核磁共振T_2谱反演影响因素

FACTORS INFLUENCING SPECTRUM INVERSION FROM NMR DATA

为了进一步改进完善核磁共振T2谱反演算法,利用核磁共振正演模拟信号,研究回波间隔、原始回波采集数量、信噪比等因素对反演结果的影响,同时在不同信噪比下对最优化T2谱反演算法、奇异值分解反演算法进行比较分析。研究表明:采集弛豫信号时,回波间隔大小的设置与回波数量、组分大小相匹配,才能得到最佳的反演效果;信噪比越高反演效果越好,当信噪比大于25时反演谱与构造谱基本吻合;在反演不同信噪比理论回波数据时,最优化反演方法对信噪比要求不高,奇异值分解反演方法对信噪比要求高,而奇异值分解反演速度较快。

The T2 spectrum inversion from NMR data has been widely used in petroleum industry both in core analysis for petrophysical studies and in logging interpretation.In order to improve and consummate algorism of inversion,the authors used the NMR numerical simulation data to study the factors influencing T2 spectrum inversion from NMR data,such as the intervals and number of echos,and signal-to-noise ratios.The method of T2 spectrum inversion was compared with optimization algorithm and singular value decomposition（SVD） at different signal-to-noise ratios at the same time.The result shows that TE should match the number of echos and components to attain the best inverse effect when the NMR relaxation signal is collected.Higher signal-to-noise ratio can reach better effect,and when the signal-to-noise ratio is larger than 25,the inverted spectrum coincides with designed spectrum.The method of T2 spectrum inversion with optimization algorithm doesn＇t require high signa-to-noise ratio,and the method of SVD could clip inversion.