Patent ID: 8511886

Claim:
An apparatus ( 1 ) for mixing an additive for drilling fluid used in drilling a petroleum well, said apparatus ( 1 ) comprising: a mixing tank ( 17 ), to which there is connected an inlet line ( 19 ) arranged to supply a drilling fluid which has been circulated out of the petroleum well to the mixing tank ( 17 ); a mixing chamber ( 3 ), to which there is connected an inlet line ( 5 ) arranged to receive the drilling fluid from the mixing tank ( 17 ) and an outlet line ( 7 ) arranged to return the drilling fluid to the mixing tank ( 17 ); at least one dosing device ( 9 , 9 ′) for an additive, the dosing device ( 9 , 9 ′) being a valve arranged for switching between a supplying position in which the additive is supplied from at least one container ( 11 , 11 ′) to the mixing chamber ( 3 ) and a non-supplying position in which the valve forms a pressure-tight barrier between the mixing chamber ( 3 ) and the at least one container ( 11 , 11 ′); means for regulating a flow of the drilling fluid into the mixing chamber ( 3 ), the regulating means being arranged at the inlet or upstream of the mixing chamber ( 3 ); and a volumetric pumping device ( 13 ), the volumetric pumping device ( 13 ) being arranged to create an underpressure in the mixing chamber ( 3 ) sufficient to suck the drilling fluid from the mixing tank ( 17 ) and also the additive from the at least one container ( 11 , 11 ′) into and through the mixing chamber ( 3 ) when the at least one dosing device ( 9 , 9 ′) is in the supplying position.