3D geometry, velocity filtering and scattered noise

In conventional 2D seismic, scattered noise used to be classified as “in-line” and “off-line”. In-line scattered noise has an opposite velocity and an identical wave-number to radial noise. It is attenuated in a similar manner: using inline field arrays and 2D velocity filtering. Off-line scattered noise is attenuated in the field by giving a lateral dimension to the field arrays (which become rectangles or parallelograms). In the most severe cases, this dimension can be larger than the inline dimension. If lateral dip is moderate, this lateral extension has no detrimental effect on data, and the gain in signal-to-noise (off-line scattered) is optimal. It is worthwhile noting here that the 2D stack array in itself is totally powerless not only against off-line but also against in-line scattered noise of which the arrival time is constant for all the seismic traces of any given CMP. In 3D seismic, the {in-line off-line} classification no longer applies. The use of wide arrays can become costly and detrimental to the data. Other tools need to be developed. The success of 3D velocity filtering in radial noise attenuation led to an analysis of the possibility of adapting this technique to scattered noise reduction.