Combined electromagnetic and seismic acquisition system and method

Abstract

A method for marine geophysical surveying according to one aspect of the invention includes towing at least one geophysical sensor streamer in a body of water. The streamer includes a plurality of spaced apart electromagnetic field receivers disposed at spaced apart locations along the streamer. The streamer also includes a plurality of seismic sensors disposed at spaced apart locations. The seismic sensors each include at least one pressure responsive receiver and at least one particle motion responsive receiver. At selected times, a seismic energy source is actuated in the water. Particle motion and pressure seismic signals, and electromagnetic field signals are detected at the respective receivers.

1 . A method for marine geophysical surveying, comprising:
 towing at least one geophysical sensor streamer in a body of water, wherein the streamer comprises:
 a plurality of electromagnetic field receivers at spaced apart positions along the streamer, 
 a plurality of seismic sensors disposed at spaced apart locations along the streamer, the seismic sensors each including at least one pressure responsive receiver and at least one particle motion responsive receiver, and 
 a signal processing module associated with each electromagnetic field receiver, the signal processing module including signal processing devices for at least one of storing and communicating measurements made by the associated electromagnetic field receiver, the modules each including an electric energy storage device associated with the signal processing devices such that the signal processing devices are operable without conducting electrical power along the streamer and a relay for closing a circuit to the energy storage device for recharging thereof, the relay configured to open; 
   at selected times, actuating a seismic energy source in the water; and   detecting particle motion and pressure seismic signals and electromagnetic field signals at the respective receivers.   
     
     
         2 . The method of  claim 1  further comprising at least one of storing the respective signals at a location along the streamer proximate the respective sensors and communicating the respective signals to a recording unit on a vessel used to perform the towing. 
     
     
         3 . The method of  claim 1  wherein the streamer is towed in the water at a depth selected to attenuate effects of reflected electromagnetic energy from the water surface on the detected electromagnetic field signals. 
     
     
         4 . The method of  claim 1  wherein the electromagnetic field signals comprise voltages induced by electric field components of an electromagnetic field. 
     
     
         5 . The method of  claim 1  wherein the electromagnetic field signals comprise voltages induced by magnetic field components of an electromagnetic field. 
     
     
         6 . The method of  claim 1  further comprising actuating an electromagnetic field generator in the water at selected times. 
     
     
         7 . The method of  claim 6  wherein the actuating the electromagnetic field generator comprises imparting electric current across a pair of spaced apart electrodes. 
     
     
         8 . The method of  claim 6  wherein the actuating the electromagnetic field generator comprises imparting electric current to a wire loop. 
     
     
         9 . The method of  claim 6  wherein the actuating comprises imparting a transient electric current to the field generator. 
     
     
         10 . The method of  claim 6  wherein the actuating comprises imparting electric current having at least one discrete frequency to the field generator.