Theoretical and Practical Aspects of the Vibroseis (Trade Name) Method

摘要

In the exploration of oil and gas using the seismic method, seismic vibrators are frequently used to generate a source signal. In the thesis, the wavefield emitted by one or more seismic vibrators acting at the surface of the earth is investigated. In theory, the shape of the far field wavelet can be determined from measurements on the vibrator. If this wavelet is cross-correlated with the measured data, the resulting seismogram will contain the desired zero phase wavelet. Normally, the measured data is cross-correlated with the pre-determined sweep, which is assumed to be equal to the feedback signal chosen on the vibrator. Therefore, the desired zero phase wavelet after cross-correlation can be obtained by choosing the right feedback signal on the vibrator. To determine which choice of feedback signal is correct from a geophysical point of view, an analysis of the wavefield emitted by the seismic vibrator is presented. The analysis contains three sequential steps: a description of the wave propagation in the earth, a description of the behavior of the seismic vibrator, and combination of the earth model and the vibrator model.