Characterization of fault damage zones by using seismic coherence and different main frequencies

Abstract:

Estimating the width and geometry of complex fault damage zones in the subsurface is challenging. We applied forward modeling and associated seismic attributes of coherence (variance), to characterize four idealized damage-zones (isolated model, parallel model, inosculation model, favored model), and the frequency effect is evaluated on the width estimation. Main results indicate: (1) The general geometrical pattern of damage-zones could be identified by using main frequencies of 10 Hz, 25 Hz, and 40 Hz; (2) The estimated widths of damage-zones at a low frequency of 10 Hz are larger (up to two-fold) than those at frequencies of 25 Hz and 40 Hz; For large damage-zones (>400 m), the best frequency is 25 Hz; (3) Scattering noises and diffraction around the fault are found in data of high frequency of 40 Hz, which results in width overestimation of the damage-zones about 17%.

However, the internal structures are difficult to distinguish as seismic signals are mixed with scattering noises and chaotic reflection. More factors that may influence the accuracy of damage-zone width estimation by using seismic attributes of variance, including the bedding thickness, fracture density, and velocity. An in-depth understanding of this approach is useful in the application of seismic attributes to characterize fault damage-zones that significantly control the fluid migration in the subsurface.