Attenuation of seismic water-column noise, tested on seismic data from the Grane field

Abstract

Seismic analysis of long-offset data is gaining increased attention for several purposes: constraining three-parameter amplitude variation with offset (AVO) methods, 4D analysis, and imaging below salt and basalt. A major challenge for exploiting long-offset seismic data is that the water-column noise mixes with and distorts the reflected seismic signal from interfaces at the target level. Traditional processing methods such as [Formula: see text] filtering often reduce this distortion problem. This article offers an alternative to conventional processing methods. The alternative exploits the difference in water depth and reservoir depth to subtract water-column noise. The proposed subtraction method works well where water depth is constant. The method was tested on a multicomponent seismic data set from the Grane field (North Sea). In this location, the water depth is fairly constant over the field. The fieldwise similarity level of water-column noise is high. A comparison of the water-column noise from various locations shows that the similarity is 10%, measured in normalized root mean squared error. The fact that the water-column noise is highly repeatable is a strong indication that the major part of it is harmonic waves that propagate in the water layer.