Three‐dimensional dip analysis of offset VSP data

Abstract

Often offset VSP data are available from only a few source positions. This creates difficulties with many standard imaging techniques. Using geometric ideas, a simple imaging technique is presented which is similar to a velocity spectra analysis of 2-D seismic data. The method involves a coherency measurement over the data along a traveltime curve corresponding to a specific dip and depth. The result for that dip and depth is placed appropriately (imaged). This coherency measurement is repeated for a range of dips at a specific depth. All depths are searched. This enables the construction of a dip spectrum of reflectors near a borehole. The dip spectrum contains information pertaining to the coordinates of source image points of reflectors. By the correlation study of coordinates of source image points obtained from a few source positions, the dip and strike of reflectors may be determined. This procedure locates the reflector in three dimensions if three source positions are available which do not lie on a straight line. 6 referenes, 19 figures.