Title of Invention

"A METHOD DEVICE FOR REMOVAL OF SUBSEA ROCKS AND SEDIMENTS"

Abstract The invention relates to a method and device for moving subsea rocks and sediments, also at significant depths, e.g. in connection with removal of protective rocks around subsea installations, where maintenance is to be conducted. The device comprises a rigid or at ieast partly flexible tubing (5) through which the masses (14) may be transported with the aid of a pressure gradient produced by an ejector nozzle (11) arranged externally in relation to said tubing. The nozzle (11) is fed with water from a water pump (12). The device further comprises a chassis (F) adapted to be transported along the (sea) bottom. The required power is arranged to be supplied through a cable (3) from the surface, while the tubing (5) preferably is arranged to be remotely controlled by a manipulator (9, 9")
Full Text 2
FIELD OF THE INVENTION
The present invention relates to a method of removing subsea rocks according to the features of the invention. The invention further relates to a device defining the structural features for implementing the method of the invention.
BACKGROUND OF THE INVENTION
For work at subsea oil and gas installations or in connections with such installations, e.g., maintenance work, there is often a need to move rocks and particulate material that partly covers the bodies that are to be repaired. It can be pipelines, valve housings and the like.
In a similar way a need may occur to remove sediments in connection with new installations on the sea bottom, or for removal of collected drill cuttings at platforms or the like.
Similar needs may also occur in connection with subsea work, like harbour works or work at barrage or quay structures.
The most common way to remove sediments in connection with subsea work, is by utilizing large ' fans', large and heavy suction devices with a high power consumption and specialty designed excavators. Disadvantages are that they require a lot of power and / or other resources, they require large surface vessels, have a limited versatility, are as good as stationary, or they are not at all suited for deep waters.

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NO patent No. 302.043 describes a dredge designed for subsea operations, especially to remove or move drill cuttings, comprising a motor, a pump device and an ejector, where the motor is described to run the pump which in its turn provides a stream of water to ithe ejector, which is positioned in a tubing through which the cuttings or the like is supposed to be transported. The apparatus is designed to rest on the sea bottom and to receive energy from the surface, while the inlet end of the tubing is supposed to be moveabfe e.g. with the aid of a remote controlled mini submarine, a so called ROV.
This apparatus is not suited to move sediments with relatively large rocks, mainly because the pipelines has an effective loss of diameter due to the ejector's design and position. Further, it has a geographically very limited work range as it is designed to rest at the sea bottom, even through the pipeline is designed to be somewhat moveable.
Japanese patent applications Numbers 0 43 25 799 A and 043 25 800 A describes an ejector pump system where the ejector is positioned mainly outside the pipeline so that the ejector does not reduce the effective diameter of the pipeline. From the abstract of these patent applications it is not possible to see what kind of utilizations these systems are meant for. Neither are there any indications of dimensions or power requirements of these systems.
OBJECTS OF THE INVENTION
It is an object with the present invention to provide a method for transportation of rocks and sediments under water, especially at deep waters.

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It is a particular objective to provide a method for transportation of rocks with a typical maximum diameter of 250-500 mm.
It is further object to provide an apparatus for performing said method, which apparatus should be versatile in its use, especially in the way that it should be easy to move around down at the sea bottom.
It is still object to provide such an apparatus that is easy to control, and which does not require more energy than what may be supplied from the surface, e.g. through a conventional electric cable.
SUMMARY OF THE INVENTION
In one aspect of the present invention there is provided a method for removing subsea rocks and sediments including removal of protective rocks around subsea installations in course of maintenance at different depths comprising significant depths, the method comprising steps of supplying the required power through one or more cables from the surface, utilizing a rigid or at least partly flexible tubing remotely controllable by means of a manipulator adapted for the purpose, producing a pressure gradient through the tubing by connecting an ejector nozzle to the tubing, and feeding water from a water pump to the nozzle. The tubing the ejector and the pump installed on a chassis capable of moving on the sea bottom, and in that the ejector nozzle being disposed externally in relation to the tubing.

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In a second aspect of the present invention there is provided a device for removing subsea rocks and sediments including removal of protective rocks around subsea installations in course of maintenance at different depths comprising significant depths, the device comprising at least one cable arranged from the surface for supplying the required power; a rigid or at least partly flexible tubing remotely controllable by means of a manipulator; a water pump connected to an ejector nozzle that rs attached to the tubing so as to enable a pressure gradient to be set up through the tubing wherein the tubing , the ejector nozzle and the water pump are disposed on a chassis adapted to be transported along the sea bottom and in that the ejector nozzle is disposed externally in relation to said tubing.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Below a more detailed description of a device according to the invention is given with reference to the accompanying drawings, where:
Fig. 1 is schematic drawings of a first embodiment of the invention,
Fig. 2 is a schematic drawing of a second embodiment of the invention,
Fig. 3 is a simplified schematic drawing of a third embodiment of the invention,
Figs. 4a - c shows details of a device according to the invention according to any one of the embodiments shown in figures 1-3.

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DETAIL DESCRIPTION OF A PREFFERED EMBODIMENT OF THE INVENTION
Fig. 1 shows a device 1 designed to move on the sea bottom S with the aid of belts 2 powered from the surface through a cable 3. The device comprises a tubing 5, preferably with a flexible section 8, said tubing having an inlet end 6 and an outlet end 7. To the tubing an ejector nozzle 11 is attached, said nozzle being supplied with water from a pump 12 powered by an hydraulic unit 13. All of said equipment are supported by a chassis F which again is supported by the belts 2. It is preferred that the tubing 5, when it includes a flexible section 6, further comprises a manipulator 9 which is able to move the tubing within certain degrees of freedom. In figure 1 manipulator 9 consists of a multi-link arm controlled by means of a hydraulic unit 16. The device is adapted to transport sediments 14 including rocks of a size up to the diameter of the tubing S from one site to another, by the pressure gradient in the tubing set up by the ejector nozzle 11, providing a Vacuum from left to right in the drawing/
Figure 2 shows an alternative embodiment of the invention. By this embodiment there is no power to the wheels or belts, as the device is supported by freely moving wheels 2' capable of being turned in several directions and preferably in ant direction. The drawing shows 2 wheels while it is understood that at least two other wheels are hidden behind these two. Most typically the device in this embodiment has 4 wheels, but it may also have e.g. 3 or 5 wheels. As an alternative to freely moving wheels, freely moving belts may be utilized.

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By the device according to figure 2, the manipulator 9' consists of a remotely operated vehicle (ROV) controlling the tubing 5, and, if the sea-bottom so allows, the ROV may pull the entire device 1 in a desired direction. It is to be understood that the freely moving wheels 2' need not have the shown shape, they may have any form suited for subsea transportation.
Figure 3 shows a further embodiment If the device according to the invention, an embodiment that may be seen as a variation of the embodiment of figure 2. Figure 3 is simplified and does not show all the features of figure 2. The central aspect of this embodiment lies in the details indicated by the reference numeral 2", which may be denoted "water cushions" (cf. air cushions of a hovercraft) which may cause the device to float just above the sea level. The so-called water cushions are supplied with water from a powerful water pump, for instance the pump that feeds the ejector nozzle 11. In the drawing this is shown schematically in the form of a particular supply conduit 18 from the pump 12. Movement of tubing 5 and possibly of the entire device 1 may as shown in figure 2, be effectuated by means of a pulling force from an ROV through the tubing 5.
Figure 4 shows details at the inlet end 6. The figure 4a shows that the outer part (mouth piece) of the inlet end 6 comprises telescopic units 21 may be pulled or pushed out. Figure 4b further shows that the mouth piece may comprise an annulus "lance" 21 which is hollow and which is able to flush water through a plurality of openings 22 inwards as well as outwards relative to the mouth piece, so that the inlet end as such becomes shielded and not so easily will become packed when the mouth piece is pressed into the sediments. The water is fed to the lance through conduit 23 which may communicate with e.g. the water pump 12 or another suitable water pump.

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At the inlet piece 10 of the tubing 5 there may also be provided a nozzle (not shown) for backflushing of rocks etc. that might get stuck in the mouth piece.
Further it is preferred that the inlet mouth piece 10 is rounded and that the. cross-section of the tubing is constant, and that any bend of the tubing 5 has sufficiently large radius to ensure that rocks will not get stuck. It is further preferred that the outlet end 7 of the tubing is shaped as a diffuser, as this reduced the frictional loss through the tubing.
The device according to the invention may be manufactured mainly in a plastic material with a density close to that of water, so that it is easy to support.
CALCULATION EXAMPLE
In the following example of utilization there is an assumption of one or two water pumps each powered by a motor of 75 kW. It is assumed that the tubing has an internal diameter of 300 mm. In the case of two pumps there is also conducted calculations for a 500 mm tubing. Further data are given in the table below.


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PRACTICAL EXAMPLE
A commission conducted shows that the invention works in practice. During the summer of 1999, 1500 m3 (dmax = ca. 150 mm) of rocks were moved with the aid of a corresponding ejector mechanism, carried by a remotely operated vehicle, ROV. The commission was conducted in Tengsfjorden, by an oil pipe at a depth of 540 m below sea level. For powering the water pumps, two hydraulic engines with a total effect of approximately 24 kW were used. The tubing was 10 m long and had an internal diameter of 250 mm. .

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During 26 effective work hours 1500 m3 of rocks were moved, which corresponds to a capacity of 60 tons/hour. Only a minimal wearage was observed-ati the tubing in PE plastic. Later, several successful tasks have been performed With this technology.
In March 2000 the present invention was utilized at the Draugen field, at a depth of 300 m. The commission was carried out from the boat Seaway Kingfisher. 5m length of a pipeline was uncovered during 40 minutes before the commission had to be interrupted. This corresponds to 20 m3 mass or 45 tons/hour. Considering that the rocks were moved from a region where frequent re-locations of the device was required, the result was very satisfying. A 75 kW pump and a tubing of 15 m with an internal diameter of 300 mm was utilized.
The drawings and the example are merely illustrations of the invention, which is only limited by the subsequent claims.

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We Claim
1. Method for removing subsea rocks and sediments including removal of
protective rocks around subsea installations in course of maintenance at
different depths comprising significant depths, the method comprising
steps of: -
- supplying the required power through one or more cables from
the surface;'
- utilizing a rigid or at least partly flexible tubing remotely
controllable by means of a manipulator adapted for the
purpose;
- producing a pressure gradient through said tubing by
connecting an ejector nozzle to said tubing, and;
- feeding water from a water pump to said nozzle,
characterized in that the tubing, the ejector and the pump
installed on a chassis capable of moving on the sea bottom, and
in that said ejector nozzle being disposed externally in relation
to said tubing.
2. Method as claimed in claim 1, wherein the chassis is provided with belts
or wheels and wherein the chassis being moved along the sea bottom
with power supplied to the belts and/or the wheels,

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3. Method as claimed in claim 1, wherein the at feast partly flexible tubing is
controlled by means of an hydraulicafly controlled multi-link arm.
4. Method as claimed in claim 1, wherein the belts or wheels are capable to turn
freely in several directions.
5. Method as claimed in claim 1, wherein the manipulator comprises a Remotely
Operated Vessel (ROV), and wherein the ROV being adapted to move the chassis
Including controlling the tubing.
6. Method as claimed in claim 1, wherein the chassis is provided with water
cushions that are filled with water from one or several water pumps enabling the
chassis to float above the sea bottom using the manipulator.
7. A device for removing subsea rocks and sediments including removal of
protective rocks around subsea installations in course of maintenance at different
depths comprising significant depths, the device comprising at least one cable
(3) arranged from the surface for supplying the required power; a rigid or at
least partly flexible tubing (5) remotely controllable by means of a manipulator
(9,90; a water pump (12) connected to an ejector nozzle (11) that is attached to
the tubing (5) so as to enable a pressure gradient to be set up through the
tubing (5),
wherein the tubing (5), the ejector nozzle (11) and the water pump (12) are disposed on a chassis (F) adapted to be transported along the sea bottom and in that the ejector nozzle (11) is disposed externally in relation to said tubing (5).

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8. The device as claimed in claim 7, wherein the manipulator (9, 9') is an
hydraulically controlled multi-link arm (9).
9. The device as claimed in claim 7 or 8, wherein the chassis (F) is
supported by belts (2) or by wheels (2') and arranged to be transported
along the sea bottom by supplying power to the belts (2) and/or to the
wheels (2') respectively.
10.The device as claimed in claim 7, wherein the manipulator (9, 9') is an ROV (9') that is controllable independent of the device (1).
11.The device as claimed in claim 10, wherein the belts (2) of the wheels (2') are turnable in any direction, and wherein the chassis (F) is transportable along the sea bottom by a pull force exerted by the ROV (9') through the tubing (5).
12.The device as claimed in claim 10, wherein the chassis (F) is provided with water cushions (2") facing the sea bottom, and wherein the water cushions are filled with water from the pump (12), so that the chassis (F) may partly float above the bottom (S) and transported along the bottom by the pull force exerted by the ROV (9') through the tubing (5).
13.The device as claimed in claim 7, wherein the tubing (5) has an inlet end (6) which is telescopically extendable,

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14. The device as claimed in claim 7, wherein the inlet end (6) of the tubing (5) comprises means (21) for penetration including pressurized water flushing (22) for disintegrating the compact or hardened sediments in
order to improve the suction capacity of the device.
15.The device as claimed in claim 7, wherein a nozzle is disposed adjacent to an inlet mouth piece (10) for backwards flushing of rocks which might get stuck in the mouth piece (10).
16. The device as claimed in claim 1, wherein the inlet mouth piece (10) is rounded, wherein the cross-section of the tubing (5) is constant with substantially large radius at any bend of the tubing (5) to eliminate stucking of any rock therein, and wherein an outlet end (17) is shaped as a diffusor to minimize the friction loss through the tubing (5).
The invention relates to a method and device for moving subsea rocks and sediments, also at significant depths, e.g. in connection with removal of protective rocks around subsea installations, where maintenance is to be conducted. The device comprises a rigid or at ieast partly flexible tubing (5) through which the masses (14) may be transported with the aid of a pressure gradient produced by an ejector nozzle (11) arranged externally in relation to said tubing. The nozzle (11) is fed with water from a water pump (12). The device further comprises a chassis (F) adapted to be transported along the (sea) bottom. The required power is arranged to be supplied through a cable (3) from the surface, while the tubing (5) preferably is arranged to be remotely controlled by a manipulator (9, 9")

Documents:


Patent Number 208775
Indian Patent Application Number IN/PCT/2002/01221/KOL
PG Journal Number 32/2007
Publication Date 10-Aug-2007
Grant Date 09-Aug-2007
Date of Filing 25-Sep-2002
Name of Patentee FOSSURA AS
Applicant Address LEIRA 6590 TUSTNA,1572 TUSTNA,NORWAY
Inventors:
# Inventor's Name Inventor's Address
1 JACOBSEN,TOM OSCAR WISTINGSVEG 54,N-7020,TRONDHEIM,NORWAY
2 FAGERVOLD,TERJE LEIRA,N-6590,TUSTNA,NORWAY
3 FAGERVOLD, GUNNAR ROELBAKKEN 5,N-7168 LYSOYSUNDET,NORWAY
4 KVALVAG,GUSTAV N-6523,FREI,NORWAY
PCT International Classification Number E02F 3/88
PCT International Application Number PCT/NO01/00143
PCT International Filing date 2001-04-04
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 20001743 2000-04-05 Norway