Superior Seismic Imaging in the Gulf of Suez - Aspects of VSP Design, Acquisition and Processing

By

 Dana Jurick¹, Avi Ghosh¹, Z Patval², H Merry³, L Walter³

(1) Ocean Energy, Houston, TX (2) Baker Atlas Geoscience, Houston, TX (3) Geospace Engineering Resources, Houston,

 Seismic imaging in the Gulf of Suez is well known to suffer from multiple-generating shale and anhydrite sequences and also complex salt geometries which can severely contaminate the seismic reflection signal. Recent experience from East Zeit well A-21 in the southern Gulf of Suez suggests that careful VSP modelling, acquisition with new multi-receiver arrays and subsequent processing with an emphasis on noise rejection is capable, in some cases, of delivering higher quality seismic images than previously observed, not only in VSP’s but also compared to surface seismic.

Modelling was performed to establish viable illumination geometries for zero-offset and multi-level walkaway VSPs acquired over this highly deviated well. The profiles were designed to image dipping reservoir units of Cretaceous age, important bounding faults and to improve confidence in ties to the existing depth-migrated 3D surface seismic. A twenty-four level 3-component geophone array was deployed with a standard airgun source.

While results from the zero-offset survey quickly produced a high quality image, the walkaway data presented significant noise challenges. Dip-based noise rejection was ultimately successful in enhancing the signal to noise ratio such that the reservoir and a critical bounding fault could be confidently identified and tied. These results demonstrate that primary seismic reflection energy may be effectively recovered from the target section in this area, despite significant noise, through careful planning, acquisition and processing.