Pre-stack sea bottom detection and swell correction within an expected hyperbolic range for noisy high-resolution 8-channel airgun seismic data

Abstract

High-resolution marine seismic data degraded by sea swell can be enhanced by swell correction. To correct for swell, two-way travel times are detected for sea bottom locations in seismic traces; linear predicted values are calculated from the previously detected travel times, and correct static shifts between the detected and calculated values before stacking. To pick sea bottom locations for very large numbers of seismic traces, automatic sea bottom detection (SBD) is normally required. However, sea bottom signal degradation by wave noise causes SBD failure. Our first SBD trial using trace-by-trace (TBT) picking from raw and energy ratio data was unsatisfactory, with many of the detected sea bottom values deviating from the correct values due to noise in the field data. However, we achieved reasonable results by considering source–receiver geometry and previously detected sea bottom values. We picked reliable sea bottom values within an expected hyperbolic range (EHR) calculated from the source–receiver offset and group interval. To prevent excessive correction for swell, we excluded unreliable picks that deviated greatly from the linear trend of previously detected sea bottom values, or from the immediately preceding value. Swell correction within the EHR significantly improved the quality of noisy data. We applied this method to noisy field seismic data acquired offshore Yeosu, Korea, and successfully detected the sea bottom, corrected for swell, and improved seismic section. Thus, high-resolution marine seismic data degraded by sea swell can be enhanced by pre-stack swell correction in shot gathers using a hyperbola calculated based on source–receiver geometry.