The Ras Marmour permit is located in an area with two significant hydrocarbon discoveries and a number of smaller ones. The onshore Ezzaouia oil and gas field discovered by Marathon in 1986, initially produced at over 30,000 BOPD, and by the end of 2005, the field is believed to have produced around 29 MMBO. The offshore El Biban oil and gas field, also discovered by Marathon in 1982, produced up to 5 000 BOPD. Reserves were estimated at 7.97 MMBO and have produced since 1998 more than 2.9 MMBO. Discoveries on the Isle of Djerba include the Robbana field, which was discovered by Marathon and Mazran field, discovered by HBS, which is understood to be under evaluation.
The main reservoir types include fractured dolomites of the Cenomanian Zebbag formation, which form the main reservoir of the Ezzaouia field and fractured limestones of the Bireno formation of Early to Middle Turonian age, which form the main reservoir of the El Biban field. In addition the Upper Jurassic sands levels of the M'Rabtine formation are productive in the Ezzaouia field.
The source rocks in the area are platey black shales of the Lower Cretaceous (Cenomanian-Albian) which has proved the source rock of the Upper and Middle Cretaceous reservoirs of El Biban and Ezzaouia fields respectively and Lower Cretaceous age Sidi Kralif shales formation which form the source of both Robbana and Mazran fields. In addition the Marls and the black clayey limestones of the Middle Jurassic (Dogger) which source the Upper Jurassic sandstone reservoirs (M’rabtine Formation) are productive in the Ezzaouia and El Biban fields.
Exploration
In the Ras Marmour permit Circle, in partnership with Exxoil Tunisie, drilled the Zita-1 and sidetrack exploration well in 2007-8. The success or failure of any individual prospect in this permit is partially linked to maintaining drilling control over good porosity and permeability in dolomitic limestone which inherently is a problem for drilling losses.
In Zita-1 both logs and drilling resulted in good oil returns to the surface but under test drilling problems and large formational mud losses caused severe problems. The well has been suspended with a view to re-entry at a later date.
Additional 2D seismic was acquired over the onshore part of the Block during 2009 and the results incorporated into the data base to de-risk closure assessment for future drilling. The additional 2D seismic included acquisition over the Ile de Djerba and has firmed up a drilling location for later in 2011 on the Sedouikch prospect.