Applications of the frequency analysis, using the spectral decomposition in the reservoir characterization

Abstract

The current research focused on characterizing sub seismic reservoirs in the Nile Delta and applies the spectral decomposition technique to delineate the direct hydrocarbon indicators (DHI’s) from the low-frequency shadow (LFS) anomalies and can use the spectral decomposition as a direct hydrocarbon indicator in El Mansoura area, Onshore Nile Delta, hence, it can provide a supplementary technique alongside the more widely used amplitude and amplitude versus offset (AVO) anomalies. The study has been applied for certain selected wells, focusing on analyzing the differently constructed frequency cubes and monitoring the responses of high and LFS anomalies, using the different algorithms of the spectral decomposition technique. The full stack 3D seismic data were imported and decomposed, using the continuous wavelet transform method and separated into several frequency cubes, ranging from 10 to 45 Hz, every 5 Hz interval. The time window used for checking the LFS, in the seismic sections is usually about 200 ms below the pay zone. The results show that, the low-frequency anomalies can be used in a sand/shale sequence very well, and in particular, can de-risk the prediction for a thick gas-bearing reservoir, when used in conjunction with the other DHI’s such as the AVO. The low-frequency anomaly can be generated by a thick limestone/shale sequence, particularly by the multiple layers of limestone.