Quality Assessment of Seismic Data Sets and the Impact on Interval Velocity Estimates in DST-Paper

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The paper presents a method for assessing seismic trace quality in Downhole Seismic Testing (DST), where compression- and shear-wave velocities are calculated from wave travel times between depths. Reliable velocity estimates depend on choosing appropriate signal-processing methods for the recorded data.<br /><br />The proposed Seismic Trace Characterization (STC) combines three measures: the cross-correlation coefficient (CCC) between full waveforms at adjacent depths, polarization-based linearity (LIN), and a Signal Shape Parameter (SSP) that measures how closely the trace’s frequency spectrum resembles a bell-shaped curve. Together, these measures produce a quality grade from A (good) to F (unacceptable). The grade is intended primarily to guide analysis choices, rather than to indicate velocity accuracy directly.<br /><br />The paper describes how individual measures can inform processing. Low CCC may indicate waveform distortion, such as skewing, which can sometimes be reduced using signal decay. Low linearity may be addressed by narrowing the analysis time window; if one sensor axis is strongly contaminated, that axis may be excluded. Low SSP can result from noise or ringing and may improve with time-windowing, stronger filtering, or notch filters. When reflections degrade both linearity and spectral shape, windowing can isolate the unaffected first arrivals.<br /><br />For each depth interval, velocities are calculated independently from left- and right-side source records. Their relative spread helps assess confidence: below 10%, the results are considered sufficiently consistent for engineering use; above 10%, greater weight should be given to the side with better trace quality, and the estimate treated as indicative. The authors note that continued application may refine the classification thresholds or introduce additional quality measures.

Keywords

seismic trace quality

downhole seismic testing

signal processing

wave travel time

compression wave velocity

shear wave velocity

cross-correlation coefficient

polarization linearity

signal shape parameter

quality grading