An investigation of statics correction methods for 3D PS-wave seismic reflection

Abstract

In the last decade converted-wave (PS-wave) seismic reflection studies have successfully demonstrated that a more complete geological interpretation can be obtained by integrated interpretation of P-wave and S-wave information, at both the petroleum and coal scales. Full 3D implementation of PS reflection presents particular challenges at the coal scale, because relative offsets and dominant frequencies are both large compared to petroleum-scale reflection. One of the most difficult steps in the PS processing sequence is estimation of the S-wave receiver statics. Statics are time delays caused by variations in the weathering layer, and changes in source and receiver elevation. These time errors can significantly degrade CMP stack quality, and the final geological interpretation of seismic images. Static errors tend to be much more significant in PS surveys since the S wave travels more slowly through the weathering layer and is therefore more likely to be affected by variations within this layer. In this presentation we evaluate of a number of different approaches for estimating 3D PS statics solutions. These include a surface-consistent inversion algorithm (analogous to the residual-statics method used in conventional P-wave processing), a so-called 'robust-statistical' method, and PPS refraction analysis. The methods are evaluated using a coal-scale 3D-3C survey acquired in the Bowen Basin. This has been used to examine the comparative performance, and the influence of various algorithmic and geological factors. The results indicate that the surface-consistent inversion method can fail under some weathering conditions. When this occurs the refraction based method or a robust statistical method are preferred.