Patent ID: 6897651
Filing Date: 2005-05-24
Classification: G01N,G01V

Abstract:
1. A method of obtaining information about an earth formation comprising: (a) conveying a Nuclear Magnetic Resonance logging tool into a borehole in said earth formation; (b) obtaining a primary sequence of NMR echo signals sequence in response to a primary applied pulse sequence, said primary pulse sequence comprising an excitation pulse and a plurality of refocusing pulses; and (c) estimating a NMR signal resulting from an auxiliary sequence including, an excitation pulse followed by a refocusing pulse after a time delay, said time delay being sufficiently large so that a non-formation signal caused by the excitation pulse of said auxiliary pulses is substantially zero at the time of an echo resulting from the refocusing pulse and wherein the time delay is different from a time interval between the excitation pulse of the primary pulse sequence and a first one of the plurality of refocusing pulses of the primary pulse sequence; and (d) using said estimate of said non-NMR signal for correcting an echo in said NMR echo signals.