Modeling the effect of multiple sets of mesoscale fractures in porous rock on frequency-dependent anisotropy

Abstract

This study models the seismic response of porous rock containing two fracture sets with different orientations, sizes, and connectivities. Modeling demonstrates frequency-dependent anisotropy controlled by two characteristic frequencies that are defined by fluid mobility and the length scales of the fractures. Fracture-related dispersion and attenuation typically occur over a wider frequency band than is seen in the case of a single fracture set. When one set of fractures is modeled as being sealed, the azimuthal variation of velocity and attenuation can be different, with the azimuth of minimum attenuation coinciding with the strike direction of the open fracture set. The results should support attempts to differentiate between open and closed fractures on the basis of seismic measurements.