The present invention relates generally to a nuclear magnetic resonance
apparatus and method for substantially eliminating the effects of phase
coherent acoustic ringing in borehole logging. A series of cycles of
measurement pulse sequences are applied to the formation surrounding the
borehole. Each pulse sequence includes an RF excitation pulse and several
RF refocusing pulses. Spin echoes are received that contain spurious
ringing signals from the excitation and refocusing pulses. Spin echo
signals from corresponding spin echoes of each cycle are combined and
substantially cancel the spurious ringing from the excitation and
refocusing pulses of the pulse sequences.