating the flexible pipe relative to the tank. This may facilitate withdrawal of the flexible pipe into the tank and/or insertion.
The flexible pipe may comprise at least one communication line located in a wall of the pipe. The communication line may serve for: transmitting data relating to one or more measured parameter to surface (which parameter may be selected from the group comprising temperature, strain in the pipe and fluid pressure); and/or transmitting a control signal from surface so that a desired operation can be performed (which may be an operation of the fluid injection device, the measurement of a parameter, the opening or closing of a valve, or operation of the motor).
The assembly may comprise a tensioning arrangement for tensioning the flexible pipe. As discussed above, the pipe may be rotated during insertion so that it adopts a helical configuration. Fluid pressure in the pipe, when fluid is directed to the injection device, may cause the helix to 'unwind', which may in turn cause the injection device to move outwardly towards a wall of the tank. The tensioning arrangement may impart a tensile force on the flexible pipe to counteract the unwinding tendency. The tensioning arrangement may comprise a plurality of elongate tension members, which may be distributed around the circumference of the pipe. The tension members may be individually or jointly tensionable for tensioning the pipe. Where they are individually tensionable, this may facilitate the maintenance or adoption of a particular helical configuration of the pipe. The tension members may be disposed within passages in a wall of the pipe.
According to a second aspect of the present invention, there is provided a method of remediating an underwater fluid storage tank to remove contaminants from the tank, the method comprising the steps of:

coupling a fluid injection device to a flexible pipe;
inserting the fluid injection device into an underwater fluid storage tank to be remediated using the flexible pipe;
passing fluid down the flexible pipe and into the fluid injection device;
directing fluid passed into the fluid injection device through at least one fluid outlet of the device, so that the fluid is jetted into the tank to agitate contaminants in the tank;
actuating a pipe gripping and rotation device to grip and rotate the flexible pipe relative to the tank, to thereby facilitate movement of the fluid injection device within the tank;
operating a motivating arrangement to generate a motive force for steering the fluid injection device around the tank when the flexible pipe is rotated by the pipe gripping and rotation device; and
withdrawing contaminants agitated by the fluid injection device from the tank using a contaminant withdrawal arrangement.

The method may comprise drilling an access hole in a wall of the tank employing a drill bit; sealing the access hole to prevent fluid leakage; and subsequently deploying the fluid injection device on the flexible pipe through the access hole and into the tank. The flexible pipe may be deployed through an annular seal element which maintains a seal around the pipe to prevent fluid leakage through the access hole during insertion of the pipe.
The step of inserting the fluid injection device into the tank may comprise setting the device down on a layer of contaminant resting on a base of the tank, or on the base of the tank itself. The fluid injection device may be laid down so that a side wall of the device rests on the contaminant layer or on the base of the tank. The method may comprise continuing to insert the flexible pipe after the fluid injection device has been laid down, so that the pipe adopts a generally helical configuration in the tank. The flexible pipe may be rotated during insertion into the tank, to facilitate adoption of the helical configuration. To achieve this, the flexible pipe may be spooled on a pipe reel prior to insertion, so that the pipe adopts a helical configuration when unconstrained, as when it is inserted into the tank.
The method may comprise rotating the flexible pipe to drag the fluid injection device around a layer of contaminant resting on a base of the tank, to thereby agitate the contaminants. The fluid injection device may be steered by controlling application of the motive force as the device is dragged around the layer of contaminant, to move the device towards or away from a centre of the tank. In this way, the fluid injection device may follow a generally circular path around the tank whose radius may be controlled according to the motive force which is applied. Where the flexible pipe is arranged in a helical configuration in the tank, the pipe may be rotated in the same direction to that which the pipe was rotated during insertion into the tank.
The method may comprise driving the fluid injection device around the tank utilising the motivating force generated by the motivating arrangement, and rotating the flexible pipe to follow the device during its movement. The fluid injection device may be steered by controlling application of the motive force as the device is driven around the layer of contaminant, to move the device towards or away from a centre of the tank. Where the flexible pipe is arranged in a helical configuration in the tank, the pipe may be rotated in an opposite direction to that which the pipe was rotated during insertion into the tank.
Application of the motive force may be controlled by varying a magnitude of the motive force. Application of the motive force may be controlled by changing a direction of the motive force. A rate of rotation of the flexible pipe may be controlled to facilitate steering of the fluid injection device; increasing a rate of rotation of the flexible pipe may cause the fluid injection device to move outwardly away from a centre of the tank; decreasing a rate of rotation of the flexible pipe may cause the fluid injection device to move inwardly towards a centre of the tank.
The step of operating the motivating arrangement may comprise operating a motor or turbine coupled to the fluid injection device to rotate the device. The motor may rotate the device in an opposite rotational direction the direction that the flexible pipe is rotated. The motive force applied to the fluid injection device by the motor may be transferred to at least one motivating element on the device, which may be a flexible abrasive element such as a brush, the motivating element contacting the contaminants or the base of the tank to steer the device. The motivating element may also agitate the contaminants.
The step of operating the motivating arrangement may comprise controlling the flow rate of fluid through the at least one outlet of the fluid injection device. The step of operating the motivating arrangement may comprise controlling the direction of the jet of fluid which is injected into the tank through the at least one outlet of the fluid injection device. The motive force may be the reaction force on the fluid injection device which results from jetting of the fluid through said outlet. Controlling the flow rate of the fluid through said outlet may thereby control the magnitude of the reactionary motive force on the fluid injection device, so that the fluid injection device can be steered around the tank. Controlling the direction of the fluid jet from said outlet may thereby control the direction of the reactionary motive force on the fluid injection device, so that the device can be steered around the tank.
The fluid injection device may be coupled to a flexible pipe having an outer flexible pipe portion and an inner flexible pipe portion located within the outer pipe portion, an annular flow channel being defined between an inner wall of the outer pipe portion and an outer wall of the inner pipe portion. The pipe portions may be secured against rotation relative to one another, and may both be coupled to the fluid injection device. The step of inserting the flexible pipe into the tank may comprise arranging the pressure of the fluid in the tank to be lower than ambient water pressure; isolating fluid in the inner pipe portion from fluid in the annular flow channel; exposing the fluid in the inner pipe portion to the pressure of the fluid in the tank; and exposing the fluid in the annular flow channel to ambient external water pressure (which is higher than that of the fluid in the tank). The pressure differential between the fluid in the inner pipe portion and that in the annular flow channel may result in a force tending to urge the flexible pipe into the tank, due to the differential pressure areas of the pipe portions. The method may comprise operating an annular seal element to grip an external surface of the outer pipe portion, and controlling the gripping force exerted on the outer pipe portion by the annular seal element so that the force resulting from the pressure differential between the inner and outer pipe portions can be utilised to urge the flexible pipe into the tank. The annular seal element may be arranged so that a leakage of water past the seal and into the tank is permitted (the tank pressure being lower than ambient external water pressure so that fluid egress from the tank is prevented). The flow of fluid past the seal may exert a frictional force on the outer pipe portion, and the method may comprise employing the frictional force to urge the flexible pipe into the tank. This may be achieved by controlling the gripping force exerted on the outer pipe portion by the annular seal element, reduction of the gripping force leading to increased leakage and thus a greater frictional drive force exerted on the outer pipe portion.
Following withdrawal of contaminants, the method may comprise removing the flexible pipe and the fluid injection device from the tank. Where the flexible pipe comprises said outer and inner pipe portions, the method may comprise raising the pressure of the fluid in the annular flow channel to above ambient water pressure, to thereby reinforce the pipe. The pipe may then be withdrawn from the tank utilising the pipe gripping and rotation device. Gripping elements of the pipe rotation and gripping device may be operated to move from retracted positions where they are out of contact with the pipe, to deployed positions where they contact and grip the pipe. The gripping elements may then be moved in an axial direction to translate the outer pipe portion and thus withdraw the coupled outer and inner pipe portions from the tank. The method may comprise gripping the outer pipe portion using an annular seal element to resist return motion of the pipes into the tank; returning the gripping elements to their retracted positions; moving the gripping elements in an axial direction back to their start positions; redeploying the gripping elements to once again grip the outer pipe returning; reducing a gripping force exerted on the outer pipe by the annular seal element; and then translating the outer pipe portion a further axial distance using the gripping elements. These steps may be repeated as necessary until the flexible pipe has been retracted from the tank. The method may comprise arranging the gripping elements to grip a rigid pipe section coupled to, or provided on, an upper end of the flexible pipe, in particular the outer pipe portion.
The method may comprise tensioning the flexible pipe to cause it to adopt a particular helical configuration, and/or to help maintain the pipe in a particular such configuration.
Further features of the method of the second aspect of the invention may be derived from elsewhere in this document, particularly from or in relation to the first aspect of the invention.
According to a third aspect of the present invention, there is provided an underwater fluid storage tank remediation unit for removing contaminants from an underwater fluid storage tank, the unit comprising:

a flexible pipe which can be inserted into an underwater fluid storage tank;
a fluid injection device coupled to the flexible pipe and arranged so that fluid flowing down the pipe passes into the fluid injection device, the fluid injection device comprising at least one fluid outlet for directing a jet of fluid into the tank to agitate contaminants in the tank, in which the flexible pipe can be rotated relative to the tank to facilitate movement of the fluid injection device within the tank;
a motivating arrangement for generating a motive force which can be used to steer the fluid injection device around the tank when the flexible pipe is rotated; and
a contaminant withdrawal arrangement for withdrawing contaminants agitated by the fluid injection device from the tank.

Further features of the unit of the third aspect of the invention are defined above in relation to the first aspect of the invention.
According to a fourth aspect of the present invention, there is provided a fluid injection device for use in agitating contaminants in an underwater fluid storage tank, the fluid injection device being in accordance with the device defined in the first aspect of the present invention.
Further features of the fluid injection device of the fourth aspect of the invention are defined above in relation to the first aspect of the invention.
It will be understood that the fluid injection device may have a utility in other environments.
According to a fifth aspect of the present invention, there is provided a pipe gripping and rotation device which can be selectively actuated to grip and rotate a flexible pipe relative to an underwater fluid storage tank.
Further features of the pipe gripping and rotation device of the fifth aspect of the invention are defined above in relation to the first aspect of the invention.
It will be understood that the pipe gripping and rotation device may have a utility in other environments or situations where it is desired to grip and rotate a pipe.
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a side view of part of an underwater fluid storage tank remediation assembly for removing contaminants from an underwater fluid storage tank, in accordance with an embodiment of the present invention;
Fig. 2 is a longitudinal sectional view of a flexible pipe and fluid injection device of the assembly shown in Fig. 1, which can be inserted into the underwater fluid storage tank;
Fig. 3 is a longitudinal sectional view of the assembly shown in Figs. 1 and 2 following location of the flexible pipe in the tank;
Fig. 4 is a view of the assembly mounted on a cap of the tank, the tank shown in longitudinal section;
Fig. 5 is a cross-sectional view of the tank and the assembly taken in the direction D-D of Fig. 4;
Figs. 6, 7 and 8 are longitudinal sectional views illustrating various steps in a method employing the assembly of Fig. 1;
Fig. 9 is an enlarged longitudinal sectional view of a fluid injection device in accordance with another embodiment of the invention;
Fig. 10 is a longitudinal sectional view of part of an underwater fluid storage tank remediation assembly for removing contaminants from an underwater fluid storage tank, in accordance with another embodiment of the present invention;
Fig. 11 is an enlarged longitudinal sectional view of a fluid injection device in accordance with another embodiment of the invention, which has a utility in the assembly of Fig. 10;
Fig. 12 is an enlarged longitudinal sectional view of a fluid injection device in accordance with another embodiment of the invention, which has a utility in the assembly of Fig. 10; -
Fig. 13 is a cross-sectional view of the device shown in Fig. 12, taken in the direction of the arrows E-E of Fig. 12;
Fig. 14 is a schematic perspective view of a fluid injection device in accordance with another embodiment of the invention;
Fig. 15 is a view of a control element forming part of the fluid injection device shown in Fig. 14, taken from a different angle;
Fig. 16 is a perspective view of part of an underwater fluid storage tank remediation assembly for removing contaminants from an underwater fluid storage tank, in accordance with another embodiment of the present invention; and
Fig. 17 is a longitudinal sectional view of the part of the assembly shown in Fig. 16.

Turning firstly to Fig. 1, there is shown a side view of part of an underwater fluid storage tank remediation assembly for removing contaminants from an underwater fluid storage tank, the assembly indicated generally by reference numeral 20. The assembly 20 has a utility in removing contaminants from an underwater fluid storage tank 24, which is of similar construction to the tank 2 shown in Fig. C and described above. Only part of a cap 26 of the tank 24 is shown in Fig. 1.
The assembly 20 comprises a flexible pipe 28 which can be inserted into the underwater fluid storage tank 24, which is shown in the longitudinal sectional view of Fig. 2. The assembly 20 also comprises a fluid injection device or end effecter 22, a pipe gripping and rotation device indicated generally by reference numeral 30, a motivating arrangement indicated generally by reference numeral 32, and a contaminant withdrawal arrangement indicated generally by reference numeral 34.
The fluid injection device 22 is coupled to the flexible pipe 28 and arranged so that fluid flowing down the pipe passes into the device, as indicated by the arrows 34 in Fig. 2. The fluid injection device 22 comprises at least one fluid outlet for directing a jet of fluid 36 into the tank 24, to agitate contaminants in the tank. In the illustrated embodiment, the device 22 comprises a plurality of such outlets, each of which directs a respective fluid jet 36 into the tank. The pipe gripping and rotation device 30 can be selectively actuated to grip and rotate the flexible pipe 28 relative to the tank 24, to facilitate movement of the fluid injection device 22 coupled to the pipe within the tank 24. The motivating arrangement 32 serves for generating a motive force which can be used to steer the fluid injection device 22 around the tank 24 when the flexible pipe 28 is rotated. The gripping and rotation device 30, and motivating arrangement 32, are used in combination to move the fluid injection device 22 around the tank 24, to agitate contaminants resting on a base of the tank. The effluent fluid with entrained contaminants that have been agitated by the jets 36 exiting the fluid injection device 22 as it travels around the tank 24 are drawn out of the tank by the contaminant withdrawal arrangement 34. In this way, the tank 24 is remediated so that it can subsequently be abandoned, with sea water allowed to flow in and out of the tank.
The assembly 20 and its method of operation will now be described in more detail with reference also to Fig. 3, which is a longitudinal sectional view showing the assembly following location of the flexible pipe 28 in the tank 24; Fig. 4, which is a view of the tank 24 showing the assembly 20 mounted on the tank cap 26 and with the tank shown in longitudinal section; and Fig. 5, which is a cross-sectional view taken in the direction D-D of Fig. 4.
The flexible pipe 28 takes the form of a pipe-in-pipe and comprises an outer flexible pipe portion 38, and an inner flexible pipe portion 40 which is located concentrically within the outer pipe portion. An annular flow channel 42 is defined between an inner surface 44 of the outer pipe portion 38, and an outer surface 46 of the inner pipe portion 40. The inner pipe portion 40 is secured against rotation relative to the outer pipe portion 38, and the flexible pipe 28 is spooled on a reel (not shown) prior to deployment from a vessel or rig (not shown) at surface, for insertion into the tank 24. In this way and as will be described in more detail below, the flexible pipe 28 will adopt a helical configuration when inserted into the tank 24. A rigid pipe section 48 is coupled to an upper end 50 of the outer pipe portion 38, and facilitates gripping of the flexible pipe 28 by the pipe gripping and rotation device 30. The rigid pipe section 48 may alternatively be an integral part of the outer pipe portion 38. The rigid pipe section 48 is of sufficient rigidity to resist deformation under the loading which is imparted by the gripping and rotation device 30. The rigid pipe section 48 may be of the same or a similar material to that of the outer pipe portion 38 but of increased wall thickness, or may be of a different material having a higher yield strength than the material forming the outer pipe portion 38.
The fluid injection device 22 is coupled to the flexible pipe 28, in particular the inner pipe portion 40, and arranged so that it is in fluid communication with a main bore 52 of the inner pipe portion. The motivating arrangement comprises a motor or turbine, and in the embodiment of Figs. 1 to 5, comprises a fluid driven motor in the form of a PDM 54. The PDM 54 is coupled to the fluid injection device 22 and is arranged to rotate the device when it is activated. The PDM 54 is coupled to the inner pipe portion 34 so that fluid passing down the pipe main bore 52 flows through the PDM to the fluid injection device 22. In this way, the fluid which is supplied to the fluid injection device 22 for injection into the tank 24 is also used to drive the PDM 54 and rotate the fluid injection device. As will be described in more detail below, the PDM 54 is arranged to rotate in an opposite direction to that of the flexible pipe 28. A rotor 56 and stator 58 of the PDM 54 are shown schematically in Fig. 2. A gearbox 60 is provided between the PDM 54 and the fluid injection device 22, to provide a geared input drive to the injection device.
The outer flexible pipe portion 38 comprises at least one inlet and, in the illustrated embodiment, comprises a plurality of inlets 62, 64 and 66, the flow area of the inlets decreasing in a direction extending upwardly from a bottom of the pipe. The inner pipe portion 40 is coupled to a high pressure supply pump 62, which supplies fluid (typically water) under pressure down the pipe bore 52 to the fluid injection device 22. In a similar fashion, a suction pump 64 communicates with the annular flow channel 42 through a port 67, for withdrawing effluent along the annular flow channel to surface. Thus, in use, fluid is supplied down through the inner pipe portion 40 to the injection device 22, jetted into the tank 24 (by jets 36) to agitate contaminants in a contaminant layer 110, and fluid with entrained contaminants is drawn into the annular flow channel 42 through the inlets 62, 64 and 66. The fluid with the entrained contaminants passes upwardly along the annular flow channel 42, through the port 67, and is recovered to surface for treatment and/or disposal.
As explained above, the flexible pipe 28 is rotated by the pipe gripping and rotation device 30. The inner pipe portion 40 is secured against rotation relative to the outer pipe portion 38 by a connection at a lower end 68 of the pipe, and at an upper termination 49. In this way, the two pipes 38 and 40 are rotated in unison by the gripping and rotation device 30. The upper termination 49 includes a housing 72 that defines the outlet port 67. A swivel bearing and seal 70 seals the outer pipe portion 38 to the housing 72, and allows for rotation of the outer pipe portion 38 whilst maintaining fluid communication between the annular flow channel 42, port 67 and pump 64. Thus, the inner pipe 38 can be rotated whilst fluid is drawn upwardly through the annular flow channel 42.
In a similar fashion, a swivel bearing and slip ring arrangement 73 is provided on the inner pipe portion 40, which includes a seal 74 for sealing pipe portion 40 relative to an upper housing 76, which provides a connection for communication lines 77. The swivel bearing and seal 74 permits rotation of the inner pipe portion 40 relative to the housing 76, whilst maintaining a seal relative to the housing so that fluid can be supplied into the pipe bore 52 through a high pressure hose 78 which extends from the pump 62 to the housing 76. An annular seal 80 also seals against the outer surface 46 of the inner pipe portion 40, to seal the housing 72, but permits rotation of the inner pipe portion. The seal 80 also enables the inner pipe portion 40 to slide to a limited extent with respect to the outer pipe portion 40. The bearing and slip ring arrangement 73 enables the communication lines 77 to be incorporated into the assembly 20, which may be power and fibre optics lines, for the purpose of navigating the fluid injection device 22 within the tank 24. Distributed fibre optics strain measurements can be obtained from suitable sensors using the fibre optic lines 77, which can be helically wound into either the high pressure inner pipe portion 40 or the outer flexible pipe portion 38. This is based on the Brillouin principle, and will enable the user to get a real time strain (and optionally temperature and pressure measurements) and enable the calculation of trajectory measurement of the pipe 28 in the tank 24 as it moves position in response to controls. The fibre optics can also be used to provide feedback on a position and orientation of the device 22 within the tank 24, by means of monitoring equipment (not shown), which may be a sonic tool or an electromagnetic device. The fibre optics may further be utilised to transmit data such as the temperature or pressure of fluid in parts of the assembly or the tank 24, measured using suitable sensors (not shown).
The pipe gripping and rotation device 30 comprises gripping elements 82, having gripping surfaces 84 which serve for gripping the rigid pipe portion 48. The gripping elements 82 may have gripping blocks (not shown) defining the surfaces 84, which may be of a plastics material such as a polyurethane material. This reduces the likelihood of any damage on the surface of the outer pipe portion 38. The gripping elements 82 are each moveable between retracted positions where they do not grip the rigid pipe section 48, and deployed positions where they grip the pipe section so that the outer pipe portion 38 can be rotated. The gripping elements 82 have inclined rear faces 86 which cooperate with corresponding inclined faces 88 on activating elements 90. The activating elements 90 are translated axially downwardly to urge the gripping elements 82 radially inwardly, by cooperation between the inclined faces 86 and 88. The gripping surfaces 84 of the gripping elements 82 may include ball grippers which serve for gripping the rigid pipe portion 48. Grippers of this type are known in the art, such as is disclosed in the applicant's International patent publication number WO2006/010906A1 . The gripping and activating elements 82 and 90 are mounted on a support 94 which is rotatable about a main axis of the flexible pipe 28.
The support 94 is mounted on a bearing and slewing ring 96, and driven by a hydraulic or electrical motor 98, to rotate the gripped outer pipe portion 38.
The assembly 20 additionally comprises upper and lower isolation valves 99 and 100, a primary annular seal 102 and an additional annular sealing mechanism 104. Fig. 1 shows the assembly 20 during drilling of an access hole 106 in the tank cap 26, where a drill string 108 incorporating a drilling motor and drill bit (not shown) has been located in the assembly. The drill string 108 passes down through the pipe gripping and rotation device 30, which includes a pressure bearing housing 109 containing appropriate seals, through the primary and additional annular seal mechanisms 102 and 104 and the isolation valves 99 and 100. The primary and additional annular seals 102 and 104 provide a seal with an external surface of the drill string during drilling of the access hole 106, to prevent fluid leakage. Following drilling of the access hole 106, the drill string 108 can be removed and the isolation valves 99 and 100 operated to close the tank 24. The flexible pipe 28 can then be run in and inserted into the tank, as shown in Fig. 3 and 4. The method of insertion will be described in more detail below.
The flexible pipe 28 is inserted into the tank 24, and the fluid injection device 22 brought into contact with a layer of contaminants 110 resting on a base 112 of the tank 24. Insertion of the pipe 28 continues so that the fluid injection device 22 is laid down in a generally horizontal orientation on or in the layer of contaminants 110. This is facilitated by the helical orientation which the pipe 28 adopts when it is inserted into the tank 24. Additionally, the pipe 28 is rotated to promote adoption of the helical configuration, in this instance in an anti-clockwise or counter-clockwise direction, when viewing Fig. 5. Rotation of the pipe 28 will be achieved using the pipe gripping and rotation device 30 The rigid pipe portion 48 connected to the flexible pipe 28 provides improved crush resistance and increases the torsion and axial loads which can be applied. However, the design of the gripping device 30 and flexible pipe 28 may allow for the gripping/rotation forces to be imparted on the pipe 28, so that the rigid pipe portion 48 can be dispensed with. This may be facilitated by pressuring-up the annular flow channel 42.
The gripping device 30 may be arranged so that it can impart a continuous rotation, or may be arranged to provide for limited angular rotation. The latter case requires cooperation with the primary annular seal 102/annular sealing mechanism 104, so that the gripping device can be rotated back to a start position for imparting a subsequent angular rotation.
It will be appreciated that if an excess length of outer flexible pipe portion 38 and high pressure inner pipe portion 40 are introduced into the tank 24, the rotating fluid injection device 22 will first touch the bottom of the contaminant sludge and then rotate into the horizontal as more pipe is introduced into the top of the tank. The pipe 28 can be designed to retain the "set" or curvature the individual pipes acquired when on a storage reel. It is known that the suspended pipes will take the form of a helix with the pitch reducing towards the top. As more pipe 28 is added, it will lay flat in a coil shape on the sediment at the bottom of the tank 24.
When the fluid injection device 22 has been laid down as shown in Fig. 4, the device can be activated by pumping fluid along the inner flexible pipe portion 40, as described above. This also activates the drilling motor 54, which rotates the injection device 22. The motivating arrangement also comprises at least one motivating element, which is a flexible abrasive element such as a brush 114. Typically a number of such brushes 114 will be provided. Clean water is directed through the device outlets to break up the contaminant sludge and clean the brush 114. The brush 114 is provided on an external surface 116 of the injection device 22, and typically extends in a helical path around the surface 116. In this way, when the injection device 22 is rotated, the brushes 114 contact the contaminants, and this provides a motive force which tends to drive the injection device 22 outwardly away from a centre of the tank, or inwardly towards the tank centre, depending upon the direction of rotation.
In the illustrated embodiment, and looking along the pipe 28 from the top-down, the PDM rotor 56 rotates in the left hand direction, tending to carry the injection device 22 outwardly away from a centre of the tank. During this time, the pipe 28 is rotated in the the same direction that it was rotated during insertion, and thus the anti-clockwise direction of Fig. 5. This motion of the pipe 28 carries the injection device 22 in a generally circular path around the tank 24, and tends to draw-in the helix of the pipe so that the injection device 22 is drawn inwardly, towards the centre of the tank. In this embodiment, therefore, movement of the injection device 22 in the circular path around the tank 24 is achieved by rotation of the pipe 28, whilst steering of the device 22 is achieved by rotation of the device using the PDM 54. For example, for a constant rate of rotation of the pipe 28, rotation of the injection device 22 can be increased or decreased to direct the device outwardly away from the tank centre, or inwardly towards the centre. In this way, the injection device 22 can be arranged to move around the entire surface of the layer of contaminants 110, so that the contaminants can be agitated for withdrawal from the tank 24. It will be noted that the helix of the pipe 28 is such that a rotation of the pipe at the top by the gripping means 30 and about its own axis is not felt at the bottom end by the injection device 22. In other words, rotation of the pipe 28 does not cause a rotation of the injection device 22. The injection device 22 is rotated by the PDM 54, and so steered around the tank 24.
Also, fluid pressure in the flexible pipe 28 during use will tend to cause the helix to 'unwind' thereby moving the injection device 22 radially outwardly. This may be counteracted by rotation of the pipe 28 using the gripping device 30. It will therefore be understood that, in general terms and across all embodiments of the invention, the position of the injection device within the tank 24 can be varied by controlling the fluid pressure in the pipe 28 and its speed of rotation. This may also depend on other factors such as the flexibility, length and/or weight of the pipe 28.
Pumping water through the high pressure inner pipe portion 40 therefore starts the water powered PDM 54, which is designed to turn to the left. This rotates the injection device 22 with the helically wound brushes 114 on the outside surface. This results in a right hand reactive torque applied to the pipe 28, which is restrained since it is resting in a curved shape on the bottom of the tank 24. The rotation of the helically wound brushes 114 forces the injection device 22 towards the wall of the tank 24, where it is naturally restrained. However rotation of the rigid pipe section 48 in the reciprocating gripping elements 82 at the top of the tank 24 allows the entire assembly, including the helix shaped pipe 28 and the injection device 22, to translate in a circular fashion around the circumference of the tank 24. The exact nature of the trajectory will depend on several factors which may include: the modulus of elasticity of the pipe 28; the water volume and pressure supplied to the water powered PDM 54; length and arrangement of the brushes 114 on the injection device 22; the size and arrangement of the outlets which direct the jets into the tank 24; and the nature of the contaminant sediment or sludge. Also, the speed of rotation of the rigid pipe section 48 at the top of the tank 24 will affect how tightly the coiled pipe 28 is wound. The torsional stiffness of the combined pipe portions 38 and 40 of the flexible pipe 28 will be designed so that the rotation of the rigid pipe section 48 can easily move the injection device around a circumference of the tank 24.
Turning now to Figs. 6, 7 and 8, the method of inserting the assembly 20 into the tank 24 will now be described in more detail. Figs. 6 to 8 are longitudinal sectional views illustrating various steps in the method. Fig. 6 shows the tank 24 following drilling of the access hole 106 in the tank cap 26. A sub-sea drilling stack 118 of the assembly 20 is shown mounted on the tank cap 26, coupled to a mounting plate which is secured and sealed to the cap. The stack 118 includes the pipe gripping and rotation device 30, upper annular seal 102, additional annular sealing mechanism 104, and the isolation valves 99 and 100 (only the valve 100 being shown). The stack 118 also comprises a guide funnel 122 which serves for guiding the flexible pipe 28 and fluid injection device 22 down into the tank 24. As described above, fluid in the tank 24 is maintained at a pressure which is lower than an ambient external water pressure. The lower isolation valve 100 is shown in Fig. 6 in a closed position, in which it closes the access hole 106, to prevent ingress of water into the tank 24. The gripping elements 82 of the pipe gripping and rotation device 30 are also in their retracted positions, and the annular seal 102 and sealing mechanism 104 deactivated.
The flexible pipe 28 and fluid injection device 22 are provided as a unit 124 which can be deployed from the platform or vessel at surface, and is suspended from a heave compensated lift line 126 which ensures that there is sufficient slack in the pipe 28 to avoid "snatch loads", particularly when a separate vessel is employed, which will move under applied wave loading. Valves 128 and 130 control fluid flow along the annular flow channel 42, and the inner pipe bore 52, respectively. The valve 128 is open during deployment so that the annular flow channel 42 communicates with the external water.
A remotely operated vehicle (ROV) 132 is used to guide the fluid injection device 22 into the guide funnel 122, and thus down into the drilling stack 118. The device is set down on the lower isolation valve 100, and a weight is set down on the valve. For example, if the complete unit 124 had a weight of around 1000kg in water, then typically 500kg of weight would be set down on the lower isolation valve 100. The primary annular seal 102 and/or the additional annular sealing mechanism 104 are then lightly closed against an external surface of the fluid injection device 22. This is illustrated in Fig. 7. The lower isolation valve 100 is then opened and immediately water starts to leak past the lightly closed primary annular seal 102/additional annular sealing mechanism 104. As explained above, the differential pressure between the fluid in the annular flow channel 42, and that in the inner flexible pipe portion 40 (which communicates with the fluid in the tank 24) will result in a net force at the injection device 22 tending to force the pipe 28 into the tank 24. In the illustrated example, the size of the drilled hole 106 is around 9"; the outer flexible pipe portion 38 is 8.5" OD, 7.0" ID; the inner pipe portion 40 is 3.2" OD, 2" ID; the total length of assembly 20 is around 100 metres; the water depth is around 80 metres; and the pressure differential is around 4 bar. As a result, it is estimated that the net force at the fluid injection device 22 will be 0.811 metric tonnes.
It is possible to adjust the hydraulic closing pressure on the primary annular seal 102 (and/or on the additional sealing mechanism 104) to control the descent of the pipe-in-pipe 28 into the tank 24, and also to minimise the leakage of water into the tank. However, it may be desirable to permit leakage of water past the seal 102/104 as this can be utilised to provide an additional motive force to push the pipe 28 into the tank 24. This is as a result of frictional forces which the water flowing past the seal 102/104 exerts upon the fluid injection device 22/pipe 28. This will be a function of the velocity of the water and the volume of water leaking into the tank 24. It will be understood however that it is possible to insert the fluid injection device 22 and pipe 28 without any fluid leakage past the seal 102/104. This can be achieved by arranging the seal 102/104 to exert a seal force which is sufficient to prevent fluid leakage, but which is not so great that it restricts movement of the pipe 28. Additionally, the typical 4 bar differential pressure between the outer flexible pipe portion 38 and the inner pipe portion 40, and appropriate control of the hydraulic closing pressure on the seal 102/104, will ensure that the outer pipe portion 38 does not collapse during deployment.
Fig. 8 shows the unit 124 following partial insertion of the pipe 28 into the tank 24. When the pipe 28 has descended a sufficient distance, the rigid pipe portion 48 provided at the upper end of the outer flexible pipe portion 38 enters the pipe gripping and rotation device 30, as shown in Fig. 3 and described above. The gripping elements 82 can then be actuated to engage the rigid pipe portion, and the lift line 126 slacked off and disconnected using the ROV 132. The gripping elements 82 can be used to hold the load resulting from the differential pressure, and to position the upper termination 49 at a desired location (Fig. 3) so that high pressure water line and the suction pump 64 can be connected, using the ROV 132. The assembly 20 is then ready for operation to remove contaminants from the tank 24 according to the method described above.
To remove the unit 124 from the tank 24, the high pressure water supply pump 62 and suction pump 64 should be disconnected with the ROV 132.. Before doing this, the valves 128 and 130 are closed. It may be useful to improve the gripping force which can be imparted on the outer flexible pipe 38 by pumping water into the annular flow channel 42, to increase the pressure of the water in the closed annulus of the pipe 28 and trap it in. This will reduce the chance of the outer pipe portion 38 collapsing when it is withdrawn from the tank 24. The outer pipe portion 38 will typically be a reinforced thermoplastic pipe (RTP) which can withstand a burst pressure of around 100 bar. It will be understood that the inner, high pressure pipe portion 40 must be capable of withstanding the pressure not only of the fluid which is pumped down into the tank 24 for injection through the device 22, but also the pressure of the fluid in the annular flow channel 42.
The ROV 132 will be used to hook up the lift line 126 from the vessel/platform, which will be operated in constant tension mode. The pipe gripping and rotation device 30 will be operated to grip the pipe 28 and draw it out of the tank 24. This is achieved by moving the gripping elements 82 inwardly, to grip the outer flexible pipe portion 38, and then translating the gripping elements 82 axially upwardly, to translate the pipe 28 upwardly relative to the tank 24. The gripping elements 82 can then be released and returned to a start position where they can be redeployed for gripping the outer pipe portion 38 and translating it a further distance. This can be repeated until the fluid injection device 22 has been withdrawn from the tank 24. The annular seal 102/additional sealing mechanism 104 closing pressure will be adjusted during the recovery process. The closing pressure can be increased when the pipe 28 is stationary, which occurs when the gripping and rotation device 30 is opened and run back to its start position to re-grip the outer pipe portion 38. The closing pressure can be reduced and some water leakage allowed as the gripping device 30 makes its upstroke, gripped around the outer surface of the outer flexible pipe portion 38. This will reduce the seal force which must be overcome to move the pipe 28. A subsea control system of the drilling stack 118 (not shown) may be designed so that this process is automated. Once the fluid injection device 22 has been translated a sufficient axial distance (Fig. 7), the lower isolation valve 100 can be reclosed to seal the tank 24. The unit 124 can then be recovered to surface.
Following completion of the remediation process, the tank 24 can be opened to allow flow of water into and out of the tank. Typically, further testing will be carried out before the tank is opened. Assuming that all contaminants have been removed, the drilling stack 118 can be recovered to surface and the tank 24 thus rendered open.
Turning now to Fig. 9, there is shown an enlarged longitudinal sectional view of a fluid injection device in accordance with an alternative embodiment of the invention, the device indicated by reference numeral 22a. The device 22a can be utilised in the assembly and method described in Figs. 1 to 7 above. Like components of the device 22a with the device 22 of Figs. 1 to 7 share the same reference numerals, with the addition of the suffix "a". Only the substantive differences between the devices 22a and 22 will be described in detail.
In this embodiment, the device 22a is coupled directly to the lower end 68 of the pipe 28. The device 22a is not rotated and so the PDM 54 is dispensed with. Again however, fluid is supplied to the device 22a through a bore 52 of the inner flexible pipe portion 40, and is returned along the annular flow channel 42. Fluid passing down the inner pipe bore 52 is directed into an internal fluid chamber or gallery 134. The device 22a comprises a plurality of outlets, four of which are shown and given the reference numeral 136. Nozzles 13 8 are mounted in the outlets 136, and serve for directing jets of fluid into the tank 24. The nozzles 138 are moveably mounted within the outlets 136 so that the direction of the fluid jets can be adjusted. The position of nozzles 138 is determined by a controller 140, which also operates valves 142 associated with each of the outlets 136, for controlling the flow of fluid through the outlets. In this embodiment, the outer flexible pipe portion 38 comprises fluid inlets 144 through which fluid can be drawn into the annular flow channel 42 and passed to surface. These communicate with corresponding inlets 146 on an upper end of the device 22a. The device 22a also comprises a number of internal flow ports, two of which are shown and given the reference numeral 150. These communicate with the internal chamber 134, and include nozzles 152 which are arranged to direct jets of fluid upwardly along the annular flow channel 42 past the aligned inlets 144/146. Flow of fluid through the flow ports 150 is controlled by valves 154, which are again operated by the controller 140. The valves 142 and 154 may be controlled via solenoids or pilot hydraulic lines (not shown).
In use, fluid passing down the inner pipe bore 52 into the chamber 134 is jetted out through the nozzles 138. These jets of fluid can be utilised to move the device 22a within the tank 24, and thus provide a motive force for steering the device. This is achieved by controlling the movement of the nozzles 138, and thus the position of the nozzles 138 within the outlets 136. Additionally, the flow rate of fluid through the nozzles 138, and indeed selective opening and closing of the outlets 136, is controlled using the valves 142, and can again be used to steer the device 22a. It will therefore be understood that, during passage of the device 22a around the tank 24 (described in relation to Figs. 4 and 5), the device can be steered without requiring rotation by a motor.
Additionally however, the device 22a may be capable of driving itself around the tank 24, rather than being dragged around the tank by the pipe 28. This is achieved by arranging the fluid jets directed into the tank 24 to provide a motive force which is sufficient to advance the device 22a along a circular path extending around the tank 24. This can be achieved by inclining the nozzles 138 relative to a main axis of the device 22a. This is illustrated in Fig. 9, where the nozzles 138 are inclined towards an upper end 148 of the device 22a. This will provide a motive force which has an axial component that is sufficiently large to drive the device forward in the direction of the arrow 156. When the fluid injection device 22a is operated in this way, the pipe 28 is rotated so as to facilitate movement of the device, rather than specifically to drive the device around the tank 24. Thus where the device 22a is driven forwards in the direction 156, the pipe 28 is rotated to follow the device and maintain fluid communication. However, a rate of rotation of the pipe 28 can be controlled to provide an additional steering effect on the device 22a. Furthermore, the nozzles 138 can be inclined in a direction away from the upper end 148, to provide a drive force in an opposite direction, as indicated by the arrow 158. The pipe 28 would then be rotated in an opposite direction.
The fluid jets agitate contaminants in the tank 24 for withdrawal through the aligned inlets 144/146. The direction of fluid through the flow ports 150 and nozzles 152 raises the velocity of fluid flowing along the annular flow channel 42 in the region of the inlets 144/146, increasing a pressure differential of fluid in the tank 24 relative to fluid in the flow channel 42 adjacent the aligned inlets 144/146, creating a Venturi effect which enhances fluid withdrawal. Operation of the controller 140 is achieved by means of a control cable 160, to thereby control the operation of the various valves 142 and 154 and orientation of the nozzles 138, and thus movement of the device 22a.
Turning now to Fig. 10, there is shown a variation of the remediation assembly and method shown in Figs. 1 to 5. In this embodiment, fluid is directed into the tank 24 along the annular flow channel 42, and is withdrawn from the tank through the bore 52 of the inner flexible pipe portion 40. To facilitate this, the assembly 20 comprises a fluid injection device 22b in accordance with another embodiment of the invention, which is shown in the enlarged longitudinal sectional view of Fig. 11. Like components of the device 22b with the device 22 of Figs. 1 to 5, or the device 22a of Fig. 9, share the same reference numerals with the addition of the suffix "b". The device 22b is mounted on a lower end 68 of the pipe 28, and comprises a number of outlets (not shown) which open externally of the device for directing jets of fluid into the tank 24 to steer the device. Typically, the device 22b will comprise four such outlets. In a similar fashion to the device 22a, the outlets may carry nozzles for directing the jets to steer the device. Alternatively, the device 22b may be rotated by a PDM, in a similar fashion to the device 22. Appropriate motivating elements such as brushes may then be provided on an external surface 116b of the device.
The device 22b also comprises an inlet 164 which opens on to a bore 166 that communicates with the inner pipe bore 52, so that fluid with entrained contaminants can be withdrawn through the inner pipe portion 40 to surface. The inlet 164 is tapered (and/or may be adjustable in shape) so that fluid is accelerated as it passes into the bore 166, resulting in a pressure drop which enhances fluid withdrawal by the Venturi principal. Additionally however, the device 22b comprises at least one secondary outlet 168 for directing secondary jets of fluid into the inlet 164, to promote the withdrawal of contaminants. With the suction pump 64, this improves the flow rate and mobility of the effluent containing the contaminants. In the illustrated embodiment, the secondary outlet 168 takes the form of an annular channel extending around a circumference of the device 22b, although it will be understood that other configurations, such as individual flow ports, may be provided. Fluid is directed to the secondary outlets 168 along a passage 172, under the control of a solenoid valve 174, which directs part of the fluid flowing along the annular flow passage 42 to the secondary outlet. The valve 174 is controlled and operated by means of a control line 175, which terminates in an electrical connector 177 that provides for connection to lines 178 embedded in the inner flexible pipe portion 40. This provides for control and operation of the valve 174, and thus flow to the secondary outlets 168. It will be understood that similar control lines are provided for the solenoid valves which control flow through the primary outlets (not shown). The high pressure inner pipe portion 40 may be constructed of composite materials, such that the power supply and communication for the injection device 22 can be built-into the wall of the pipe portion. Another power and communication method would be to simply install a power and data cable through the centreline of the high pressure inner pipe portion 40.
The high pressure pump 62 is coupled to the housing 72 through the port 67, for supplying high pressure fluid into the annular flow channel 42. This fluid passes down to the device 22b, and is jetted through the device outlets into the tank 24. A portion of the fluid is also directed to the secondary outlet 168. The jets agitate the contaminants, which are drawn upwardly to surface through the inner flexible pipe portion 40 by the suction pump 64. Fluid withdrawal is enhanced by the tapered shape of the inlet 164 and the optional secondary fluid jets 170.
Turning now to Fig. 12, there is shown a fluid injection device 22c which is a variation on the device 22b. Like components share the same reference numerals with the addition of the suffix "c". The device 22c is similar in structure and operation to the device 22b, save that secondary outlets 168c open externally of the tool, to direct jets 170c externally rather than into an inlet 164c of the device. These jets 170c may facilitate mobilisation of contaminants for withdrawal through the inlet 164c, and may also help to prevent the inlet 164c from becoming blocked. The secondary outlets 168c are supplied with fluid from the annular flow channel 42 along passages 172c, one of which is shown in broken outline in Fig. 12. The device 22c comprises primary outlets, two of which are shown and given the reference numeral 136c, and which are controlled by valves 138c. Fig. 13 is a cross-sectional view of the device 22c taken in the direction of the arrows E-E of Fig. 12, and shows the passages 176 which supply fluid to the primary outlets 136c. The relative position of the secondary outlet passages 172c, which additionally communicate with the annular flow channel 42, are also shown in the Figure. Control lines 175c terminate in an electrical connector 177c, for connecting to the electrical lines 178c in the inner pipe 40, for providing power and controlling operation of the solenoid valves 138c. Similar control lines (not shown) are provided for controlling flow through the secondary outlets 168c through an electrical connector 180 which communicates with lines (not shown) in the inner pipe portion 40.
The invention provides a mixing and remediation device 22 that can be deployed from a dynamically positioned mono-hull vessel that is positioned adjacent to a concrete platform, or from the platform itself. The fluid injection device 22 is the bottom element of the assembly 20, and may be a rotating end effecter which can incorporate a helically wound arrangement of brushes on the outside surface. The invention provides the means for controlling the entry of said mixing and remediation device 22 into a tank or cell 24 through proportional control of an annular seal 102/104. The device 22 can be rotated around the cell 24 and also deflected and steered within the cell. The typical device 22 has the means of simultaneously introducing water under pressure into the cell to break up contaminant sediment and mobilise it, while at the same time recovering contaminated sediment back to the surface up the annular flow channel 42 between the pipe portions 38 and 40.
The reciprocating pipe gripping device 30 has an innovative feature for the purpose of deploying and operating remediation tools such as the fluid injection device 22. This is the ability to grip the flexible pipe 28 with the reciprocating grippers (gripping elements 82), and also to rotate it axially using a motor and gearing system 96, 98. The hydraulic functions of the reciprocating gripper assembly are engineered with a sealed bearing and hydraulic gallery arrangement to enable the rotation.
Constructing a mixing and remediation assembly 20 that has the flexibility within the outer flexible pipe portion 38 and the high pressure inner pipe portion 40 to enable the fluid injection device 22 to be positioned within the tank 24, yet can be deployed from a floating vessel, is an advantage of the present invention.
Deployment using the reciprocating gripping elements 82 pushes the injection device 22 into the tank 24 in compression. This has a disadvantage that the outer flexible pipe portion 38 has its external surface gripped by the reciprocating gripping elements 82 and pushed through the closed annular seal 102/104, with the possibility of external damage and uncontrolled buckling loads that may damage the outer flexible pipe portion. The invention and control system implemented on the drilling stack 118 may eliminate this risk. This is done by using the 4 bar differential pressure between the tank 24 and ambient seawater pressure, to provide the motive force at the bottom of the device 22 to push it into the tank.
Turning now to Fig. 14, there is shown a schematic perspective view of a fluid injection device in accordance with another embodiment of the present invention, the device indicated by reference numeral 22d. The device 22d is a variation of the device 22c shown in Fig. 12. Like components share the same reference numerals with the suffix "c" replaced by the suffix "d".
The device 22d is similar in structure and operation to the device 22c in that it comprises a number of outlets 136d. Fluid is supplied to the injection device 22d through the flexible pipe 28 and jetted into the tank 24 through the outlets 136d. The device 22d comprises a flow control element 182, which is best shown in Fig. 15. The flow control element 182 is mounted in a main body 184 of the device, which is coupled to the outer flexible pipe 38. The flow control element 182 surrounds an inner pipe 186 which is connected to the inner flexible pipe 40, and which communicates with the main bore 52 of the inner pipe. The flow control element 182 takes the form of a manifold, and is rotatable for selectively opening fluid communication with the annular flow channel 42 of the flexible pipe 28, along an annular region 188 defined between the main body 184 and the inner pipe 186.
The manifold 182 comprises an outlet portion in the form of a cutaway 190 which, when rotationally aligned with one or more of the outlets 136d, permits fluid communication between the outlet and the pipe annular flow channel 42. It will be understood that the cutaway 190 may be shaped, and/or the outlets 136d positioned, so that communication can be opened with more than one of the outlets at any one time. Indeed, the manifold may comprise a plurality of outlet portions (not shown), so that communication can be achieved with more than one outlet at a particular time. The manifold 182 may be rotated by any suitable method, but in the illustrated embodiment a gear arrangement comprising a motor 192, gear ring 194 on the manifold, and drive gear 196 coupled to the motor, is employed. Control signals are sent from surface to control the operation of the motor 192.
Contaminants in the tank 26 are withdrawn along a main bore 166d of the device 22d, which is defined by the inner pipe 186. It will be appreciated that the principles of the device 22d, in particular the flow control element 182, may be employed in other embodiments of fluid injection device disclosed herein. Thus a flow control element may be provided in embodiments where flow is achieved down through the inner flexible pipe 40, and fluid with entrained contaminants withdrawn along the annular flow channel 42.
Turning now to Fig. 16, there is shown a perspective view of part of an underwater fluid storage tank remediation assembly for removing contaminants from an underwater fluid storage tank, in accordance with another embodiment of the present invention, the assembly indicated generally by reference numeral 20e. Fig. 17 is a longitudinal sectional view of the part of the assembly shown in Fig. 16. The assembly 20e is the same as the assembly 20 shown in Fig. 1, save that it includes a tensioning arrangement 198. Like components of the assembly 20e of Fig. 16 with the assembly 20 of Fig. 1 share the same reference numerals, with the addition of the suffix "e". Only the tensioning arrangement 198 is shown in Fig. 16, mounted on the rigid pipe portion 48e provided at the top of a flexible pipe is shown in the Figure. The flexible pipe is the same as the pipe 28 of Fig. 1.
As discussed above, the flexible pipe is rotated during insertion so that it adopts a helical configuration. Fluid pressure in the pipe, when fluid is directed to an injection device, causes the helix to "unwind", with the result that the injection device can move outwardly towards a wall of the tank 24. The tensioning arrangement 198 can impart a tensile force on the flexible pipe to counteract this unwinding tendency. The tensioning arrangement 198 comprises a number of elongate tension members, which are typically multi-strand ropes or wires, and which are indicated by the reference numeral 200. The ropes 200 are distributed around a circumference of the rigid pipe portion 48e, and are located in passages 202 formed in a wall 204 of the pipe portion 48e. The ropes 200 pass on down through the outer flexible pipe (not shown), and are anchored towards a lower end of the pipe, typically adjacent to the fluid injection device provided at the lower end of the pipe.
The ropes 200 are individually or jointly tensionable, for imparting the tensile force on the flexible pipe. In the illustrated embodiment, the tensioning arrangement comprises a hydraulic actuator 206 associated with each rope 200. The actuator 206 comprises a cylinder 208 mounted on the wall 204 of the rigid pipe portion 48e, and a piston 210 which translates within the cylinder. The piston 210 carries a pulley 212 over which the rope 200 passes, and the rope is securely anchored to a mounting block 214 on the pipe wall 204. In this way, when the actuator 206 is activated, to translate the piston 210 in the direction of the arrow X, a tensile load is imparted on the rope 200 and thus the flexible pipe. As explained above, this can assist in maintaining a particular helical configuration of the flexible pipe, and/or causing the pipe to adopt a particular configuration. The ability to individually tension the ropes 200 may further enhance the adoption/maintenance of a particular configuration in that varying tensile loads can be imparted upon the flexible pipe around its circumference. Operation of the actuators 206 is controlled by a control signal sent from surface.
Various modifications may be made to the foregoing without departing from the spirit and scope of the present invention.
For example, the nozzle in the fluid injection device may be fixed and not adjustable. A valve in the outlet of the fluid injection device may control the flow of fluid therethrough. This may enable adjustment of the velocity of the fluid jet.

Claims

An underwater fluid storage tank remediation assembly for removing contaminants from an underwater fluid storage tank, the assembly comprising:
a flexible pipe which can be inserted into an underwater fluid storage tank;

a fluid injection device coupled to the flexible pipe and arranged so that fluid flowing down the pipe passes into the fluid injection device, the fluid injection device comprising at least one fluid outlet for directing a jet of fluid into the tank to agitate contaminants in the tank;

a pipe gripping and rotation device which can be selectively actuated to grip and rotate the flexible pipe relative to the tank, to facilitate movement of the fluid injection device coupled to the pipe within the tank;

a motivating arrangement for generating a motive force which can be used to steer the fluid injection device around the tank when the flexible pipe is rotated by the pipe gripping and rotation device; and

a contaminant withdrawal arrangement for withdrawing contaminants agitated by the fluid injection device from the tank.
An assembly as claimed in claim 1, in which the motivating arrangement comprises a motor coupled to the fluid injection device, for rotating the fluid injection device relative to the flexible pipe, and at least one motivating element provided on the fluid injection device, the element arranged so that it can contact an inner surface of the tank or materials in the tank to steer the device when it is rotated by the motor.
An assembly as claimed in either of claims 1 or 2, in which the fluid injection device is secured against rotation relative to the flexible pipe, and in which the motivating arrangement comprises a fluid nozzle positioned in the at least one outlet of the fluid injection device, the nozzle being movable relative to a main body of the fluid injection device so that the direction of the jet of fluid into the tank can be controlled to thereby steer the device.
An assembly as claimed in any preceding claim, in which the flexible pipe comprises an outer flexible pipe portion, and an inner flexible pipe portion located within the outer pipe portion so that an annular flow channel is defmed between an inner surface of the outer pipe portion and an outer surface of the inner pipe portion, the inner pipe portion being secured against rotation relative to the outer pipe portion.
An assembly as claimed in claim 4, in which the annular flow channel communicates with a pump, and the assembly comprises a valve for selectively closing the annular flow channel so that the pressure of the fluid in the channel can be raised to above ambient external water pressure, to support the flexible pipe during gripping by the pipe gripping and rotation device.
An assembly as claimed in either of claims 4 or 5, comprising a rigid pipe section coupled to or forming an upper end of the outer flexible pipe portion, to facilitate gripping and rotation of the flexible pipe by the pipe gripping and rotation device, the rigid pipe section being of greater rigidity than a remainder of the outer flexible pipe portion.
An assembly as claimed in any one of claims 4 to 6, in which:
the at least one outlet of the fluid injection device is arranged so that it is in fluid communication with the inner pipe portion, and the assembly arranged so that fluid flows down the inner pipe portion to the fluid injection device for injection into the tank;

and in which the contaminant withdrawal arrangement comprises at least one fluid inlet formed in a wall of the outer pipe portion or the fluid injection device, said inlet being in fluid communication with the annular flow channel so that contaminants agitated by the fluid injection device can be withdrawn along the channel; or

the at least one outlet of the fluid injection device is arranged so that it is in fluid communication with the annular flow channel, and the assembly arranged so that fluid flows down the annular flow channel to the fluid injection device for injection into the tank;

and in which the contaminant withdrawal arrangement comprises a fluid inlet defined by the fluid injection device and which can be arranged so that it is in fluid communication with the inner pipe portion so that contaminants agitated by the fluid injection device can be withdrawn along the inner pipe portion;

and in which the fluid inlet of the fluid injection device optionally comprises a tapered portion to promote withdrawal of contaminants, and in which the contaminant withdrawal arrangement comprises at least one secondary outlet which opens on to an internal bore of the device and which is arranged to direct a jet of fluid into the tapered portion to promote the withdrawal of contaminants.
An assembly as claimed in any preceding claim, in which:
the pipe gripping and rotation device comprises a plurality of pipe gripping elements which are movable between retracted positions out of contact with the flexible pipe, and deployed positions where they contact and grip the flexible pipe so that the pipe can be rotated;

the gripping elements are mounted on a support which can be rotated about an axis that is parallel to an axis of the flexible pipe, to thereby rotate the gripping elements and thus the flexible pipe; and

the gripping elements are movable in a direction parallel to an axis of the flexible pipe whilst gripping the pipe, for translating the flexible pipe relative to the tank.
An assembly as claimed in any preceding claim, in which the flexible pipe comprises at least one communication line located in a wall of the pipe and which serves for at least one of: transmitting data relating to one or more measured parameter to surface; and transmitting a control signal from surface so that a desired operation can be performed.
A method of remediating an underwater fluid storage tank to remove contaminants from the tank, the method comprising the steps of:
coupling a fluid injection device to a flexible pipe;

inserting the fluid injection device into an underwater fluid storage tank to be remediated using the flexible pipe;

passing fluid down the flexible pipe and into the fluid injection device;

directing fluid passed into the fluid injection device through at least one fluid outlet of the device, so that the fluid is jetted into the tank to agitate contaminants in the tank;

actuating a pipe gripping and rotation device to grip and rotate the flexible pipe relative to the tank, to thereby facilitate movement of the fluid injection device within the tank;

operating a motivating arrangement to generate a motive force for steering the fluid injection device around the tank when the flexible pipe is rotated by the pipe gripping and rotation device; and

withdrawing contaminants agitated by the fluid injection device from the tank using a contaminant withdrawal arrangement.
A method as claimed in claim 10, comprising drilling an access hole in a wall of the tank; sealing the access hole to prevent fluid leakage; and subsequently deploying the fluid injection device on the flexible pipe through the access hole and into the tank; and in which the step of inserting the fluid injection device into the tank comprises setting the device down on a layer of contaminants resting on a base of the tank and then continuing to insert the flexible pipe after the fluid injection device has been laid down so that the pipe adopts a generally helical configuration in the tank.
A method as claimed in either of claims 10 or 11, in which:
the flexible pipe is rotated to drag the fluid injection device around a layer of contaminants resting on a base of the tank, to thereby agitate the contaminants, and in which the fluid injection device is steered by controlling application of the motive force as the device is dragged around the layer of contaminants, to move the device towards or away from a centre of the tank; or

the method comprises driving the fluid injection device around the tank utilising the motivating force generated by the motivating arrangement, and rotating the flexible pipe to follow the device during its movement;

the method optionally including steering the fluid injection device by controlling application of the motive force as the device is driven around the layer of contaminant, to move the device towards or away from a centre of the tank, and rotating the flexible pipe in an opposite direction to that which the pipe was rotated during insertion into the tank.
A method as claimed in any one of claims 10 to 12, in which the fluid injection device is coupled to a flexible pipe having an outer flexible pipe portion and an inner flexible pipe portion located within the outer pipe portion, an annular flow channel being defined between an inner wall of the outer pipe portion and an outer wall of the inner pipe portion, and in which the step of inserting the flexible pipe into the tank comprises:
arranging the pressure of the fluid in the tank to be lower than ambient water pressure;

isolating fluid in the inner pipe portion from fluid in the annular flow channel;

exposing the fluid in the inner pipe portion to the pressure of the fluid in the tank; and

exposing the fluid in the annular flow channel to ambient external water pressure.
A method as claimed in claim 13, comprising:
operating an annular seal element to grip an external surface of the outer pipe portion, and controlling the gripping force exerted on the outer pipe portion by the annular seal element so that the force resulting from the pressure differential between the inner and outer pipe portions can be utilised to urge the flexible pipe into the tank; and/or

in which the method comprises raising the pressure of the fluid in the annular flow channel to above ambient water pressure, to thereby reinforce the pipe, and then removing the flexible pipe and the fluid injection device from the tank utilising the pipe gripping and rotation device.
A method as claimed in any one of claims 10 to 14, comprising operating gripping elements of the pipe rotation and gripping device to move from retracted positions where they are out of contact with the pipe, to deployed positions where they contact and grip the pipe, and then moving the gripping elements in an axial direction to translate the pipe from the tank.