Amplitude variation with offset analysis for gas-prospect delineation: Pleistocene and Pliocene reservoirs of the Baltim Field, Nile Delta, Egypt

Unlocking the untapped gas potential of the Nile Delta requires moving beyond conventional seismic interpretation, which often struggles to distinguish between economic gas accumulations and non-commercial lithological variations. This study addresses this challenge by implementing a quantitative Amplitude Variation with Offset (AVO) workflow to delineate new gas prospects within the Pleistocene El Wastani and Pliocene Kafr El Sheikh formations of the offshore Baltim Field. The methodology integrates three-dimensional partial-stack seismic data (Near, Mid, and Far offsets) with petrophysical logs from six exploratory wells. A calibrated workflow was applied, utilizing super-gathers and trim statics, seismic-to-well calibration (correlation coefficient > 0.85), and the extraction of primary (intercept A , gradient B ) and secondary AVO attributes \((A × B\) , \(A-B\) , \(A+B\) ). Quantitative classification was achieved using AVO cross-plotting to isolate gas-bearing anomalies from the background lithology trend. Results reveal Class III AVO anomalies at the reservoir tops, characterized by a distinct "brightening" of amplitude with offset. The gas sands exhibit a strong positive AVO Product response and a negative Scaled Poisson’s Ratio, successfully mapping the 3D geometry of the reservoirs. Specifically, the analysis identified high-potential gas zones with negative shear reflectivity ( \(A-B\) ) anomalies, confirming a decrease in shear impedance. The novelty of this work lies in the successful application of a calibrated, attribute-driven AVO workflow to the often-overlooked shallow Pliocene section, challenging the traditional focus on deeper targets. By providing a quantitative " stoplight " mechanism for prospect ranking, this approach offers a transferable model for risk-mitigated exploration in similar deltaic environments, potentially reducing drilling risks and enhancing discovery rates in mature basins.