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.