Brazilian state-run energy giant Petrobras expects to bring up to four more drilling rigs to a prospect in the offshore Santos basin in the second half of the year.

The ultra-deep-water rigs will be used to "attack" areas in the pre-salt region in the Santos basin, Petrobras executive Mario Carminatti said.

The rigs will be used to complete studies of the Tupi, as well as other pre-salt drill targets, Carminatti said.

Carminatti's comments followed the announcement earlier Friday that Petrobras had reached a deal with ExxonMobil and Norwegian driller Seadrill to take over control of Seadrill's West Polaris rig, a Dow Jones Newswire report said.

The West Polaris was drilling for ExxonMobil in the BM-S-22 Block, site of the Azulao and Guarani prospects.

Similar deals could be reached with other foreign oil companies with drilling rigs operating offshore Brazil, Carminatti said.

The idea is to use downtime between contracts to squeeze in some drilling.

This has already been done with Repsol, Anadarko and now with ExxonMobil, Carminatti said.