Analyses of wavefields by the common excitation array (CEA) method

Abstract

There is a number of problems associated with the processing of seismic data acquired over crystalline rocks where velocities vary as much in the horizontal direction as in the vertical direction and near-surface low-velocity layers may distort the signals recorded on the surface. In addition, waves arriving at the same time but at different dips will interfere with one another thereby masking reflections of interest. Traditional CDP processing has some difficulties associated with it in separating out the interfering events, as well as in imaging steeply dipping events. By employing a series of closely spaced shotpoints in an array, quasi-planar waves emanating at different angles may be simulated through slant stacking. Slant stacking is preferably done in the common receiver domain where statics and trace signal variations are less of a problem since near-surface velocity variations are less of a problem. After slant stacking to illuminate interfaces of various dips, the major reflecting events may be picked automatically and the data quantity reduced to the time, slowness and amplitude of the picked events. These picked events can then be migrated onto a depth section image where the interfering waves have been separated from one another and steeply dipping events are imaged. We apply the method to seismic data from the Urals near the SG4 deep borehole and compare the results with CDP processing of the same data. Results show that the common excitation array method matches the geological interpretations in the area better and that it images steeply dipping reflectors better.