OVT-Domain Azimuthal Traveltime-Constrained AVO Inversion Method

Azimuthal traveltime analysis provides comparatively stable fracture-orientation estimates but limited information on fracture-related elastic changes, whereas amplitude variation with offset (AVO) inversion is sensitive to residual azimuthal moveout. We propose a sequential offset vector tile (OVT)-domain azimuthal traveltime-constrained AVO inversion workflow for reservoir-scale fracture characterization. Traveltime responses are first used to estimate the locally dominant fracture orientation and reduce azimuth-dependent event misalignment. Prestack AVO inversion is then applied separately to representative fracture-parallel and fracture-perpendicular gathers to obtain two sets of apparent elastic parameters, from which a relative tangential-weakness attribute (Δe) and Poisson’s ratio ratio (Rν) are derived. Synthetic tests show that the mean fracture-orientation error is no greater than 1.1° for prescribed noise levels of 0–50%, and that varying the maximum incidence angle from 20° to 40° causes no systematic deterioration in the recovered attributes. In the field application, the predicted dominant orientation of N 45° E–N 60° E agrees with the approximately N 50° E fracture trend identified from an independent structure-tensor-based seismic interpretation near ZT3. Compared with the uncorrected results, the corrected Δe and Rν maps exhibit improved continuity and better spatial correspondence with the independently interpreted fracture pattern. These results demonstrate that the proposed workflow effectively integrates the stable directional constraint provided by azimuthal traveltime analysis with the fracture-related elastic information obtained from directional AVO inversion, enabling reservoir-scale characterization of the dominant fracture orientation, relative fracture-related weakness variation, and possible fluid sensitivity. Within the stated assumptions and applicability conditions, the method provides a practical seismic framework for fractured-reservoir characterization and evaluation.