Patent ID: 9482776
Filing Date: 2016-11-01
CPC Classification: E21B,G01V

Claim Text:
1. A method of investigating a subterranean formation comprising: (a) providing a tool string in a borehole that intersects the subterranean formation; (b) providing a first current at a first location in the tool string that has a frequency of up to about 50 kHz and that induces a magnetic field in the formation; (c) measuring a first induced voltage at a second location in the tool string that is induced by the magnetic field in the formation; (d) measuring a second induced voltage that is induced by the magnetic field in the formation and that is at a third location in the tool string which is spaced a distance from the first location that exceeds a distance from the first location to an end of the tool string proximate a bottom of the borehole; (e) interferometrically comparing the measured first induced voltage with the second induced voltage to define an interferometric comparison; and (f) identifying a bed boundary that is spaced away from a bottom of the borehole where a value of the interferometric comparison exceeds a threshold value.