WO2003056132A1

WO2003056132A1 - Underwater soil survey apparatus and method

Info

Publication number: WO2003056132A1
Application number: PCT/GB2002/005832
Authority: WO
Inventors: David Ellison; Lain Fraser Jarvies
Original assignee: Fugro-Udi Limited
Priority date: 2001-12-22
Filing date: 2002-12-20
Publication date: 2003-07-10
Also published as: GB0130891D0; AU2002353188A1

Abstract

An underwater survey apparatus comprising a soil survey device (20), a deployment means (10) for deploying the soil survey device and/or locating the soil survey device adjacent to an underwater bed, and at least one anchor (40) to engage the underwater bed is described. A method for using the apparatus is also described.

Description

UNDERWATER SOIL SURVEY APPARATUS AND METHOD

The present invention relates to a survey apparatus and method, and particularly, but not exclusively, to a remotely operated vehicle (ROV) that is provided with a cone penetration test (CPT) system.

A number of different types of CPT systems exist, where the CPT system includes a cone penetrometer . Conventional CPT systems are deployed on a sub-frame that is lowered to and retrieved from the seabed using, for example, a crane on board a vessel. The CPT system is capable of determining a number of factors including, but not limited to, resistivity, radiological, conductivity, pore pressure and shear data of the seabed by the controlled deployment of a push rod into the seabed, the push rod including an instrumented "cone" as a tip. The instrumentation in the cone tip typically measures vertical penetration into the seabed, cone resistance, sleeve friction and pore-water pressure. The conventional methods and apparatus have a number of associated disadvantages in terms of efficiency, and the quality of the data obtained in terms of accuracy, consistency and reliability.

According to a first aspect of the present invention there is provided an underwater survey apparatus comprising a soil survey device, a deployment means for locating the soil survey device adjacent to an underwater bed, and at least one anchor to engage the underwater bed.

The anchor typically provides a reaction force against actuation of the soil survey device.

The soil survey apparatus typically includes an extendable device to project a data sensor into the underwater bed.

The present invention also provides an underwater survey apparatus comprising a soil survey apparatus, and an anchor to engage an underwater bed.

According to a third aspect of the present invention, there is provided a method of surveying underwater structures, the method comprising the steps of: locating an underwater survey apparatus adjacent to an underwater bed, the apparatus comprising at least one anchor and a soil survey device; engaging the anchor with the underwater bed; and gathering data with the soil survey device. The soil survey apparatus can be of any conventional type, but is preferably extendable into the soil of the underwater bed. The preferred form of extending soil survey apparatus is a cone penetration test (CPT) system. A CPT system is a soil surveying apparatus that is used to ascertain the geotechnical characteristics of underwater bed soils, generally for the purpose of engineering design.

The soil survey apparatus typically includes a push rod that is extendable into the underwater bed using, for example, a hydraulic ram or cylinder. Alternatively, the soil survey apparatus can include a push-pull chain, articulated rod or other flexible member that can be used in place of a conventional push rod. A cone is typically located at one end of the push rod or push-pull chain. The cone is typically a CPT cone, and can be a single or multi- function unit, and is typically in the order of 5cm² or up to 10cm² in size. The cone and/or the push rod typically include conventional instrumentation to obtain the geotechnical characteristics of the soil.

The soil survey apparatus is typically actuated for between 50 and 250 seconds, although this can be varied to suit the particular system used and application thereof.

The deployment means is preferably a remotely operated vehicle (ROV) . Alternatively, the deployment means may comprise a crane, winch or the like provided on a surface vessel. An ROV is preferred as this allows the soil survey apparatus to be positioned and/or located more accurately.

Where an ROV is used as the deployment means, the apparatus typically includes a frame (e.g. an ROV sub frame) and the soil survey apparatus is typically coupled to the frame. The frame can be releasably coupled to the ROV by one or more latches. The latches may be, for example, API17H latches.

The remotely operated vehicle (ROV) may comprise any work class ROV. The ROV typically has a power rating of between 100 and 200 horsepower.

The underwater bed is typically a seabed, but may comprise a lake or riverbed.

The anchor is preferably a suction anchor.

The suction anchor typically includes a housing, the housing typically being coupled to the frame. The housing typically includes an open end and a closed end. The suction anchor includes a pump, and one or more fluid inlets/outlets in fluid communication with the pump. Four fluid inlets/outlets are typically provided, each inlet/outlet being circumferentially and equally spaced around the closed end of the housing.. The pump is typically reversible so that it can remove fluids from and inject fluids into the housing. Alternatively, two separate pumps can be provided; one pump to remove fluids from within the housing, and a second pump to inject fluids into the housing. The pump can be of any conventional type and is generally capable of producing a pressure differential between an interior and exterior of the housing in the range of 0 to 5 bar, although higher differential pressures may be required and thus provided using an appropriate pump. The housing is typically provided with one or more differential pressure transducers or sensors to monitor the pressure differential . The transducers or sensors are typically coupled to a pump controller that controls the pump. This provides a feedback loop to the pump so that the differential pressure can be maintained at a substantially constant level.

The open end of the housing is typically adapted to be engaged in the underwater bed. This allows the suction anchor to engage the bed and thereby provide the reaction force required for extension of the push rod or push-pull chain into the bed. The housing is preferably circular in cross-section, although other shapes may be used.

The housing is optionally movable relative to the ROV. Thus, the depth of penetration of the housing into the underwater bed can be varied. The housing can be pivotally coupled to the ROV using an arm, and the housing moved using a cylinder for example, coupled to the arm. The depth of penetration into the underwater bed is optionally monitored (e.g. by an underwater camera provided to the ROV) . The housing can be moved manually or automatically (e.g. by the use of hydraulic rams) . In certain embodiments, the housing can be pivotally coupled to the ROV.

The suction anchor is thus controllable in terms of penetration into the underwater bed. The anchor is also controllable in terms of the differential pressure applied to it. As both of these are continually monitored and adjusted (either manually or automatically) , the stability of the reaction force can be increased. Additionally, it is possible to see if there is a problem with the suction anchor, as this can be observed by changes in the depth of penetration and/or changes in the differential pressure.

The apparatus typically includes a responder and/or transponder so that the range and bearing to the ROV and/or the soil survey apparatus can be measured. This allows the precise position of the ROV and/or the soil survey apparatus adjacent the underwater bed to be measured relative to a reference (e.g. a transducer on a surface vessel) . The surface vessel is preferably provided with a positioning system (e.g. a global positioning system (GPS/DGPS) . This has the advantage that the position of the vessel is known so that the soil survey apparatus can be positioned at a specific target location adjacent 1 the underwater bed. Other positioning systems may

2 be used, such as ultra-short base line (USBL) , long

3 base line (LBL) and long range real time kinematic

4 (LRTK) . _5

6 The step of locating the soil survey apparatus

7 underwater typically comprises deploying the

8 apparatus from a surface vessel . The apparatus may

9 be deployed using any conventional means such as a

10 crane, winch or the like. Alternatively, the

11 apparatus can be deployed using an ROV. 12

13 The step of actuating the soil survey apparatus

14 typically includes the step of actuating a hydraulic

15 ram to push the extendable device of the apparatus

16 (e.g. the push rod) into the underwater bed. The

17 step of actuating the soil survey apparatus

18 typically also includes the additional steps of

19 obtaining data from the instrumentation in the cone, 0 and either storing this for subsequent retrieval and 1 analysis, or transmitting the data to a surface 2 vessel or facility for real-time gathering and 3 analysis (e.g. via the ROV umbilical) . 4 5 The method preferably includes the additional step 6 of locating the soil survey apparatus adjacent to or 7 in contact with the underwater bed using the ROV. 8 The method preferably includes the additional step 9 of locating the soil survey apparatus at a precise 0 target location on the seabed. The source can be 1 positioned precisely using any positioning system, 2 such as GPS/DGPS, USBL, LRTK or LBL. The method typically includes the additional step of engaging at least a portion of the housing in the underwater bed. The step of engaging the housing in the underwater bed typically includes the step of creating a differential pressure between an exterior and an interior of the housing. The step of creating the pressure differential typically includes the step of removing fluids from within the housing. The pressure differential causes the housing to be sucked into and thus become embedded in the seabed.

The method optionally includes the additional step of monitoring the pressure differential.

The method typically includes the additional step of removing the housing from the underwater bed. The step of removing the housing typically includes the step of reducing the pressure differential. The step of reducing the pressure differential typically includes the step of injecting fluids into the housing. This causes a reduction in the differential pressure that facilitates removal of the housing from the underwater bed. The method optionally includes the additional step of actuating the thrusters of the ROV during removal of the housing from the underwater bed. Thrust from the ROV thrusters can be used to aid in freeing the housing from the bed if required.

The method optionally includes one, some or all of the additional steps of a) moving the soil survey apparatus to another target location using the ROV, b) engaging the housing in the underwater bed, and c) actuating the soil survey apparatus.

The method optionally includes the additional step of repeating steps a) to c) .

Embodiments of the present invention shall now be described, by way of example only, and with reference to the accompanying drawings, in which: - Fig. 1 is a side elevation of a remotely operated vehicle (ROV) provided with an embodiment of a cone penetration test (CPT) system; Fig. 2 is a side elevation of the ROV of Fig. 1 showing the CPT system in use; Fig. 3 is a side elevation of an ROV provided with an embodiment of a cone penetration test (CPT) system and a batch sampler; Fig. 4 is a plan view of the batch sampler of Fig. 3; Fig. 5 is (a) a side elevation, (b) a view from above and (c) an end view of a push-pull chain for use with a CPT system; Fig. 6 is a schematic cross-section of a suction anchor for use with the ROV of Figs 1 to 4; and Fig. 7 is a view of the suction anchor of Fig. 6 from an underside.

Referring to the drawings, Fig. 1 shows a remotely operated vehicle (ROV) 10 in side elevation. The ROV 10 is provided with a soil survey apparatus that in this embodiment comprises a cone penetration test (CPT) system 20, and a suction anchor 40.

The ROV 10 is typically a 100 to 200 horsepower (HP) multi-role vehicle (MRV) in this particular embodiment, but can be any suitable work class ROV or equivalent. The ROV 10 is preferably rated between 100 and 200 HP (approximately 75kW to 150kW) , but any suitable rating can be used, depending upon the application and power requirements.

The CPT system 20 is attached to the ROV 10. The ROV 10 is preferably used to deploy the CPT system 20 as this allows for more precise location of the CPT system 20 adjacent to an underwater bed (e.g. a seabed 21, lake bed, river bed or the like, not shown) . Use of "seabed" herein will be understood to be a reference to any underwater bed.

CPT system 20 includes a hydraulic ram or cylinder 22 that can be actuated to drive a CPT rod 24 into the seabed 21. The CPT rod 24 is attached at an upper end 24u thereof to the hydraulic ram or cylinder 22. A number of slotted guides are provided on the frame. The guides 26 constrain the movement of the CPT rod 24 so that in use the CPT rod 24 is driven substantially vertically into the seabed 21. The CPT rod 24 in this embodiment is approximately 1.2 metres in length, but this can vary between around 1 metre to around 3 metres or more, depending upon the application. The slots in the guides 26 can also allow for the passage of an ancillary rod (not shown) , and a ROD cable (not shown) .

A CPT cone 28 is provided at the end of the CPT rod 24 that is pushed into the seabed 21. The cone 28 is typically a 5cm² probe but can be a 10cm² probe, and is provided with instrumentation to take readings as the cone 28 is pushed into the seabed 21, as is known in the art. For example, the cone 28 can be used to obtain data such as, but not limited to, resistivity, radiological, conductivity, pore pressure, sleeve friction, temperature and shear data. The CPT cone may also be provided with fibre optic sensors (for oil, organic and heavy metal detection) and any other sensors or instrumentation as required. The data obtained from the instrumentation in the cone 28 is typically transmitted to the surface (e.g. to a surface vessel or facility) via an umbilical (not shown) , as is conventional in the art. The CPT cone can also be used to provide a time-tagged frequency response from the seabed 21.

The instrumentation in or around the cone 28 can include a friction sleeve that measures the friction on the cone 28 as it is pushed into the seabed 21; cone penetrometer load sensors (e.g. 10kN load sensors) ; optional pore pressure measurement at the face of the cone (face filter) or immediately above the base of the cone (base filter) for pressure measurements up to around 2.5 MPa pressure; and an inclinometer within the cone penetrometer . The cone 28 may be interchangeable to provide for the recording of a plurality of different parameters using different instrumentation, or can be a multi- function unit. In the latter case, the different functions can be controlled and timed using software .

The CPT system 20 is attached to a frame 30 that is capable of being attached to any work class ROV sub frame 32. A skid 34 is attached to the ROV 10 sub frame 32, and the frame 30 is conveniently attached to the sub frame 32 together with the skid 34 so that they can both be attached and detached from the ROV 10 (e.g. using latches). The skid 34 includes various hydraulics and valves, schematically shown as 36, and is provided with CPT interface electronics 38. The CPT skid 34 typically operates independently of the ROV 10, other than for communication purposes to transfer data to and from the surface vessel or facility via the umbilical, and also for electrical power. The ROV 10 preferably has sufficient power and data communication capability to the surface (typically via an umbilical) . The sub frame 32 and the other components of the ROV 10 and CPT system 20 are preferably rated to at least 3500 metres water depth, but again this can be varied depending upon the depth of water in which the system is operating. The skid 34 is generally provided with suitable clamps, systems and interfaces so that it can be coupled to the ROV 10. The sub frame 32 and skid 34 are constructed to withstand normal operational stresses, loads and strains, and can be insulated from one another using a plurality of steel/rubber shock mounts and/or tendons if required.

Fig. 5 shows a push-pull chain 90, such as that manufactured by Morat KG, that can be used as an alternative to the use of a CPT rod 24. The push- pull chain 90 comprises a number of chain links 92 that are structured and coupled so that they can only pivot in one direction. The push-pull chain 90 can be stored in a very compact housing 94, and is driven into and out of the housing 94 using a sprocket wheel 96. As the push-pull chain 90 is driven out of the housing 94 (to the left in Fig. 5a as shown, but this is arbitrary) , the chain 90 can flex around the sprocket wheel 96, but as it comes off of the wheel 96, it becomes rigid and acts much like a rod (e.g. the CPT rod 24) . This can be achieved by neighbouring links 92 engaging by interlocking means to hold the chain 90 straight under compression, but which disengage when the chain is put under tension (i.e. to bend around the sprocket wheel 96 ) . Thus, the use of the push-pull chain 90 has its advantages in that the space required to store the chain 90 is less than that for a conventional CPT rod 24. In particular, the push- pull chain 90 can allow for an increased depth of penetration into the seabed 21 (up to around 5 metres or more) when compared to a conventional CPT rod 24. The CPT cone 28 can be attached to the chain 90 in any conventional manner.

Referring again to Figs 1 and 2, suction anchor 40 is pivotally coupled to the skid 34 by an arm 42 with a pivot 42a (e.g. a pin or bearing) at one end to attach it to the skid 34, and a pivot 42b at the other end to attach it to the suction anchor 40. Thus, the suction anchor 40 can pivot between a retracted position shown in Fig. 1 where the ROV 10 is in motion, to an extended position, shown in Fig. 2, where the anchor 40 is in use. The pivoting of the arm 42 can be actuated by a hydraulic system (not shown) such as a cylinder, ram, piston or the like so that the anchor 40 can be moved relative to the ROV 10. This is advantageous as it allows the depth of penetration of the suction anchor 40 into the seabed 21 to be varied. The depth of penetration could alternatively be adjusted manually.

The ROV 10 can have any number of suction anchors 40 mounted abreast to provide a reaction force against the CPT push force required to push the CPT rod 24 (or push-pull chain 90) into the seabed 21. The reaction force that can be provided by the suction anchor (s) is generally dependent upon the size of the anchor 40, so that the number of anchors 40 and their size can be selected to provide the requisite reaction force. The description herein shall refer to only one suction anchor 40 being provided, however, multiple suction anchors 40 may alternatively be used.

The suction anchor 40 is best shown in Figs 6 and 7, and includes a cylindrical housing 44 that is open at a first end 46, and closed at a second end 48. Housing 44 can be of any convenient size and shape and need not be cylindrical. For example, the housing 44 may be oval, square, rectangular, triangular etc in cross-section. The open end 46 of the housing 44 is adapted to be engaged in the seabed 21, as shown schematically in Fig. 2, and thus a circular cross-section for the housing 44 is preferred.

The closed end 48 of the housing 44 is preferably provided with concentric and cross bracing 50, best shown in Fig. 7. The bracing divides the interior of the anchor 40 into separate coaxial cylindrical portions 63, the radial limits of which are defined by the bracing 50. The cylindrical portions 63 are typically linked by radial cross bracing. The sections should preferably all still be in fluid communication with one another (e.g. by apertures formed through the bracing) . The bracing 50 provides additional strength for the housing 44 so that it can be used in deep water where the pressure on the housing 44 can be significant, and also to help absorb normal operational stresses and strains. In this embodiment, the concentric bracing in particular extends towards the open end 46 of the housing 44. This provides multiple-facing for engagement with the seabed 21 to increase the stability of the suction anchor 40, particularly during actuation of the CPT system 20. The increase in stability is advantageous for use with soft sand and other soft soil types (e.g. unconsolidated materials and soils) as it helps to prevent sinking, and thus allows the overall system to be used in softer seabed materials.

The housing 44 typically has an inner diameter (ID) of around 1500mm, an outer diameter (OD) of around 1503mm (i.e. the wall thickness is 3mm) and a height of around 600mm. However, it will be appreciated that the particular dimensions of the housing 44 can be varied for the particular application, and especially to suit the type of seabed material and depth of water. The suction anchor 40 is relatively light weight (in the order of around 20 kilograms) , and has a relatively small wall thickness in the order of 2 to 3mm. The suction anchor 40 is capable of being used in water depths in excess of 1000m.

The housing 44 typically has an exterior skirt 72 extending .around its outer circumference, which can serve as a visual indicator as to how far the anchor has penetrated into the seabed. The vertical position of the skirt 72 on the housing 44 is typically adjustable.

The housing 44 is typically coupled to the ROV sub frame 32, or the skid 34. One or more two-way fluid inlets/outlets 52 are coupled to the housing 44 to inject fluids into and remove fluids from within the housing 44. In the case that more than one inlet/outlet 52 is provided, each inlet/outlet 52 may be circumferentially and equally spaced from the others, as this facilitates equalisation of pressure differentials within the anchor 40.

Each fluid inlet/outlet 52 can be supplied by an individual fluid source or alternatively each fluid inlet/outlet 52 may be supplied from a common fluid source via an appropriate manifold. Since the interior portions divided by the bracing are in fluid communication with each other, this means that fluid is injected and removed from the whole of the anchor 40.

Each inlet/outlet 52 is in fluid communication with a pump (not shown) via a respective conduit 54. The pump is typically a low pressure reversible pump (e.g. a Zip pump system or similar) capable of generating a pressure differential of between 0 and 5 bar, although higher pressure differentials may be provided with an appropriate pump as required. The pump can be provided as part of the ROV 10, or on the skid 34. The pump is typically reversible by actuation of a slide (not shown) that changes the direction of flow between removing and injecting fluids, and is typically controlled by a pump controller (not shown) that is in turn controlled by an ROV hydraulic control system (not shown) , or the hydraulics and valves 36 on the skid 34. Alternatively, two or more separate pumps may be provided; e.g. one or more to pump fluids into the housing 44 and one or more to remove fluids therefrom. Thus, the suction anchor 40 is reversible so that it can be engaged and disengaged from the seabed 21.

The closed end 48 of the housing 44 is provided with a mud filter 56 that is used to filter out the larger particles of seabed material so that the particles do not adversely affect the operation of the pump(s). The mud filter 56 typically extends across the entire surface area of an inner surface of the housing 44 at the closed end 48, but may alternatively be located only in the vicinity of the inlets/outlets 52 if required, or any other suitable location.

The ROV 10 and the suction anchor 40 are generally configured to the optimal configuration on board the surface vessel (not shown) before being launched. This typically includes adjusting the position of the skirt 72 and checking/unblocking the anchor filters and ports. Suitable provisional soil data of the seabed 21 and water depth information can be used (where available) to configure the ROV 10 and suction anchor 40 before deployment. For example, the soil type and water depth information can be used to calculate how far the anchor should extend into the seabed. The skirt 72 can then be set at that distance from the bottom of the anchor; thus, when the skirt becomes level with the seabed, the anchor has reached its required depth.

An advantage of embodiments of the present invention is that the position of the ROV 10 on the seabed 21 can be precisely known and monitored by the use of a positioning system such as a Global Positioning System (GPS/DGPS) , ultra-short base line (USBL) acoustic positioning system, a long base line (LBL) system and/or a long-range, real-time kinematic system (LRRTK) so that the CPT system 20 can be located precisely at the target co-ordinates for each survey. This has the advantage that the CPT system 20 can be positioned precisely at a particular target area of the seabed 21, thus making the overall system more efficient, and improving the quality and reliability of the data obtained over conventionally deployed CPT systems.

In addition to this, the use of the positioning system can provide for accurate placement of the ROV 10 and the CPT system 20 at precisely the same position on the seabed 21 any number of times to facilitate repeat surveys. This has the advantage that the data obtained from actuation of the CPT system 20 can be made more consistent giving a better indication of, for example, any changes in the stability of the seabed 21.

The GPS/DGPS (not shown) is generally provided on the surface vessel, which in itself is provided with a transponder or the like that can be used to record the range and bearing to the ROV 10 and/or the CPT system 20 on the seabed 21. This, together with the position of the surface vessel (e.g. from GPS/DGPS readings) , facilitates the precise position of the ROV 10 and thus the CPT system 20 to be known. The positioning information can be used to give precise repeat surveys at the same location, offering the advantages set out above. The GPS/DGPS may be provided on the ROV 10 and/or the CPT system 20 where the CPT system 20 is being used in relatively shallow water (typically less than 100m in depth) . The position of the ROV 10 and the CPT system 20 can also be set precisely using a USBL responder link to the surface vessel or with respect to a previously established long baseline array. Inertial ^■ navigation may also be used, or a combination of these systems.

Referring now to Fig. 1, the ROV 10 with the suction anchor 40 and CPT system 20 coupled thereto are launched from the surface vessel, typically over- side or via a moonpool (not shown) . The ROV 10 is then piloted to the seabed 21 in any conventional manner.

The ROV lands on the seabed and the suction anchor 40 is moved from the retracted position shown in Fig. 1 to the extended position shown in Fig. 2 (e.g. by a hydraulic ram acting on arm 42) so that the anchor 40 engages the seabed. The hydraulic ram acting on arm 42 can also be used to increase and decrease the depth of penetration of the housing 44 into the seabed 21, as required.

When the housing 44 engages the seabed 21, a seal 60 (see Fig. 2) is created at the interface between the edge of the housing 44 and the seabed material . The seal 60 creates a barrier between the internal space 62 (Fig. 6) in the anchor 40 and the surrounding seabed material .

The depth of penetration of the anchor into the seabed is typically controlled so that the anchor penetrates sufficiently to anchor the apparatus against the action of the CPT cone being driven into the seabed, but not so far that the whole of the space 62 of the inside of the housing 44 becomes full of seabed material and has no liquid content at all (in which case there would be no liquid to pump) .

The depth of penetration is adjusted by moving the arm 42 (e.g. hydraulically) to extend or retract the anchor 40 as appropriate.

An underwater camera could be used to monitor the depth of penetration, e.g. by using graduated markings on the outer surface of the housing 44, and/or by observing the relative positions of the skirt 72 and the seabed 21.

The pump is then actuated to remove fluids from within the anchor 40. The mud filter 56 prevents large particles of the seabed material from being drawn in by the pump and thus reduces the likelihood that the pump and/or the conduits 54 will become blocked. A pressure differential is created between the interior space 62 in the anchor 40 and the surrounding seawater, and this pressure differential anchors the ROV 10 to the seabed. The suction anchor pump is proportionally controlled so that the pressure differential is increased gradually to around 3 to 5 bar. The pressure differential is increased gradually to prevent loss of the seal 60 during actuation of the pump.

The differential pressure also provides a reaction force against the action of the CPT rod 24 (or push- pull chain 90) driving into the seabed 21. The reaction force is provided by the differential pressure and is generally around 20 to 60 tonnes, depending on the surface area of the suction anchor 40 and the differential pressure. Other factors may also affect the reaction force, such as the water depth, the internal space 62 in the suction anchor 40, and seabed friction.

The reaction force can be calculated using the relationship that the differential pressure is equal to the reaction force divided by the area of the top surface of the suction anchor 40, and thus the reaction force is equal to the differential pressure multiplied by the top area of the suction anchor 40. Thus, if the differential pressure is known and is limited to a certain value, the corresponding reaction force provided by the differential pressure can be calculated. If a particular reaction force is required by the CPT system 20 to react against the CPT rod push force, the required pressure differential and/or surface area can be calculated. The pressure differential can then be set at the required value, and the top surface area of the housing 44 can be designed to give the appropriate reaction force.

The anchor of Figs 6 and 7 has a height of 600mm, and an inner radius (IR) of 750mm. The area of the top surface is 17671.46 cm², which is the equivalent of 1.767146 m². Where the reaction force required is, for example, 60 tonnes (60000 kg) , then the required differential pressure is 3.395 kg/cm² or 3.46 bar or 48.28 psi. The required differential pressure is provided by the suction anchor pump which pumps water out of the internal space 62 in the anchor 40, thus creating a vacuum which then has to be filled by an ingress of seabed material. The force provided by the pump depends on the power of the pump, but also on the internal volume of the pump, seabed friction, and the type of seabed material. For example, if the internal volume is small, the amount of water able to be sucked out of that internal volume is small, which limits the strength of the vacuum and hence the suction power.

The type of seabed material is relevant because if the seabed comprises large grains of sand, and if the anchor does not penetrate deeply enough into the seabed, when the pump is activated, seawater from the outside of the pump could be sucked into the anchor between the large grains of sand. In other words, the quality of the seal would be affected. Therefore, water pumped out of the anchor 40 could be replaced by water from outside the anchor 40, instead of the anchor 40 being sucked into the seabed.

Small grains of sand provide a better seal, so if the seabed material is composed of small grains, the anchor need not be so deeply embedded in the seabed, which leaves a larger proportion of the volume of the anchor to be filled with seawater. This gives the advantage of larger suction power, as explained above .

In any event, the suction force provided by the pump can be increased accordingly if the full internal space 62 is not available, which in turn will increase the reaction force. Friction between the housing 44 and the seabed material has been neglected, but is typically in the order of 1% to 2% of the reaction force. A nominal 6 tonnes of reaction force is typically provided per approximately 50 litres of suction anchor volume capacity (i.e. the volume of the internal space 62 of the anchor 40) .

The required pressure differential to anchor the ROV 10 against the action of the CPT rod driving into the seabed is generally dependent upon the type of seabed material, but is typically in the range of around 3 to 5 bar.

The pressure differential can be monitored using one or more differential pressure transducers or sensors 64 (Figs 6 and 7) mounted between the radial and concentric bracing 50 or otherwise in the internal volume 62 of the anchor 40. The transducer 64 provides feedback to the pump controller so that the pressure differential can be monitored and maintained throughout the actuation of the suction anchor 40. It is advantageous to monitor the pressure differential because this generally reduces over time due to fluid ingress past the seal 60. Also, the transducer 64 allows for continual monitoring of the pressure differential to ensure that the appropriate reaction force is maintained during actuation of the hydraulic cylinder 22 (or sprocket wheel 96) to drive the CPT rod 24 (or push- pull chain 90) into the seabed 21. A differential pressure transducer or sensor 64 may also be located externally of the housing 44 (e.g. on the ROV 10) for reference purposes.

Reaction force is also a function of water depth, and the size of the surface area of the suction anchor 40 can be varied to optimise operation. Table 1 below sets out the reaction force in varying water depths with three different surface areas, the pressure differential being in the order of 3 to 5 bar. The reaction forces are shown in tonnes. Table 1

The CPT system 20 can be used to confirm the type of seabed material, from which the depth of penetration can be calculated, and this information can be fed back to a user to provide for automatic and/or manual adjustment of the penetration by moving the housing 44 accordingly. Alternatively, or additionally, one or more strain gauges can be mounted to the outer surface of the housing 44 to measure the sleeve friction to give an indication of penetration. As a further alternative, a transponder may be attached internally of the housing 44 to measure the height of the closed end relative to the seabed, to ensure that the housing 44 has penetrated a sufficient depth. Another option is to provide one or more load cells at the open end 46 of the housing 44 to measure the reaction force generated by the housing 44 as it penetrates the seabed 21. If the circumference, depth, radius or other dimensions of the housing 44 are changed, this will change the volume of the housing 62, which will in turn affect the pressure differential and the reaction force provided.

The CPT system 20 is preferably located in close proximity to the suction anchor 40 so that rotational moments are minimised, and so that the instrumentation on the CPT cone 28 provides reliable data.

Fig. 2 shows schematically the housing 44 embedded in the seabed 21 after actuation of the pump. Once the pressure differential has been created, the pump may be stopped and the pressure differential maintains the suction anchor 40 in the seabed 21. In some circumstances, it may be desirable to continue the pumping action. For example, if the seal 60 is weak, water pumped out of the housing will be continually replaced by water from outside of the housing 44, which will also need to be pumped away to maintain the pressure differential. Optionally, the pump may be stopped and reactivated as necessary during the operation of the CPT system. In any event, the suction anchor pressure differential is preferably continually monitored to ensure no movement takes place that could affect the integrity of the data obtained by the CPT system 20.

The pump is actuated until the housing 44 has penetrated a sufficient depth into the seabed 21 to provide for stability of the ROV 10, and also the required reaction force. Typically, it is desirable to remove as much water as possible from the inside of the anchor 40, so that the anchor penetrates into the seabed to its fullest extent. The stability and the reaction force can be monitored using any of the devices or systems described above (e.g. the transponder, strain gauges, load cells, cameras etc) . The pressure differential transducer 64 can be used to continually monitor the pressure differential to keep it substantially constant by automatic or manual control of the pump.

The combined mass of the ROV 10, CPT system 20 and the or each suction anchor 40 gives the ROV 10 a negative buoyancy to facilitate landing of the ROV 10 and the CPT system 20 on the seabed 21 under their own weight. Indeed, the ROV 10 and in particular the suction anchor 40 remains in contact with the seabed 21 due to this negative buoyancy.

In some instances, the ROV sub frame 32 may be in contact with the seabed 21, depending upon the depth of penetration of the suction anchor 40 into the seabed 21, and indeed this may be advantageous as it can increase the stability of the ROV 10, particularly during actuation of the CPT system 20.

The hydraulic cylinder 22 is actuated to drive the CPT rod 24 into the seabed 21. It is useful if the CPT rod 24 is driven into the seabed material at a constant speed of around 2 centimetres per second. The rate of progress of the rod 24 into the seabed 21 and the hydraulic pressure in the cylinder 22 can be monitored in real time to keep the speed constant. The rod 24 is pushed into the seabed 21 to the required test depth (generally limited by the length of the rod 24) , while data acquisition from the instrumentation in the cone 28 is monitored (e.g. sleeve friction, pore pressure etc) . The cone 28 may be piezo-cone penetrometer or a friction-cone penetrometer for example. The driving in of the CPT rod 24 creates an upwards reaction force, which is countered by the engaged anchor 40.

The CPT system 20 is then actuated in any conventional manner, and the data obtained therefrom can be gathered by the instrumentation in the cone 28, and passed to the CPT electronic interface 38. Timing and control of the CPT system 20 can be achieved using conventional electronic methods through the ROV umbilical, and data and control signals transmitted to and from the surface vessel or facility. The data can either be stored on board the ROV 10 in an appropriate storage device for subsequent retrieval and analysis, or transmitted via the ROV umbilical to the surface vessel or facility for real time gathering and analysis. The CPT system 20 is typically actuated for a period of around 50 to 250 seconds per location, but this is dependent upon the depth of the sample specification. The transducer 64 can be used to provide feedback to the pump controller to maintain the desired pressure differential within acceptable limits.

The CPT cone probe 28 is typically capable of operating in water depths of around 20 to 3000 metres, but this is generally limited by the capability of the particular ROV 10. The CPT cone 28 provides a controlled spectrum of energy so that the resolution to determine the strata can be clearly defined and measured. The energy levels required to transmit the data over the ROV umbilical is generally sufficient to ensure coherent data can be received and recorded at the surface vessel or facility.

The ROV 10 can be configured to provide for a measurement of water depth.

After actuation of the CPT system 20 and collection of the data, operating the hydraulic cylinder 22 in reverse retracts the CPT rod 24 and cone 28. The CPT system 20 can be reset via software control or electronically for example, so that the ROV 10 does not need to be recovered to the surface vessel or facility for manual reset.

Thereafter, the slide on the pump is moved to reverse the pumping direction, and water (or another fluid) is injected or pumped into the internal space 62 of the housing 44. As the water is pumped in, the pressure within the internal space 62 increases and the pressure differential between the interior space 62 and the surrounding seawater is reduced. The rate at which fluid is pumped into the housing 44 is not critical, and indeed it may be advantageous to pump the fluid in at high speed and/or pressure to aid in freeing the housing 44 from the seabed 21. The increase in pressure tends to push the housing 44 out of the seabed 21 by increasing the pressure in the internal volume 62 with respect to the seabed 21. The thrusters on the ROV 10 can be used to assist in releasing the housing 44 from the seabed 21 if required.

The ROV 10 can then piloted to a new target location using the GPS/DGPS system or the like and the transponder on the surface vessel to facilitate precise and accurate positioning of the ROV 10 and the CPT system 20 on the seabed 21 at a different target location. Once the ROV 10 has been moved to the second target location (if required) , the suction anchor 40 is re-actuated (by actuating the pump to remove fluids from within the housing 44 as described above) so that the housing 44 penetrates to the required depth into the seabed 21. Thereafter, the CPT rod 24 is forced into the seabed 21 and the CPT system 20 is actuated, as described above .

This process can be repeated any number of times at any number of different locations. The ROV 10 and thus the CPT system 20 can be accurately and precisely positioned at each location, making the overall system more accurate and efficient. The ROV 10 may be provided with one or more hydraulic accumulators (not shown) that can be used in the event of an emergency to release the ROV 10, CPT system 20 and suction anchor 40 from the seabed 21.

Referring now to Figs 3 and 4, there is shown a modified ROV, generally designated 110, that is similar to ROV 10 so that like reference numerals have been used to designate like parts, prefixed "1".

In this embodiment, the ROV 110 is again provided with a cone penetration test (CPT) system 120, and a batch sampler 200. The ROV 110 includes one or more suction anchors 40 as before, but these are not shown in Fig. 3.

The CPT system 120 is attached to the ROV 110, and in this embodiment includes first and second hydraulic rams or cylinders, generally designated 122. The first hydraulic ram can be actuated to drive the CPT rod 124 into the seabed (not shown) . The second hydraulic ram can be actuated to drive a batch sample tube contained in a cartridge 202 into the seabed. The CPT rod 124 is attached to the first hydraulic ram or cylinder in the same manner as the previous embodiment. As before, guides (not shown) can be provided with slots to constrain the movement of the CPT rod 124 so that, in use, the CPT rod 124 is driven substantially vertically into the seabed. The CPT rod 24 in this embodiment is approximately 1.2 metres in length, but this can vary between around 1 metre to around 3 metres or more. The CPT cone 28 is provided at the end of the CPT rod 124 and is generally a 5 square-centimetre probe, as before.

The CPT system 120 is attached to a tooling frame 130 that is capable of being attached to any work class ROV 110.

The push-pull chain 90 shown in Figs 5a and 5b could also be used with this embodiment in place of (or in addition to) the CPT rod 124.

The main difference between the embodiments shown in Figs 1 and 2, and in Figs 3 and 4 is the provision of the batch sampler 200. The batch sampler 200 includes the batch sample tubes (typically around 1 metre in length) provided in a plurality of cartridges 202. The cartridges 202 are mounted on a carousel drive system 204 that includes a driven belt 206 where the cartridges 202 are attached to the belt 206 so that there is a continued supply of sample tubes to facilitate continual operation for longer periods of time before recovery of the ROV 110 to the surface. The belt 206 is driven by a hydraulic motor 208 and a drive wheel 210.

In use, the second hydraulic ram is actuated to drive a sample tube into the seabed. Once the sample has been taken, the sample tube is retracted into the cartridge 202 by reversing the direction of the second hydraulic cylinder. The carousel 204 is then revolved so tihat a new sample tube in a new cartridge 202 is engaged by the second hydraulic cylinder so that a new sample can be taken. The advantage of having the carousel 204 is that a number of samples can be taken without having to retrieve the ROV 110 to the surface. The cartridges 202 are designed to be interchangeable by the carousel 204 so that the ROV 110 can remain at the seabed for as long as necessary to complete the sampling.

The sample tubes contain a variable opening iris at a lower end thereof that facilitates passing of the soil sample into the tube whilst the tube is forced into the seabed, but retains the sample during retraction of the tube and recovery to the surface. An upper end of the tube is provided with a non- return or one-way valve that allows water in the tube to escape as the soil sample enters the tube, and also as the tube is being recovered to the surface.

This allows a sample of the seabed material to be taken simultaneously with operation of the CPT system. Once this is done, the ROV is typically un- anchored and moved to a new location on the seabed, where new measurements and a further sample can be taken, and this may be repeated as necessary. The number of samples which can be recovered may be limited by the density of the seabed material - i.e. if the material is very dense, the ROV may not be able to lift off the seabed 21 if every cartridge is filled.

An advantage of certain embodiments of this invention is that the CPT system can be accurately positioned at the same location on the seabed any number of times, (e.g. by using GPS/DGPS) allowing repeat surveys which provide consistent results. A further advantage is that the data can be transmitted to the surface and analysed in real time.

The use of embodiments of the invention including the ROV and the CPT system has many different applications. The system can be used in support of shallow seismic data acquisition, either to gather data as a stand-alone system, or to act as a quality control source for conventional data acquisition systems.

Additionally, the apparatus can be used for field trenching and engineering design studies, and the monitoring of field trenching system performance, backfill data, convection studies and thermal properties, shallow foundation studies and for obtaining general geotechnical data.

Further, the apparatus can be used to enhance existing geotechnical data and information in areas where conventional operations may be hazardous, e.g. samples in close proximity to seabed structures, buried pipelines or cables, or morphologically complex areas, as identified by multiples or blanking on shallow seismic records. Also, data can be obtained from under platforms or other structures and facilities, for example in terms of mud mound sampling.

The ability to precisely locate the CPT system on the seabed, together with a multi-sensor performance capability, can enhance the quality of the data obtained. This is particularly advantageous for engineering projects that rely on the data from the CPT system to determine if a particular structure or facility can be supported by the seabed material.

The system can be used to provide accurate and precise placement of the CPT system (using the ROV) so that it could be permanently installed in permanently instrumented fields. The system can be coupled to the field facilities as required.

The CPT probe and deployment system can provide a broad spectrum of characteristics for geotechnical, environmental and engineering requirement . Additionally, the CPT probe can be configured as a single or multi-function unit to provide any data that is required.

Depth of penetration of the probe can be achieved from around 1 metre using a conventional CPT rod and standard hydraulic capabilities of the ROV, or can be up to 5 metres or more using a flexible push-pull chain, articulated rod or other flexible member, thereby offering considerable advantages.

The system can provide seabed samples using the CPT probe actuator as a mechanism to push in and recover sample tubes. Additionally, use of the batch samples offers advantages in that a larger number of samples can be taken without having to recover the ROV to the surface. It is advantageous to combine the soil sample and soil surveying operations in a single unit.

The ROV deployed system is low in terms of risk to seabed features (i.e. it has minimal environmental impact) , requires less energy comparable with that normally arriving at the seabed, is little affected by interference, currents and water depth limitations, and gives soil data acquisition performance comparable with current mass frame deployed systems.

System coupling with the seabed is predictable and controllable, and the overall data quality obtained can be superior to conventional data as the CPT system can be placed immediately adjacent to seabed structures, or in trench backfill areas to determine pip and cable positions.

Embodiments of the present invention also offer the advantage that the apparatus can be deployed from a wider range of vessels than some conventional systems that require specialised vessels. Certain embodiments can also be used to provide a CPT system that can be conveyed to the seabed using an ROV and left permanently installed on the seabed.

Embodiments of the present invention are also more cost-effective and easier to operate than conventional systems.

Modifications and improvements may be made to the foregoing without departing from the scope of the present invention.

For example, the anchor need not be a suction anchor. Any anchor which can counter the reaction force from the penetration of the soil survey device would be sufficient.

The soil survey device does not need to include a cone. Some instrumentation or sensors could be situated on the road as well as or instead of on the cone.

The anchor is not necessarily movable relative to the rest of the apparatus.

The data does not need to be transmitted to the surface via an umbilical - it could be stored on the apparatus and recovered later with the apparatus.

The bracing is not an essential feature of the anchor. The bracing could be in the form of bars, (i.e. extending across the inside of the housing) instead of walls.

Claims

1. Underwater survey apparatus comprising a soil survey device, a deployment means for locating the soil survey device adjacent to an underwater bed, and at least one anchor to engage the underwater bed.

2. Apparatus as claimed in any preceding claim, wherein the deployment means is a remotely operated vehicle (ROV) .

3. Apparatus as claimed in claim 1 or claim 2, wherein the apparatus includes a frame and the anchor is moveable relative to the frame.

4. Apparatus as claimed in any preceding claim, having an extension means to insert the soil survey device into the underwater bed.

5. Apparatus as claimed in claim 4, wherein the soil survey device can be extended into the underwater bed by at least two metres.

6. Apparatus as claimed in claim 4 or claim 5, wherein the extension means comprises an articulated member.

7. Apparatus as claimed in claim 6, wherein the bending of the articulated member is limited.

8. Apparatus as claimed in any of claims 4 to 7, wherein the extension means comprises a rod or a chain.

9. Apparatus as claimed in any preceding claim, wherein the soil survey device comprises a cone penetration test (CPT) system which supports measuring instrumentation.

10. Apparatus as claimed in any preceding claim, having a sampler device adapted to collect samples of the underwater bed.

11. Apparatus as claimed in claim 10, wherein the sampler device has means for taking sequential samples.

12. Apparatus as claimed in claim 11, wherein the means for taking sequential samples comprises multiple sample tubes mounted on a carousel drive system.

13. Apparatus as claimed in any preceding claim, wherein the mass of the anchor is less than 20kg.

14. Apparatus as claimed in any preceding claim, wherein the anchor is recoverable.

15. Apparatus as claimed in any preceding claim, wherein more than one anchor is provided.

16. Apparatus as claimed in any preceding claim, wherein the at least one anchor is a suction anchor.

17. Apparatus as claimed in claim 16, wherein the at least one suction anchor includes one or more fluid inlets/outlets in communication with at least one pump.

18. Apparatus as claimed in claim 17, wherein the at least one pump is reversible.

19. Apparatus as claimed in any of claims 16 to 18, wherein the at least one anchor includes a housing having an open end for engagement with the underwater bed.

20. Apparatus as claimed in claim 19, wherein the housing has interior bracing.

21. Apparatus as claimed in claim 19 or claim 20, wherein the housing is cylindrical and the interior bracing comprises a plurality of coaxial cylinders of different radii.

22. Apparatus as claimed in claim 21, wherein cross bracing links the cylindrical bracing.

23. Apparatus as claimed in any one of claims 19 to 22, having one or more differential pressure transducers or sensors to monitor the pressure differential between the exterior and the interior of the housing.

24. Apparatus as claimed in any preceding claim, including a monitoring means to monitor the depth of penetration of the anchor into the underwater bed.

25. Apparatus as claimed in any preceding claim, including a responder and/or a transponder to measure the range and bearing of the soil survey device relative to a reference point.

26. Apparatus as claimed in claim any preceding claim, including a positioning system to monitor the position of the apparatus with respect to the underwater bed.

27. Underwater survey apparatus comprising a soil survey device, and an anchor to engage an underwater bed.

28. A method of surveying underwater structures, the method comprising the steps of: locating an underwater survey apparatus adjacent to an underwater bed, the apparatus comprising at least one anchor and a soil survey device; engaging the anchor with the underwater bed; and gathering data with the soil survey device.

29. A method as claimed in claim 28, wherein the apparatus is deployed and located adjacent to an underwater bed by an ROV.

30. A method as claimed in claim 28 or claim 29, including the step of using a positioning system to locate the soil survey device at a desired location on the underwater bed.

31. A method as claimed in any one of claims 28 to 30, including the step of creating a differential pressure between an exterior and an interior of the at least one anchor to engage the anchor with the underwater bed.

32. A method as claimed in claim 31, wherein the pressure differential is created by removing fluids from within the at least one anchor.

33. A method as claimed in any one of claims 28 to 32, including the step of monitoring the pressure differential.

34. A method as claimed in claim 33, wherein data from transducers or sensors mounted on the body of the at least one anchor is fed back to a pump controller so that the differential pressure and thus the force of engagement of the anchor can be controlled.

35. A method as claimed in any of claims 28 to 34, wherein the soil survey device includes an extension means, and the extension means is activated to insert the soil survey device into the underwater bed.

36. A method as claims in claim 35, wherein the anchor provides a reaction force against the action of the soil survey device penetrating the underwater bed.

37. A method as claimed in claim 35 or claim 36, wherein at least a portion of the soil survey device is extended at least two metres into the underwater bed.

38. A method as claimed in any one of claims 35 to 37, wherein the extension means comprises an articulated member which is uncoiled from a coiled position to an extended position to insert the soil survey device into the underwater bed.

39. A method as claimed in any of claims 28 to 38, including the additional step of transmitting the data obtained by the at least one sensor via an umbilical to a facility for real-time analysis.

40. A method as claimed in any of claims 28 to 39, including the step of taking sequential samples of the material of the underwater bed.

41. A method as claimed in claim 40, wherein a plurality of sample tubes are successively driven into and removed from the underwater bed, the sample tubes being mounted on a carousel drive system which rotates to provide successive sample tubes.

42. A method as claimed in any one of claims 28 to 41, including the step of recovering the at least one anchor from the underwater bed.

43. A method as claimed in claim 42, whereby the at least one anchor is removed from the underwater bed by injecting fluids into the anchor to reduce the pressure differential between the exterior and the interior of the anchor.

44. A method as claimed in claim 42 or 43, including the step of actuating the thrusters of the ROV during removal of the housing from the underwater bed to aid in freeing the anchor from the bed.

45. A method as claimed in any one of claims 28 to 44, wherein the method is carried out in water depths greater than 1000m.