Orientation Estimation for Multiple Large Fractures by Scattering Energy

Abstract

We have done the numerical modeling of seismic response to multiple sets of vertical large fractures by using finite-difference method (FD), which can easily handle media with monoclinic anisotropy. We consider three types of fracture distributions: a set of parallel fractures, two sets of orthogonal fractures and two sets of non-orthogonal fractures intersecting at 45 degrees. We address the seismic scattering response to large fractures by using a 3-layer model and a 5-layer model, where a fractured reservoir is in the middle layer of these two models. Seismic scattered energy is analyzed by the Scattering Index (SI) method to estimate the orientation of these multiple fractures. In both models, SI indicates the correct orientation of the two orthogonal fracture sets but is ambiguous for non-orthogonal fracture sets. Information about the fracture spacing and compliance can also be extracted from the azimuthal SI in some situations. More compliant fracture sets result in higher SI values while the relationship between fracture spacing and SI depends on the source wavelength. Variations in the SI energy can be caused by fracture spacing and compliance variations, and these relationships need further investigation.