3-D Seismic Discontinuity for Faults and Stratigraphic Features: The Coherence Cube
Mike B. Bahorich and Steven I. Farmer
Seismic data are traditionally acquired and processed for the purpose of imaging seismic reflections. This paper describes a method of processing seismic data for the purpose of imaging seismic discontinuities including faults and stratigraphic features (U.S. and foreign patents pending, Bahorich and Farmer). One application of this non-traditional process results in a 3-D data volume, or "cube", of coherence coefficients, within which faults are revealed as numerically separated surfaces. This is the first known method of revealing fault surfaces within a 3-D volume for which no fault reflections have been recorded.
3-D seismic data are generally binned into a regular grid. By using relatively simple mathematics to calculate localized waveform similarity in both the in-line and cross-line directions, estimates of 3-dimensional seismic coherence are obtained. Small regions of seismic traces cut by a fault surface generally have a different seismic character than corresponding regions of neighboring traces. This results in a sharp discontinuity in local trace-to-trace coherence. Calculating coherence for each grid point along a time slice results in lineaments of low coherence along faults. When this process is repeated for a series of time slices, these Iineaments become fault surfaces.
Since coherence is calculated from non-interpreted seismic data, it can quickly provide the geoscientist with a non-biased view of regional faulting and stratigraphic features. Unlike time slices, faults are revealed equally well whether parallel or perpendicular to bedding. Coherence displays simultaneously image structural and stratigraphic features and can aid in recognizing the interrelationship between them.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California