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

ABSTRACT 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 VTI brittleness index (EBIVTI). An approximate formula for c12 and a method to extract EBIVTI directly from seismic data were proposed. Initially, an approximate formula for EBIVTI was derived using petrophysical analysis. Its accuracy was verified with logging data. Subsequently, a Jacobian matrix that includes horizontal slowness was constructed based on the exact reflection coefficient equation. This supported EBIVTI extraction from prestack seismic data. Finally, the proposed inversion strategy was applied to synthetic well and field data from a shale reservoir. The results demonstrated that the method was accurate and robust against noise, suggesting its potential for brittleness evaluation in shale reservoirs.