Ocean bottom seismic sensor cable system including torque-relieving swivel

Abstract

An ocean bottom cable system includes: a cable adapted to be extended from a vessel at the surface of a body of water to the bottom of a body of water. The cable includes at least one electrical conductor or at least one optical fiber. A plurality of sensor units is disposed at spaced apart locations along the cable; and at least one swivel is disposed in the cable between the vessel and at least one of the sensor units. The swivel is adapted to enable relative rotation thereby relieving torsional stress between ends of the cable coupled thereto, and is adapted to transmit axial force along the cable therethrough.

1 . An ocean bottom cable system, comprising: 
 a cable extended from a vessel at the surface of a body of water to the bottom of the body of water, the cable including at least one of an electrical conductor and an optical fiber;    a plurality of sensor units disposed at spaced apart locations along the cable; and    at least one swivel disposed in the cable between the vessel and at least one of the sensor units, the swivel including a slip ring and mating contact to enable relative rotation between ends of the cable coupled thereto, the swivel including means to transmit axial force along the cable therethrough.    
   
   
       2 . The system of  claim 1  wherein the sensor units each include at least one particle motion sensor and a sensor responsive to pressure in the body of water.  
   
   
       3 . The system of  claim 1  wherein the cable is divided into segments each having a selected length, the segments terminated at each end thereof with a connector, each connector including a contact element to provide at least one of electrical contact and optical contact between an end of the cable segment and a device coupled to the end of the cable segment.  
   
   
       4 . The system of  claim 4  wherein each sensor unit includes a connection device to couple to one of the connectors at each end thereof.  
   
   
       5 . The system of  claim 1  wherein the cable comprises a coaxial cable disposed within a plurality of concentric, contrahelically wound layers of armor wires.  
   
   
       6 . The system of  claim 1  wherein the at least one swivel is disposed between a portion of the cable which rests on the bottom of the body of water and a lead in cable extending from the water bottom to the vessel at the water surface, such that any loops formed in the portion of the cable during extension into the water are relieved when the cable is retracted onto the vessel.  
   
   
       7 . (canceled)  
   
   
       8 . An ocean bottom cable seismic sensor system, comprising: 
 a lead in cable extended from a vessel at the surface of a body of water to the bottom of the body of water, the lead in cable including at least one of an electrical conductor and an optical fiber, the lead in cable including a plurality of helically wound armor wires surrounding the at least one of the electrical conductor and the optical fiber, the lead in cable having a connector at a water bottom end thereof, the connector including a connection element to make at least one of electrical contact and optical contact to a device connected thereto, and to transmit axial stress from the cable to the device;    a plurality of sensor units each having at each axial end thereof a receptacle adapted to mate with the connector, each receptacle configured as the connector on the water bottom end of the lead in cable, each sensor unit having seismic sensors therein, each sensor unit having a housing adapted to transmit axial stress therethrough;    at least one swivel having a receptacle at each axial end thereof adapted to mate with a connector configured as the connector on the water bottom end of the lead in cable, the swivel including a slip ring and mating contact to enable relative rotation between axial ends thereof, the swivel including means to transmit axial stress therethrough; and    a plurality of cable segments each having a connector at each axial end thereof, each connector configured as the connector on the water bottom end of the lead in cable, wherein the system is configured by coupling the connector at the water bottom end of the lead in cable to one axial end of at least one of a sensor unit and a swivel, the system configured by connecting a cable segment to the other axial end of the at least one of the swivel and the sensor unit, a remainder of the system configured by selective connection together end to end of cable segments and sensor units, and at least one swivel if the connector at the water bottom end of the lead in cable is coupled to a sensor unit.    
   
   
       9 . The system of  claim 8  wherein the sensor units each include at least one particle motion sensor and a sensor responsive to pressure in the body of water.  
   
   
       10 . The system of  claim 8  wherein the cable segments each comprise at least one of an electrical conductor and optical fiber and a plurality of layers of contrahelically wound armor wires surrounding the at least one of the electrical conductor and the optical fiber.  
   
   
       11 . (canceled)