Fabio PalmigianiAmericas correspondent at UpstreamFollow meOpinionChambriard to take reins at Petrobras after Prates fallsMagda Chambriard will become the sixth Petrobras chief executive in three yearsIn and out: Jean Paul Prates’ rocky 15 months as Petrobras chief executive came to an end this week when the Brazilian government announced that former regulator Magda Chambriard would be taking the top role, making her the sixth head of the state oil giant in just over three years.UPSTREAM/RYTIS DAUKANTAS