Patent ID: 7622916
Filing Date: 2009-11-24
Classification: G01N

Abstract:
1. A method for determining structural features of a borehole casing, comprising: using a first field generator to generate a first dynamic magnetic field; using a second field generator to generate a second dynamic magnetic field; configuring the first and the second dynamic field generators such that the first and the second dynamic field generators produce a dynamic magnetic test field, wherein the test field includes a magnetic field null point where the first and the second dynamic magnetic fields substantially cancel each other out; passing the first and the second dynamic field generators through the borehole casing; and sensing at least one of a change in location of the null point or a change in magnetic field strength at the null point resulting from a change in permeability of the casing; using at least one of the sensed change in the location of the null point or the change in the magnetic field strength at the null point to detect changes in the permeability of the casing; and using the changes in the permeability to determine the structural features of the casing.