EFFECTIVENESS OF WIDE MARINE SEISMIC SOURCE ARRAYS¹

In recent years, the use of wide source arrays in marine seismic surveys has been a topic of interest in the seismic industry. Although one motivation for wide arrays is to get more guns in a source array without increasing the in‐line array dimension, wide arrays can also provide the benefit of suppressing side‐scattered energy. Comparisons of common midpoint (CMP) stacks of data acquired offshore Washington and Alaska with wide and conventional‐width source arrays, however, show only small and sometimes inconsistent differences. These data were acquired in areas where side‐scattered energy is a problem. Comparisons of pre‐stack data, however, show substantial differences between the wide and conventional source array data.

The disparity between the stacked and prestack data is explained by analysing the effective suppression of back‐scattered energy by CMP stacking. Energy reflected from scatterer positions broadside to a given CMP location has a lower stacking velocity than that of the primary reflection events. Thus, CMP stacking attenuates the side‐scattered energy. In both survey areas the action of CMP stacking was so powerful in suppressing the broadside energy that the additional action of the wide array was inconsequential in the final stacked sections. In other areas, where the scattering velocity is comparable to the primary stacking velocity, wide arrays could provide considerable advantage.

Even though CMP stacked data from wide and conventional‐width arrays may appear similar, the reduced amount of side‐scattered energy in wide‐array prestack data may provide a benefit for data dependent processes such as predictive deconvolution and velocity analysis. However, wide arrays cannot be used indiscriminately because they can degrade cross‐dipping primary events. They should be considered primarily as a special tool for attacking severe source‐generated noise from back‐scattered waves in areas where the action of CMP stacking is insufficient.