The relationship between the signal-to-noise ratio of downhole data and vibroseis source parameters

Abstract

The signal-to-noise ratio of vibroseis data is theoretically proportional to the force of the vibrator multiplied by the square root of the product of: the sweep length and the number of sweeps. These relationships are confirmed using both simple synthetic and real downhole data. Other noise sources are, however, likely to be much stronger than the ambient noise and the ability to overcome or remove their effect may not be reflected by the theoretical relationship. Using this relationship we compared different source parameters that could be combined to produce equivalent signal-to-noise ratios. These comparisons showed that the most effective way to improve vertical seismic profile (VSP) productivity, and therefore reduce survey cost, is to increase the drive-level or force of the vibrator because that is the only factor that lies outside the square root sign in the relationship.