THE DIFFERENCES IN THE DETECTABILITY OF PERFORATION SHOTS AND MICROSEISMIC EVENTS IN THE SURFACE MONITORING: THE ATTENUATION EFFECT
Abstract
Detection of the seismic signal from perforations or string shots is crucial for calibration of velocity model for surface or downhole monitoring. While in the borehole recordings perforation shots have higher signal to noise ratio of the P-waves than microseismic events, in the surface monitoring recordings it is often opposite.
We investigated amplitude spectra of microseismic events and perforation shots in the downhole data and found that amplitude ratios in the band of 20-30 Hz relative to band 100-200 Hz are stronger for the microseismic events. Thus we suggest that detectability of the perforations in surface recorded data is limited by attenuation of the higher frequency signal which increases exponentially with frequency.
This suggests that longer duration of calibration shots can improve detectability of string shots at the surface.