Minimizing the Exploration Risk by Using 3DVSP
By
T. M. Taha Ali1, Hoda Badir1, Fadel Awny1
(1) Gebel El Zeit Petroleum Company (PetroZeit), Cairo, Egypt
Most of the surface seismic
data acquired, especially at the pre-Miocene
horizons, from Ras El Ush offshore area, Southern Gulf of Suez, can be rated
poor. As a result,
seismic
mapping of the horizons below the Miocene salt is
difficult and unreliable. This is due to the masking of the
seismic
energy by
South Gharib Formation salt, generated multiples from Zeit Formation interbeds
and geologically and geometrically complex target reservoir horizons.
Two 3 Dimensional Walkaway Vertical
Seismic
Profiling Surveys (3DWVSP) have
been acquired, for the first time in Egypt and Middle East, from two of Ras El
Ush Field deviated wells (Ras El Ush#5 & #6). This is where the receivers were
emplaced below the Miocene salt. For the first time, the recorded
seismic
energy, especially of the pre-Miocene horizons, were not attenuated or masked.
The 3 DWVSP depth volume was merged and integrated with post stack depth
migration of the surface 3-D
seismic
data acquired in may 1997 from Ras El Ush
Offshore area. This provided a great chance, for the first time, to work with
real sub-salt data in 3D volumes. Also this enabled us to conduct serious and
valuable trials for interpreting and mapping precisely complex sub-salt
pre-Miocene horizons.
For aggressive petroleum exploration in remote areas (e.g. Deep seated
targets in the Gulf of Suez, Red Sea, Mediterranean sea...etc.), 3D VSP seismic
receivers, can be designed, to be spread, below the salt or above the
exploration target, in a highly deviated or horizontal single or multiwell
pattern. This is before or at the same time with the surface 3D
seismic
surveys.
The 3D VSP can be used (e.g. In Modeling) for designing better field parameters
for further 3D
seismic
acquisition, and if combined with surface 3D
seismic
,
seismic
coverage will be improved.