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ABSTRACT: Discovery of the Ezzaouia and Robbana Accumulations, Gulf of Gabes, Tunisia

M. R. Rodgers, D. C. Beahm, M. A. Touati

Discovery of the Ezzaouia oil field on Zarzis peninsula in 1986 rejuvenated the interest in exploration in Tunisia. This oil anticline consists of two pay intervals: a karsted and fractured dolomite (Cenomanian Zebbag Formation) and a marginal marine clastic sequence (Kimeridgian M'rabtine Member of the Foum Tataouine Formation). The anticline formed as a result of a large-scale inversion of a Late Jurassic/Early Cretaceous half-graben. The limits of the present-day accumulations are believed to be related to the sealing capacity of lateral formations at faults.

The Robbana oil discovery, located 30 km to the northwest of the Ezzaouia field on Djerba Island, was discovered in 1988. This feature, also located on a northeast-trending inversion structure, tested oil from a series of thin, marginal marine sandstones within the Neocomian Meloussi Formation.

These discoveries have demonstrated the presence of two new productive reservoirs in Tunisia, the M'rabtine and the Meloussi, as well as confirmed the potential of the Zebbag Formation, which contains oil and gas in the offshore El Biban structure. Similarities between these discoveries include the following.

(1) Each of the fields is on an en echelon anticline which formed during an episode of Late Cretaceous wrench tectonics. The proximity to these major fault systems has improved the efficiency of hydrocarbon migration and reservoir permeability through fracturing.

(2) Each of the fields is located in an area that was a Jurassic/Early Cretaceous depocenter. This relative basinal setting improved the intraformational sealing capacity of these intervals.

These recent discoveries indicate that successful exploration is still possible in a moderately mature province such as Tunisia.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990