How to Rejuvenate Interest in Exploring An Old Production Area in Gabon

J. M. Fontaine, M. Jones, M. L. Ombagho, S. Raillard, and Tran Van Nhieu D.

The Mandji peninsula area is the oldest explored petroleum province in Gabon. The Clairette, Lopez North and South, N'Tchengue fields were discovered in the 50's in Senonian and Tertiary turbidites structured by salt domes. A total of 120 wells have led to a production of 12,5 MT (91 MMbls) oil. However, some gaps in the understanding of reservoir distribution and fluids regime appeared as production went on and could not be resolved with the available seismic data which was old (1974 to 1982) and irregular.

A new 3D seismic survey was shot in 1992 (245 km²) over an area fringed with shallow water and mangrove forests, covered with savannah liable to flooding, and including several populated areas. The acquisition setup was adjusted to every type of environment: Airgun in shallow water, explosive in uninhabited areas, and Vibroseis (TM) through the city of Port-Gentil. A carefully designed processing sequence led to consistently good quality throughout the survey, allowing a complete and detailed review of the area.

In addition to building a coherent reference model, multi-disciplinary studies have already unveiled new opportunities: complex structural and stratigraphic components in the old fields together with unexpected structural closures and stratigraphic leads are revealed by the 3D interpretation. They will constitute new targets for further exploring an area at late production stage, and may help build a model for the exploration of the turbidites in the Senonian basin.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California