Extended Elastic Impedance and its Application in Prediction of Reservoir and Fluid Properties for Late Messinian Reservoir, Onshore Nile Delta Egypt

Abstract

The study area is situated within the eastern portion of the Nile Delta. As the Mediterranean Sea "dried up" during the Messinian extensive erosion process resulted in the formation of large canyons and valleys which cut into the underlying Qawasim and Sidi Salim Formations, but the number of such incised valleys may have been limited. The entrenched valleys became filled predominantly with sandstone as sea levels frequently rose and dropped in the late Miocene to early Pliocene. The marine influence on deposition during the late Messinian became strong toward the end of the Miocene when thick marine shale separated the sand bodies. Late Messinian reservoir within the study area exhibits a good quality reservoir for gas and condensate accumulation. The target reservoir section consists of structural and stratigraphic elements that control the gas presence and the GWC. Late Messinian reservoir has a lot of heterogeneity and ambiguity for the attributes and amplitude interpretation, so the DHI within the study area has pitfalls and uncertainty to determine the hydrocarbon prospects, which caused the drilling of several dry wells. For lithology and pore fluid prediction, several hypotheses and approaches had been proposed. Amplitude versus offset (AVO) modeling and analysis for the wells log and seismic angle gathers data results in non-unique output, whereas several AVO classes were found for the gas sand within the study area. The AVO analysis for gas sand of the late Messinian reservoir could be Class II and Class IIp, while the wet sand is Class I. Following the first discovery within the study area, Extended Elastic Impedance (EEI) inversion was carried out for the Late Messinian reservoir for better identification and delineation of the reservoir boundaries and to determine the pore fluid content. During this study, several iterations have been made to determine the most appropriate chi angles to illuminate the presence of both reservoir and borehole content. The EEI inversion results show a strong correlation between a certain chi angle and the presence of gas. Maps for the late Messinian reservoir have been produced to illuminate the gas sand presence, which matches the results of the drilled wells. The technique has been so successful, as there are unexplored EEI anomalies that have a gas signature within the fault downthrown area. These EEI anomalies had been tested with encouraging results of a gas-bearing sand reservoir, as the EEI anomaly had been predicted correctly. This paper discusses the methodology involved, the calibration, and the selection of the appropriate chi angles for the Late Messinian Reservoir within the study area.