초록

A device is provided 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, and pulsating means for inducing a pulsed flow of the particles through the flow passage.

대표청구항 ▼

1. 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 con

1. 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; anda 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; andwherein 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. 2. The device of claim 1, further comprising a control system adapted to control the pulsed magnetic field induced by the magnetic field generator in the flow passage. 3. The device of claim 2, wherein the control system is adapted to control at least one of the pulse duration and the pulse frequency of the pulsed magnetic field. 4. The device of claim 2, wherein the magnetic field generator comprises at least one electromagnet. 5. The device of claim 4, wherein a plurality of said electromagnets is provided including a first electromagnet and a second electromagnet, whereby the conduit is arranged between said first and second electromagnets. 6. The device of claim 4, wherein the control system comprises a current source arranged to supply an electric current to each electromagnet. 7. The device of claim 6, wherein the control system further comprises means for controlling the magnitude of said electric current. 8. The device of claim 1, wherein the injection vessel is provided with a level sensor for determining the level of particles in the injection vessel. 9. The device of claim 8, wherein the level sensor includes an electromagnetic coil having a self-inductance depending on the level of particles in the coil, and means for measuring said self-inductance of the coil. 10. The device of claim 1 wherein when the magnetic field is switched on, particles inside the conduit are captured and block the flow of particles from the injection vessel and when the magnetic field is switched off, the abrasive particles flow from the injection vessel. 11. A method of feeding a plurality of particles into a stream at a controlled rate, the method comprising: providing a conduit in fluid communication between an injection vessel containing the particles and a drill string containing the streamfeeding the particles into the stream via a flow passage of a conduit; andcontrolling a magnetic field generator to induce a pulsed flow of the particles through the flow passage, wherein the particles have a magnetic susceptibility and said pulsed flow is induced by inducing a pulsed magnetic field in the flow passage; 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; andwherein 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. 12. The method of claim 11, wherein the step of controlling the pulsed magnetic field comprises controlling at least one of the pulse duration and the pulse frequency of the pulsed magnetic field. 13. The method of claim 11 wherein when the magnetic field is switched on, particles inside the conduit are captured and block the flow of particles from the injection vessel and when the magnetic field is switched off, the abrasive particles flow from the injection vessel.