Abstract:
A seismic cable ( 1 ) and a method of manufacturing such a cable. The cable includes a plurality of elongated electrical/optical elements which are arranged to be interconnected with a number of seismic sensor devices arranged at intervals along the cable. A polymeric sheath and a protective outer armoring surround the elements to provide protection against radial stress of said cable. The sensor devices are installed outside of the elements and the armoring.

Description:
This is a continuation of U.S. patent application Ser. No. 09/334,683 filed Jun. 17, 1999, now U.S. Pat. No. 6,333,898, the disclosure of which is incorporated reference. 
    
    
     DESCRIPTION 
     The present invention relates to seismic cables in general and in particular to seabed laid seismic cables. Such cables are arranged to be installed in arrays to cover a certain area on the seabed. The seismic cables are designed to detect sound wave signals reflected from subsea oil and gas reservoirs when air guns are detonated in the sea. 
     The seismic cables include a number of sensor devices which are powered from a surface vessel. The array of seabed seismic cables may also include electronic units for signal processing. The cables therefore also include power conductors for the electronic units and for the sensors, as well as signal conductors for interconnections and transmitting processed signals detected by the sensors to the vessel. 
     The object of the present invention is to provide an improved seabed laid seismic cable which can be manufactured in long lengths. The main features of the invention are defined in the accompanying claims. With this invention a type of seismic cable has been obtained, which is suitable for installation on the seabed and which can be connected in arrays. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Above mentioned and other features and objects of the present invention will clearly appear from the following detailed description of embodiments of the invention taken in conjunction with the drawings where 
     FIG. 1 schematically illustrates a cross section of a cable, 
     FIG. 2 illustrates a cross section of the same cable where a sleeve surrounds the cable core, 
     FIG. 3 illustrates a side view of the said sleeve integrated in the cable corresponding to FIG. 2, 
     FIG. 4 illustrates a side view of the sleeve arranged on the seismic cable, partially in section, and 
     FIGS. 5 and 6 illustrate the seismic cable with a housing for the sensor elements outside the cable armouring. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, which is not drawn to scale, the sensor cable  1  corresponding to the invention includes power and signal conductors  5  (electrical and/or optical). These conductors  5  which may include pairs  6 , quads  7  or other conductor elements  8  and  9  may be stranded helically or SZ-wise, but they may also be arranged axially. 
     All the conductors will be wrapped by a tape  10  made of a polymeric material and a protective inner sheath  11  made e.g. of thermoplastic polyester, which will be surrounded by an armouring  12 , e.g. made of stranded steel wires. The interstices  13  in the cable core may be filled with a water blocking compound, such as petroleum jelly, the interstices  14  in the armouring are filled with a bitumen compound. 
     A seismic cable corresponding to the invention includes a number of electrical/optical elements  7 ,  8 ,  9  which are arranged to be interconnected with a number of seismic sensor devices, e.g. geophones and hydrophones, amplifiers etc., arranged at intervals along the cable. As corresponding to the invention these sensor devices are installed outside of the elements  5  and the armouring  12  at intervals along the cable there are arranged sleeves  15  (FIG. 2) surrounding the elements  5 . These sleeves  15  consist of two interlockable halves  16  and  17  having at least one outlet  18  for electrical/optical elements  19  (FIG. 3) of the elements  5  in the cable core. To adjust the outer configuration of the sleeves  15  to the cable core covered by the sleeves at intervals these sleeves  15  have conical end portions  26 , as shown in FIG.  3 . 
     FIG. 4 illustrates the interlockable status of the two halves  16  and  17  having grooves  20  and tongues  21  to ensure a water tight connection when pressed together. Guiding means or studs  22  on the outer surface of the sleeve distribute the wires of the armouring wires  12  surrounding the cable (FIG. 1) as well as the sleeve (FIG.  2 ). 
     In accordance with the invention the sensor elements are to be installed outside of the armouring  12 . Therefore, this armouring, at the location of the sleeve  15 , is covered by a housing  23  (FIGS. 5,  6 ) within which the sensor devices  24  are integrated. The electrical/optical elements  19  inside the cable core and being guided through the outlet  18  of the sleeve  15  are to be interconnected with the sensor elements  24  inside the housing  23 . The housing  23  and the sleeve  15  are e.g. interlockable by screws means  25  and known sealing means  27  (FIG. 3) between the individual parts to be connected will avoid any water penetration. 
     The above detailed description of embodiments of this invention must be taken as examples only and should not be considered as limitations on the scope of protection. The principles of the invention which have been described in connection with marine seabed laid seismic cables, can also be used in connection with towed seismic cables and on shore seismic cables.