Patent ID: 6570381
Filing Date: 2003-05-27
Classification: G01N,G01V

Abstract:
A method for obtaining nuclear magnetic resonance measurements from formations surrounding an earth borehole, comprising the steps of:providing a logging device that is moveable through the borehole and through formations in which a static magnetic field is present; producing, from said logging device, a series of cycles of pulse sequences in the formations, each of said pulse sequences including at least an RF excitation pulse and several RF refocusing pulses, the series of pulse sequences including at least one modified pulse sequence having at least one modified pulse; receiving, at said logging device, spin echoes from the formations to produce spin echo signals that may include spurious ringing signals from the excitation and refocusing pulses, wherein the modified pulse causes a shift of a spin echo polarity for the spin echoes associated with the modified pulse sequence relative to the polarity of spurious ringing signals from the excitation pulse associated with the modified pulse sequence; and combining spin echo signals from corresponding spin echoes of each of said cycles of pulse sequences to obtain combined spin echo signals in which spurious ringing from the excitation pulses and refocusing pulses of said pulse sequences is substantially canceled.