Characterization of Fluid-Saturated Fractures Based on Seismic Azimuthal Anisotropy Dispersion Inversion Method
Yuedong Li, Zhiqi Guo, Cai Liu
Abstract
Prediction of fluid-saturated fractures is crucial for characterizing tight hydrocarbon reservoirs. Elastic amplitude variation versus azimuth (AVAz) methods are commonly employed for fracture prediction. Although frequency-dependent anisotropy has been explored using various experiments and numerical modeling, there is a lack of applicable methods for fracture prediction based on seismic anisotropy dispersion. To address this gap, we propose a frequency-scanning AVAz (FS-AVAz) method to predict fluid-saturated fractures by extracting anisotropy dispersion properties associated with fluid flow in fractured porous rocks from wide-azimuth seismic data. In this context, the presented FS-AVAz method offers a new perspective for fracture prediction that differs from elastic AVAz approaches. In the FS-AVAz method, the reflectivity equation formulated by azimuthal amplitude differences enables a robust estimation of the anisotropy dispersion inversion by eliminating the effect of the isotropic host rock. Meanwhile, as a critical inversion framework, the proposed frequency-scanning scheme ensures a reliable calculation of anisotropy dispersion attributes. Synthetic tests validate the capability of the FS-AVAz method in hydrocarbon-saturated fracture prediction. The effectiveness of the presented method for fracture prediction is further confirmed by field data applications using wide-azimuth seismic data. The predicted anisotropy dispersion attribute shows a good agreement with logging permeability and can serve as an indicator of fluid-saturated fractures. Meanwhile, incorporating the results of FS-AVAz and frequency-dependent amplitude variation versus offset can achieve a comprehensive characterization of fluids and fractures in tight rocks.