Method for Acquiring and Interpreting Transient Electromagnetic Measurements

Abstract

A method for interpreting transient electromagnetic survey data includes measuring response of subsurface Earth formations to a plurality of time separated transient electromagnetic fields imparted thereto. An amplitude time decay of a selected one of the measured responses is modeled. An amplitude from the modeled amplitude time decay is added to a one of the measured responses later in time than the selected measured response if the amplitude is less than a selected threshold. The method includes at least one of storing and displaying a result of the adding.

1 . A method for interpreting transient electromagnetic survey data, comprising:
 measuring response of subsurface Earth formations to a plurality of time separated transient electromagnetic fields imparted thereto;   modeling an amplitude time decay of a selected one of the measured responses;   adding an amplitude from the modeled amplitude time decay to a one of the measured responses later in time than the selected measured response if the amplitude is less than a selected threshold; and   at least one of storing and displaying a result of the adding.   
   
   
       2 . The method of  claim 1  further comprising modeling an amplitude time decay of a measured response prior in time to the selected one of the measured responses; and
 adding an amplitude of the prior in time modeled amplitude, the modeled amplitude of the selected measured response and the later in time measured response if the modeled amplitude of the prior in time response is below a selected threshold.   
   
   
       3 . The method of  claim 1  wherein the induced transient electromagnetic field comprises switching off direct current passed through an antenna. 
   
   
       4 . The method of  claim 1  wherein the induced transient electromagnetic field comprises switching on direct current and passing the current through an antenna. 
   
   
       5 . The method of  claim 1  wherein the induced transient electromagnetic field comprises switching polarity of direct current passed through an antenna. 
   
   
       6 . The method of  claim 1  wherein the measured responses comprise voltage measurements made in response to electric current imparted into the Earth's subsurface. 
   
   
       7 . The method of  claim 1  wherein the measured responses comprise voltage measurements made in response to a magnetic field imparted into the Earth's subsurface. 
   
   
       8 . The method of  claim 1  wherein the measured responses comprise magnetic field amplitude measurements made in response to electric current imparted into the Earth's subsurface. 
   
   
       9 . The method of  claim 1  wherein the measured responses comprise magnetic field amplitude measurements made in response to a magnetic field imparted into the Earth's subsurface.