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.