The Computation of Attributes from Multi-fold Seismic Refraction Data

Abstract

Seismic attributes are any measure that helps to better visualize or quantify features of interest in seismic data. Refraction attributes can be readily computed from multifold seismic data using the standard algorithms of the generalized reciprocal method (GRM), a common offset refraction (COR) modification of the GRM, and the refraction convolution section (RCS). The COR GRM algorithms are applied prior to the parameterization of the traveltime data into individual layers. The COR GRM presentations facilitate the efficient quality control and interpretation of large sets of multi-fold data. Furthermore, the COR GRM algorithms can be readily applied to single ended refraction data, which are routinely recorded with marine and land streamers. The time model attribute obtained with the COR GRM algorithm is of comparable accuracy to that computed with the standard multi-fold GRM. However, the COR GRM seismic velocity model is a smoothed version of the fully optimized standard GRM model. The refraction attributes computed from the head wave amplitudes include the multi-fold head coefficient, and a COR equivalent with the amplitude product. Although the COR amplitude product for each offset is of comparable accuracy to the multi-fold head coefficient, it also includes a residual geometric spreading component. Another refraction attribute computed from the head wave amplitudes is the geometric spreading coefficient, which is generally assumed to be two in the far field for plane homogeneous refractors. This parameter is consistent over a wide range of offsets, but varies considerably from less than one to up to four along the seismic traverse The attribute derived from the RCS is bandwidth in octaves. It is proposed that refraction attributes can be employed to derive more useful models of the regolith using multivariate geostatistics. It is concluded that, refraction attributes offer the opportunity of extending the refraction method to new applications.