Dual Axis Geophones For Pressure/Velocity Sensing Streamers Forming a Triple Component Streamer

Abstract

A seismic streamer includes a sensor comprises an axially oriented body including a plurality of axially oriented channels arranged in opposing pairs; a plurality of hydrophones arranged in opposing pairs in the channels; a pair of orthogonally oriented acoustic particle motion sensors; and a tilt sensor adjacent or associated with the particle motion sensors. The streamer has a plurality of hydrophones, as previously described, aligned with a plurality of accelerometers which detect movement of the streamer in the horizontal and vertical directions, all coupled with a tilt sensor, so that the marine seismic system can detect whether a detected seismic signal is a reflection from a geologic structure beneath the streamer or a downward traveling reflection from the air/seawater interface.

1 . A seismic sensor comprising;
 an axially oriented body including a plurality of axially oriented channels arranged in opposing pairs;   a first opposing pair of particle motion sensors arranged in a first pair of the channels;   a second opposing pair of particle motion sensors arranged in a second pair of channels, the second pair of particle motion sensors radially offset by 90° from the first pair of particle motion sensors; and   a tilt sensor in a known orientation to the first and second pair of particle motion sensors.   
     
     
         2 . The seismic sensor of  claim 1 , further comprising a key assembly adapted to positively orient the sensor to an adjacent component. 
     
     
         3 . The seismic sensor of  claim 1 , further comprising:
 a jacket covering the sensor; and   a permanent magnet inside the jacket adapted to find the orientation of the accelerometer after the final skin is extruded over the cable.   
     
     
         4 . The seismic sensor of  claim 1 , wherein the particle motion sensors comprise accelerometers. 
     
     
         5 . The seismic sensor of  claim 1 , wherein each particle motion sensor comprises:
 a base;   a box mounted to the base, defining an interior chamber, the box having an interior upper surface;   a hole in the base, defining a fluid flow path into the interior chamber; and   a pierzoelectric element mounted on the interior upper surface of the box.   
     
     
         6 . The seismic sensor of  claim 1 , wherein the first opposing pair of particle motion sensors are electrically coupled together to define a first signal channel and the second opposing pair of particle motion sensors are electrically coupled together to define a second signal channel. 
     
     
         7 . A marine seismic cable comprising:
 a plurality of hydrophones arranged in groups along the cable;   a plurality of particle motion sensors arranged in groups between at least some of the groups of hydrophones; and   a field digitizing unit, the field digitizing unit including a tilt sensor arranged in a known orientation to the particle motion sensors.   
     
     
         8 . The marine seismic cable of  claim 7 , wherein each of the plurality of particle motion sensors comprises:
 an axially oriented body including a plurality of axially oriented channels arranged in opposing pairs;   a first opposing pair of accelerometers arranged in a first pair of the channels;   a second opposing pair of accelerometers arranged in a second pair of channels, the second pair of accelerometers radially offset by  90 ° from the first pair of accelerometers; and   a tilt sensor in a known orientation to the first and second pair of accelerometers.   
     
     
         9 . The marine seismic cable of  claim 8 , wherein each accelerometer includes a key assembly adapted to positively orient the accelerometer to an adjacent component. 
     
     
         10 . The marine seismic cable of  claim 8 , wherein each accelerometer includes:
 a jacket covering the accelerometer; and   a permanent magnet inside the jacket adapted to find the orientation of the accelerometer after the final skin is extruded over the cable.   
     
     
         11 . The marine seismic cable of  claim 8 , wherein each accelerometer comprises:
 a base;   a box mounted to the base, defining an interior chamber, the box having an interior upper surface;   a hole in the base, defining a fluid flow path into the interior chamber; and   a pierzoelectric element mounted on the interior upper surface of the box.   
     
     
         12 . The marine seismic cable of  claim 8 , wherein the first opposing pair of accelerometers are electrically coupled together to define a first signal channel and the second opposing pair of accelerometers are electrically coupled together to define a second signal channel.