Seismic prediction methods for evaluating in situ stress in tilted transversely isotropic and monoclinic media

The formation of tectonic fractures is primarily influenced by stress distribution during the tectonic period. Therefore, in situ stress plays a crucial role in predicting fracture development zones. It significantly impacts the effectiveness of fractures by determining the size, orientation, and distribution pattern of fractures, thereby affecting stimulation results. Existing seismic methods for in situ stress prediction utilize seismic data to estimate stress parameters and calculate the horizontal stress difference ratio or the orthorhombic horizontal stress difference ratio (DHSR). These methods are based on the horizontal transverse isotropy or the orthorhombic anisotropy medium models. However, shale formations are often subject to tectonic movements that can rotate the symmetry axis of a transversely isotropic medium, leading to the formation of a tilted transversely isotropic (TTI) medium or a monoclinic medium with an inclined symmetry plane. Based on the TTI and monoclinic medium assumptions, this paper proposes new formulas for calculating the DHSRs (tilted transverse isotropy DHSR and monoclinic DHSR). The formulas are further validated through sensitivity analyses. Finally, this study demonstrates the effectiveness of the in situ stress seismic prediction method, grounded in TTI, and monoclinic medium theory through model-based examples.