Fracture Spacing and Orientation Estimation from Spectral Analyses of Azimuth Stacks

Abstract

Discrete, vertically aligned fracture systems impart one or more notches in the spectral ratios of stacked reflected seismic traces. This apparent attenuation is due to the azimuth dependant scattering introduced by the fractures. The most prominent notch is located at the frequency where the P wavelength is about twice the fracture spacing. The frequency location of the notches can be used to determine the fracture spacings. Azimuth stacks with an orientation parallel to the fractures tend not show these spectral notches – allowing for another way to detect the fracture orientation. An analysis of the vertical component of the 3D, ocean bottom cable seismic survey data from the Emilio field, offshore Italy, shows a prominent set of fractures with a spacing of about 30 to 40 meters with orientations that agree with previous studies.