Optimization of Development Well Locations After a New Gas Discovery Using EEI Approach, Baltim South Field, Offshore Nile Delta, Egypt

Abstract Extended Elastic Impedance (EEI) approach was first introduced by Whitcombe (2002) as a method for lithology and fluid prediction, and a highly effective framework for relating the Amplitude Versus Offset (AVO) attributes to the different elastic and petro-physical parameters. The objective of this paper is to use the concept of extended elastic impedance inversion for deriving petro-physical parameters and reservoir facies distribution to settle the optimum development wells locations after the gas discovery. We adopted the methodology of this work to estimate reservoir petro-physical properties (Water Saturation Sw, Porosity Φ, and Clay Volume Vsh) through EEI approach. EEI workflow starts with computing the entire range of chi (χ) angle using measured density and sonic logs and defining the optimum value of chi (χ) angle for the target properties, which gives the maximum cross-correlation. This is followed by Extracting AVO intercept (A) and gradient (B) attributes from seismic angle stacks and calculating EEI reflectivity for the target properties using the pre-defined chi (χ) angle. Finally, EEI calculated reflectivity is inverted using broadband seismic inversion to obtain impedance volumes, which are rescaled to provide the quantitative estimation for our chosen properties. In 2016, an important gas discovery was announced after two wells encountered two gas sand reservoirs of Messinian age, characterized by stacked fluvio-deltaic sandstones with excellent petro-physical parameters. Using available well logs for EEI approach application, it was observed that the optimum projection χ angle for porosity shows a maximum correlation of 70% at χ = 12°, while water saturation gives a maximum correlation of 55% at χ = 25°, whereas clay volume exhibits maximum correlation of 76% at χ = 44°. These results were then used to create EEI reflectivity volumes for each corresponding petro-physical parameter, which were subsequently inverted and rescaled to the real values of the target properties. The final inverted results have proved a strong match between estimated and measured properties. Furthermore, development wells have been optimized relying on these results and have strongly exhibited an effective and accurate estimation of the reservoir properties. Moreover, inverted EEI volumes have impressively distinguished the extension of reservoirs and their connectivity. With these accurate estimated results, EEI approach proved to be a powerful tool for lithology and fluid discrimination and can be used for reservoir characterization which in turn adds a great value for exploration and development of gas fields and enhance volumetric calculations through well-established petro-physical models.