초록

A method for performing a downhole operation includes marking at least one location in a wellbore using a magnetized material. The magnetized material may generate a magnetic field stronger than a magnetic field generated in the wellbore by a surrounding formation.

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1. A method for performing a downhole operation, comprising: fixing a magnetized material at at least one location along a wellbore, the magnetized material generating a magnetic field stronger than a magnetic field generated in the wellbore by a surrounding formation, wherein the at least one locat

1. A method for performing a downhole operation, comprising: fixing a magnetized material at at least one location along a wellbore, the magnetized material generating a magnetic field stronger than a magnetic field generated in the wellbore by a surrounding formation, wherein the at least one location includes a plurality of locations, each of the locations having a magnetized material generating a magnetic field having at least one unique characteristic, wherein the at least one unique characteristic is varied to form a unique sensitivity for each of the plurality of locations along the wellbore. 2. The method of claim 1, wherein the formation includes at least one of: (i) a diamagnetic material, and (ii) paramagnetic material. 3. The method of claim 1, wherein the magnetized material is at least partially formed of a material having a magnetic susceptibility greater than the surrounding formation. 4. The method of claim 1, wherein the magnetized material is at least partially formed as nanoparticles, wherein the nanoparticles are superparamagnetic microspheres that incorporate nanometer-sized iron oxide crystals into micron-sized polymer particles. 5. The method of claim 1, further comprising: estimating a parameter relating to the magnetized material; andusing the estimated parameter to locate the magnetized material. 6. The method of claim 5, wherein the estimated parameter is a strength of the magnetic field. 7. The method of claim 1, wherein the magnetized material is positioned in one of: (i) a cement, (ii) a wellbore wall and (iii) inside the pore space in the rock formation in the immediate vicinity of the borehole wall. 8. The method of claim 1, wherein the magnetized material includes at least a spinel ferrite. 9. The method of claim 1, wherein the plurality of locations are depths along the wellbore, and further comprising identifying depths along the wellbore by detecting each unique sensitivity. 10. An apparatus for performing a downhole operation at a selected depth along a length of a wellbore, comprising: a magnetized material configured to be fixed along a wellbore, the magnetized material being further configured to generate a magnetic susceptibility greater than a magnetic susceptibility of a surrounding formation, the magnetized material marker being configured to generate a unique electromagnetic signal, wherein the at least one unique characteristic is variable to form a unique sensitivity for each of a plurality of depths along the wellbore; anda detector configured to detect the unique sensitivity and identify the selected depth along the wellbore. 11. The apparatus of claim 10, wherein the magnetic susceptibility is stronger than a magnetic susceptibility associated with one of: (i) a diamagnetic material, and (ii) a paramagnetic material. 12. The apparatus of claim 10, wherein the magnetized material is at least partially formed of a material having a magnetic susceptibility greater than the surrounding formation. 13. The apparatus of claim 10, wherein the magnetized material includes at least one nanoparticle, wherein the nanoparticles are superparamagnetic microspheres that incorporate nanometer-sized iron oxide crystals into micron-sized polymer particles. 14. The apparatus of claim 10, further comprising a substrate on which the at least one nanoparticle is disposed, and a coating securing the at least one nanoparticle to the substrate. 15. The apparatus of claim 10, wherein the magnetized material includes at least a spinel ferrite. 16. An apparatus for performing a downhole operation, comprising: a plurality of markers configured to be positioned along a wellbore, each marker of the plurality of markers being positioned at a different location along the wellbore, each marker being configured to generate a unique signal in response to a received signal, wherein the at least one unique characteristic is varied to form a unique sensitivity for each of the different locations along the wellbore, wherein the unique signal is an electromagnetic signal. 17. The apparatus of claim 16, wherein each marker resonates in response to the received signal. 18. The apparatus of claim 16, wherein at least one of the plurality of markers includes one of: (i) an RLC circuit, and (ii) a microwave resonant cavity device. 19. The apparatus of claim 16, wherein each location is a depth along the wellbore, and wherein each unique sensitivity identifies the associated depth along the wellbore.