Patent ID: 8087480

Claim:
A device for feeding a plurality of particles into a stream at a controlled rate, the device comprising: a conduit having a flow passage for feeding the particles into the stream, said conduit being in fluid communication between an injection vessel containing the particles and a drill string containing the stream; and a magnetic field generator arranged and controlled so as to induce a pulsed magnetic field in the flow passage so as to induce a pulsed flow of the particles through the flow passage; wherein the particles have a magnetic susceptibility and are abrasive particles; wherein the stream is a stream of drilling fluid flowing through the drill string extending into a borehole formed in an earth formation and the device is arranged to feed the particles into the stream of drilling fluid; and wherein the drill string is provided with a recirculation system for re-circulating abrasive particles in the borehole and the device is adapted to feed abrasive particles into the stream of drilling fluid at a rate corresponding to a rate at which abrasive particles bypass the recirculation system.