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.