Seismic Characterization of Reservoirs with Multiple Fracture Sets Using Velocity and Attenuation Anisotropy Data

Abstract

The successful management of fractured reservoirs depends upon improved characterization of fractured systems which often provide pathways for fluid flow during production. Knowledge about spatial distribution of fracture density and azimuthal fracture orientation can greatly help in optimizing production from fractured reservoirs. Frequency dependent measurements of seismic anisotropy or seismic velocity and attenuation can potentially give important information about the fractures present in the reservoir. In this study, we use frequency dependent velocity and attenuation data to infer information about the multiple fracture sets present in the reservoir. We model a reservoir containing two sets of fractures oriented in different directions characterized by unknown azimuthal fracture orientations and fracture densities. The method is based on a viscoelastic T-matrix approach and a Bayesian method of inversion that provides information about uncertainties as well as the mean values. We then try to estimate the unknown azimuthal fracture orientations and fracture densities from velocity and attenuation data as a function of frequency and azimuth. Our synthetic example shows that velocity data alone cannot recover the unknown fracture parameters. It also shows how joint inversion of velocity and attenuation data greatly reduces the uncertainty in the unknown fracture parameters.