Elf Aquitaine SA and partners have hit the exploratory jackpot on Block 17 off Angola.
The firms have made six major oil discoveries on the block since 1996. To date, 14 of the 15 wells drilled there have proved positive.
Following the discovery of Girassol in 1996, the block has yielded five other finds: Dalia, Rosa, Lirio, Tulipa, and Orchidea, all named after flowers. And three promising prospects remain to be explored.
Elf's current estimate of the reserves potential of Block 17 is 3.5 billion bbl. "This is three times the energy equivalent of Frigg in the North Sea or of Lacq in France," said Jean-Fran?ois Gavalda, head of Elf's African exploration and production division. These fields were Elf's largest until it made the Block 17 discoveries.
Elf's estimate of the Offshore Angola block's potential may be on the conservative side, however, as exploration will soon intensify in the western part of the block, where the main discoveries have been made.
The recent discovery of Tulipa, in the central part of the block, will lead to further exploration in this area, as well.
Upon the arrival of two new drilling rigs, exploration will begin on the Cravo, Jacinto, and Jasmim prospects in the deeper waters of the western portion of the block. These areas were not accessible with the rig Elf has been using, the Jim Cunningham.
Drilling on the Cravo, Jacinto, and Jasmim prospects will begin by yearend, says Elf. The Pride Africa drillship was built in South Korea and is on its way to Block 17; it is expected to arrive by the end of this month. The Sedco Express semisubmersible is being built in Brest, France, and is due for delivery in second quarter 2000.
Plans call for drilling 5-10 wells by mid-2000, so Elf does not expect to know the full extent of Block 17's reserves before yearend 2000.
Awarded to Elf Exploration Angola and partners in 1993, the 4,000 sq km block lies 200 km northwest of Luanda in 300-1,700 m of water. Angolan state oil firm Sonangol is the concession holder. Interests in the block are: Elf Exploration Angola, 35%; Esso Exploration Angola (Block 17) Ltd., 20%; BP Exploration Angola Ltd., 16.67%; Statoil AS, 13.33%; Norsk Hydro ASA, 10%; and Fina Exploration MB BV, 5%.
The scope of discoveries made so far on Block 17 has led to the idea of grouping them in at least three development centers, each capable of producing 200,000-250,000 b/d (see map).
The first center would be Girassol field, which has estimated reserves of 725 million bbl and an upside reserves potential of 1 billion bbl, according to Elf. Girassol is under development and is expected to come on stream in mid-2001 (OGJ July 20, 1998, p. 42).
The second production center would be Dalia field, which is at the pre-project stage. Its potential, including satellites, is 1.0-1.2 billion bbl, and production could start in late 2003. The third center, currently under study, would encompass the recent discoveries Rosa, Lirio, and Orquidea, as well as any subsequent finds in the area, which include the three remaining prospects. This area is thought to have a potential of 1 billion bbl.
Discovered in 1996 in 1,350 m of water, Girassol field will be the first Block 17 find to come on stream, barely 5 years after its discovery. The Girassol development schedule can be considered a technological feat, considering the size of the field, water depths, and the novel technology employed.
The project, which is 43% completed, is designed around a floating production, storage, and offloading vessel (FPSO), which Elf says is the largest built to date. The FPSO contract was awarded to Mar Profundo Girassol, a joint venture of Bouygues Offshore and ETPM. The main equipment (turbogenerators, turbocompressors, and water treatment facilities) are under construction and will be delivered within 6 months.
Topsides construction was transferred at the end of June 1999 from Fos-sur-Mer, France, to South Korea's Hyundai Offshore Industries. Sister firm Hyundai Heavy Industries Co. Ltd. had been awarded the contract for construction of the Girassol hull, which left dry dock in July.
Engineering of the umbilicals and flowlines that will link the 40 subsea wells to the surface installations is being completed; testing will take place on lakes in France. The umbilicals and flowlines contract was awarded to the Alto Mare Girassol JV of Bouygues Offshore, ETPM, and Stolt Comex Seaway.
Work on the innovative system of rigid towers and bundles will be done in Angola by local firm AMG. All flowlines will be assembled in Soyo, and the riser towers will be built in Lobito. Work will start early in 2000.
The production scheme calls for 277 subsea link-ups, to be made without divers or guide lines. A portion of the subsea production system equipment is being tested in shallow water off Bergen under a contract awarded to Norway's Kongsberg.
The linking of flowlines and manifold systems will be done via a new system designed by Stolt Comex Seaway. The scheme will involve 40 subsea wellheads, 13 manifolds, an associated control system, and about 500 valves.
Jean-Philippe Magnan, director of Block 17 activities for Elf, said, "This is a major technology breakthrough because it has never been done on such a scale on an oil field in 1,400 m of water. It has only been done with one or two subsea wells or on gas fields."
The main problem, he said, is that the water temperature at the seabed is 4-5° C.
The flowlines will therefore be insulated with a synthetic foam sleeve containing glass marbles; the sleeves will be manufactured by Balmoral Co.
Total costs over the life of Girassol field are expected to reach $6 billion.
Dalia
Work on Block 17's second production center, Dalia, is being managed by G?rard Rabier.
Discovered in 1997, Dalia holds 23° gravity crude oil, heavier than Girassol's 32° gravity crude. Rabier explained that Girassol is in the Oligo- cene, while Dalia is higher, in the Mio- cene.
"There is less earth to drill but more oil to go through," he said. But the nature of the oil is the main difference between the fields.
Thermal insulation of the flowlines will be necessary with Dalia as well, but the oil processing will be different. "Dalia's oil is less paraffinic than Girassol's and congeals less," said Rabier.
Four wells have already been drilled on Dalia. The next well to be drilled is Camelia, towards the eastern part of the area.
Studies are under way to select the most economic development scheme for Dalia and its satellites. The choice is between comprehensive or staged development.
Investments would be lower in the first case. A decision may be made as early as second half 2000, and production could begin by yearend 2003.
Several production systems are being considered for Dalia. These include: a large FPSO plus subsea wells; and a large FPSO plus a surface wellhead platform and a few subsea wells.
Rabier said that the problem is one of maintenance. The dry christmas tree concept provides greater accessibility to take measurements or to work over wells. The investment for the dry and wet tree designs is the same, he says, but the expected life span of the field will influence which scheme is chosen.
The concepts are being studied with the Swiss-Swedish group ABB, he said.
Rosa-Lirio
A third production center is looming on Block 17. It will likely involve four or five fields, including Rosa, Lirio, and the recently discovered Orquidea. The oil discovered to date in this area is 26-32° gravity.
"The 1 billion bbl potential has already been confirmed," said Rosa-Lirio project head Alain Gu?not. When reserves are known more definitively, by the end of 2001, a production concept will be chosen, probably early in 2002.
The usual technical difficulties involved in deepwater developments await Lirio. But there are some added problems, as some of the satellite fields are far from the planned production center. Lirio is 16 km from the Rosa fields, and Tulipe 1 is nearest Dalia and might be linked to it, instead.
Innovative technical solutions, such as subsea pumping and mudline technology, will be needed to optimize development.
Several development schemes are being examined, including an FPSO combined with subsea wells, and dry trees combined with a tension-leg platform, spar, or floating storage and offloading unit.
Elf estimates total development costs for Block 17 to be $8-12 billion, spread over 10 years. But despite the high cost, Gavalda is confident that the block's enormous reserves will make the projects profitable, even if oil prices fall to $9-10.
