Chinese Journal of Magnetic Resonance

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A Method for Correcting of the Effects of Stimulated Echo in NMR Logging

SONG Gong-pu1, FAN Wei1, ZHANG Jia-wei1, XUE Zhi-bo1, WU Lei2*   

  1. 1. Well-Tech R&D Institutes, China Oilfield Service Limited, Beijing 101149, China;
    2. School of Chemical Engineering and Environment, Beijing Institute of Technology, Beijing 100081, China
  • Received:2012-06-21 Revised:2012-07-23 Online:2013-03-05 Published:2013-03-05
  • Contact: Wu Lei,Tel: +86-18810329931,E-mail: wulei@bit.edu.cn. E-mail:wulei@bit.edu.cn
  • About author:宋公仆(1956-),男,山西人,硕士,测井技术首席工程师.目前主要从事核磁共振油气资源评价与仪器研制.

Abstract:

The CPMG sequence is the most widely used pulse sequence in NMR logging. However, the formation of stimulated echo will distort the first two echoes acquired with the CPMG sequence, affecting the signal-to-noise ratio (SNR) of logging tools and the outcome of reservoir evaluation. To improve the performance of NMR logging tools, a correction method for stimulated echo was proposed, based on theoretical studies on the how the stimulated echoes are formed and what are their effects on CPMG acquisition. Because the radio frequency (RF) field generated by a RF pulse might vary by the load, a relationship between stimulated echo correction coefficient and the RF field was established to calibrate the CPMG measurement made under different environment. With real logging data of low SNR, the correction method proposed  resulted a measurement error of 4.9%, which was a significant improvement from a 24.6% measurement error resulted from the traditional cast-out-the-first-two-echoes correction method. 

Key words: NMR logging, stimulated echo, CPMG sequence, radio frequency pulse

CLC Number: