A Novel Method for NMR Ringing Reduction under Downhole Condition
一种降低井下核磁共振振铃的新方法

In NMR logging,the noise amplitude of ringing is often high,impacting echo signals detection.The phase-alternate pulse sequence(PAPS) technique is a conventional method to reduce NMR ringing.However,the amplitude of ringing is frequency-dependent,and the PAPS technique is effective at certain frequency,leading to a lower vertical resolution.Taking advantage of the feature that the echo signals change with the variation of RF pulse wherase the ringing noise keeps constant,we proposed a novel method,combining PAPS and stacking-between-echoes,to reduce NMR ringing under downhole condition.The results showed that this method has improved efficiency.The echo train measured by the new method had the characters of high SNR and high vertical resolution compared to that measured by the PAPS technique,and the stacking between the echo trains was not limited to one frequency.