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Improved Mapping of Discontinuous Cretaceous Sandstone Reservoirs Using Reprocessed 3-D Seismic - Offshore Cote D’Ivoire, West Africa

Brzozowy, Carl P.1
1 Gustavson Associates, Boulder, CO.

The reprocessing of a 140 square kilometer 3D seismic survey over Gazelle Field improved the quality of the seismic data so that previously discovered thin and discontinuous sands could be mapped. The UMIC 3D seismic survey, which covers Gazelle Field, was reprocessed by Tricon Geophysics, Inc. This reprocessed version was interpreted using Seisvision software. The reprocessed 3D data yielded a new and clearer picture of sand body geometry over Gazelle Field. As a result, four of the discovered zones from the Gazelle-1 and IVCO-21 wells can now be mapped and their potentially productive areas can be calculated. Two additional potential sand reservoirs that were missed by the Gazelle-1 well can also be mapped adding additional resources to the field.

Oil and gas reservoirs were discovered on Block CI-202, offshore Cote d’Ivorie, by Exxon, Petroci and UMIC from the mid 1970s up through 2000. The discoveries known as Gazelle Field, IVCO-10, IVCO-22 and Hippo 1-X occur in Cretaceous Albian to Upper Senonian age reservoirs. The price of oil at the time of their discovery rendered these tested hydrocarbon accumulations uneconomic. C & L Natural Resources acquired Block CI-202 in 2006, and with the help of Gustavson Associates have reevaluated the hydrocarbon potential and economic viability of the block.

Approximately 525 square kilometers of 3D seismic data were acquired over Block CI-202 by UMIC (140 km2) in 1995 and Santa Fe Energy (385 km2) in 1998. These data sets were merged into a single volume and interpreted during 2007.

In the 2007 interpretation of the original 3D seismic data, it was ascertained that the twelve Albian through Senonian age zones that were tested over Gazelle Field were not seismically mappable due to their thin and discontinuous nature. Senonian age reservoirs encountered in the IVCO-22 & Hippo 1-X wells are thicker and more continuous than those in Gazelle Field. They were, therefore, seismically mappable prior to the reprocessing of the UMIC 3D survey. Two new prospects were generated during 2007 at IVCO-22 & Hippo 1-X wells and reserve calculations were possible.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009