Gabon is no stranger to oil exploration — the first surveys began in 1928, and the first well was drilled in 1934. Gabon since boasted several large fields, mostly onshore, and has an estimated 250,000 b/d of oil production and 3 Bbbl of reserves.

But its deepwater blocks are seriously underexplored, primarily because of a large and complex salt sheet that covers the Southern Basin (Zone Sud), which on current seismic data, masks the prospective geology below it. The few wells drilled in the deepwater areas of this basin so far targeted post-salt plays and were unsuccessful.

However, the Petrobras discoveries in the Santos and Campos basins offshore Brazil, which were quite close to offshore Gabon before the continents split, have given Gabonese officials hope for their deepwater blocks.

Very little exploration has taken place in Gabon’s deepwater blocks. (Map courtesy of CGGVeritas)



Earlier this year the Ministere des Mines, du Petrole, des Hydrocarbures announced a license round over these deepwater blocks. The Ministere, through the Direction Generale des Hydrocarbures (DGH), has hired CGGVeritas to undertake a series of surveys in the area to better assess the hydrocarbon potential and to have current data to offer during the licensing round, which will open in June 2010.

“It’s a complex area seismically,” said Jim Gulland, business development, EAME Data Library for CGGVeritas. “There’s a lot of existing seismic, but it all targets the post-salt potential. Because of the complexity in imaging beneath the salt, this existing data does not produce good pre-salt imaging, and this has hindered the exploration effort.”

So far the company has shot a test line in Zone Sud, which has created interest among potential clients.

In the Northern Basin (Zone Nord) CGGVeritas will shoot a new grid of about 1,340 miles (2,200 km) and will reprocess about 2,435 miles (4,000 km) of existing data.

In the Zone Sud, the company is taking a three-phase approach. First, it will complete a basin-wide study that will determine an estimate of depth to basement and a pre-salt sediment isopach to identify the major zones with pre-salt potential. The second element is a gravity gradiometry survey. “We believe it’s an essential element to accurately identify the salt in the deepwater area and to provide a clear picture of the pre-salt basins and basement geometry,” Gulland said.

Additionally, the company will shoot a new 2-D seismic program of about 4,500 miles (7,400 km). It also will access an existing 3-D survey acquired in the area by the previous operator to image the Tertiary play and reprocess it with a prestack depth migration (PSDM) to view the deeper structures.

Given that subsalt imaging is best accomplished with a high-resolution 3-D survey with PSDM processing, and is even better accomplished with a wide-azimuth 3-D survey, acquiring 2-D lines over the region might seem to be a low-tech substitute. “What we’re trying to do is speed up the exploration process,” Gulland said. “The acquisition of the 2-D surveys before the round will enable interested companies to advance their submitted work programs to the acquisition of 3-D surveys and well commitments.”

Added Steve Toothill, chief geologist for CGGVeritas in Europe, “To cover the entire area in 3-D data would be prohibitively expensive. The 2-D will be sufficient to delineate larger structures, and once the key sub-salt prospects are identified, targeted 3-D surveys can be acquired.”

For those used to huge signing bonuses in other African countries, Gulland said Gabon has “very friendly” production sharing contract (PSC) terms. “It’s a long-term oil province, and it’s a very stable environment to work in,” he said.

Despite jitters caused by the worldwide economic situation, there is much early interest from oil companies in the project. “We have good support from companies in these early stages of the project,” Gulland said. “The first phase study is complete, and the new 2-D acquisition will start in March. ”

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