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Shallow Nile Delta: Data Challenges and Possible Solutions

Garcea, Bruno 1; Carbonara, Stefano 1; Tornaghi, Milly 1; Sonika, Sonika *2; Abdelaty, Magdy 2; Doheim, Mohamed 2
(1) Edison, Cairo, Egypt. (2) WesternGeco, Schlumberger, Cairo, Egypt.

The Nile delta basin, offshore Egypt has been an important gas province with continued exploration and development. The exploration targets have now shifted to deeper horizons, in the pre Messinian, thus creating a need to acquire new seismic data with longer offsets and also to reprocess existing datasets with advanced processing techniques for uplift in deeper sections.

Shallow water towed streamer data in the Nile delta are usually contaminated by strong ambient noise and by surface multiples. Strong noise is usually the effect of nearby fishing activity and shipping. Surface multiples in shallow water are abundant and usually complex because of presence of short as well as long period multiples, of various orders at same locations and they show little velocity differentiation especially those generated in the shallow section. An additional challenge is due to the complexity of the shallow sub-seafloor, with shallow gas pockets creating sags and low amplitude anomalies in the section and reducing the continuity of deeper events.

In this paper, we present the combination of processes that were applied to address the various issues and provide a better subsurface image. Noise attenuation was applied in various domains followed by a suite of multiple attenuation techniques - deterministic water-layer demultiple (DWD), which is specially designed to target the shallow water layer multiple and leave the remaining multiple consistent with the SRME assumption, 3D General surface multiple prediction(GSMP) which is true azimuth 3DSRME and finally tau-p deconvolution. These processes were effective in removing the various orders of the surface multiples allowing better interpretation of the primary events. The effect of shallow gas anomalies was addressed by employing residual reflection statics and careful velocity analysis.

With all the processes applied, the reprocessed time migrated volume shows clear improvements from legacy processing, increasing confidence in interpretation and reduces velocity uncertainty. This provides an appropriate initial velocity model and gathers for tomography in depth imaging.


AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain