Introduction

[0001] The invention is a marine geophysical spreading/diverting deflector for towing of a seismic array. The marine geophysical spreading/diverting deflector, the diverter, comprises a float with one or more deflector wings or deflector foils extending down into the sea and wherein the deflector is arranged to run deep in the sea. A seismic survey vessel or a towing vessel is towing a wide and long seismic cable tow of cables, an array, and the array of cables is spanned out by a starboard and a port side diverter which is towed by the vessel as well. Prior art

[0002] The general method is to spread the array with a deflector wherein the float is a part of the deflector, the diverter, and wherein the diverter then extends from the sea surface and down into the sea. The float helps keeping the diverter in the sea surface and, but it also represents a stabilizing force during towing.

[0003] In the field of seismic there is a development towards a deeper run of the seismic equipment which means that with a deflector which is for instance 10 m deep one which the streamers to run another 20 meter further down. The intermediate array of seismic cables etc., which may be several kilometer long and a couple of kilometers wide, generally runs at a 25 meters depth and will have a sinker/depressor in front of one or more of the lengths in the array.

[0004] The diverter, spreading deflector, with belonging equipment and especially connection lines, shackles etc. which run in or near the sea surface, are exposed to high forces form the depressors and the intermediate array. The different units runs in different sea depths and will thus be exposed to different flow and running paths which introduce additional and variating forces to the diverter.

[0005] A depth controllable depressor is known in the field. This runs free without a stabilizing float or buoyance.

Short summary of the invention

[0006] The invention is a submerseable seismic diverter (0) for towing a seismic array, comprising a main float (10) comprising at least a main float body (1), in an operative condition submerged deflector paravane (2) connected to a main float (10) and extending down in the sea, and wherein the deflector paravane (2) is arranged to run in a desired depth under the sea surface. An advantage to the invention is that by running submerged, it will run close to, or at the same level as the streamers in a seismic tow. [0007] Another advantage to the invention is that by running submerged will run at a depth significantly less affected by the surface waves, thus lead to a smoother run through the sea.

[0008] A third advantage to the invention is the reduced top load to the towing lines, bridle lines and to the line between the seismic lengths.

[0009] A fourth advantage is that one may reduce the total number of depressors in the array, or reduce the size of one or more of the depressors.

Figure captions

[0010] The attached figures shows some embodiments of the claimed invention.

[0011] Fig. 1 is a simplified sketch of an embodiment of the invention wherein the deflector vane/ deflector paravane (2) is towed in a conventional way in an array and the float (10) "hangs" in float lines (4a, 4b, ...) as a slave in the surface.

[0012] Fig. 2a shows a deep running length of seismic cables in an array with a sinker/depressor in front. The shallow running deflector in front/starboard side is not shown in the figure.

[0013] Fig. 2b shows prior art with a shallow running (surface running) starboard and port side deflectors and a deep running intermediate array of seismic cables. Here, the streamers etc. are equipped with depressors in the front of at least the outer positions to force the seismic cables down to desired depth.

[0014] Fig. 3a shows a deep running deflector (2) with a surface running float (10, 1, 3) according to an embodiment of the invention, and a seismic cable length in the array is drafted at same depth as the deflector.

[0015] Fig. 3b shows an array with a starboard and port side deep running deflector according to the invention and an array of seismic cable lengths at the same depth as the deflectors.

[0016] Fig. 4a upper part illustrates an embodiment of the invention in side view wherein the diverter comprises a main float (1,10) arranged to float in, or near, the water surface, here in the water surface. The deflector paravane is submerged to a desired depth and the float and the paravane are connected by three float lines (4a, 4b, 4c). Two of the float lines (4a and 4b) have an attachment point to one or two close fasteners at the upper frame portion of the deflector paravane, and runs to each respective fore and rear portion of the float (1). The third anchor line (4c) runs from a rear portion of the upper part of the deflector paravane and to a fastener at the rear portion of the float to limit the lateral movement of the float. The lower part of Fig. 4c is a top view of the same embodiment, and illustrates how the float (1) will adjust to the towing vessels running direction, while the deflector paravane will have a diverting direction to the array in an angle from the running direction of the vessel. Both figures also shows bridle lines and towing lines.

[0017] Fig. 4 bl upper part is a side view of an embodiment of the invention, submerged in water, wherein the main float (10) comprises a main float body (1) and a top float (3). The float lines (4a, 4b, 4c) runs between the main float body (1) to the top float (3) The figure is partly section cut to show that the main float body (1) has a ballast tank (7).

[0018] Fig- 4bl lower part shows the same embodiment as upper part but in a top view and partly cut through. The top float (3) runs parallel to the running direction of the towing vessel, while the diverter runs in a diverting direction compared to the towing vessel.

[0019] Fig. 4b2 upper part shows a similar embodiment to the one in Fig. 4bl, but arranged with depressor wings (5), arranged for active control of the deflector up and down motion in the sea. The figure does not show a ballast tank, but in an embodiment a ballast tank (7) may be arranged in the float (1).

[0020] Fig. 4C1 upper part shows a side view, partly cut through, of a diverter according to an embodiment of the invention. This runs submerged at a desired depth. The float main body (1) has a ballast tank (7) for adjustment of the buoyance. This embodiment runs without a top float [0022] In the lower part of the figure the invention is illustrated in a top view.

[0023] Fig. 4c2 upper part shows a side view of a submerged diverter (0) according to the invention. The figures shows a similar embodiment of the one in Fig. 4cl, but arranged with depressor wings (5) arranged for active control of the up and down motion of the deflector in the sea. The figure does not show a ballast tank, but in an

embodiment a ballast tank (7) may be arranged in the float (1).

[0024] Fig. 4d is a sketch of different embodiments of the invention given in Fig 4a - c. The main issue here is to illustrate different embodiments of the top float. These variations are not limited to the drafted embodiments of the main body and depressor systems or ballast tanks.

[0025] Fig. 5a shows an embodiment of the diverter (0) according to the invention in a side view. The float is subdivided in a float main body (1) and a top float (3). The top float in this embodiment is a small and slim float, which will stay at the surface as a weather vane and follow the main running direction. The main float body (1) and the top float (3) is connected by float lines (4, 4a, 4b). At the float line there is indicated a corresponding shock absorber (8). Depressor wings (5) is arranged in link portions (11) between the float main body (1) and the deflector paravane (2).

[0026] Fig. 5b shows the same embodiment of the invention as Fig. 5a in a front view. The figure shows the diverter in a stationary condition in the sea with extended bridle lines, ready for towing. In this embodiment the float lines (4) lowers the deflector paravane (2) with the float main body (1) to a towing depth of ab. 20 m, which corresponds to the approximate depth of the running depth for the streamers, illustrated in the figure. The main float may accomodate depth sensors (not shown) for control of the depressor wings (5) for active diving of the main float (10) with the deflector paravane (2). The depressor wings is arranged at the top of the deflector paravane in a link portion (11) and pivotable arranged about the axis A.

[0027] Fig. 5c shows a perspective view of an embodiment of the invention with a deflector wing and a main float structure (10) for proper diverting properties for the deflector paravane (2) and a good run in the sea, for the, in the horizontal asymmetric main float body (1). The top float may accomodate radio communication and GPS equipment, not shown. The figure shows an embodiment of the invention wherein the deflector paravane (2) is equipped with sections of deflector foils (20), an upper section with the foils (20u) and a lower section with the foils (201).

[0028] Fig. 5d shows the embodiment of Fig. 5c in a top view.

Fig. 6 is a detail of the depressor wing (5) in the link portion (11). The upper left illustration shows the wing in a side view, the upper right shows the wing in a front sketch, the lower left shows a perspective view from below and lower right shows a perspective view from above. The deflector paravane (2) may in an embodiment of the invention be arranged with two or more depressor wings (5). The link portion (11) is in an embodiment arranged with an upper and a lower connection plate (12) for connection to the deflector paravane frame and the main float body (1) respectively. A stem (13) extends between those with a partly, or totally, through shaft (not shown) holding the depressor wing (5) close to its center. The wing will be pivotable around a horizontal axis, Ho. The wing is controlable and will force the deflector to a desired depth on demand signals according to calculated, preset parameters, or based on measured data given by e.g. real-time depth measurements or load values, by pivoting up or down depending of the desired direction to run.

Embodiments of the invention

[0029] The invention will in the following be described with reference to the attached figures.

[0030] The invention solves the above mentioned problems and is a submergeable diverter (0) for towing of seismic arrays, comprising a main float (10) comprising at least a main float body (1), in an operational state submerged deflector paravane (2) connected to the float main body and extending down in the sea and wherein the deflector paravane is arranged to run at a desired depth under the sea surface. The main float body (1) of the main float (10) is in an embodiment an extended float body with an, in the running direction, fore bow portion and a rear, aft, portion. In an embodiment of the invention the main float may be constituted by two or more smaller floats. In an operational state the whole array is towed in the sea and a diverter is arranged at each side, starboard and port side of the seismic array and the deflector paravane (2) is arranged to spread the seismic array by being controlled to port side or starboard . The deflector paravane (2) may in an embodiment be arranged with control elements such as e.g. regulating winch systems in bridle lines connected to towing lines etc. Al towing lines and spanning lines are connected to the deflector paravane (2). The diverting paravane will, after launching, sink to a desired depth, pre-set, based on buoyance of the main float. It is an advantage to have the deflector paravane (the diverter door itself) close to the same depth as the streamers in the array. The towing point will then be at a corresponding depth as the intermediate streamers. This will reduce drag forces to the deflectors and the connected equipment such as e.g. shackles and lines. There will be less dynamic forces causing equipment damage and wear. A further advantage of the submerged diverter is that it is removed from the surface and is less prone to obstruction and interference from objects in the upper water layer, down to the depth where the deflector runs, and in the sea surface. A diverter comprises a float arranged horizontally in the upper part of the diverter, will in an operational state, give a stable run in the sea and be orientated, standing, both in an operative and a passive condition. It will not rotate in sea during operation.

[0031] The deflector paravane (2) is connected to a tow line (102) from the seismic vessel (100). The tow line (102) comprises bridle lines (102) which is connected to the deflector paravane (2). In an embodiment of the invention the deflector paravane (2) comprises at least a generally horizontal upper frame plate (21) constituting its upper portion, and a lower generally horizontal frame plate (23) for deflector wings (20) and wherein the frame plates (21, 23) are arranged for connection to the bridle lines (103).

[0032] In an embodiment of the invention comprising the seismic deflector, one or more float lines (4a, 4b, 4c...), such as chain, rope, wire or the like, form at least one main float body (1) and extends down to the upper portion (21) of the deflector paravane (2) and wherein the main float body (1) is arranged to float in or near the sea surface and the deflector paravane (2) is arranged to run submerged in the sea at a depth limited by the one or more float lines (4a, 4b, 4c ...) full or partial length (L). The depth is determined by forces: towing forces, paravane forces and the load forces from the seismic streamers. The float line will limit the possible distance between the float and the deflector paravane. In an embodiment of the invention the float lines are arranged with shock absorbers to take shock loads. Such absorbers may be arranged within the line itself or in their connections between the float main body, the top float or the deflector paravane and the line. The absorbers may be a cylinder and or a flexible support of the attachment, rope or an elastic item so a dampening effect or the like, is achieved. . In an embodiment of the invention the length of the float lines (4a, 4b, 4c, ...) and thus the depth regulation of the deflector paravane (2) is controlled by one or more float line winches (43). The float line winches (43) may be arranged at the main float body (1) or at the deflector paravane (2). An advantage by the adjustable length of float lines by one or more winches (43), is that one may adjust the submerge depth to a deflector paravane and keep the main float body in or near the water surface. Another advantage is that by adjusting the float lines by winches is that one has more alternatives by launching or hauling the complete diverter. One may winch in the float lines before desired launching or hauling operations, thus the diverter is as compact operateable unit as possible or one may have full float lines lengths during launchin/hauling and operate one unit at a time, i.e, floats and deflector paravanes in two or more operations. The fact that the float lines are adjustable in lengths by means of the winches is a further advantage in terms of operational state. The diverter may in the one and the same embodiment be operated with floats in surface position, wherein the float lines are winched out to a desired length, or the float lines may be winched in and the diverter either may run as a in or near surface deflector, or a complete submerged deflector at a desired depth, preferably about the same depth as streamers. Thus, by flexible float lines and winches to control their lengths, one gains a wide range of possibilities both with regards to launching and hauling from towing vessel, and also regarding desired running depths for the paravanes and/or the seismic array as a whole. The one or more winches may in an embodiment of the invention operate by preset values or based on real time data and a remote controllable or locally arranged control system.

[0033] In an embodiment the winch will be controlled by a remote control, after the deflector is launched into the sea. The wane/deflector is lowered to a desired depth as far as the connection line/the chain allows. In embodiments wherein a depressor wing or a ballast regulation are used those may be remote controlled to sink the deflector paravane to a desired depth. The float will stay in the surface and be controlled as a slave of the running direction control of the deflector.

[0034] In an embodiment there is a fixed length of wire rope, rope, chain or the like, between the deflector and the float, so there are no need of a remote control of releasing mechanisms after launching of the system. The wane, the deflector paravane, sinks to a desired depth, preset depth, after launching. I an embodiment of the invention the number of float lines (4a, 4b, ...) are at least two, and wherein two of the two or more float lines (4a, 4b) first ends (41a, 41b) are connected to attachment point, in the running direction, fore portion, of the deflector paravane (2), while the float lines (4a, 4b) each opposite second ends (42a, 42b) is attached near a fore and rear portion, accordingly, of the float main body (1). The float lines may in its first end be attached in the one and same attachment point. They may be attached in the one and same shackle, thimble, eyelet, or the like. This is an advantage and will give a swivel function and the float may move freely in the surface and follow the surface moves in the water surface and the running direction of the vessel.

[0035] In an embodiment of the invention the number of float lines (4a, 4b,...) are at least two, and one float line (4c) of the two or more float lines (4a, 4b, 4c....) is longer than the remaining float lines (4a, 4b, ...), and with its one end, and connected to, in the running direction rear portion of the main float body ( 1) with its other end and arranged to limit lateral movement of the rear portion of the float main body (1). This is then a slack line that limits deflection to the side of the stern of the main float. Thus causing little impact to the deflector paravane that runs submerged in the water, even with rough sea, and holding the float in a running position, and does not allow free turns of 360 degrees around the fore float line. With such a limiting line one also have an indication of the direction of the deflector paravane. .In an embodiment of the seismic deflector according to the invention the main float body (1) is arranged to run submerged by a desired depth in the sea.

In an embodiment of the invention the main float (10) is arranged with one or more surface floats (3) arranged to run at, or just below, the sea surface, and two or more float lines (4a, 4b, ..) are attached between the main float body (1) and the surface float (3) and wherein at least two the two or more float lines (4a, 4b,...) are attached to the, in the running direction , fore portion of the main float body (1), and the main float body (1) and the one or more top floats (3) has a combined buoyance arranged to hold the top floats (3) in or near the sea surface and the deflector paravane is arranged to run submerged in the sea at a desired depth limited by the partial or full length (L) of the two or more float lines (4a, 4b, 4c...).

[0036] In this way benefits one buoyancy volume on multiple devices and one can have smaller and leaner float bodies thereby improving seagoing properties of the float bodies. By having a smaller unit in the sea surface heave is reduced and the submerged deflector paravane will go steadier. An advantage by having a float close to the submerged paravane in addition to a surface float, is that the surface float may hold for instance electronic communication equipment and at the same time keep the paravane floating during a stop in towing. The main float (10) has a stabilizing effect of the deflector paravane (2) when it is connected close to this, both in operating condition and in passive condition tin the sea. In addition to being a floating body, the float can accommodate various equipment for operating the diverter (0), including devices for communication with control units on the towing vessel or another monitoring station, control equipment for the deflector wings, the depressor wings, eg. hydraulic systems etc. The float will be at the top of the deflector paravane and hold the deflector in an upright position. In an embodiment the main float (10) may be arranged with ballast tanks. Those may be adjustable or pre-ballasted.

The seismic deflector according to an embodiment of the invention has a float line (4c), of the two or more float lines (4a, 4b, 4c, ...), that is longer than the full extended length of the at least one of the remaining float lines (4a, 4b, ...), and attached to, in the running direction, rear portion of the surface float (3) with its first end, and a rear portion of the main float body (1) with its second end, and arranged to limit the surface float rear portion lateral movement. The properties of this "slack line" will be similar to the limiting lines between the deflector paravane and the float.

[0037] .In an embodiment of the invention the buoyance of the surface float (3) will be substantially less than the buoyance of the main float body (1). This is to reduce heave and to lower the center of gravity to increase the stability.

[0038] . In an embodiment of the invention the number of surface floats are 2 or more. Two or more surface floats may be an advantage when it comes to redundancy, i.e. to improve strength of the equipment with respect to critical components. Should a float be damaged or otherwise inoperative, the remaining maintaining float properties, or the minimum of what is required for the remaining equipment will not be lost. Using several floats is also an advantage in terms of standardization and modularization of float equipment. Large deflectors may thus be equipped by more small floats of the same type which are also usable for smaller deflectors in a limited number.

[0039] In an embodiment of the invention the surface float (3) has a small volume and only for setting depths.

[0040] In an embodiment of the invention the surface float (3) is substantially smaller than the main float body (1). This will result in lower towing / propulsion resistance due to a smaller waterline than an embodiment where the surface float is equal or greater.

[0041] In an embodiment of the invention one or more link portions (11) connects the deflector paravane (2) and the main float body (1).

The float main body (1) is in an embodiment of the invention equipped with at least one ballast tank (7). The advantage by ballast tanks is that the float body flowability may be customized for a desired buoyance.

In an embodiment of the invention the ballast tank (7) is arranged for filling or draining to regulate the buoyance of the main float body. The regulation may in an embodiment comprise a remote controllable valve and possibly a pump to regulate the water content of the ballast tank (7). Such regulation of buoyance is a relatively slow process but a rough adjustment of the running depth for the deflector paravane is achieved. The seismic deflector according to an embodiment of the invention is arranged with one or more controllable depressor wings for depth control. In an embodiment of the seismic deflector the controllable depressor wing (5) is pivotable arranged about a horizontal axis (Ho) at a shaft (15) at the deflector paravane (2). In an embodiment the shaft is arranged in at least one of the link portions (11).

[0042] This provides for a fast, dynamic depth control, much faster than regulation of ballast. Such a depressor can be dimensioned to take down the total buoyance volume, for example in a way that the surface float dives to avoid surface resistance if desired. It is an advantage to have the possibility to run the whole deflector submerged under the sea surface if, during operation, meet some local obstructions that may destroy the operation, direction or the equipment as such. Such depressor wing may be arranged in an upper or lower fore or rear position of the deflector paravane (2) or in the bottom of the float body (10). In an embodiment of the invention one or more depressor wing is arranged as a link potion between the float main body (1, 10) and the deflector paravane (2).

[0043] Ballast tanks and depressor wings may be utilized in embodiments with or without surface floats and those functions may in embodiments be remote controlled by e.g. radio signals or acoustic signals from sending systems e.g . at vessels and to receivers and transmitters in or under the sea surface so that the regulating system may be operated.

[0044] In an embodiment of the invention where surface floats is used there is arranged equipment for radio communication in the surface float. Cables and possible hoses may then run between the deflector and the float and also to controlling systems in the line systems. This is an advantage of the use of surface floats. Such radio communication may be used for control of ballast volumes, depressor wings, regulation deflector wings, winch systems both for float lines and towing lines and for the streamer connection lines and spanning lines. In such embodiment the receiver and regulating systems may be decentralized and fewer hoses and cables may be used between the un its, but controlled directly.

[0045] In an embodiment of the seismic deflector according to the invention a pressure sensor, Doppler equipment etc for sensing position and depth relative to surface, speed, angles through the sea, orientation of the deflector, attach angles, roll angle etc., location related to other towed equipment, towing vessel or the like. In a combination with communication equipment, speed measurements etc. this will give a good control of the diverters position and one may have a control over the forces acting on the deflector, lines and other equipment at any time. This information may be utilized in a PLS or a PC- based controlling.

[0046] In an embodiment of the invention the deflector paravane (2) is arranged with at least two sections of deflector foils (20), an upper section with the foils (20u) and a lower section with the foils (20I). The deflector paravanes has historically developed parallel to the development of seismic equipment and towing arrays in the technical field in general. In an embodiment of the invention the foils then in the upper section filled with foam, and contributes to the buoyance capacity of the paravane. The foils in at least the lower section having voids filled with water when the paravane is lowered into the sea and ensures that the paravane is stable in the vertical position, and that the paravane for towing has an upright position. An advantage by foam filled foils is that the volume of the float body may be reduced. This is positive for towing resistance, saves space, simplifies handling of the diverter and again contributes to standardization of floats and associated equipment. The same float size may be used for deflector paravanes of different sizes.

[0047] In an embodiment of the invention a diverter will be equipped with emergency buoyancy means in the form of inflatable flotation elements which are inflated if paravane runs to deep in the sea. The Emergency buoyancy device may be provided with its own preset depth sensor triggers, gas cartridges or the like, or trigger mechanism controlled by the paravane depth or pressure sensor. This will be an assurance not to lose deflector if the other buoyancy devices of the diverter should fail. An example to such event may be punctures by a impact with ship wreck or other collision items in the sea. If the diverter will sink, the whole seismic array may be drawn down to an undesired depth and be damaged or lost.

[0048] An advantage to the invention is that the towing resistance in relation to the deflector force is reduced. Another advantage is that the running direction is improved. A further advantage is that noise from towing, that adversely is applied form the deflector door due to the travel through the sea, is reduced. This also includes reduced wave formation in the sea surface.

[0049] .The submerged paravane float will experience calmer sea conditions and thus reduce heave and pitch, thus reducing heave and pitch motion for the whole submerged wing structure, resulting in a more even and less variation of force to the tow line. This improves the general quality of the towing and reduces the mechanical low frequency noise from the deflectors on the seismic array spanned out by the deflectors. Reduced heave and pitch will also result in lower fuel consumption.

[0050] Furthermore, the lower variation of towing forces reduces wear to the equipment such as to the towing line, bridle blocks, bridle lines/craw foot lines, and the anchoring lugs for bridle lines at the horizontal plates at the deflector wings, and shackles and thimble/eyelets for the bridle lines.