Predicting Microcracks in Tight Sandstones Using Seismic Dispersion Attributes Derived From a New Frequency-Dependent AVO Inversion

Predicting microcracks is crucial for identifying tight sandstones with high permeability, which is essential for economic gas production. However, effective methods for directly detecting microcracks using prestack seismic data are currently lacking. Rock physics modeling and experiments suggest that microcracks can cause frequency-dependence of elastic properties and seismic responses, which are not fully utilized in existing seismic methods for microcrack prediction. This article addresses this gap by introducing an approach for identifying microcracks using seismic dispersion attributes derived from a new frequency-dependent amplitude variation with offset (AVO) inversion. A new AVO equation is derived, parameterized by a proposed microcrack indicator and relevant elastic properties, with its accuracy verified against exact solutions from the Zoeppritz equations. A frequency-dependent AVO inversion approach is then developed to compute the microcrack-related dispersion attribute from prestack seismic data. The effectiveness of the proposed dispersion attribute for robust microcrack prediction is validated using synthetic data. The results suggest that the proposed dispersion attribute increases with microcrack density and is unaffected by varying gas saturation. In real seismic data applications, high-value anomalies of the proposed dispersion attribute indicate tight sandstones with high permeability. Given the geological understanding that microcracks significantly enhance the permeability of tight sandstones, the reliability of the proposed dispersion attribute for detecting microcracks is further confirmed by this result. The presented method provides valuable information for the comprehensive characterization of prospective areas in tight sandstone gas reservoirs.