It is claimed that there may be an extra half-trillion barrels of oil than was formerly reckoned, but even if there is, does it really matter? Dr Marcio Mello presented an analysis at the Denver ASPO conference that there may be 500 billion (half-trillion) barrels worth of oil in the sub-salt basins on the margins of the South Atlantic Ocean. The discovery of "diamondoid" structures in oil found at shallow depths in Brazil suggests that a mixing occurs of two types of petroleum, one of which had formed at great depths, below the salt layer that blankets the basin.
I recall, in writing previously about the Tupi field in the Brazilian Santos Basin, that one of the problems attendant to extracting oil from there was the need to drill through the salt, which was over a mile thick, and hot enough that it had semi-plastic properties, which meant that there was a tendency for the hole to close should the bit be withdrawn for any reason. It is also necessary to drill in substantial depths of water and through rock layers too, that act as the "bread" in a salt sandwich, both of considerable thickness too.
The Tupi field is enclosed in a reservoir of limestone at depths of around 6 km, and beneath a salt layer of around 2 km in thickness. It would not normally be expected for oil to exist there as at such depths it would be too hot, but due to a geological effect of deep water and the high thermal conductivity of salt, the temperature is lower than it would otherwise be.
Dr Mello reckoned that overall there may be another 500 billion barrels of oil down there, although there are questions of EROEI and cost of a barrel of oil. Most likely these fields will eventually be developed but the cost of a barrel of oil so derived will be very high, and so this "find" is not the cheap oil the world needs to maintain its energy status quo, but is the stuff of specialist applications for a world which is by then sorely short of oil, given that it is not expected that the Santos Basin will yield significant oil before 2020.
"Half a trillion barrels more," By Euan Mearns. http://thepildrum.com/node/5867