The application of frequency-dependent AVO inversion in tight reservoirs area

摘要

Fluid-saturated rocks are generally expected to have frequency-dependent velocities, and it is attractive to try to use this property to discriminate different fluids with seismic data. When the reservoirs are saturated with different fluid types, the magnitude of dispersion is different. In this paper, the frequency-dependent AVO inversion method is combined with the technology of Smoothed Pseudo Wigner-Ville Distribution (SPWVD), which is used for spectral decomposition intended to get the excellent time-frequency localization. We use SPWVD for spectrally decomposing post-stack seismic data to find the frequency anomalies, pre-stack CMP gathers at the location of these frequency anomalies are extracted for frequency-dependent AVO inversion. Compared the identical frequency profiles of post-stack data with the result of inversion on pre-stack data, we can eliminate the high amplitude energy group caused by elastic interfaces and reserve the dispersion anomalies resulted from dispersive interfaces. The real seismic example from XN gas field of Sichuan basin, southwest of China, proved that this method is effective in discriminating gas and water in tight reservoirs.