Patent ID: 8836335
Filing Date: 2014-09-16
Classification: G01V

Abstract:
1. An apparatus for estimating a property of an earth formation penetrated by a borehole, the apparatus comprising: a carrier configured to be conveyed through the borehole; a first switchable-magnet disposed at the carrier and configured to change a first magnetic field in the formation; a first energy storage device coupled to the first switchable magnet and configured to discharge stored first electrical energy to the first switchable-magnet; a second switchable-magnet disposed at the carrier and configured to change a second magnetic field in the formation in a direction different from the first magnetic field; a second energy storage device coupled to the second switchable-magnet and configured to discharge stored second electrical energy to the second switchable-magnet; at least one voltage source having a first polarity and a second polarity opposite of the first polarity; and an electrical circuit configured to charge the first energy storage device and the second energy storage device at the same time and to sequentially discharge the first energy storage device to the first switchable-magnet and the second energy storage device to the second switchable-magnet, the electrical circuit being further configured to charge the first and second energy storage devices to the first polarity using the at least one voltage source and then charge the first and second energy storage devices to the second polarity using the at least one voltage source after the first and second energy storage devices are discharged; wherein the change in the first magnetic field caused by the discharging of the first energy storage device and the change in the second magnetic field caused by the discharging of the second energy storage device induce currents in the formation that generate signals used to estimate the property.