Field of the Invention

The present invention relates to the obtaining of core samples and/or data from a seabed.

Background to the Invention

The resolution of many offshore geotechnical problems, such as those involved in the anchoring of floating structures, requires an understanding of the properties of the seabed involved. Generally, these properties are determined by taking a vertical core sample of the seabed, which can then be analysed.

A common method of taking such samples involves the use of a 'piston corer'. A piston corer generally comprises a corer pipe or barrel which has a piston located inside. The corer barrel is dropped from a height above the seabed and, under the influence of gravity, embeds itself into the seabed. A piston is located within the corer barrel and, once the piston is immediately above the seabed, stays stationary as the corer barrel progresses down into the seabed. At the conclusion of this downward movement, the corer barrel contains a seabed core topped by the piston.

The relative position of piston and barrel are then fixed, so that the water is unable to enter the top of the core as the corer barrel is removed. This promotes maintenance of the core in position within the barrel as the barrel is withdrawn to the surface.

Many piston corers also include a core catcher, which is located towards the head of the corer barrel. The core catcher acts in a manner broadly similar to a one-way valve, in that it permits the movement of material into the corer barrel but restricts movement out. Core catchers are generally formed by bands of spring steel, aligned so as to allow movement in only one direction through the core catcher.

The use of core catchers is known to cause problems in sampling. In general, the stronger and stiffer a core catcher is, the more effective it will be at maintaining the core in position within the corer barrel, but the greater effect it will have on the sample as the sample is being collected. This is similar in some ways to the effect of friction on the inner walls of the corer barrel. Increased friction leads to increased sample retention, but also to increased stress effects through the sample, and loss of sample integrity.

The use of pistons can also lead to some problems in sample recovery. Improper positioning of the piston, or movement of the piston and resulting fluctuations in pressures, can lead to a significant loss of integrity of the sample.

The present invention seeks to provide a seabed core sampler with associated core retaining means which addresses, at least in part, some of these concerns.

It is also envisaged that the present invention can be used for other seabed applications, in addition to or instead of core sampling. These include the taking of measurements for geotechnical engineering purposes, such as cone penetration testing or reflection seismology testing.

Summary of the Invention

According to a first aspect of the present invention there is provided a seabed coring device including a core barrel having an outer end arranged to penetrate the seabed, the coring device including a core retainer near its outer end, the core retainer being formed by at least one expandable member; the expandable member being moveable between an unexpanded configuration in which it does not substantially restrict the movement of material through the outer end of the coring device, and an expanded configuration in which the expandable member substantially restricts the movement of material through the outer end of the coring device.

Preferably, the expandable member is able to move from the unexpanded configuration to the expanded configuration through the application of pressurised fluid. It is envisaged that liquid subjected to hydraulic pressure may be used, although it may be possible to use air subjected to pneumatic pressure. Alternatively, the expandable member may be moved to its expanded configuration by the supply of reacting chemicals, such as a chemical cement or similar. In its broadest sense, the expandable member could be formed by such reacting chemicals, without requiring a bladder or similar container.

The expandable member may be a single bladder. It may, in the alternative, be a plurality of bladders spaced around the coring device.

In a preferred embodiment, the coring device includes an inner sealing member, located near an inner end of the core barrel. The inner sealing member may be a second expandable member. The second expandable member, similar to the first expandable member, can act in a similar fashion to a piston, eliminating the need for a piston to be used. In the alternative, the inner sealing member may be an actuator valve.

According to a second aspect of the present invention there is provided a seabed engaging device comprising a seabed penetrator arranged to engage within a support structure, the seabed engaging device including a sensing means arranged to determine the distance between the seabed engaging device and a seabed, and means being provided to disengage the seabed penetrator from the support structure when the sensing means determines the seabed engaging device to be at a desired distance from the seabed.

Preferably the sensing means is a range sensor, such as a sonar-operated range sensor. The sensing means may also include other means for determining position, such as a camera, pressure sensor, tilt sensor and the like.

In one embodiment the seabed engaging device is a seabed coring device; the seabed penetrator is a core sampler, and the support structure is a core sampler positioning means.

In alternative embodiments the seabed penetrator may include a cone penetrometer, a hydrophone, and/or other seabed testing device.

According to a third aspect of the present invention there is provided a seabed engaging device including a seabed penetrator having an outer end arranged to move through the sea and into the seabed, the seabed penetrator including a supply of pressurised gas able to be supplied in advance of the outer end in order to assist the movement of the seabed penetrator through the sea. According to a fourth aspect of the present invention there is provided a seabed engaging device including a seabed penetrator arranged to engage within a support structure, the support structure including a potential energy source able to be supplied to an inner end or the seabed penetrator to propel the seabed penetrator through the sea.

The potential energy source may be a supply of compressed gas. Alternatively, the potential energy source may be a coil spring.

In one embodiment the seabed engaging device is a seabed coring device; the seabed penetrator is a core sampler, and the support structure is a core sampler positioning means.

In alternative embodiments the seabed penetrator include a cone penetrometer or a hydrophone.

According to a fifth aspect of the present invention there is provided a method for extracting sample cores from seabeds, the method involving lowering a seabed coring device comprising a core sampler and core sampler positioning means to a desired position above the seabed, releasing the core sampler from the core sampling positioning means such that the core sampler embeds in the seabed, expanding an expandable member near an outer end of the core sampler to form a core retainer, drawing the core sampler into the core sampling positioning means, and bringing the seabed coring device including a contained core sample to the sea surface.

Brief Description of the Drawings

It will be convenient to further describe the invention with reference to preferred embodiments of the seabed coring device of the present invention. Other embodiments are possible, and consequently the particularity of the following discussion is not to be understood as superseding the generality of the preceding description of the invention. In the drawings:

Figure 1 is a side view of a seabed coring device in accordance with the present invention;

Figure 2 is a cross-sectional view of an upper portion of the seabed coring device of Figure 1 ;

Figure 3 is an enlarged view of a core head portion of a core sampler within the seabed coring device of Figure 1 ; Figure 4 is an enlarged view of an outer end of the core sampler within the seabed coring device of Figure 1 ;

Figure 5 is a cross section view of the outer end of the core sampler shown in Figure 4;

Figures 6 to 9 are sequential side views of the seabed coring device of Figure 1 shown during use; and

Figures 7a and 8a are enlarged cross-sectional views of the outer end of the seabed coring device during use.

Detailed Description of Preferred Embodiments

Referring to the Figures, Figure 1 shows a seabed engaging device, being a seabed coring device 10, comprising a seabed penetrator being a core sampler 12 located within a support structure, being a core sampler positioning means or cage 14.

The cage 14 extends from an upper end 16 to a lower end 18, and is primarily composed of an outer supporting structure 20 and inner guiding rails 22, aligned between the upper end 16 and lower end 18.

The core sampler 12 includes a substantially cylindrical core barrel 24, which is axially aligned within the cage 14 between an outer end 26 near the lower end 18 of the cage 14 and a head portion 28 located towards the upper end 16. In the embodiment shown, the core barrel 24 has an outer diameter of 125mm, in contrast with cage width which is in the order of 1600mm.

The core sampler 12 also includes a guiding portion 30 and an intermediate portion 32. The guiding portion 30 is located at the upper end 16 of the cage 14, and is sized and shaped so as to engage with the inner guiding rails 22. The guiding portion 30 is fixed in position relative to the inner guiding rails 22 by means of an actuator 31 . The guiding portion 30 is weighted to as to provide additional momentum to the core sampler during coring.

The intermediate portion 32 extends between the guiding portion 30 and the head portion 28. The intermediate portion 32 is substantially similar, with an outer diameter in the order of 300mm. The cage 14 includes a sensing means, being a range sensor 34, located at its lower end 18. The range sensor 34 may be a sonar device. It is arranged to monitor the distance between the lower end of the cage 14 and the seabed. Alternatively, the range sensor 34 may calculate depth by measurement of water pressure.

The coring device 10 is supported at its upper end 16 by a supporting arrangement 36. This can be best seen in Figure 2. The supporting arrangement 36 includes two first cables 38 coupled to the upper end 16 of the cage 14 at releasable couplings 40, and one second cable 42 coupled to the guiding portion 30 of the core sampler 12.

The supporting arrangement may include a shock absorbent means associated with the second cable 42. This may, for instance, comprise a resilient rubber core about which a cable is curled, or may comprise a hydraulic shock absorption system. The shock absorption system acts to prevent snapping of the second cable 42 and loss of the core sampler 12 in the event of false firing of the core sampler.

The coring device 10 includes two hydraulic actuators located at the upper end 16. A first hydraulic actuator 44, fixed to the cage 14, is connected to the releasable couplings 40. A second hydraulic actuator 46, located within the guiding portion 30, supplies a hydraulic pressure line 48 within the core sampler 12. In an alternative embodiment, the hydraulic pressure line may be located outside the core sampler 12.

The head portion 28 of the core sampler 12 is shown in greater detail in Figure 3. It includes a core head 50 connected to the intermediate portion 32, and a core barrel adaptor socket 52 connecting the core head 50 to the core barrel 24.

The outer end 26 of the core barrel 24 can be seen in Figure 4. The core barrel 24 ends with an adaptor socket 54, which connects the core barrel 24 to a core cutting shoe 56.

The adaptor socket 54 includes an expandable member in the form of a bladder 58 located internally. This can be best seen in Figure 5. The bladder 58 is connected to the hydraulic pressure line 48. The bladder 58 is moveable between a collapsed configuration (not shown), in which it presents no impediment to matter moving through the adaptor socket 54 into the core barrel 24, and an expanded configuration as shown in Figure 5 in which movement of matter through the adaptor socket 54 is prevented.

In a preferred embodiment of the invention, an inner sealing member, being a second expandable member, is located within the adaptor socket 52 of the head portion 28. The second expandable member is similarly connected to the hydraulic pressure line 48.

Use of the coring device 10 will now be described with reference to Figures 6 to 9.

In the configuration of Figure 1 , the coring device 10 is lowered into the ocean, suspended by a cable 60 connected to the supporting arrangement 36. The range sensor 34 monitors the distance between the lower end 18 of the cage 14 and the seabed 62.

When the range sensor 34 records an appropriate distance, the lowering of the coring device 10 ceases. This is the position shown in Figure 6.

The core sampler 12 is then urged into the seabed 62. This is done by releasing the actuator 31 . Release of this actuator 31 causes the core sampler 12 to fall downwards under the action of gravity. The inner guiding rails 22 ensure that the core sampler 12 remains vertically oriented as it falls.

The core barrel 24 embeds within the seabed 62 as shown in Figure 7. As can be observed in Figure 7a, the bladder 58 is maintained in an unexpanded state at this time.

Once the core barrel 24 has embedded in the seabed 62, and a core sample thus been lodged within the core barrel 24, the second hydraulic actuator 46 is used to supply pressure to the bladder 58, thus inflating it to expanded position shown in Figure 8a. This has the effect of locking the core sample within the core barrel 24. The second expandable member may be similarly inflated to seal against the top of the core sample. In an alternative embodiment, the second expandable member can be replaced with another inner sealing member such as an actuator valve, serving essentially the same purpose.

The first hydraulic actuator 44 can then be used to release the releasable couplings 40. This decouples the cage 14 from the cable 60, and allows it to come to rest on the seabed 62 around the core sampler 12. This is shown in Figure 8. Retraction of the cable 60 then withdraws the core barrel 24 from the seabed 62 into the cage 14. This ensures continued vertical orientation of the core barrel 24, reducing the chance of shearing.

Once the core barrel 24 has been withdrawn from the seabed into the cage 14, as shown in Figure 9, it can be safely returned to the surface for analysis of the core sample.

Other modifications are envisaged by the application. For instance, it is envisaged that compressed gas may be supplied to the outer end 26 of the core sampler 12 as it falls through the sea under the influence of gravity. This may have the effect of decreasing the resistance posed by the water, and increasing the velocity of the core sampler 12 through the water.

It is also envisaged that compressed gas may be used to propel the core sampler 12 through the water. Other means may also be employed to propel the core sampler 12 through the water, such as coil springs or other mechanical energy stores.

Although the system arrangement shown has the guiding portion 30 of the core sampler 12 held within the cage 14 during use, it will also be appreciated that in an alternative embodiment the core sampler 12 may disengage completely from the cage 14 during use. In this embodiment, a winch may be provided between the cage 14 and the core sampler 12, whereby the winch can be activated (for instance, hydraulically) to retract the core sampler 12 into the cage 14. This embodiment has an advantage that the core sampler 12 can stay in the seabed, coupled to the cage 14 by a loose tether, and thus be unaffected by movement of a vessel on the sea surface.

It will also be appreciated that the embodiment discussed herein above, being a core sampler, is but a single embodiment of an invention having wider application. Instead of being a core sampler, the seabed penetrator could be designed to take geotechnical engineering measurements. It could, for instance, be employed as a cone penetrometer; or as a locater for hydrophones used in reflective seismology. Other such uses will be apparent to a skilled worker in the field.

It is anticipated that a common support structure could be used in conjunction with a number of different seabed penetrators. This could significantly increase the efficiency of off-shore geological explorations, with the possibility of a range of seabed penetrators being deployable from a single vessel without the need to return to shore in between.

Further modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present application.