Angola's deepwater golden Block 17

By Moses Aremu, Lagos, Nigeria

Tako Koning stood in front of a room filled with Canadian geologists in Calgary last June and pointed a finger at an east-west block squeezed between offshore Blocks 4 and 32 on the concession map of Angola.

"This Block 17," he said, "is informally described as the golden block of the Angolan deepwater province."

Koning, the development manager for Texaco's shallow water Block 2 off Angola, was giving an overview of Angola's oil industry activity to the Canadian Society of Petroleum Geologists.

By describing a competitor-operated lease (Block 17 is operated by TotalFinaElf) in such lofty terms, Koning was only confirming the over-arching importance of Block 17 in the annals of deepwater activity in Angola.

There are 17 licensed blocks in deepwater Angola, operated by Chevron, BP, ExxonMobil, Texaco, Agip, TotalFinaElf, BHP, and the state-owned company Sonangol. These operators have collectively discovered five billion bbl of oil since 1995, when the current phase of the deepwater foray took off. Sixty percent of these reserves, or 3 billion bbl, are estimated to be stored in the 11 fields that have so far been discovered in Block 17.

Today, only 70,000 b/d, or 9% of Angola's current oil production of about 800,000 b/d, are produced from deepwater. The rest is produced from the shelf, most of which is in a narrow producing fairway approximately 250 km long and 80 km wide, located in northern Angola and in the enclave of Cabinda. But as Angola increases its production from 800,000 b/d to 1.5 million b/d by 2005, it is the deepwater fields that will be feeding the increase. And, more than any other lease, Block 17 will become the main producing block.

Block 17's race to become the crown jewel of West African deepwater began with a false start in February 1995, when the drillship Pelerin Explorer plugged and abandoned Margarida-1 with oil and gas shows.

Things took a twist almost immediately. In April 1996, TotalFinaElf (TFE) discovered the famous Girassol Field on the block, with the semisubmersible rig Jim Cunningham. The field is 18 km long and 10 km wide, with a substructure of meandering sand complex with overlapping channels. The oil is stored in tertiary sands of the Congo Basin, distinct from the much older, Albian Age carbonates of the Pinda formation which currently make up most of the production in shallow water Angola.

Seismic profiles in the deepwater Lower Congo and Kwanza show that the structures in the mid to lower slope are dominantly created by compressional folding, with subordinate salt-withdrawal and diapirism. Oligocene and Miocene deepwater sands of the deepwater turbidite sands (Malembo Formation) currently are the main prospective intervals in the deepwater wells of the Lower Congo Basin (Congo Fan). This is where all the big discoveries have been made.

Block 17's first discovery well Girassol-1, located in 1,365 meters of water in Block 17, tested 2,800 b/d on a reduced choke. Drill stem test on Girassol 2A, the second well on the structure, flowed 18,000 b/d. Girassol 2B flowed 14,000 b/d. With these flow rates in such a large field, the industry was no longer in doubt that the field's recoverable reserves were in excess of 1 billion bbl. The field development plan, which is currently being implemented, indicates that production per well will range as high as 40,000 b/d.

As if on cue, other large finds came after Girassol—in 1997, Dalia and Rosa, located eight km SE and 19 km NW of Girassol respectively, were discovered. The Lirio discovery, located 32 km NW of Girassol, was announced in late 1998. Dalia 1 flowed 16,000 b/d. Dalia 2 flowed 6,000 b/d. Lirio-1 flowed 11,000 b/d. The discoveries of Tulipa, Orquidea, Cravo, Camelia, Jasmin, and Perpetua came between 1998 and 2000,even as TFE went ahead with appraisal of the three earliest discoveries Girassol, Dalia, and Rosa.

After a slow start, TFE has gotten a grip on its field development of Girassol. The company completed first development well on Girassol (GIR-101) in September 2000 with the drillship Pride Africa. "In early October 2000, the US$2.6 billion development program (except drilling) was 75% completed, with first production from Girassol expected for the third or fourth quarter of 2001 building to a peak of 200,000 b/d," according to TFE. The company expects the drillship Sedco Express to join in the field development in December 2000. The screening phase had led to the selection of a subsea completion system and FPSO barge. There will be 40 subsea wells, of which 23 will be producing, 14 water injection and three gas injection wells.

As the Girassol development is ongoing, TFE is working on defining the reservoirs in Dalia and Rosa. Five holes each have been made in these two fields, including sidetracks.

In the effort to get the first oil out in deepwater, TFE is racing against Chevron, whose Kuito, in Block 14, is the only deepwater oilfield in production in Angola. Chevron is currently developing other fields in Block 14, which has the economic advantage of being in far shallower water depths (400 meters) than Block 17 (1,350 meters). But there is no doubt that Block 17 will gain a lot of production rapidly. The high reservoir quality, as well as the size allows for building to a high plateau in a very short time.