PreSDM and PoSDM Imaging of Sub-Salt Structures in Southern Gulf of Suez, Egypt

By

 Ivar Mundal¹, Ibrahim Hanbal², Skip Lemanski³, Ben Turner⁴

(1) BP, Forus, Norway (2) GUPCO, New Maadi - Cairo, Egypt (3) BP Egypt, Digla, Maadi, Cairo, Egypt (4) PGS-Tensor, Cairo, Egypt

 Subsalt seismic imaging in the southern Gulf of Suez, Egypt, is hampered by destructive multiples and high frequency attenuation in the Miocene supra-salt Zeit Formation and by large lateral velocity contrasts associated with salt swells and diapirs. Pre-stack depth migration has been applied to alleviate the smearing of seismic energy in conventional stacks due to distortion of ray paths across the salt flanks. However, uncertainty in the exact location of these boundaries limits the ability of pre-stack depth migration to accurately position the low signal-to-noise seismic energy.

A regional 3D survey covering 570 square kilometers in the southern Gulf of Suez was recently acquired. The objective was to image the prolific B-Trend, a structural trend with several moderate sized mature oil fields and significant additional potential. The survey was acquired in the strike direction with respect to the salt swells and main structural trend. A post-stack depth migrated volume was generated for initial interpretation, and a pre-stack depth migrated volume was generated for comparison and evaluation.

There are significant differences in the seismic image in the pre-stack versus the post-stack depth migrated volumes. The pre-stack migration is the preferred dataset. However, well-control suggests the post-stack volume is able to image structure where the pre-stack image is overwhelmed by multiples. This is primarily attributed to the enhanced signal-to-noise of the post-stack volume in poorly illuminated areas, and suggests that, until a better solution for the multiple contamination problem is found, both datasets need to be integrated in the final interpretation.