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自旋回波作为测量T2时间的重要脉冲序列,由该脉冲系列交变磁场激发而获得的核磁共振信号不受磁场不均匀性的影响,这对于以地磁场作为稳定磁场的SNMR方法来说,可以减小地磁场不均匀对NMR信号的影响,得到真实、可信的T2值,提高信噪比。将自旋回波信号应用到地面核磁共振找水方法中求取T2分布,在国内尚属首例,本文借鉴核磁共振测井中的多指数反演方法,采用奇异值分解算法编程,反演得到T2分布,并与SNMR反演软件的结果 T2*对比。结果证明,用SE信号提取T2时间,可以减少地磁场不均匀对NMR信号的影响,更真实地反映T2分布,提高信噪比。
As an important pulse sequence for measuring T2 time, spin echo is not influenced by magnetic field inhomogeneity by the magnetic field excited by the pulsed alternating magnetic field. For SNMR method, which uses the geomagnetic field as a stable magnetic field, Reducing the effect of inhomogeneous geomagnetic field on the NMR signal, obtaining a true and credible T2 value and improving the signal-to-noise ratio. It is the first case in China that the spin echo signal is applied to find the T2 distribution in the terrestrial NMR. This article uses the multi-exponential inversion method in NMR logging and the singular value decomposition T2 distribution and compared with the T2 * results of the SNMR inversion software. The results show that using SE signal to extract T2 time can reduce the effect of inhomogeneous magnetic field on NMR signal, reflect T2 distribution more faithfully and improve signal to noise ratio.