Unlocking East Nile Delta's Opportunities using Improved Seismic Acquisition and Advanced Imaging

Abstract The East Nile Delta, offshore Egypt, is a challenging area for seismic imaging due to the presence of substantial velocity heterogeneity created by the complex Messinian evaporites geometries and overlaying syn-depositional Plio-Pliestocene fault structures. The Atoll field located offshore in the East of Nile Delta basin, is very promising for hydrocarbon exploration and production, where multiple levels of reservoirs lie beneath the producing gas field. Existing towed streamer (TS) seismic data has been pushed to its technical limit but remains insufficient for adequate representation of the subsurface. A step change in imaging was required to unlock and de-risk this opportunity. Therefore, advanced acquisition, processing, and velocity modeling building techniques are employed to improve the resolution of the reservoirs by increasing the signal to noise, expanding the bandwidth, improve illumination, accurate amplitude versus offset (AVO), and robust velocity models. Ocean Bottom Node (OBN) acquisition followed by advanced processing in areas with similar subsurface challenges has shown that a step change in imaging can be achievable (Kommedal et al., 2013). Acquisition of the Atoll Ocean bottom node (OBN) survey was a first for the Nile Delta and the design allowed for a dense grid of shots with full azimuthal and long offset coverage. The OBN survey also enabled a robust pre-processing workflow and subsurface velocity model to be created. The model building workflow consisted of innovative techniques with Time lag full waveform inversion (FWI) being the primary tool. To address subsurface complexities, an elastic full waveform inversion (QFWI) and density inversion were introduced which allowed for the velocity model to be more accurately inverted up to 40Hz. Having an accurate velocity model has resulted in final migrated images showing improved resolution and a significant uplift over previous towed streamer volumes. Further improvement was achieved by utilizing the velocity to generate an FWI derived reflectivity (FDR) image. This was seen to provide additional uplift especially in areas where illumination challenges still exist resulting in improved resolution and amplitude without compromising signal-to-noise ratio. Criteria for the post migration sequence was to ensure true primary amplitudes were preserved and AVO matched well synthetics. Results from the OBN acquisition and imaging project have provided a significantly improved image over the Atoll field, suitable for forthcoming exploration and appraisal activities.