Stepped frequency seismic method with acquisition time optimization

Vibroseis technology is a seismic method for geological exploration and it is often applied in the search for underground oil reservoirs. Current methods vibrate the earth with a swept frequency "chirp" signal and results are obtained through correlation. This paper proposes a new stepped frequency method that will produce similar results with increased resolution. Resolution is improved by compensating for dispersion and by using coherent detection to eliminate harmonic components caused by nonlinearities. In addition to the reflection magnitude, the new technique is able to measure reflection angle which might assist in determining the type of subsurface discontinuity. This proposed technique energizes the ground with sinusoids in the frequency range of 5 Hz to 150 Hz where frequency is incremented in discrete steps. The amplitude of the reflected signal that is in phase with the transmitted signal is then recorded for each individual frequency step. Fourier transformation of the recorded data then shows the locations of subsurface discontinuities. Stepped frequency measurements take much longer than the current swept frequency measurement and ideas for minimizing this time are discussed in the paper