Method of and apparatus for operating equipment installed in marine seismic tows

Abstract: In order to be able to operate special equipment provided in seismic cables, which comprise gun cables and streamers (2, 3), during seismic surveys at sea, a method and a device are provided which enable energy to be supplied through wires (4) to the equipment (B, C, D) in the cables, without this energy supply affecting the seismic surveys. In order to achieve this, low output energy is supplied through the wires (4) and used to charge batteries (6) of operating devices, which batteries can emit for brief periods sufficiently high outputs of energy in order to perform the necessary operation of the equipment. The device also comprises equipment required for control of the operation.

Description: The invention relates to a method of and an apparatus for controlling and/or operating equipment which is installed in marine seismic tows at a distance from a towing vessel, e.g. adjusting mechanisms for deflectors in the tow-line, tailbuoy streamers or electronic equipment, where the equipment is supplied with an energy source. Seismic surveys at sea are conducted by towing through the water behind a vessel seismic devices which transmit seismic signal pulses to the seabed, and equipment to record the reflected signals. These seismic devices are normally placed in or along tow-lines which are pulled parallel to and at a distance from each other behind the towing vessel. The actual signal transmission for the seismic surveys is controlled in the usual way from the towing vessel by means of electrical or hydraulic trigger signals in the normal manner. In seismic tows, however, there are a number of other elements which are more difficult to handle. Examples of such equipment are the deflectors or otter board devices which are used to pull tow-lines out to the side of the vessel and to position them in relation to the centre line, where it is desirable to have adjusting mechanisms which, when activated, can effect an alteration in position in order to change the distance to other parallel tow-lines. The tow lines are also usually equipped with tailbuoys which contain equipment for recording their positions. Similar equipment can also be placed along the length of both the seismic gun cables as well as the receiver cables, the so-called streamers. The problems involved in the operation of such additional equipment in the cable have been due to the fact that this equipment has often required a relatively large supply of power for its operation, while it has not been possible to supply the required energy through the cables in the tow- lines, since greater amounts of energy could affect the other seismic equipment. Published European Patent Specification No. 0 193 215 discloses a streamer levelling device including the features defined in the preamble of Claims 1 and 5 of the present application, and in particular having a sealed chamber housing batteries and electrical equipment. However, the power able to be supplied by the batteries would be insufficient and/or would not last long enough to operate other elements of a marine seismic two. Separate power supply means would have to be provided which would affect the seismic surveys or recordings. Published French Patent Specification No. 2 283 571 discloses apparatus for power control and information reception in which a power supply in the form of batteries is provided, together with an arrangement for recharging the batteries. However, the arrangement of the charging means and the batteries is such that it would be unsuitable for use in a marine seismic tow, because it is not waterproof. Ocean Engineering and the Environment, Conference Record November 12-14, 1985 pages 686-692 discloses a marine seismic tow comprising a plurality of radio floats, each float having a battery mounted in a watertight compartment in the float centre. Again, however, the battery would not be suitable for supplying power to other elements of the marine seismic tow, and separate power supply means would have to be provided which would affect the seismic surveys or recordings. According to a first aspect of the invention, there is provided an apparatus as defined in Claim 1. According to a second aspect of the invention, there is provided a method as defined in Claim 5. Preferred embodiments of the invention are defined in the dependent claims. It is thus possible to provide a method and an apparatus which facilitate the operation of such additional equipment in seismic streamers, enabling this equipment to function satisfactorily without the necessity of supplying energy amounts through the streamers which can affect the seismic surveys or recordings. It is also possible to facilitate the operation of equipment, which is operated both electrically and hydraulically, while at the same time safeguarding the equipment against environmental effects. It is further possible for the energy transfer to the equipment to be kept at a low level, thus preventing a continuous energy supply from affecting the seismic recording devices in the tow. Despite this, by means of the use of rechargeable batteries, the possibility is offered to have available at the operational site for the equipment an energy source which can supply a high power output when necessary, thus ensuring reliable operation of the equipment. Operation is possible during brief operating periods when, e.g., an adjustment of a deflector is performed or it may involve the operation of electronic equipment in the streamer or in tailbuoys where, by means of the battery elements, continuous, uninterrupted operation is guaranteed with sufficient power, which is maintained by means of the weak but continuous charge. A preferred apparatus contains the elements required for operation and control of the operation. In order to safeguard these elements against external influences and possibly from influencing one another, the equipment may be separated into two chambers both of which are sealed. The first chamber contains the electrical and electronic equipment, whereas the second chamber contains the storage media, such as batteries and hydraulic accumulators. Gas from the batteries which could constitute a risk of explosion in their chamber will thus be less dangerous since the batteries are separated from the electrical components such as a motor and transformer which could cause an ignition spark. In the same way, hydraulic leaks from an accumulator are unable to reach the electrical motor and destroy it. This separation also enables the equipment to be positioned in a simpler and more flexible way, thus making it simpler to instal in a deflector, a streamer, a tailbuoy etc. Should one of the elements nevertheless have to be replaced, it is possible to disconnect the two chambers from each other, thus enabling separate replacements to be performed. The apparatus may also comprise transmitters and receivers for pulses controlling the operation, whereby the device receives a signal that an operation is required and sends this signal to the towing vessel which provides for the transmission of activating pulses for the operation of the equipment. Controls of this kind may be installed in the first "electrical" chamber. Many variations of this type of equipment are possible. The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of the configuration of a vessel and tow in a seismic survey; Fig. 2 is a block diagram illustrating the principles of an embodiment of the invention; and Fig. 3 illustrates the construction of an apparatus constituting an embodiment of the invention. Fig. 1 illustrates a seismic tow configuration, where a towing vessel 1 tows three cables behind it, viz. two gun cables 2 with a seismic energy source and a receiver cable or streamer 3 between the cables 2. The cables 2 are pulled out to the side by means of deflectors which are indicated by B. In order to adjust the position of these deflectors to enable the cables 2 to be be moved further in or further out, it is desirable to use an operating device at or on the deflector. For this purpose a device according to the invention can be used. Similarly in the gun cables 2 at reference letter C there are indicated symbols for equipment. This can, e.g., be equipment for raising and lowering of the guns which are suspended from the cable or for the control of groups of guns. Devices according to the invention can be used for the operation of such equipment. Finally, in the streamer 3 a tailbuoy is illustrated at D. This tailbuoy is capable of transmitting signals indicating its position, and if necessary the position can also be altered. Devices according to the invention can be used for this purpose. In Fig. 1, broken line 4 indicates power supply wires to these operating devices. The power comes from a power source A on board the towing vessel, which can preferably carry a 24 volt voltage source which supplies a maximum current of 5 ampere. Thus, low voltage current is led through the wires which are incorporated in the towed cables. Control cables for the operating devices can also be run together with the wires 4. In Fig. 2 the principles used in the method and device according to the invention are illustrated in a block diagram. From the above-mentioned power source A of, e.g., 24 volts and maximum 5 ampere current capacity, current is supplied through the wires 4 to a transformer unit 5 which is provided in the operating device. The transformer unit transforms the voltage to a level which is suited to a power storage unit 6 such as batteries provided in the operating device. The transformer can, e.g., transform the voltage from 24 volts to 12 volts with a higher amperage. The transformer can be combined with a voltage regulator and possibly other regulators and switches as well as safety devices for the power supply. The batteries 6 receive a continuous power supply, if possible only during those periods when no seismic recordings are being performed. Continuous care is taken, however, to ensure that the or each battery 6 is full or charged to its maximum, thus ensuring that, when adjustment or activation of the operation of the equipment is required, the battery 6 can supply sufficient energy to a motor 7 which provides the necessary activation, either directly or via an hydraulic unit or in some other way. The control of activation of the motor and its running time can be performed via a cable 8 from a control unit 5 on board the towing vessel. The control unit can receive impulses from a recording device, e.g. in the deflector, which effects the transmission of a control pulse from the unit S. This control mechanism can also be remotely controlled, e.g. by means of transmitting/receiving units, the operating device also being capable of containing both a transmitter and a receiver in order to transmit signals back to the control unit on board the vessel. The operating device is schematically illustrated in Fig. 3. The elements illustrated in Fig. 2 are installed in sealed chambers. In order to make the operating device as safe as possible, the elements are arranged in at least two chambers, but more chambers could be used. In the illustrated embodiment, it has been decided to instal the electrical elements, control elements etc. in a first chamber 9, whereas the energy supplies are placed in a separate second chamber 10. The chambers are sealed by means of covers 11 and 12. In the first chamber is placed a control unit 13, which, e.g., can be the above-mentioned remote-control unit, i.e. a transmitter and/or receiver for control signals for starting and stopping operations. The power supply from the towing vessel, i.e. from the energy source A, is transmitted via the cables 17, which are conveyed to the device via the tow-line cable, and are connected to the transformer unit 5 which can also contain voltage regulators, switches, etc., and which transforms the voltage from 24 volts to 12 volts. From this transformer unit, a set of wires 18 leads to a rechargeable battery 6 which is provided in the second chamber. The battery is thus more or less continuously charged with a 12 volt charging current. When operations are to commence, e.g. on the basis of a signal from the unit 13, a current is transmitted from the unit 5, possibly supplemented with current, or merely current from the battery 6 via the cable 18 through the cables 19 to the motor 7 which is an electrical motor and which thereby starts, e.g., a pump 14. The pump 14 is connected via a pressure pipe 20 with a supply 15 of hydraulic fluid which is sucked in by the pump and activates, e.g., an hydraulic cylinder via a connection 16. In this manner, an hydraulic cylinder in a deflector as described in Norwegian patent application No. 92 1155 can, for example, be activated or deactivated for adjustment of the deflector. For other purposes the hydraulic elements can be omitted. In this case, a second chamber 10 would be available which contains only the rechargeable battery. Should the battery for some reason be overloaded, thus causing the formation of gas, it will not be possible for this gas to ignite, since any sparks from the other electrical components are separately located in the chamber 9. The installation of the individual components in several chambers gives an extremely flexible construction, whereby individual components can be replaced quite simply by changing chambers, since the chambers require to be equipped with connectors of a known type, such as cables/hoses. The chambers can also be placed one behind the other or adapted in some other way for special purposes. The operating device is particularly advantageous in combination with a remote control device, but can also be used in performing adjustments in advance, when activating pulses are only transmitted from the towing vessel.

Claims: An apparatus for operating equipment disposed in a marine seismic tow remote from a towing vessel (1) and towed by towing cables (2, 3), the equipment including adjusting mechanisms for deflectors on the towing cables (2, 3), and/or devices for lowering and raising seismic guns, and/or devices for use in tailbuoys in streamers, and electronic equipment, the apparatus comprising a first sealed chamber (9) on the towing cable (2, 3) housing control means (13) and electrically powered equipment operating means (7) electrically connected to power storage means (6) for operation thereby, the control means (13) being electrically connected to the equipment operating means (7) for controlling operations of the equipment operating means (7), characterised by: the first chamber (9) housing charging means (5) for receiving electrical current less than a maximum value, the charging means (5) being operatively connected to the power storage means (6) for charging the power storage means (6), a second sealed chamber (10) on the towing cable (2, 3) housing the power storage means (6), the second chamber (10) being separate and sealed from the first chamber (9), the control means (13) being electrically connected to the charging means (5), and central control means (S) on the vessel (1) for transmitting control signals to the control means (13). An apparatus as claimed in Claim 1, wherein the power storage means (6) comprise rechargeable batteries, the charging means (5) comprise step down transformer means, and the central control means (S) comprise a power source (A) having a higher voltage output than the batteries, control signal means for transmitting control signals, and electrical conduit means (17) supported by the towing cable (2, 3) connecting the power source (A) and the control signal means to the transformer means and the control means (13) so that transmission of electric power and control signals from the central control means (S) does not effect operation of other devices in and on the towing cables (2, 3). An apparatus as claimed in Claim 1 or Claim 2, wherein the central control means (S) comprise transmitter/receiver means for transmitting control signals, and the control means (13) comprise receiver/transmitter means for receiving the control signals from the central control means (S) so that signals from the central control means (S) remotely control the operation of the equipment without effecting operation or other devices in the towing cable (2, 3). An apparatus as claimed in Claim 1, Claims 2 or Claim 3, wherein the adjusting mechanisms comprise an hydraulic operating device on the equipment, and further comprising: a source of hydraulic fluid (15) housed in the second chamber (10); a hydraulic pump (14) and pump drive motor therefor housed in the first chamber (9); fluid conducting means (20) for conducting fluid from the hydraulic fluid source (15) to the hydraulic pump (14); and wherein the control means (13) is electrically connected to the pump motor for operating the pump. A method for control and operation of equipment disposed in a marine seismic tow remote from a towing vessel (1) and towed by towing cables (2, 3), the equipment including adjusting mechanisms for deflectors on the towing cables (2, 3), and/or devices for lowering and raising seismic guns, and/or devices for use in tailbuoys in streamers, and electronic equipment, the method comprising providing power storage means (6) and a first sealed chamber (9) on the towing cable (2, 3) housing control means (13) for operating the equipment, characterised by: providing charging means (5) within the first chamber (9), the charging means (5) being electrically connected to the power storage means (6), providing a second sealed chamber (10) on the towing cable (2, 3) housing the power storage means (6), the second chamber (10) being separate and sealed from the first chamber (9), electrically connecting the control means (13) to the charging means (5) for controlling operation of the charging means (13), remotely operating and controlling the operation of the control means (13) by a central control means (S) on the vessel (1) transmitting electrical current to the control means (13) which is less than a maximum value so as to maintain the power storage means at maximum charge, the electrical current being transmitted by electrically conductive wires supported by the towing cables (2, 3), transmitting demand signals from the equipment to the central control means (S) indicating demands for power for operation of the equipment, transmitting control signals from the central control means (S) to the control means (13) in response to the equipment demand signals for operating the control means (13) to provide electric power from the power storage means (6) to operate the equipment. A method as claimed in Claim 5, wherein the adjusting mechanisms comprise an hydraulic operating device and/or a source of hydraulic fluid (15), and a hydraulic pump (14) connected to the source of hydraulic fluid (15) and pump drive motor therefor in the second chamber (10); and providing electrical power from the batteries to the pump drive motor in response to a demand signal from the equipment.

Inventors: CAPPELEN HANS, SORBOTTEN OYVIND, VATNE ODD OLAV, CAPPELEN, HANS, SORBOTTEN, OYVIND, VATNE, ODD OLAV
Applicants: GECO AS, GECO A.S.
Application year: 1993
Main classification: G01V1
IPC codes: H02J7, G01V1