Autonomous underwater vehicle, system and method for acquiring marine seismic data

Abstract

The disclosure relates to an autonomous underwater vehicle for marine seismic data acquisition, the autonomous underwater vehicle comprising a cavity for accommodating an ocean bottom node such that a coupling surface of the ocean bottom node is at least partially exposed for coupling the ocean bottom node to a sea floor. The disclosure further relates to a marine seismic data acquisition system comprising an autonomous underwater vehicle and an ocean bottom node provided in the cavity. The disclosure further relates to a marine seismic data acquisition method comprising installing an ocean bottom node in a cavity of an autonomous underwater vehicle; releasing the autonomous underwater vehicle to a sea floor; and recording marine seismic data while the ocean bottom node is coupled to the sea floor.

Description

Client Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067AUTONOMOUS UNDERWATER VEHICLE, SYSTEM AND METHOD FOR ACQUIRING MARINE SEISMIC DATARELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application Ser. No. 63 / 736,674, filed December 20, 2024, the disclosure of which is hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The present invention relates to the field of marine seismic data acquisition. More particularly, the invention relates to an autonomous underwater vehicle for marine seismic data acquisition, a marine seismic data acquisition system and a marine seismic data acquisition method.BACKGROUND

[0003] Information on the geology on and below a sea floor may be useful to identify and monitor oil and gas deposits, to explore suitable sites for carbon storage or for offshore wind farming and to carry out archaeological research. Such information may be gathered by marine seismic exploration.

[0004] Marine seismic exploration techniques typically utilize a seismic energy source to create an acoustic signal that travels into the earth and is partially reflected and / or refracted by interfaces and inhomogeneities in the earth's subsurfaces. These reflected and refracted signals, known as “seismic data” are detected and recorded by seismic receivers positioned at or near the earth's surface, e.g., at or near the surface of a body of water, thereby generating a seismic survey of the subsurface. The recorded signals, or seismic energy data, can then be processed to provide information about the subsurface formations.

[0005] Two main techniques are generally employed for acquiring the marine seismic data. One involves deploying hydrophones mounted in streamers and towed behind a vessel. The other involves collecting seismic signals at the ocean bottom using ocean bottom nodes containing both hydrophones and geophones. The ocean bottom nodes may be arranged into an array at predetermined locations on the sea floor. This latter technique can provide more accurate and complete data than collecting the seismic signals at the surface of the water.Client Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067

[0006] In recent times, efforts have intensified to enhance marine seismic investigations by collecting seismic data at the ocean bottom. Ocean bottom nodes are deployed and recovered in the ocean depths through the use of a remotely operated vehicle (ROV) or by simply dropping the ocean bottom nodes into the water from vessels such that the ocean bottom nodes descend down to the sea floor for acquiring seismic data. The dropped ocean bottom nodes can be equipped with an inflatable device that is triggered for the recovery process such that the ocean bottom nodes can surface to be collected on the sea surface. Another approach involves deploying ocean bottom nodes attached to a flexible rope to the ocean bottom and, then after the data collection is finished, subsequently recovering the nodes by winching up the rope.

[0007] In these techniques, the deployment of the ocean bottom nodes is limited by the speed of a surface vessel deploying the ocean bottom nodes. The process of positioning the ocean bottom nodes for data acquisition may also require several steps and be energy intensive. For example, each ocean bottom node may need to be individually unloaded from a basket by an ROV which may be required to place each ocean bottom node in turn on the sea floor. This may be a slow process requiring a large and energy-intensive ROV. Further, the ocean bottom node may be subjected to unwanted movement after positioning on the sea floor, e g., due to subsea currents and / or certain unwanted reflected or refracted acoustic waves, which may introduce noise and hence reduce the quality of data acquired.

[0008] The present deployment methods are very time consuming and therefore costly. In light of these difficulties, improved solutions are required for acquiring marine seismic data.SUMMARY OF INVENTION

[0009] An objective of certain embodiments of the present invention is to overcome one or more of the disadvantages of the prior art and to provide an alternative or improved apparatus, system and method for acquiring marine seismic data. It is an objective of some embodiments of the invention to provide an apparatus, system and method for acquiring marine seismic data in a more efficient manner. It is also an objective of some embodiments of the invention to increase a signal to noise ratio when acquiring marine seismic data.

[0010] Aspects of the invention are defined by the independent claims. Other embodiments of the present invention are defined by the dependent claims.

[0011] In accordance with an aspect of the present invention, there is provided an autonomous underwater vehicle for marine seismic data acquisition. The autonomous underwater vehicleClient Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067 comprises a cavity for accommodating an ocean bottom node such that a coupling surface of the ocean bottom node is at least partially exposed for coupling to the sea floor.

[0012] By allowing the ocean bottom node to be accommodated in the cavity of the autonomous underwater vehicle, the ocean bottom node may be more efficiently delivered to a recording location, e.g., within an array of recording locations. As the autonomous underwater vehicle may self-navigate to the recording location on the sea floor, it may be accurately positioned. Due to the range in which of the autonomous underwater vehicle can self-navigate, it is not necessary for a remotely operated vehicle to be “freed up” for positioning the respective ocean bottom node. For example, several ocean bottom nodes may self-navigate to their respective locations on the sea floor substantially at the same time, rather than being carried in turn by a remotely operated vehicle. This can dramatically increase the speed at which an area of the sea floor is covered by an array of ocean bottom nodes.

[0013] The use of autonomous underwater vehicles allows multiple ocean bottom nodes to be deployed substantially simultaneously, e.g., from a vessel or node transfer device such as a basket. This may be used to simplify or improve the route or speed of vessels from which the autonomous underwater vehicles are deployed. In contrast to techniques which require the ocean bottom nodes to be dropped directly onto the sea floor, the invention allows the route of a surface vessel not to correspond precisely to the positions at which the ocean bottom nodes are to be located on the sea floor. This is because the autonomous underwater vehicle may be capable of both vertical and lateral movement in the water. In particular where very large areas of the sea floor are to be covered by an array of ocean bottom nodes, this can save significant time and reduce the disruption to marine life.

[0014] Further, as the coupling surface of the ocean bottom node can be left at least partially exposed for coupling to the sea floor, a step of releasing the ocean bottom node from the autonomous underwater vehicle can be omitted. This can speed up the seismic survey and reduce energy usage by the autonomous underwater vehicle. At the same time, a direct coupling between the ocean bottom node and the sea floor is made possible, improving the quality of marine seismic data acquired.

[0015] In the sense of the invention, an “autonomous underwater vehicle” may be a vehicle configured to operate underwater without continuous input from an operator. The autonomous underwater vehicle may further be configured to self-navigate to a predetermined location without continuous input from an operator. Self-navigation preferably comprises controlledClient Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067 movement in both vertical and lateral directions.

[0016] In the sense of the invention, a “cavity” may be a hollow volume.

[0017] In the sense of the invention, an “ocean bottom node”, also referred to as an “autonomous seismic sensor node”, may be an apparatus for acquiring marine seismic data. The ocean bottom node may in particular be a wireless or battery-operated device, electronically separate from the autonomous underwater vehicle. Further, the ocean bottom node may comprise one or more sensors such as a geophone, a hydrophone, a geophysical sensor, an inclinometer and / or a rotational sensor. A clock may also be included. The autonomous underwater vehicle may further comprise a data acquisition unit for digitizing and storing data from the sensors.

[0018] In the sense of the invention, a “coupling surface” may be a surface of the ocean bottom node which is configured to be in contact with the sea floor for collecting seismic data from the sea floor, e.g., reflected or refracted seismic waves.

[0019] In the sense of the invention, a “sea floor” may be any underwater surface on which the ocean bottom node may rest.

[0020] In some embodiments of the invention, the autonomous underwater vehicle further comprises a releasable locking mechanism for releasably locking the ocean bottom node to the autonomous underwater vehicle.

[0021] The ocean bottom node may thus be secured to the autonomous underwater vehicle during deployment, in particular such as to withstand the pressures at the sea floor. The ocean bottom node may also be quickly replaced when the autonomous underwater vehicle is retrieved, recharged, and / or re-deployed.

[0022] In some embodiments of the invention, the releasable locking mechanism comprises a quick-release lock. The quick-release lock may comprise a releasable latch mechanism, a hydraulic release shackle, quick-release pin, a pawl latch, a quick-release knob or a quick-release toggle.

[0023] The use of a quick-release lock advantageously allows the ocean bottom node to be released from the autonomous underwater vehicle after data acquisition, preferably without the need for specialist tools. Thus the acquired data can be quickly retrieved and the ocean bottom node can be recharged.

[0024] In some embodiments of the invention, the releasable locking mechanism is configured to be locked and / or released by a robot. For example, the releasable locking mechanism may comprise features for engagement with a robotic arm. Alternatively or additionally, the releasableClient Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067 locking mechanism may be electronically controlled.

[0025] Advantageously, the ocean bottom nodes may thus be systematically positioned in the cavity of the autonomous underwater vehicle and systematically removed therefrom after the marine seismic data has been acquired. This may substantially improve the efficiency of marine seismic data acquisition.

[0026] In some embodiments of the invention, the autonomous underwater vehicle further comprises a support surface for supporting the autonomous underwater vehicle on the sea floor. The support surface of the autonomous underwater vehicle may be configured to extend along a support plane. The cavity of the autonomous underwater vehicle may be configured to accommodate the ocean bottom node such that the coupling surface of the ocean bottom node also extends along the support plane.

[0027] Advantageously, the support surface may stabilize the autonomous underwater vehicle on the sea floor. In particular where the coupling surface and the support surface extend along the same support plane, the weight of the autonomous underwater vehicle may be equally distributed over both surfaces and the vehicle may be stabilized against unwanted rocking or tilting, improving the signal-to-noise ratio of the data acquired.

[0028] In the sense of the invention, a “support surface” may be a surface of the autonomous underwater vehicle which is configured to be in contact with the sea floor when the coupling surface is also in contact with the sea floor. The support surface may comprise a flat portion extending in the support plane. Other features of the support surface may extend out of or be formed as reliefs in the flat portion.

[0029] In some embodiments of the invention, the cavity is configured for accommodating the ocean bottom node such that the coupling surface of the ocean bottom node is substantially flush with the support surface of the autonomous underwater vehicle.

[0030] Advantageously, this may provide a substantially unbroken surface extending across the ocean bottom node and the autonomous underwater vehicle, such that the autonomous underwater vehicle may rest on the substantially unbroken surface.

[0031] In some embodiments of the invention, the autonomous underwater vehicle further comprises a pressure compartment. The support surface may be a surface of the pressure compartment.

[0032] Advantageously, this may allow electronic components of the autonomous underwater vehicle to be safely stored such as to withstand the hydrostatic pressures between the sea surfaceClient Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067 and the sea floor. Further, this arrangement may allow the pressure compartment - which may be relatively dense compared to the remainder of the autonomous underwater vehicle - to be positioned substantially in the same plane as the ocean bottom node during the acquisition of marine seismic data, reducing any moments acting on the autonomous underwater vehicle. This improves the mechanical stability of the autonomous underwater vehicle and improves the signal- to-noise ratio.

[0033] In some embodiments of the invention, the pressure compartment comprises an extruded casing. The support surface may be a surface of the extruded casing. The extruded casing may be an extruded aluminum casing.

[0034] Advantageously, such a pressure compartment may provide the autonomous underwater vehicle with improved rigidity, reducing or eliminating the need for structural support members within the autonomous underwater vehicle.

[0035] In some embodiments of the invention, a density of the pressure compartment is equal to 80% to 120% of a density of the ocean bottom node. The density of the pressure compartment may optionally be equal to 90% to 110%, 95 % to 105%, 97% to 103% or 100% of a density of the ocean bottom node.

[0036] Advantageously, this may allow the mass of the pressure compartment to be substantially balanced with the mass of the ocean bottom node. This can reduce moments acting on the autonomous underwater vehicle and thus reduce the risk of the ocean bottom node rocking in response to subsea currents. This can reduce current generated noise in the detected signals. The quality of the detected signals is improved.

[0037] In some embodiments of the invention, an area of the support surface is smaller than or equal to the area of the coupling surface. For example, an area of the support surface is equal to 50% to 100% of an area of the coupling surface.

[0038] Advantageously, this can provide an especially stable coupling of the ocean bottom node to the sea floor.

[0039] In some embodiments of the invention, the pressure compartment may be configured to withstand an absolute pressure of at least 300 bar, optionally at least 400 bar. The pressure compartment may additionally or alternatively be rated for deployment down to a depth of at least 3000 meters, optionally at least 4000 meters.

[0040] In some embodiments of the invention, the autonomous underwater vehicle further comprises one or more flotation elements.Client Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067

[0041] Advantageously, such flotation elements can provide a difference in density and / or buoyancy between the support surface and an upper portion of the autonomous underwater vehicle. This can improve the orientation of the autonomous underwater vehicle, in particular such that the support surface automatically faces the sea floor. This can also ensure that the autonomous underwater vehicle and the ocean bottom node apply an even pressure on the sea bed, improving their mechanical stability. Further, the one or more flotation elements may be used to adjust the overall weight of the autonomous underwater vehicle, e.g., by adjusting the number, volume or density of the flotation elements, such as to apply an optimal pressure between the ocean bottom node and the sea floor.

[0042] In some embodiments of the invention, positions of the one or more flotation elements in the autonomous underwater vehicle are variable.

[0043] Advantageously, this may improve the hydrodynamics of the autonomous underwater vehicle and its orientation when in motion and at rest.

[0044] In some embodiments of the invention, the one or more flotation elements comprise a plurality of beads. The beads may be foam beads or hollow beads.

[0045] In some embodiments of the invention, the autonomous underwater vehicle comprises propulsion means. The propulsion means may comprise a plurality of thrusters. The thrusters may be arranged to provide both a lifting force and propulsion forces.

[0046] Advantageously, such an autonomous underwater vehicle can self-propel towards a predetermined recording location on the sea floor and can return to a retrieval point in the body of water or on the surface of the water.

[0047] In some embodiments of the invention, the plurality of thrusters comprises four thrusters.

[0048] Advantageously, this may improve balance when the autonomous underwater vehicle is on the sea floor.

[0049] In some embodiments of the invention, the autonomous underwater vehicle comprises one or more engagement features for engagement with a sea floor. In some embodiments of the invention, the one or more engagement features of the autonomous underwater vehicle may comprise one or more studs, spikes, grooves or ridges.

[0050] Advantageously, this may improve coupling of the autonomous underwater vehicle to the sea floor. For example, the engagement features may become embedded in sediments on the sea floor as the autonomous underwater vehicle comes to rest, reducing the risk of unwantedClient Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067 movement between the autonomous underwater vehicle and the sea floor.

[0051] In some embodiments of the invention, the autonomous underwater vehicle comprises a hull. The hull may may comprise a plastic shell. The pressure compartment may be coupled to the hull, in particular to an underside of the hull.

[0052] This advantageously provides a lightweight vehicle which may also be streamlined for movement within a body of water.

[0053] In some embodiments of the invention, the autonomous underwater vehicle comprises one or more of: a navigation means, an acoustic transmitter and receiver, a battery unit, a memory and attachment means for attaching the ocean bottom node to the autonomous underwater vehicle. The autonomous underwater vehicle may further comprise a control unit. One or more of these components may be provided in the pressure casing of the autonomous underwater vehicle.

[0054] Advantageously, sensitive and / or heavy components of the autonomous underwater vehicle may thus be protected from the surrounding pressure and may be positioned for an even weight distribution in the support plane when the autonomous underwater vehicle carries the ocean bottom node.

[0055] In accordance with an aspect of the present invention, there is provided a marine seismic data acquisition system comprising an autonomous underwater vehicle and an ocean bottom node. The ocean bottom node is provided in the cavity of the autonomous underwater vehicle such that the coupling surface of the ocean bottom node is at least partially exposed for coupling the ocean bottom node to a sea floor.

[0056] Advantageously, the system may self-navigate to a predetermined recording location on the sea floor where the at least partially exposed coupling surface of the ocean bottom node can couple to the sea floor. The ocean bottom node may remain installed in the cavity of the autonomous underwater vehicle before and during coupling, such that a step of releasing the ocean bottom node from the autonomous underwater vehicle can be omitted. The efficiency of the system is thus improved.

[0057] In some embodiments of the invention, the ocean bottom node is electronically independent of the autonomous underwater vehicle.

[0058] Advantageously, the ocean bottom node may thus be replaced and / or charged separately from the autonomous underwater vehicle. The autonomous underwater vehicle may be placed in standby mode while the ocean bottom node is coupled to the sea floor, improving the battery lifeClient Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067 of the autonomous underwater vehicle. Further, an electronic malfunction in the autonomous underwater vehicle does not necessarily affect the electronic functioning of the ocean bottom node and vice versa. This can improve the reliability of the system as a whole.

[0059] In some embodiments of the invention, the ocean bottom node is removably installed in the cavity. Different ocean bottom nodes may thus be used with the same autonomous underwater vehicle. For example, ocean bottom nodes can be easily replaced for data download and / or recharging.

[0060] In some embodiments of the invention, the autonomous underwater vehicle comprises a support surface. The support surface of the autonomous underwater vehicle and the coupling surface of the ocean bottom node may be configured to extend along a support plane.

[0061] Advantageously, the system may thus rest on the sea floor in a mechanically stable manner, improving the system's resistance to unwanted movement which can be caused by subsea currents and acoustic signals. As a result, noise is suppressed and the signal to noise ratio is improved.

[0062] In some embodiments of the invention, the ocean bottom node comprises an extruded casing and the coupling surface is a surface of the extruded casing. The extruded casing may be an extruded aluminum casing.

[0063] Engagement features such as grooves can easily be integrated into the extruded casing by including these in the design of the extrusion die. The extruded casing can thus have a high mechanical integrity. Further, the extruded casing surprisingly provides rigidity to the ocean bottom node. This can advantageously reduce the need for rigid structural members in the autonomous underwater vehicle.

[0064] In some embodiments of the invention, the autonomous underwater vehicle comprises a pressure compartment. The pressure compartment may comprise an extruded casing. The support surface of the autonomous underwater vehicle may be a surface of the extruded casing. A cross sectional shape of the extruded casing of the ocean bottom node may be identical to a cross sectional shape of the extruded casing of the pressure compartment.

[0065] Advantageously, the extruded casing can withstand high hydrostatic pressures, protect the components within the pressure compartment and provide rigidity to the autonomous underwater vehicle. By making the cross sectional shape of the ocean bottom node and the pressure compartment identical, the coupling surface of the ocean bottom node and the support surface of the pressure compartment may have the same form and be aligned with one another.Client Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067The system is thus especially stable when resting on the sea floor.

[0066] In some embodiments of the invention, the coupling surface of the ocean bottom node comprises one or more engagement features for engagement with the sea floor. In some embodiments of the invention, the one or more engagement features of the ocean bottom node may comprise one or more studs, spikes, grooves or ridges.

[0067] Advantageously, the engagement features may be embedded into sediments on the sea floor, stabilizing the system. This improves the coupling of the ocean bottom node and improves the signal to noise ratio.

[0068] In accordance with an aspect of the present invention, there is provided a marine seismic data acquisition method. The method comprises: installing an ocean bottom node in a cavity of an autonomous underwater vehicle, such that a coupling surface of the ocean bottom node is at least partially exposed for coupling the ocean bottom node to a sea floor; releasing the autonomous underwater vehicle to a sea floor, such that the coupling surface of the ocean bottom node couples to the sea floor; and recording marine seismic data while the ocean bottom node is coupled to the sea floor.

[0069] Advantageously, the autonomous underwater vehicle can self-navigate from a surface vessel, subsea vessel or other apparatus (e.g., a basket), to a predetermined recording location on the sea floor. The path of the vessel from which the autonomous underwater vehicle is released does not need to correspond precisely to the recording locations on the sea floor, as the autonomous underwater vehicle may have its own navigation range. As the ocean bottom node does not need to be released from the autonomous underwater vehicle to couple to the sea floor, a robotic arm or other manipulator can be omitted from the autonomous underwater vehicle.

[0070] In some embodiments of the invention, the ocean bottom node may be configured to withstand an absolute pressure of at least 300 bar, optionally at least 400 bar. The ocean bottom node may additionally or alternatively be rated for deployment down to a depth of at least 3000 meters, optionally at least 4000 meters.

[0071] Advantageously, such an ocean bottom node may be deployed to most regions of the sea floor.

[0072] In some embodiments of the invention, the ocean bottom node is checked before being installed into the cavity of the autonomous underwater vehicle. The check may ensure that the ocean bottom node is sufficiently charged and / or electronically operational. The check may be a self-check.Client Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067

[0073] Advantageously, this may ensure that only ocean bottom nodes which are expected to be functional for the duration of the data acquisition are released to the sea floor.

[0074] In some embodiments of the invention, the ocean bottom node is installed into the cavity of the autonomous underwater vehicle while the autonomous underwater vehicle is on a surface vessel or subsea vessel. The ocean bottom node may be installed automatically, e.g., by a robot. Alternatively, the ocean bottom node may be installed manually by an operator.

[0075] In some embodiments of the invention, the method further comprises releasably locking the ocean bottom node to the autonomous underwater vehicle before releasing the autonomous underwater vehicle to the sea floor.

[0076] Advantageously, the ocean bottom node may be securely installed in the cavity during deployment to the sea floor, whilst also being easily replaceable.

[0077] In some embodiments of the invention, the autonomous underwater vehicle is released to the sea floor from a node transfer device. For example, one or more autonomous underwater vehicles may be arranged in a node transfer device, such as a basket. The node transfer device may be lowered into the body of water from a surface vessel or subsea vessel. The node transfer device may then be opened and the autonomous underwater vehicles may self-navigate out of the node transfer device to their predetermined recording locations on the sea floor.

[0078] Advantageously, this further improves the efficiency of deployment of the autonomous underwater vehicles to the sea floor. For example, a remotely operated vehicle is not required to dock to the node transfer device to transfer the ocean bottom nodes to their predetermined recording locations on the sea floor. The ocean bottom nodes can thus be distributed more quickly over the sea floor.

[0079] In some embodiments of the invention, the method comprises substantially simultaneously releasing a plurality of autonomous underwater vehicles to the sea floor, such that respective coupling surfaces of respective ocean bottom nodes couple to the sea floor at predetermined locations.

[0080] Simultaneously releasing a plurality of autonomous underwater vehicles may comprise releasing the plurality of autonomous underwater vehicles in quick succession such that a later autonomous underwater vehicle is released whilst a prior autonomous underwater vehicle is still in motion in the water.

[0081] Advantageously, this may improve the speed at which a seismic survey area can be covered. For example, limitations in the speed of a surface vessel can be compensated for byClient Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067 deploying multiple autonomous underwater vehicles at a time, without the need to wait for one autonomous underwater vehicle to reach its recording location before releasing the next autonomous underwater vehicle.

[0082] In some embodiments of the invention, the autonomous underwater vehicle is retrieved after recording marine seismic data. For example, the autonomous underwater vehicle is retrieved to a surface vessel or subsea vessel.

[0083] Advantageously, this allows the ocean bottom node to be released from the autonomous underwater vehicle for the download of data, recharging and / or replacing the ocean bottom node.

[0084] In some embodiments of the invention, the autonomous underwater vehicle is retrieved by self-navigating to the surface vessel or subsea vessel.

[0085] In some embodiments of the invention, a plurality of autonomous underwater vehicles are retrieved to a node transfer device such as a basket. For example, the autonomous underwater vehicles may self-navigate into the basket. The basket may then be moved onto a vessel.

[0086] Advantageously, this allows the autonomous underwater vehicles to be retrieved more efficiently.

[0087] A person skilled in the art understands that technical features and advantages that have been disclosed in regards to the autonomous underwater vehicle described herein, apply equally to the system and the method, and vice versa.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0088] Without intending to be limiting, embodiments of the invention are further described in more detail with reference to the accompanying drawings, in which:

[0089] FIG. l is a top view of an autonomous underwater vehicle according to an embodiment of the invention;

[0090] FIG. 2 is a front view of the autonomous underwater vehicle of FIG. 1;

[0091] FIG. 3 is a perspective view of the autonomous underwater vehicle of FIGs. 1-2;

[0092] FIG. 4 is a bottom view of the autonomous underwater vehicle of FIGs. 1-3 carrying an ocean bottom node such as to form a marine seismic data acquisition system according to an embodiment of the invention;

[0093] FIG. 5 is a bottom view of the autonomous underwater vehicle of FIGs. 1-3 showing the cavity without an ocean bottom node;

[0094] FIG. 6 illustrates a marine seismic data acquisition method according to an embodimentClient Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067 of the invention;

[0095] FIG. 7 illustrates a further marine seismic data acquisition method according to another embodiment of the invention.DETAILED DESCRIPTION

[0096] FIG. 1 is a top view of an autonomous underwater vehicle 10 adapted to carry an ocean bottom node 12 according to an embodiment of the invention. The autonomous underwater vehicle 10 comprises a hull 30. The hull 30 may be configured to withstand the hydrostatic pressures at the sea floor, which may be up to several thousands of meters below a surface of a body of water. The hull 30 may comprise a plastic shell. The hull 30 may also comprise in its interior one or more flotation elements. The one or more flotation elements may be permanently attached or embedded inside the hull 30. The one or more flotation elements may be used to adjust the combined overall weight of the autonomous underwater vehicle 10 and an ocean bottom node 12 (not visible in FIG. 1) which is carried by the autonomous underwater vehicle. The combined overall weight may be tuned for optimal coupling of the ocean bottom node to the sea floor when the autonomous underwater vehicle is submerged in water, in particular such that the ocean bottom node's surface pressure on the sea floor is optimized. The one or more flotation elements may be lightweight elements such as hollow beads.

[0097] The autonomous underwater vehicle 10 may comprise four thrusters 14. The four thrusters 14 may be arranged symmetrically on the sides of the hull 30. The autonomous underwater vehicle 10 may also comprise navigation means configured for sending and receiving position data for use in correcting the autonomous underwater vehicle's trajectory when descending or surfacing. Such data may be sent and received acoustically, e g., via another component of the autonomous underwater vehicle.

[0098] For example, the hull 30 may further comprise an acoustic transmitter and receiver 16 which may be in communication with the navigation means. The acoustic transmitter and receiver 16 may be configured for communication between the autonomous underwater vehicle 10 and a surface vessel, remotely operated vehicle or operator. The acoustic transmitter and receiver 16 may also be configured to support the navigation of the autonomous underwater vehicle 10.

[0099] FIG. 2 is a front view of the autonomous underwater vehicle 10 of FIG. 1. The autonomous underwater vehicle 10 may carry an ocean bottom node 12 as a detachable payload. The ocean bottom node 12 may comprise a coupling surface 24 on which the ocean bottom nodeClient Docket No. P390851 WO Taft Ref. No.: HGFO 1-4006712 and autonomous underwater vehicle 10 may rest on the sea floor. The coupling surface 24 may extend along a support plane 28. The coupling surface 24 is at least partially exposed such that it may couple to the sea floor, in particular such as to receive seismic signals from the sea floor.

[0100] FIG. 3 is a perspective view of the autonomous underwater vehicle 10 of FIGs. 1-2. The autonomous underwater vehicle 10 may comprise an altimeter 18. The altimeter 18 may measure the height of the autonomous underwater vehicle 10 above the sea floor and may be used in positioning the autonomous underwater vehicle 10 at a predetermined recording location on the sea floor.

[0101] The ocean bottom node 12 may comprise a pressure casing configured to withstand hydrostatic pressures at the sea floor. The ocean bottom node 12 may comprise one or more sensors and a sensor electronic board. The one or more sensors may comprise a geophysical sensor, a geophone, a hydrophone and / or an auxiliary sensor. The ocean bottom node 12 may further comprise a battery unit, an analog to digital recording electronic unit, a memory unit and / or an oscillator clock. The oscillator clock may be for precise timing of the recorded seismic data. The ocean bottom node 12 may be self-contained and electronically separate from the autonomous underwater vehicle 10.

[0102] FIG. 4 is a bottom view of the autonomous underwater vehicle 10 of FIGs. 1-3 carrying an ocean bottom node 12. The ocean bottom node 12 may be provided in a cavity 22 (see FIG. 5) of the autonomous underwater vehicle 10. The cavity 22 may be shaped such as to securely house the ocean bottom node 12 whilst exposing the coupling surface 24. The ocean bottom node 12 may also be releasably locked to the autonomous underwater vehicle 10. For example, a releasable locking mechanism may be provided on the autonomous underwater vehicle 10 to releasably lock the ocean bottom node 12 in the cavity 22. The ocean bottom node 12 may further comprise a handle, which may be used for manually or automatically inserting and / or removing the ocean bottom node 12 from the autonomous underwater vehicle 10.

[0103] The autonomous underwater vehicle 10 may further comprise a support surface 26 on which the autonomous underwater vehicle 10 may rest on the sea floor. The support surface 26 and the coupling surface 24 may be coplanar when the ocean bottom node 12 is provided in the cavity 22 of the autonomous underwater vehicle 10.

[0104] The support surface 26 may be a surface of a pressure compartment 20 of the autonomous underwater vehicle 10. The pressure compartment 20 may house electronicClient Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067 components of the autonomous underwater vehicle 10. For example, the pressure compartment 20 may comprise an internal battery of the autonomous underwater vehicle 10, navigation means, a control unit and / or an internal processor. The battery of the autonomous underwater vehicle 10 may be configured to provide power to the thrusters 14 and the control unit. One or more of these components may alternatively be provided in the hull 30.

[0105] The pressure compartment 20 may have an identical cross section to the ocean bottom node 12. Both the pressure compartment 20 and the pressure casing of the ocean bottom node 12 may comprise extruded aluminum. Respective ends of the pressure compartment 20 and the ocean bottom node 12 may comprise a lid sealingly coupled to the extruded aluminum of the casing. Additionally, both the pressure compartment 20 and the ocean bottom node 12 may be configured to have the same density. This can improve the stability of the marine seismic data acquisition system on the sea floor, improving the signal to noise ratio of the data acquired by the ocean bottom node 12.

[0106] FIG. 5 shows the autonomous underwater vehicle 10 of FIG. 4 without an ocean bottom node 12 in the cavity 22. The autonomous underwater vehicle 10 may comprise a handle 32 for ease of manual or automatic manipulation of the autonomous underwater vehicle 10. The cavity 22 may be shaped to securely house the ocean bottom node 12. For example, walls of the cavity 22 may curve around edges of the coupling surface 24 such as to hold the ocean bottom node 12 in place. The cavity 22 may comprise additional features such as a releasable locking mechanism (not shown) for detachably installing the ocean bottom node.

[0107] FIG. 6 illustrates a method of marine seismic data acquisition according to an embodiment of the invention. The method comprises a step 602 of installing an ocean bottom node 12 in a cavity 22 of an autonomous underwater vehicle 10 such that a coupling surface 24 of the ocean bottom node 12 is at least partially exposed for coupling the ocean bottom node 12 to a sea floor. The method further comprises a further step 604 of releasing the autonomous underwater vehicle 10 to a sea floor, such that the coupling surface 24 of the ocean bottom node 12 couples to the sea floor.

[0108] The method comprises a further step 606 of recording marine seismic data while the ocean bottom node 12 is coupled to the sea floor. The method advantageously does not require the ocean bottom node 12 to be released from the autonomous underwater vehicle 10 between steps 604 and 606.

[0109] FIG. 7 illustrates a method of marine seismic data acquisition according to a furtherClient Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067 embodiment of the invention. The method comprises a step 702 of initiating a self-check of an ocean bottom node 12. The self-check may ensure that the ocean bottom node 12 is adequately charged and electronically operational. The ocean bottom node 12 may be configured to emit a signal if the self-check is failed. Step 702 may be repeated for a plurality of ocean bottom nodes 12.

[0110] The method comprises a further step 704 of installing an ocean bottom node 12 in a cavity 22 of an autonomous underwater vehicle 10 such that a coupling surface 24 of the ocean bottom node 12 is at least partially exposed for coupling the ocean bottom node 12 to a sea floor. Such a step may be carried out on a vessel by an operator or by a robot. This step may be repeated for a plurality of autonomous underwater vehicles 10 to provide a plurality of marine seismic data acquisition systems.[OHl] The method comprises a further step 706 of releasably locking each installed ocean bottom node 12 to the respective autonomous underwater vehicle 10. This may improve the integrity of the marine seismic data acquisition systems, in particular at high hydrostatic pressures. This step may also be carried out manually or by a robot. This step may also be controlled electronically, e.g., by triggering a hydraulic locking mechanism of each autonomous underwater vehicle 10 to move to a locked position.

[0112] The method comprises a further step 708 of loading a plurality of marine seismic data acquisition systems onto a node transfer device, e.g., a basket. For example, at least ten marine seismic data acquisition systems may be loaded onto the same node transfer device.

[0113] The method comprises a further step 710 of lowering the loaded node transfer device from the vessel into the water. This may be carried out by a rope system or by a remotely operated vehicle.

[0114] The method comprises a further step 712 of releasing one or more marine seismic data acquisition systems from the node transfer device such that these self-navigate to predetermined recording locations on the sea floor. Optionally, all of the marine seismic data acquisition systems loaded on the node transfer device may be released substantially simultaneously, e.g., in quick succession. The marine seismic data acquisition systems may also self-navigate substantially simultaneously to their respective recording locations.

[0115] The method comprises a further step 714 of recording marine seismic data while each ocean bottom node 12 is coupled to the sea floor at its respective recording location. During this step, the ocean bottom node 12 may be activated while the autonomous underwater vehicle 10Client Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067 enters a standby mode.

[0116] The method comprises a further step 716 of retrieving the marine seismic data acquisition systems. During this step, the autonomous underwater vehicles 10 are re-activated and self-navigate to a retrieval point, which may be the same or a different node transfer device. Alternatively, the retrieval point may be a subsea or surface vessel.

[0117] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0118] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0119] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

Client Docket No. P390851 WO Taft Ref. No.: HGFO 1-40067CLAIMSWhat is claimed is:

1. An autonomous underwater vehicle (10) for marine seismic data acquisition, wherein the autonomous underwater vehicle (10) comprises: a cavity (22) for accommodating an ocean bottom node (12) such that a coupling surface (24) of the ocean bottom node (12) is at least partially exposed for coupling the ocean bottom node (12) to a sea floor.

2. The autonomous underwater vehicle (10) of claim 1, further comprising: a releasable locking mechanism for releasably locking the ocean bottom node (12) to the autonomous underwater vehicle (10).

3. The autonomous underwater vehicle (10) of any of the previous claims, wherein the autonomous underwater vehicle (10) further comprises: a support surface (26) for supporting the autonomous underwater vehicle (10) on the sea floor, wherein the support surface (26) of the autonomous underwater vehicle (10) is configured to extend along a support plane (28), and the cavity (22) of the autonomous underwater vehicle (10) is configured to accommodate the ocean bottom node (12) such that the coupling surface (24) of the ocean bottom node (12) also extends along the support plane (28).

4. The autonomous underwater vehicle (10) of claim 3, wherein the cavity (22) is configured for accommodating the ocean bottom node (12) such that the coupling surface (24) of the ocean bottom node (12) is substantially flush with the support surface (26) of the autonomous underwater vehicle (10).

5. The autonomous underwater vehicle (10) of the claim 3 or claim 4, wherein the autonomous underwater vehicle (10) further comprises: a pressure compartment (20) and the support surface (26) is a surface of the pressure compartment (20).Client Docket No. P390851 WO Taft Ref. No.: HGFO 1-400676. The autonomous underwater vehicle (10) of claim 5, wherein the pressure compartment (20) comprises an extruded casing and the support surface (26) is a surface of the extruded casing.

7. The autonomous underwater vehicle (10) of claim 5 or 6, wherein a density of the pressure compartment (20) is equal to 80% to 120% of a density of the ocean bottom node (12).

8. The autonomous underwater vehicle (10) of any one of claims 3 to 7, wherein an area of the support surface (26) is equal to 50% to 100% of an area of the coupling surface (24).

9. The autonomous underwater vehicle (10) of any of the previous claims, wherein the autonomous underwater vehicle (10) further comprises one or more flotation elements.

10. The autonomous underwater vehicle (10) of claim 9, wherein the one or more flotation elements comprise a plurality of beads.

11. The autonomous underwater vehicle (10) of any of the previous claims, the autonomous underwater vehicle (10) comprising a plurality of thrusters (14).

12. The autonomous underwater vehicle (10) of the previous claim, wherein the plurality of thrusters comprises four thrusters (14).

13. The autonomous underwater vehicle (10) of any of the previous claims, the autonomous underwater vehicle (10) comprising one or more engagement features for engagement with a sea floor.

14. A marine seismic data acquisition system comprising an autonomous underwater vehicle (10) according to any of the previous claims and an ocean bottom node (12) provided in the cavity (22) of the autonomous underwater vehicle (10) such that the coupling surface (24) of the ocean bottom node (12) is at least partially exposed for coupling the ocean bottom node (12) to a sea floor.

15. The marine seismic data acquisition system of the previous claim when dependent on claimClient Docket No. P390851 WO Taft Ref. No.: HGFO 1-400673, wherein the support surface (26) of the autonomous underwater vehicle (10) and the coupling surface (24) of the ocean bottom node (12) are configured to extend along a support plane (28).

16. The marine seismic data acquisition system of claim 15, wherein the ocean bottom node (12) comprises an extruded casing and the coupling surface (24) is a surface of the extruded casing.

17. The marine seismic data acquisition system of claim 16, wherein the autonomous underwater vehicle (10) comprises a pressure compartment (20), the pressure compartment (20) comprises an extruded casing and the support surface (26) is a surface of the extruded casing; and wherein a cross sectional shape of the extruded casing of the ocean bottom node (12) is identical to a cross sectional shape of the extruded casing of the pressure compartment (20).

18. The marine seismic data acquisition system of any one of claims 14 to 17, wherein the coupling surface (24) of the ocean bottom node (12) comprises one or more engagement features for engagement with a sea floor.

19. The marine seismic data acquisition system of claim 18 wherein the one or more engagement features are one or more studs, spikes or grooves.

20. A marine seismic data acquisition method comprising: installing an ocean bottom node (12) in a cavity (22) of an autonomous underwater vehicle (10), such that a coupling surface (24) of the ocean bottom node (12) is at least partially exposed for coupling the ocean bottom node (12) to a sea floor; releasing the autonomous underwater vehicle (10) to a sea floor, such that the coupling surface (24) of the ocean bottom node (12) couples to the sea floor; and recording marine seismic data while the ocean bottom node (12) is coupled to the sea floor.

21. The method of claim 20, wherein the method further comprises releasably locking the ocean bottom node (12) to the autonomous underwater vehicle (10) before releasing the autonomous underwater vehicle (10) to the sea floor.Client Docket No. P390851 WO Taft Ref. No.: HGFO 1-4006722. The method of claim 20 or 21, wherein the autonomous underwater vehicle (10) is released from a node transfer device.

23. The method of any one of claims 20 to 22, wherein the method comprises simultaneously releasing a plurality of autonomous underwater vehicles (10) to the sea floor, such that respective coupling surfaces (24) of respective ocean bottom nodes (12) couple to the sea floor at predetermined locations.

24. The method of any one of claims 20 to 23, wherein the method further comprises retrieving the autonomous underwater vehicle(s).

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