An anisotropic brittleness index characterization method based on exact reflection coefficient equation

Shale reservoirs often exhibit low porosity and low permeability. Accurate characterization of brittleness, particularly the anisotropic brittleness index, is essential for effective hydraulic fracturing. However, it is difficult to obtain the stiffness coefficient c12 from seismic data in transversely isotropic (VTI) media, which limits the direct extraction of the transversely isotropic brittleness index (EBIVTI). We propose an approximate formula for c12 and a method to extract EBIVTI directly from seismic data. Initially, we derive an approximate formula for EBIVTI using petrophysical analysis. Its accuracy is verified with logging data. Subsequently, we construct a Jacobian matrix that includes horizontal slowness, based on the exact reflection coefficient equation. This supports EBIVTI extraction from pre-stack seismic data. Finally, the proposed inversion strategy is applied to both a synthetic well and field data from a shale reservoir. The results demonstrate that the method is accurate and robust against noise, suggesting its potential for brittleness evaluation in shale reservoirs.