The present invention relates to a device, a system and a method for efficient removal of clay and other sediments on the ocean bottom as described in the introduction of the respective independent claims 1 , 9 and 17.

Today, there are technologies where water and high pressure are used for this type of task. However, these have limitations with respect to which water pressure that can be generated. Normally, one talks of about 100 bar maximum and with small amounts of water in addition.

The invention preferably relates to a device and a system for efficient removal of clay and other sediments of a hardness >0.5 Mpa. If this concerns removal of materials on the ocean bottom and if these are of hardness greater than 0.5 Mpa, traditional dredging (use of vacuum) can not be used. Then, one must use water with a pressure above 100 Mpa (100 bar) to break up these sediments. To do this more efficiently than with traditional methods, the present invention relates to a system which combines ultra high pressure and low pressure.

These are combined by leading both these supply-media into a compact unit where ultra high pressure is fed in to a centre nozzle and where low pressure is fed in to an outer nozzle. The ultra-high pressure nozzle is supplied such a high water pressure that the sediments on the ocean bottom are fractured. Then, by supplying water with low pressure, these sediments are further fractured. By further combining several such nozzle arrangements in the same system, one can efficiently dig ditches on the ocean bottom.

Consequently, it is an object of the present invention to provide a device and a system as described above.

This object is achieved, for example, with a device as described in the inde¬ pendent claim 1 , in that the device comprises a main body with at least one high-pressure nozzle and at least one low-pressure nozzle arranged to receive and supply of fluid under high pressure and fluid under low pressure, respectively, whereby the main body is arranged to be placed on the ocean bottom for supply of said fluids to break up adjoining sediments.

Alternative preferred embodiments of the device are characterised by the dependent claims 2-8.

The main body preferably comprises a centrally arranged high-pressure nozzle and a surrounding outer low-pressure nozzle, where the high-pressure nozzle is arranged to supply fluid with a sufficient high pressure for sediments within a distance of up to 1 metre to be broken up, and the low-pressure nozzle is arranged to further break up said sediments. Water is preferably used as the working fluid. The main body can further comprise a hook-formed part arranged to further break up and/or remove said sediments.

The device according to the invention can be coupled to one or more frequency-controlled fluid pumps for control of the velocity of the supplied fluid. Said device is further coupled to a flexible multi-line, in which line said fluid is supplied to the device under high pressure and low pressure.

A second aspect of the present invention provides a system as described in the independent claim 9, in that the system for efficient removal of clay and other sediments on the ocean bottom, in connection with offshore cleaning and/or digging of ditches on said ocean bottom, comprises an underwater module incorporating a number of devices according to the invention, where the devices are arranged next to each other mutually spaced apart, collecting means arranged to collect sediments made loose by said one or more devices, and means to disperse sediments that are collected by the collecting means.

Alternative preferred embodiments of the system are characterised by the dependent claims 10-16.

The collecting means can preferably comprise at least one suction pipe arranged adjoining said device(s), and a pump connected to said pipe arranged to suck up sediments that have come loose. The suction pipe can be a flexible pipe. Furthermore, the means to disperse sediments that have been collected by the collecting means can comprise an ejector system. The collecting means and the means to disperse the sediments can also be connected to one or more frequency-controlled electric motors for driving associated pumps, and also valve means for control of said pumps.

The underwater module can comprise one or more monitoring means that are chosen from a group comprising video camera, gyro, sonar, echo probe, MRU, light, etc. The underwater module can comprise control means, such as

propellers, to steer and control the placing of the underwater module in relation to the ocean bottom. Furthermore, the control means and monitoring means of the underwater module can be connected to a status and monitoring system.

A third aspect of the present invention provides a method that is described in the independent claim 17, in that the method for efficient removal of clay and other sediments on the ocean bottom, in connection with offshore cleaning and/or digging of ditches on said ocean bottom, comprises the steps to lower down onto the ocean bottom an underwater module comprising one or more devices according to the invention, to supply fluid under high pressure and fluid under low pressure to said device(s), where said fluid is supplied in a high- pressure nozzle and a low-pressure nozzle, respectively, to break up adjoining sediments on the ocean bottom with the help of said fluid under high pressure, and to supply said fluid under low pressure to the same sediments to further break up said sediments.

Alternative preferred embodiments of the method are characterised by the dependent claims 18-23.

The underwater module is preferably moved along the ocean bottom to perform said cleaning and/or digging of ditches. High-pressure fluid is supplied at an ultra high pressure, preferably above 200 bar, and more preferably above 250 bar, where high-pressure fluid and low-pressure fluid can be supplied alternatively, or high-pressure fluid and low-pressure fluid can be supplied at the same time.

Sediments made loose are preferably collected with the help of collecting means arranged in or adjoining the underwater module, and sediments that have been collected by the collecting means can be dispersed over the ocean bottom in an area far from the working area of the underwater module.

The invention shall now be described in more detail with reference to the enclosed figures, in which:

Figure 1 shows a perspective drawing of a device according to the invention.

Figure 2 shows a section of the device shown in fig. 1.

Figure 3 shows a system according to the invention comprising a number of devices according to figs. 1 and 2.

Figures 1 and 2 shows a device according to the invention for efficient removal of clay and other sediments on the ocean bottom, preferably in connection with offshore-related drilling operations. As can be seen in the figures, the present device comprises a preferably compact main body 10 encompassing at least one high-pressure nozzle 12 and at least one low-pressure nozzle 14 set up to receive and supply fluid under high pressure and fluid under low pressure, respectively. Consequently, the device is arranged to be placed on the ocean bottom for supply of said fluids to break up adjoining sediments.

The main body 10 preferably comprises a centrally arranged high-pressure nozzle 12 and a surrounding outer low-pressure nozzle 14, but the nozzles can be placed in ways other than shown here. The high-pressure nozzle and the low-pressure nozzle are standard, known types and will therefore not be described in any detail as they are considered to be known to those skilled in the art.

The high-pressure nozzle 12 is, in one embodiment, arranged to supply fluid with sufficiently high pressure for the sediments within a distance of up to 1 metre to be broken up. In another embodiment, the high-pressure nozzle 12 can be set up to break up sediments at a distance of more that 1 metre. The low-pressure nozzle 14 is consequently set up to further break up said sedi¬ ments within the same distances. It is preferred that the fluid used is water, but other liquid media can also be used.

As can be seen, the main body 10 can also comprise a hook-formed part 16 set up to further break up and/or remove said sediments. This hook-formed part 16 is preferably arranged to the underside of the main body, and at a suitable distance from said nozzles.

The device(s) according to the invention is preferably connected to one or more frequency-controlled fluid pumps for control of the speed of supplied fluid, such as, for example, the fluid pump 22 shown in connection with the system in figure 3, but if the device according to the invention shall be used alone, i.e. not in connection with the present system, the fluid pump can be arranged in a different way. Furthermore, the main body 10 is coupled to a flexible multi-line 18, in which line said fluid under high pressure and low pressure is supplied to the device through separate channels 18a and 18b.

The ultra-high pressure nozzle is preferably supplied with such a high water pressure that the sediments on the ocean bottom are broken up within a distance, for example, of 40-50 cm depth from the position of the nozzle in the sediments. Then, by supplying water with low pressure, these sediments are further broken up. By combining several such nozzle arrangements in the same system, one can effectively dig ditches on the ocean bottom in sediments >0.5 Mpa.

Initially, the high pressure of water can lie between 250 bar - 1200 l/min to 930 bar - 230 l/min. Low pressure can be constant at 8.5 bar- 13300 l/min. Nozzles will vary according to size and amount of water. Normally, this means a variation of about ø1.5 mm - 4.5 mm at high pressure. At low pressure, the nozzle size can in a preferred embodiment be at about ø77 mm inner diameter against 30 mm outer diameter on a small nozzle in the centre (i.e. area of the annulus). However, it must be clear that nozzles with other characteristics can be used, and that other pressures and amounts of fluid can be used, both above and below that described here.

As mentioned, the present invention also comprises a system for efficient removal of clay and other sediments on the ocean bottom, in connection with offshore cleaning and/or digging of ditches on said ocean bottom, comprising an underwater module 20 encompassing a number of devices according to that described above, where the devices are arranged next to each other mutually spaced apart. Furthermore, the underwater module 20 comprises collecting means 24 arranged to collect sediments made loose by said one or more devices, and also means 26 to disperse sediments that are collected by the collecting means 24.

The collecting means preferably comprises at least one suction pipe 28 with a suction head, arranged adjoining said device(s), and a pump connected to said pipe, arranged to suck up sediments that have been made loose. The suction pipe 28 is preferably a flexible pipe.

The means 24 of the underwater module 20 to disperse sediments that have been collected by the collecting means 24 comprises an ejector system which can be comprised of, for example, two or more outlets 30 that are arranged across the working direction and which disperse said sediments over the ocean bottom a distance sufficiently far from the underwater module so that said

sediments do not come into conflict with the working area. In the embodiment shown, the outlets 30 are shown more or less inside the underwater module, but the outlets can be displaced so that they are far in front or to the side of the underwater module.

The collecting means 24 and the means 26 to disperse sediments are prefer¬ ably connected to one or more frequency-controlled electric motors to drive associated pumps. Pumps and motors are preferably arranged adjoining the fluid pump shown as 22, but all pumps and motors can be arranged in other ways than that shown in figure 3 as the placing of these is not essential for the operation of the invention.

To ease the operation of the underwater module 20, it can comprise one or more underwater monitoring means that are chosen from a group encom¬ passing video camera, gyro, sonar, echo probe, MRU, light, etc. Furthermore, the underwater module comprises control means to steer and control the placing of the underwater module in relation to the ocean bottom. The control means can, for example, comprise a number of propellers 32 that can be placed in different locations on the underwater module to steer its movements in all necessary directions.

The controlling means and monitoring means of the underwater module can be connected to a status and monitoring system above the ocean surface.

When in use, the underwater module 20 is lowered down to the ocean bottom, preferably comprising one or more devices according to the invention, where¬ upon fluid under high pressure and fluid under low pressure are supplied to said device(s), where said fluids are supplied to a high-pressure nozzle and a low-pressure nozzle, respectively. Adjoining sediments on the ocean bottom are broken up with the help of said fluid under high pressure and supply of said fluid under low pressure on the same sediments breaks up said sediments further, at the same time as the underwater module is moved along the ocean bottom to carry out said cleaning and/or digging of ditches.

As mentioned, high-pressure fluid with an ultra-high pressure, preferably above 200 bar and more preferably above 250 bar, is supplied. High-pressure fluid and low-pressure fluid can be alternately supplied, or high-pressure fluid and low-pressure fluid can be supplied at the same time.