* Bidding round for 269 blocks scheduled for Oct. 7
* Lower oil prices force Brazil to "adjust calculations"
* Country seeks to double output and exports by 2025
By Vladimir Soldatkin
LONDON, June 2 (Reuters) - Brazil said on Tuesday that lowercrude prices had presented a major challenge to its plans tosell dozens of oil and gas fields and that it had been forced to"adjust all calculations".
The Brazilian oil industry has been struggling with erraticproduction levels, tough regulation and a major corruptionscandal involving the state-run oil company Petrobras.
The bidding round, scheduled for Oct. 7, will offer 269blocks in 22 sectors of 10 sedimentary basins. But Brazilianauthorities, who aim to double national oil production andexports by 2025, acknowledged the auction may not go as smoothlyas they had envisaged a year ago.
"Companies are telling us that they are conservative becauseof the current level of oil prices ... From August to Februaryoil prices fell from $110 per barrel to $48. And this is thereal difference for all the petroleum industry," said MagdaChambriard, director of Brazil's state oil agency ANP.
"This is something that made us adjust all calculationsrelated to this bidding round that were ready in 2014," she toldreporters after the bidding round presentation in London.
She did not specify what the agency had been forced toadjust regarding the sale.
In 2013, the ANP held three auctions in a single year,including one for the massive "subsalt" prospect Franco that waswon by a Petrobras-led consortium with France's Total,Royal Dutch Shell and Chinese oil companies.
"Of course, doing a bidding round (now) you cannot expectthe same kind of results."
Giant untapped offshore oil deposits known as subsalt orpre-salt could play a major role if Brazil is to meet its targetof doubling oil production and exports in a decade.
Such deposits have not been included in the current biddinground. Chambriard said the "pre-salt" auction could be held nextyear or at the beginning of 2017.
These high-quality but technically challenging cruderesources get their name from a layer of mineral salts that trapoil thousands of metres beneath the seabed off Brazil's coast.
Announced in 2007, the discoveries are some of the world'slargest in decades. Estimates range from 30 billion to 100billion barrels of oil and gas, enough to supply all the world'sneeds for one to three years. (Editing by Pravin Char)