Kenneth L. Craft

Determination of the principal directions of azimuthal anisotropy from P-wave seismic data

In an azimuthally anisotropic medium, the principal directions of azimuthal anisotropy are the directions along which the quasi-P- and the quasi-S-waves propagate as pure P and S modes. When azimuthal anisotropy is induced by oriented vertical fractures imposed on an azimuthally isotropic background, two of these principal directions correspond to the directions parallel and perpendicular to the fractures. S-waves propagating through an azimuthally anisotropic medium are sensitive to the direction of their propagation with respect to the principal directions. As a result, primary or mode‐converted multicomponent S-wave data are used to obtain the principal directions. Apart from high acquisition cost, processing and interpretation of multicomponent data require a technology that the seismic industry has not fully developed. Anisotropy detection from conventional P-wave data, on the other hand, has been limited to a few qualitative studies of the amplitude variation with offset (AVO) for different azimutha...

Repeatability of 3-D ocean-bottom cable seismic surveys

Recent advances allow time‐lapse 3-D (sometimes called 4-D) seismic surveys to map gas‐oil and oil‐water contacts. Some have used “legacy” 3-D data (i.e., data not originally acquired for a 4-D study) and found that the varying quality of the different vintages of the data limited the resolution that could be attained. How then, do we best carry out acquisition and processing for a 4-D seismic program so that the data are repeatable to the extent that differences are attributable to movement of the reservoir fluids and not to the acquisition, processing, or other factors?