Patent ID: 6686737
Filing Date: 2004-02-03
Classification: G01R,G01V

Abstract:
A method for determining a parameter of interest of a volume of an earth formation surrounding a borehole with a logging tool conveyed in the borehole, the method comprising:(a) using a magnet assembly on the logging tool to produce a static magnetic field in said formation; (b) producing a radio frequency (RF) magnetic field in said volume of the formation with an antenna on the logging tool, said RF magnetic field having a direction substantially orthogonal to a direction of the static field, the RF field having a carrier frequency related to an intensity of the static field in said volume, said RF field modulated by a pulse sequence comprising an excitation pulse and a plurality of refocusing pulses; and (c) measuring with the logging tool spin echo signals induced by the RF field in the formation; wherein a phase of at least one of said plurality of refocusing pulses varies nonlinearly with frequency.