The in situ stress prediction of a fractured shale reservoir based on amplitude variation with angle and azimuth inversion: A case study from Southwest China

Abstract

In-situ stress estimation of a shale reservoir is critical for the design of shale hydraulic fracturing and well-bore stability analysis. Fractured shales have orthogonal anisotropy (OA) because of the presence of vertical fractures and lamination. However, the existing in-situ stress estimation method mainly focuses on transversely isotropic media. To accommodate orthogonally anisotropic media, an in-situ stress estimation method is proposed by using amplitude variation with angle and azimuth (AVAZ) inversion and linear slip theory. First, an orthogonal anisotropic media is introduced to characterize the fractured shale by using a linear slip model, and then we formulate a reflection coefficient approximation for OA media to perform the seismic inversion. Next, a fracture weakness inversion strategy that incorporates the VTI background is proposed to obtain the stiffness matrix of the media. Finally, the in-situ stresses of the OA medium are formulated by using a stress-strain relationship. Inversion tests and a real data application show that the proposed method is effective.