Exploring Deepwater Presalt Plays by Reimaging the Offshore Nile Delta Basin, Egypt

Abstract The Nile Delta Basin has supplied Egypt with natural gas for several decades. The complexity of the Messinian evaporitic units has challenged legacy seismic data processing and imaging. Thirteen legacy 3D seismic surveys covering 35,000 km2 were reprocessed to improve pre-salt imaging and advance our understanding of the pre-Messinian hydrocarbon potential. This paper presents new insights from the recent basin-scale reimaging, aiding explorers in de-risking proven plays and defining new exploration opportunities. The input datasets were processed from the field data to minimize survey-by-survey variations from the commencement of the signal processing sequence to guarantee a seamless seismic response at the imaging phase. The data processing sequence, earth model building, and imaging strategy have been designed to address illumination and data quality challenges. The sequence includes variable-aperture demultiple for the different water depths, phase matching to equalize the wavelet between surveys, and a dedicated tomography and full-waveform-inversion sequence to improve the resolution down to the pre-Messinian level. Furthermore, we integrated available well data into our analysis to calibrate our updated earth model. This comprehensive workflow delivered a consistent earth model over a significant proportion of the Nile Delta basin's deepwater areas that correlate well with the drilled wells. The imaging of the top and base of the Messinian layer has substantially improved as demonstrated by the increased continuity of the seismic reflectors associated with clastic and anhydrite sequences within the Messinian layer. This will help guide well planning by providing enhanced seismic imaging over planned casing points across proposed well locations. The improved resolution of the post-salt faults supports evaluations of potential linkages to Plio-Pleistocene gas pockets, enabling enhanced geohazard assessments. The definitions of the pre-Messinian structures have improved, and new deeper pre-Tertiary structures have been identified. This work presents Phase 2, which builds upon the foundation in Phase 1, covering 12 surveys over 12,000 km². Phase 2 extends the workflow with 13 additional surveys spanning 35,000 km², incorporating advanced processing techniques to further enhance imaging and interpretation by leveraging insights gained from the first phase. The improved event continuity in the pre-salt section aided us in seamlessly mapping key pre-Messinian horizons from shallow to deepwater areas. The seismic amplitude maps of the pre-Messinian horizons indicate the extension of potential sand fairways into the distal parts of the study area. Hence, this finding suggests the continuation of reservoir fairways into previously unresolved areas. Furthermore, we have utilized the recent depth image in evaluating the structural validity and risks of legacy drilled wells. This paper presents the findings of the recent basin-scale depth image over an extensive area of the prolific Nile Delta basin. The consistent earth model has enabled increased confidence in mapping structural and stratigraphic features that straddled the borders of the legacy surveys. The improved imaging of deeper pre-Messinian horizons provides upside exploration potential. These encouraging results support explorers in delineating new perspectives in the study area.