JARVIS, IAN, AMINA MABROUK, RICHARD MOODY, and, SANDRA DE CABRERA, Kingston University, Kingston-upon-Thames, Surrey KT1 2EE, United Kingdom

Abstract: Correlation of the Abiod Chalk Formation (Campanian - Maastrichtian), Offshore and Onshore Tunisia: Geologic Development of a Major North African Petroleum Reservoir

Elemental and isotopic geochemical data, foraminiferal biostratigraphy and gamma profiles have been used to subdivide, date and correlate the Upper Cretaceous Abiod Chalk Formation (Campanian - Maastrichtian) in northern Tunisia. High-resolution (1-metre interval) elemental and isotopic geochemical data have been obtained for the Abiod Chalk reservoir in four offshore wells from the Miskar Gas Field, Gulf of Gabes, where the formation is <100 m thick. Results have been compared to data obtained from a well-exposed 500-m-thick onshore chalk section at Le Kef, NW Tunisia.A preliminary foraminiferal biostratigraphy has been developed for one well and the onshore section.

Vertical geochemical variation through the Abiod Formation provides a basis for high-resolution correlation between wells and with the onshore section. Results are consistent with our lower resolution biostratigraphic data. Some chemo-stratigraphic units may be recognised on gamma and other elogs. Our data indicate that high porosity zones in the Abiod correlate with intervals of purer chalk; primary sediment characteristics are a major influence on reservoir quality.

Large stratigraphic gaps and attenuated sequences can be demonstrated in the Miskar Field, providing evidence of several phases of movement on the bounding faults of the Miskar Horst. Oxygen, carbon and strontium isotope data indicate complex and variable burial diagenesis in the offshore area. Our multi-disciplinary study enables an improved understanding of  the depositional history and diagenesis of this important petroleum reservoir.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England