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Tunisko - geologie (Geology of Tunisia)

Tunisko - geologie (Geology of Tunisia)
Tunisia´s phosphates, base metals and petroleum industry provide most of its foreign earnings. Phosphates alone accounted for nearly 45% of the countries export earnings. The minerals industry contribute around 3% to Tunisia´s GDP.

The countrys cement industry that produces approximately 5Mt per year has been privatised, with two of its largest companies being sold to European investors. The parastatal Société du Djebel Djerissa produced iron ore from the underground mine at Djerissa and from the open-pit operations at Tamera and Douaria.

As in neighbouring Algeria, the geology of Tunisia is dominated by a post-Paleozoic unconformity. The main source of its oil is a set of Silurian shales with most oilfields producing from Triassic reservoirs. It is believed that the onset of generation was delayed until well after the Hercynian orogeny. Traps are found in faulted anticlines.

Tunisia is the smallest of the North African countries. Its 164,150 sq km onshore area is wedged between Algeria and Libya. The northern region and a large part of the country's eastern frontiers are delineated by a Mediterranean coastline stretching about 1,300 km. Geographically, the country is divided into a northern region lying above the eastward extension of the Algerian range of Atlas Mountains, a middle section of low plateaux and plains sloping towards Tunisia's eastern coast, and a southern region adjacent to the Saharan areas of Libya and Algeria.

Onshore: The geological elements which are best developed in neighbouring Libya and Algeria enter into Tunisia and cross the country. The Triassic Province, a prolific petroleum region in Algeria, enters into the southern tip of Tunisia. The Cretaceous trend for oil onshore is best developed in Tunisia. It is also found on the Algerian side of the border (see 2003 survey of Algeria in Vol. 60).

Several oil and gas fields have been developed on the Tunisian side, with the main reservoirs in Triassic sandstones and subordinate reservoirs in Silurian clastics. Traps are found in faulted anticlines.

The Ghadames Basin straddling Algeria, Libya and Tunisia has become a very interesting prospect for companies investing on the Tunisian side. Of particular interest to Tunisia-based operators is the TAGI sands play. Big oil discoveries in TAGI sands on the Algerian side included fields in the prolific Berkine Basin, where large oil reserves have been proven. Agip in 1964 was the first foreign operator in Tunisia to find the TAGI horizon, having discovered and developed the billion-barrel field of El Borma in those sands (see Part 2).

The series of Berkine fields and Qoubba discovered in the more recent years has also led new E&P operators in Tunisia, like EuroGas of Canada, to identify many targets on their blocks. TAGI reservoirs typically produce oil at high rates from relatively shallow depths giving low development costs.

The Ghadames Basin extends from Algeria and runs across Tunisia into Libya. On the Tunisian side, this has been relatively unexplored. Several companies are now drilling exploration wells on the Tunisian side, to the east of Algeria's Berkine Basin where large oil reserves have been discovered.

Agip, active on the Algerian and Libyan sides of this basin, has also made some oil and gas discoveries on the Tunisian side in a Silurian formation called Acacus and a lower formation called Tannezuft. Agip is an oil producer in Tunisia, Libya and Algeria. On the Tunisian side of the Berkine Basin, Agip's Hammouda-1 wildcat was in 1998 tested at 3,508 b/d of 42[degrees] API oil, 1,400 b/d of condensate and 14.2 MCF/day of gas in the Tannezuft formation. In March 2001 Agip completed the drilling of Hammouda North-1 well at a depth of 3,507 metres. Two drillsteam tests were run in the Acacus sands and these flowed a combined 3,873 b/d of oil and 2.9 MCF/day of gas. Further finds have been made by Agip and other companies in the past two years and these now are producing (see Part 2).

To the north of the country, a series of oilfields associated with the southern margin of the Atlas Mountains is found in a north-east and south-west trending basin. Reservoirs are in Cretaceous carbonates, mostly dolomites sourced by Cretaceous shales, and traps are anticlinal closures.

In the Cap Bon region, in the north-east, an interesting oil discovery was made in 1998 by Ecumed. The weld flowed at 3,007 b/d of 52[degrees] API oil and about 0.57 MCF/day of gas from a formation called Bou Dabbous.

The Eocene has attracted the attention of foreign companies in recent years. This followed Marathon's discovery in June 1992 of gas and condensates in the Zarat block in the south. Located in 90 metres of water about 106 km north-east of Marathon's Ezzaouia oilfield, the first wildcat there flowed at around 17.5 MCF/day of gas and 1,498 b/d of condensates.

Geological map:http://www.circleoil.net/rasmarmour.htm

More on:http://www.entrepreneur.com/tradejournals/article/115217747.html

ZDROJ: www.entrepreneur.com, http://www.mbendi.com, kráceno

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