Subsalt seen as promising exploration frontier for Brazil
Dayse Abrantes
Peter Howard Wertheim
“From the first (1-RJS-617D) to the second (1-RJS-628A) well drilled in 2005 and 2006 involving deep drilling, ultra deepwater, and thick salt sections, yes, there was a significant evolution in the time of drilling and in the final well integrity, resulting in a much less expensive well, reducing the time and cost more than 200%,” said Nepomuceno.
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Campos is the most productive of Brazil’s offshore sedimentary basins. It is along Santos, Rio de Janeiro, and Espírito Santo states, in southeastern Brazil, extending over an area of about 600,000 sq km (2,300 sq mi). Graphic courtesy Marcio Mello, -president, High Resolution Technology
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Tests carried out by Petrobras through vertical well 1-RJS-628A drilled at 2,140 m (7,021 ft) water-depth in BM-S-11 block, a new exploratory frontier off Santos basin, confirmed last October the existence of a significant volume of 30° API light oil with the discovery of a highly productive reservoir beneath a 2,000-m (6,562-ft) thick salt base.
Petrobras is the operator of the BM-S-11 block, with 65% interest in partnership with BG (25%) and Petrogal (10%).
The 1-RJS-628A indicated a flow of 4,900 b/d of oil and 150,000 cu m/d (5.3 MMd) of natural gas (5/8 in. choke with stabilized pressure) and the gas oil ratio (GOR) around 180, said Nepomuceno.
Especially challenging, the drilling of the 1-RJS-628A well penetrated sandstone, shales, salt, and, eventually, lava flows in the subsalt. However, high pressure rather than high temperature was one main concern, said sources at Cenpes, Petrobras R&D center.
Geological information from the 1-RJS-628A well, only the second exploration well drilled in subsalt target in Santos basin, still is being evaluated. Large structures were mapped.
Although an appraisal well of this discovery is planned to be drilled early in 2007, some believe that Petrobras may have discovered a new giant field with a 90 m (295 ft) thick reservoir in a 450 sq km (174 sq mi) area.
“Now, the whole discovery area is under re-mapping and re-interpretation,” said Nepomuceno, who declined to detail the characteristics of the light oil and the natural gas Btu content produced in the well.
“Estimates concerning the future development of production (from 628) are premature. The next two wells will be drilled at 2,100 m (6,890 ft) water depth, seeking reservoir depth near 6,000 m (19,685 ft) after cutting through 2,000 m (6,562 ft) - thick salt layer,” he said.
Drilling in the adjacent BM-S-10 block also revealed good subsalt oil indications, confirmed Nepomuceno. Well 1-RJS-617D reached 7,628 m (25,026 ft) and its TVD will be 6,938 m (22,762 ft).
The region in the Santos basin is known as “cluster blocks” in the ultra deepwater (over 2,000 m [6,562 ft] water-depth) of the basin. It includes the exploration blocks BM-S-8, BM-S-9, BM-S-10, BM-S-11 (acquired during Bid Round 2 in 2000), BM-S-21, BM-S-22 and BM-S-24 (Bid Round 3 in 2001).
The “cluster blocks” total area of around 12,300 sq km (4,749 sq mi) is covered by high resolution, high quality 3D seismic. (Figure 1).
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The greater Campos basin is composed of a series of basins formed at the Brazilian southeastern margin during the breakup of Gondwana beginning in Early Cretaceous time. It is separated on the north from the Cumuruxatiba basin, and on the south from the Pelotas basin. Graphic courtesy Petrobras.
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Volume 67 Issue 1
January 2007
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