Extending the Low Frequency Content for Improved Vibrator Performance

Subsurface image resolution can be improved by extending signal frequency bandwidth toward both higher and lower frequencies. Particularly, the low frequencies are very important in seismic trace inversion to improve the accuracy of the surface velocity. However, the vibrator performance at low frequencies is restrained by mechanical and hydraulic limits that exist in the vibrator system. For example, the reaction mass stroke and harmonic distortion significantly limit the vibrator drive level and the quality of the ground force output from the vibrator. This paper compares downhole and surface geophone data produced by two different vibrators, a unmodified vibrator and a modified vibrator. The results demonstrate that the modified vibrator enhances signals at low frequencies.