Rheological Model for a Vertically Fractured Source Rock

The elastic stress-strain relation of deep source rocks must account for the presence of fractures and lamination due to thermally mature kerogen layers. Clay lamination describes the variation in transverse isotropy with a vertical symmetry (VTI) characteristic of shale background, and vertical fractures induce the transverse isotropy with a horizontal symmetry (HTI) perturbations. Thus, the fractured shale rock can be described as a medium with an orthorhombic symmetry in terms of effective anisotropy. We present a new workflow for calculating the elastic constants of a pressure-dependent fractured shale rock and the effects of clay lamination and microfractures. We investigate the shale fabric that can result in the orthorhombic elastic symmetry and the effect of pressure on elastic parameters, and propose an inversion methodology. Results based on well-log data show that the proposed methodology can be effectively applied to field data.