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.