The effect of noise generated by previous shots on seismic reflection data

Abstract

In marine seismic acquisition, the typical time interval between two adjacent shots is about [Formula: see text]. This interval is considered sufficient to avoid the signal from one shot interfering with the signal from the next shot. However, when we are looking for very weak signals or weak changes in a given signal (time-lapse seismic), the influence of the shot-generated noise can be of importance. In the present work, shot records with a recording time of [Formula: see text] are used to analyze the influence of the shot-generated noise from the previous shot. Simple decay models are used to match the observed rms decay curves. These calibrated models are used to estimate variations in signal-to-noise ratio versus shot time interval and source strength. For instance, if the source strength is doubled and the time interval between two shots is increased from [Formula: see text], an improvement in the signal-to-shot-generated noise from the previous shot of [Formula: see text] is expected. Especially for time-lapse seismic using permanently installed receivers, this way of increasing the S/N might be useful.

Streamer depth versus vessel and seismic interference noise

“…Figure 16: RMS amplitude of the seismic vessel noise extracted from the noise data using a fan filter that accepts events with apparent velocity ranges from 1400 to 1700 m/s. Example Figure 19: RMS amplitude of a long trace computed using a sliding window to infer the relationship between shot interval and shot gun generated noise (modified from Landrø (2008)). …”

“…Landrø (2008) used a 30-second-long trace recorded 2,600 m away from the source to infer the relationship between amplitude and time between shots. In Figure 19, the background noise level is the lower end of the rms amplitude curve after the source has been fired for 20 seconds.…”

“…In time lapse seismic, data quality has been greatly improved by more accurate source and receiver positioning (Landrø, 1999). However, it has reached a plateau where it is extremely difficult to further improve repeatability due to uncontrollable noise sources other than the seismic acquisition itself (Bjørlykke, 2010).…”

Tools and Techniques: Marine Seismic Methods

“…Landr (2008), showing the typical energy decay of a seismic shot over 30 s. The time between shots must be large enough that the reverberation has decayed to a sufficiently low level.…”

Flow and swell noise in marine seismic data

“…For seismic streamers, Parrish (2005) on the other hand, shows that such oscillations most likely will only be found at frequencies well below one Hz. In recent work presented by Landrø (2008) the signal remaining from the previous seismic shot is considered as a source of noise. For a seismic line acquired in the North Sea he shows that after 8 s, using a 5.3 Hz low-cut filter, the rms noise from the previous shot is 2.5μBar.…”