1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to birds that are attached to streamers or sources of marine seismic survey systems and are being used to control depth and/or lateral position of the streamer or source, and, in particular, to birds having foldable wings.
2. Discussion of the Background
Marine seismic surveys are used to generate an image of the geophysical structure under the seafloor in order to make drilling a dry offshore well unlikely.
During a seismic survey, as shown in
The vessel 10 also tows acoustic detectors 12 arranged along a cable 14. The cable 14 and the detectors 12 are known as a streamer 16. The detectors 12 acquire information (seismic data) about the reflected waves 22b, 22c and 22d.
The streamer 16 may be towed horizontally, i.e., lying at a constant depth relative to the water's surface 18 (as illustrated in
The vessel 10 may tow plural streamers at the same time. During seismic data acquisition, the streamers' depth and lateral positions may be controlled using steering devices 30 known as “birds.” The birds are attached to the streamers.
A bird typically has solid control surfaces (referred to as wings or fins) that are attached to a body and allowed to rotate around an axis while an area of the control surfaces is constant. When a bird's control surface moves through water, pressure on one side of such a surface may become greater than pressure on the other side thereof. The pressure difference yields a force perpendicular to the control surface and proportional to the area of the projection of the control surface. This force is used to adjust a bird's location in a plane perpendicular to the tow direction and, because the bird is attached to the streamer, also the streamer's depth and/or lateral position.
When the streamers are no longer used (i.e., the seismic survey has ended), they are retrieved on the vessel 10. Conventional birds, and, in particular, their control surfaces extending away from the cable 14, may be damaged during recovery. In view of their length and flexibility, the streamers are usually retrieved and stored on spools located on the deck of the vessel. When the streamers are retrieved, the solid control surfaces of conventional birds may be damaged or may get entangled, making it difficult to later roll out the streamers. Therefore, the wings of the birds or the birds have to be removed from the streamers when the streamers are retrieved, which is a time-consuming procedure.
In instances when an accidental loss of towing speed occurs, the control surfaces may not produce the intended steering, but instead cause undesirable drag forces that amplify the slow-down. In other instances, if the streamers get too close to one another, the bird's control surfaces may become entangled with neighboring streamers. In still another instance, a wing of the bird may be damaged (e.g., broken) and thus, the bird may start to spin. In this situation, although the operator may be aware of the damaged bird, he or she can do nothing to minimize the disturbance created by this bird.
Furthermore, there are instances in which the streamers need to be cleaned while deployed underwater to remove bio-fouling settlement that accumulates on their exterior surface. The cleaning devices used on the streamers are negatively impacted by the bird's control surfaces extending away from the streamer, which prevents the cleaning devices to pass over the bird's location. Therefore, cleaning devices have to be manually repositioned.
Accordingly, it would be desirable to provide birds and methods that avoid the afore-described problems related to the control surfaces.
A bird having one or more foldable wings is easier to recover and may benefit from the wing being foldable in various situations occurring during a marine seismic survey (e.g., when the towing speed decreases, when marine growth gets attached to the wing, etc.).
According to one exemplary embodiment, there is a bird for a streamer or a source of a marine seismic survey system. The bird has a body configured to be attached to the streamer or the source, and a first wing connected to the body and having an active surface used to control depth and/or lateral position of the body. The first wing is configured to be switched between an operational state in which the active surface is extended away from the body, and a folded state in which the active surface is folded close to the body.
According to another exemplary embodiment, there is a marine seismic survey system including a streamer or a source configured to be towed through water, and a bird connected to the streamer or the source. The bird has a body configured to be attached to the streamer or the source, and a first wing connected to the body and having an active surface configured to control depth and/or lateral position of the body. The first wing is configured to be switched between an operational state in which the active surface is extended away from the body, and a folded state in which the active surface is folded close to the body.
According to another exemplary embodiment, there is a method for steering a streamer or a source towed through water. The method includes connecting a bird having a foldable wing to the streamer or the source, and actuating the foldable wing to change from a folded state in which the foldable wing is folded to an operational state in which the foldable wing is extended. The method further includes using the bird to adjust a depth and/or lateral position of the streamer or the source.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:
The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to the terminology and structure of a bird for a streamer of a marine seismic survey system. However, such a bird may be used with other parts of a seismic survey system, e.g., a source.
Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.
Each of the wings 120a and 120b has an active surface 130a and 130b, respectively, used to control depth and/or lateral position of the body. The active surfaces 130a and 130b are configured to extend away from the body 110 in an operational state, and to fold close to the body 110 in a folded state as illustrated in
The force caused by a wing while towed through water is proportional to the area of the active surface's projection in the plane perpendicular to the towing direction. In the operational state, the active surface is extended to have a first area that is the maximum substantially flat area achievable for the given wing. The active surface is controlled (e.g., rotated) to have a non-zero projection on a plane perpendicular to the towing direction in order to generate a steering force. The steering force is understood to be a force the changes a lateral position of the bird, or a depth position of the bird or both. The steering force may be varied by varying the orientation of the active surface, as described, for example, in U.S. Pat. No. 7,610,871 by Leclercq et al., the entire content of which is incorporated herein by reference.
In the folded state, as illustrated in
The wings are in the operational state while the seismic survey is performed so that the active surfaces can efficiently be used for steering if needed. When the streamer is retrieved after finishing the seismic survey, the wings are preferably in the folded state. While the streamer having the bird attached is towed through water, the wings may be switched from the operational state to the folded state when the towing speed decreases (because by folding the wings, the drag force decreases), or when the streamer becomes too close to another streamer (to avoid entangling of the bird with the other streamer and its instrumentation). The wings may be later unfolded (extended) when the towing speed recovers or when the distance between streamers increases.
Having the wings folded is also preferable when an equipment failure occurs. Folding the wings may also have the beneficial effect of releasing marine growth that has undesirably become attached to the active surfaces.
The wings may be folded and/or unfolded manually or by an actuating mechanism 140. The actuating mechanism 140 may receive commands from a controller 150 located in the body 110 of the bird 100. Alternatively, the controller may be located on the towing vessel.
The controller 150 may be connected to (i.e., in communication with) one or more sensors that provide information enabling the controller to determine whether the wing(s) should be switched to/from the operational state (i.e., to be folded or extended). For example, sensors may enable the controller to determine if a cleaning device approaches the bird, and/or if the towing speed has decreased below a predetermined speed threshold, and/or if the distance to a neighboring streamer decreases below a predetermined distance threshold. The controller may also receive information (e.g., from the towing vessel via the streamer) indicating that the streamer is retrieved on the towing vessel.
In one embodiment, the actuating mechanism 140 may consist of elements 136a or 136b (which may also operate as a support structure) biasing the wing(s) to be in the operational state, and a string 142a or 142b usable to manually or automatically fold the respective wing. The actuating mechanism 140 may include an electric motor.
In the embodiment illustrated in
In an embodiment illustrated in
In another embodiment 200 illustrated in
In another exemplary embodiment 300 illustrated in
In another exemplary embodiment 400 illustrated in
Each segment (440a, 440b, 440c, 440d) of the telescopic support element is connected to one of plural portions (430a, 430b, 430c, 430d) of the active surface. The plural portions 430a, 430b, 430c, 430d of the active surface may be made of semi-rigid sheets in order to be able to withstand the pressure difference on opposite sides thereof. The number and shape of the portions of the active surface of wing 420 are exemplary and are not intended to be limiting.
In the operational state, the plural segments 440a, 440b, 440c, 440d of the telescopic support element and the plural portions 430a, 430b, 430c, 430d of the active surface are arranged in a sequence extending away from the body 110. In the folded state, plural portions 430a, 430b, 430c, 430d of the active surface may slide one near the other close to the body, while the segments 440a, 440b, 440c, 440d may slide one inside the other as illustrated in
In a different embodiment 500 illustrated in
In another embodiment 600 illustrated in
Due to the ballast body 635, the keel 620c tends to maintain a downward orientation and is less likely to get entangled with neighboring streamers or to have marine growth attached. Additionally, since the keel 620c is free to rotate, it is likely that keel 620c would cause no or a small drag force. Therefore, in one embodiment, only the wings 620a and 620b are configured to switch between an operational state in which their respective active surfaces 630a and 630b are extended away from the body 110 (as shown), and a folded state in which the active surfaces 630a and 630b are folded close to the body 110. However, in another embodiment all three wings (620a, 620b and 620c) are foldable.
The controller 115 and motors 105a and 105b are operable to control the wings 620a and 620b, respectively, between the operational state and the folded state. They may be located inside the body 110. One or more sensors 120 may also be located on or inside the body 110. The sensor 120 may be used to determine when the cleaning device is approaching the bird and to instruct the controller 115 to automatically fold the wings so that the cleaning device can pass over the bird, when moving along the streamer.
In still other embodiments illustrated in
In another embodiment illustrated in
The seismic source 920 is configured to generate seismic waves 922a that propagate downward toward the seafloor 24 and penetrates the formation 25 under the seafloor 24 until it is eventually reflected at discontinuity locations 26 and 27. The seismic source may include plural individual sources that may be located on a horizontal line, slanted line, etc.
The reflected seismic waves such as 922b and 922c propagate upward and can be detected by one of the receivers 932 on the streamer 930. Based on the data collected by the receivers 932, an image of the subsurface formation 25 is generated.
To maintain the streamers or sources at a desired position (i.e., such as to have predetermined cross-line distances and predetermined depths), one or more birds 940 may be attached to the streamer 930 or to the source 920. At least one bird 950 has one or more foldable wings as described above. Although relative to
The disclosed exemplary embodiments provide birds that have foldable wings. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.
Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.
This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that would be obvious to those skilled in the art. Such other examples are intended to be within the scope of the claims.
Number | Date | Country | Kind |
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1350631 | Jan 2013 | FR | national |