This summer is set to reveal a few clues as to the viability of pre-salt hydrocarbons plays off the coast of southwest Africa and offshore Kazakhstan as a handful of oil and gas explorers pursue targets deep below ancient salt layers.
So far the world's best-known pre-salt play has been Brazil's Santos Basin, where Petrobras is aiming to achieve production in excess of a million barrels per day by 2017.
The term 'pre-salt' comes from the aggregation of rocks that is located offshore in a large portion of the Brazilian coastline, including the Santos Basin. This aggregation forms a rock interval that ranges under an extensive layer of salt that, in certain areas of the coast, can be as much as 6,500 feet thick. And the total depth of these rocks – the distance between the surface of the sea and the oil reservoirs that lie beneath the salt layer – can be as deep as 23,000 feet.
Petrobras has been exploring the Santos Basin for some time now, having sunk 11 wells into the area between 2006 and 2011.
Initial results suggest very large volumes of hydrocarbons, which include high-quality, high-value oil. For example, Tupi – one of the accumulations located in the Santos Basin – has recoverable volumes estimated at between 5 and 8 billion barrels of oil equivalent. Meanwhile, oil has already been found in the pre-salt layer of the Santos Basin that has a specific gravity as high as 28.5 degrees API, with low acidity and low sulfur content.
Of course, the downside for companies exploring in pre-salt zones is that drilling through all that rock and salt is very costly – along with the risk that commercial hydrocarbons might not be found.
But exploration continues in the Santos Basin pre-salt, with Petrobras completing the drilling in April of an extension well at the Iara Evaluation Area of the Basin and coming up with good-quality oil ranging from between 21 and 26-degrees API from samples taken at 17,815 feet.
The well, dubbed Iara Oeste, is located some 139 miles off the coast of Rio de Janeiro state and some six miles from the Iara discovery well.
The Brazilian oil firm also reported in April that its Dolomita Sul well, located 110 miles off Rio de Janeiro, had found a new oil accumulation of good quality oil to the north of the Lula field.
But offshore Brazil is not the only part of the world where oil companies are investigating the hydrocarbon potential of pre-salt layers at this moment.
On the other side of the Atlantic, independent explorer Chariot Oil & Gas is targeting a part of the West African salt basin known as the Namibe Basin, which is off the coast of Namibia.
And there is some reason to believe that Chariot – and its partners – could achieve similar success to that experienced by Petrobras and others in the Santos Basin. Prior to the Atlantic Ocean opening up (more than 100 million years ago) the Namibe Basin lay adjacent to the Santos Basin, which suggests that they share the same geology.
Chariot has interests in a number of licenses offshore Namibia. In most of these the firm has a 100-percent or 90-percent holding, although one – Block 2714A – has seen both Petrobras (30%) and BP (45%) acquire significant equity.
Unfortunately for the firm, this week saw the first drill in its Namibian pre-salt campaign – Tapir South – come up dry.
On Monday, May 14, Chariot announced it was plugging and abandoning the well, which it rated as having a 25-percent chance of success. After reaching a total depth of 16,005 feet (4,879 meters), the targeted reservoirs were found to contain no commercial hydrocarbons.
However, Chariot will use information garnered from the drill in order to calibrate its data set for other prospects in the Namibe Basin, and turn its attention to the next drill that it is involved with.
"Whilst the results of the Tapir South well are disappointing, this is the first well of a longer term drilling campaign within a frontier region and only the second well ever to have been drilled in the Namibe basin," said Chariot CEO Paul Welch in a statement on Monday.
Next up is the drilling of the Kabeljou (2714/6-1) well on the Nimrod prospect on the 2714A block to the south. Operator BP plans to begin this drill during the third quarter of this year.
Pre-salt exploration is not confined to the South Atlantic Ocean, however. In Central Asia's Caspian Sea – the largest lake in the world – Max Petroleum has a pre-salt portfolio of 10 prospects and five leads offshore Kazakhstan that range in size from 100 to 600 million barrels of oil equivalent of estimated un-risked mean resources.
Currently, Max is still drilling its NUR-1 well on the Emba B pre-salt prospect in Block E. The well, which was spud last November, is being drilled to an intended total depth of 23,785 feet (7,250 meters) and is targeting Devonian and Carboniferous reservoirs that have an un-risked mean resource potential of 467 million barrels of oil equivalent. Max says it has a 29-percent chance of success.
Although originally expected to have been completed by the end of April the drilling of NUR-1 hit a snag in early April, when tools became stuck after the well had reached a depth of 18,760 feet (5,718 meters). This problem was resolved thanks to Max sidetracking the well around the stuck drilling tools and the firm now expects the well to reach its total depth in June.
So, the summer of 2012 is shaping up to be a key moment in the question of whether pre-salt plays have a future beyond Brazil's Santos Basin.
A former engineer, Jon is an award-winning editor who has covered the technology, engineering and energy sectors since the mid-1990s. Email Jon at email@example.com
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