S U M M A R Y A method of multicomponent multisource shear-wave interpretation, utilizing the output of the Alford rotation for separating the fast and slow particle motion stacks in azimuthally anisotropic media, yielded a qualitative prediction of lateral fracture intensity variation prior to horizontal drilling. The method exploits a fundamental difference between the two particle motion stacks when vertical, aligned fractures are the source of the shear-wave splitting. The fast shear wave (Sl) section is insensitive to the lateral variation in fracture intensity since its particle motion is parallel to the fractures; hence, reflectivity on the S1 CDP-stacked section should be likewise insensitive to fractures. The slow shear wave (S2) section, however, possesses particle motion perpendicular to the fracture planes, so variation in lateral fracture intensity will affect velocity and reflectivity. Examination of the reflectivity on the two sections for a seismic line reveals laterally consistent reflector strength on the S1 section for the Austin Chalk, the horizon of interest, but laterally inconsistent reflector strength for the same horizon on the S2 section in the study area. Reflector dimming on the S2 section was interpreted as indicating fracture intensity maxima. Horizontal drilling confirmed both fracture azimuth and intensity predictions, and resulted in significantly higher initial hydrocarbon production than for surrounding wells.
Alford rotation analysis of 2C × 2C shear‐wave data (two source components, two receiver components) for azimuthal anisotropy is valid only when the orientation of that azimuthal anisotropy is invariant with depth. The Winterstein and Meadows method of layer stripping vertical seismic profiling (VSP) data relaxes this restriction for coarse‐layer variation of the orientation of the anisotropy. Here we present a tensor generalization of the conventional convolutional model of scalar wave propagation and use it to derive generalizations of Winterstein and Meadows layer stripping, valid for 2C × 2C data and for the restricted 2C-only case, in the VSP and reflection contexts. In the 2C × 2C VSP application, the result reduces to that of Winterstein and Meadows in the case where both fast and slow shear modes have the same attenuation and dispersion; otherwise, a balancing of mode spectra and amplitudes is required. The 2C × 2C reflection result differs from the 2C × 2C VSP result since two applications of the mode‐balancing and mode‐advance operations are required (since the waves travel up as well as down). Application to a synthetic data set confirms these results. The 2C × 2C reflection algorithm enables the exploration for sweet spots of high fracture intensity ahead of the bit without the restrictive assumption that the anisotropy orientation is depth invariant.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.