Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
New Insights on the Upper Cretaceous Bireno-Douleb Carbonate Reservoirs Within the Gulf of Gabes-Tunisia- Pelagian Basin, North Africa: Facies, Depositional Models, Reservoir Characterization and Fairways
(1) Faculty of Sciences, Department of Geology, University of Tunis, Tunis, Tunisia.
(2) Atlas Petroleum EXploration Worldwide, Ltd, Tunis, Tunisia.
(3) Atlas Petroleum EXploration Worldwide, Ltd, Houston, TX.
The Turonian-Coniacian Bireno-Douleb carbonates are an attractive exploration target in the northern portion of the Gulf of Gabes, part of the prolific Pelagian Basin extending offshore Tunisia and Libya. They are the host for several producing and undeveloped oil fields in the region.
Several Facies associations have been interpreted on the basis of cored wells. They were deposited within a carbonate-evaporitic sedimentary system encompassing different depositional environments that migrated through time landward to the south-southwest and seaward to the north-northeast in response to the sea level fluctuations. These facies and their distribution indicate a distally steepening ramp model for the Turonian Bireno platform. Local steepening of the shelf due to the presence of syn-depositional faulting, most likely caused an outer deep-water re-deposited ramp facies. The tectonically dislocated and steepening Turonian Bireno ramp eventually drowned and deep marine shale-dominated sedimentation subsequently took place. The depositional model of the succeeding Coniacian Douleb Member corresponds to a rather homoclinal carbonate ramp with a basal sub-unit consisting of wackestones-packstones and an upper sub-unit represented by an oolitic grainstone barrier complex. Sequence analysis indicates that the numerous Turonian-Coniacian facies are stacked within three major retrogradational-progradational carbonate dominated cycles each of which is composed of retrogradational facies followed by aggradational-progradational regressive carbonate facies.
The Bireno-Douleb succession contains several proven and potential carbonate reservoir intervals encased mainly within the shallow marine aggrading/prograding deposits of the regressive hemi-cycles of cycles 2 and 3. The highest reservoir potential seems to occur within the carbonates deposited in the middle shelf environment particularly within the facies deposited in the high energy shoal setting for the Coniacian Douleb Member, and within the lagoonal facies for the Turonian Bireno Member. Associated near surface conditions, with episodic emersions, favored active diagenetic processes that affected the Turonian Coniacian Bireno-Douleb carbonates. In particular, near surface dissolution & dolomitization greatly enhanced the reservoir quality.
Fairways for the main Bireno-Douleb reservoirs were generated for exploration and development of these reservoir targets within the Sfax Offshore Exploration Permit.