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Abstract The area under study is the West Al-Khilala Field, which is a Messinian (Late Miocene) gas field, located in the southern part of the Onshore Nile Delta, North West El Mansoura concession, Egypt. The main objective of this study is the delineation of the structural and stratigraphic features, and the formation evaluation of the Messinian Abu Madi reservoir. These are carried out through the classical interpretation of seismic data and conventional electrical logs, then applying seismic inversion techniques, to get much more information about the Messinian Abu Madi reservoir. Geologically, West Al Khilala Field is controlled by two major normal faults trending NW-SE, down throwing to the east. It shows an elongated four-way dip closure trending NW-SE, parallel to the main eastern bounding faults. The available data for this study is twenty 2-D post-stack seismic sections and wireline logs of four wells, which are not sufficient to perform a detailed study of the structural and stratigraphic features, as well as reservoir characterization analysis for West Al-Khilala Field. So, it is needed to resample the given 2-D seismic lines into a 3-D grid, this resampling process was carried out using Petrel 2017.1 software. The first interpretation step is the seismic to well tie, to define the formation tops and the interested horizons to be picked. The traced faults across the field are normal faults, with the trend of NW-SE and a down thrown side to the east. Then, applying several stratigraphic and structural seismic attributes on the resampled 3D volume and have several time slices on the attributes volumes, to track the trend of the Abu Madi gas-bearing Summary and Conclusions 145 sandstones channel across West Al-Khilala field, which is in the NW-SE, parallel to the normal faults trend. Then, time depth conversion is applied, using the velocity model as needed to have geologic interpretations at depth, relative to the elevation datum. To build an accurate velocity model, first, we calibrated the sonic logs with checkshots for each well in West Al Khilala Field, using spline calibration technique. This checkshot times are used, to correct the sonic log, that used as input to generate synthetic seismograms, instead of the original sonic log. The sonic and surface seismic data were measured at different frequencies, due to the dispersion effect. This process is based on the assumption that, the check shot times are representative of the correct velocity. By building the velocity model, it can be displayed and used to convert the produced maps from time to depth domains. Then, three types of seismic inversion techniques are carried out, these are: Colored, Model-Based and Sparse-Spike seismic inversions. The results are analyzed, to determine the gas-bearing sand zone of Abu Madi channel, that had high acoustic impedance, as appeared on the inversion results. The inversion algorithms used in this study was depending only on the post-stack seismic data, which helped in tracking the gas-bearing sandstone channel, depending on the low acoustic impedance values. The results of this study support the idea that, seismic inversion can enhance the interpretability of the given data and gives a feasible approach to obtain reservoir delineation, better than the conventional seismic interpretation. So, we can say that, post-stack seismic inversion successfully identified and delineated the gas sand reservoir in the study area. Summary and Conclusions 146 Then, the well log data recorded from four wells in West Al Khilala Field (West Al Khilala-2, West Al Khilala-4, West Al Khilala-5 and West Al Khilala-6) are analyzed. It can be used to track the change in thickness and petrophysical parameters, like, porosity, gas saturation and net-pay thickness variations of Abu Madi Formation, where these variations are due to the depositional environment conditions. from this study, we can follow the lateral variations of the petrophysical characteristics, added to the acoustic impedance values, that represented in iso-parametric maps. The petrophysical characteristics of Abu Madi Formation reflect the ability of these rocks to store and produce hydrocarbon fluids. The measured effective porosity ranges between 9.1 and 19.8%, the shale volume content ranges from 19.8 to 63.7% and the hydrocarbon saturation ranges between 9 and 30.2%, which reflect the characterization of the studied reservoir to be a gas charged reservoir. Recommendations For the future prospection, the following recommendations are made: Perform a 3-D interpretation of all the sandstone bodies, using the PreStack seismic inversion techniques. Execute AVO analysis to delineate the expected fluid types, using PreStack seismic cubes. Carry out a detailed study of the petrophysical parameters of the interested reservoirs, using core samples to adequately evaluate the reservoir intervals and to compare the reservoir parameters from logs with those derived from core data. Drilling another new wells at the high acoustic impedance zones depending on the acoustic impedance model |