Optimization of the sweep signal of a vibration source
© Y.K. Tiapkin
One of the seismic sources used in the oil industry is the seismic vibrator, the basis for the Vibroseis method. Though it has been successfully utilized worldwide for more than forty years a number of difficulties with the method are still recognized but not widely solved. One of these is the problem of optimizing the pilot sweep in order to coordinate field operations with subsequent data processing in achieving their common object. The current approaches to pilot sweep parameter determination are rather subjective, with no regard for the vibrator energy to be emitted, the total transfer function of the seismic system, and the spectral properties of the target interval and additive noise. In order to eliminate the defect, an iterative method for computing the optimum pilot sweep is suggested. The method enables the most effective use of the vibrator energy owing to its rational distribution along the frequency axis. Emitting such a signal provides the maximum data resolution within the Wiener optimality criterion at the output of processing under a natural restriction on the energy radiated. In the paper, the results of testing the developed solution with model data are demonstrated. The results agree well with practice of using the Vibroseis method in various seismic and geologic conditions for many years. They also corroborate the physical and mathematical validity of the model assumptions on which the solution is based. Furthermore, algorithms are described for calculating the characteristics that the method requires to be implemented in practice.