Determination of Crack Orientation in a Fractured Reservoir from Effective Medium Modelling and Multi-azimuth Inversion

We propose in this study to characterize a fractured reservoir using elastic impedances cubes by a 3D prestack multi-azimuth isotropic inversion workflow. The first part of this work deals with a theoretical approach. We use an effective medium modeling to build a geological synthetic model with cracks having a Horizontal Transverse Isotropy. On this model we compute direct synthetic impedances and reflectivity profiles as functions of incidence and azimuth angles. The direct impedances calculated for P-wave and slow and fast S-waves allow us to characterize the impact of fracturation on seismic response. In a second part we performed a multi-azimuth seismic inversion using synthetic reflectivity profiles convolved by a given wavelet. Finally we compare results obtained by inversion to results obtained with the direct synthetic model on which we know the fracture parameters. Seismic inversion applied by azimuth appears to be a powerful workflow to characterize seismic anisotropy due to fracturation in reservoirs. The encouraging results of this theoretical study lead us to apply the workflow on real field data.