Azimuthal Binning For Improved Fracture Delineation

We propose an alternate way to define azimuth binning in Kirchhoff prestack migration. This new definition takes into account the location of the image point in addition to the source and receiver locations. In this manner, we more properly acknowledge the side-scattering component of the propagation path grouping, assigning our contribution to a given azimuthal bin. We find that data binned in this manner provide better focusing of steeply dipping reflectors, fractures and faults when our velocity model is only approximate. We examine the impact of this new imaging approach on mapping karst-altered fractures in Dickman Field, Ness County, Kansas. Azimuthal binning in prestack migration Kirchhoff migration is a relatively simple operation that can be understood to a great extent using simple geometric concepts to visualize the relationship between the input data and the output image. In Kirchhoff migration, an image at a given position in the subsurface is obtained from data collected at a number of locations within the aperture surrounding the image location. In Figure 1 this is sketched in a map view, where we can see that the surface separation between the source-receiver line and the image location can be considerably large. Figure 1. Map view of a seismic survey and imaging using Kirchhoff migration. Energy is excited by the source and scatters from subsurface reflectors and diffractors. In prestack time or depth migration, each subsurface location is a candidate image point. If the travel time from the surface source location to the subsurface image point is tsi, and the time from the subsurface image point to the surface receiver group is tig, then in Kirchhoff migration we add a properly scaled value of the amplitude at time tsi + tig measured at the receiver group to the image point. In a number of applications, including velocity and/or anisotropy analysis, AVO/AVA and prestack inversion and prestack noise attenuation, the data are not migrated into a single image trace but rather organized into partial images obtained from subsets of the data pertaining to a given value or range of values of some geometrical parameter(s). As illustrated in Figure 2, the usual choices for binning parameters are offset, measured as the surface distance between source and receiver, and azimuth, similarly taken as the strike of the line connecting the source and receiver. Common-offset binning is the workhorse for velocity analysis, and common-azimuth binning has mostly been used for azimuthal anisotropy analysis. Offset binning is being increasingly used also for VTI anisotropy analysis.