We developed a numerical simulation algorithm to explore the nuclear magnetic resonance (NMR) response of the porous media based on the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence and the Bloch equation. The evolution of the magnetization vector of two representative pores at different pulse properties, including the excitation angle, the refocusing angle, the phase angle, as well as the pulse duration are simulate to understand the NMR relaxation signals. The result showed that the normalized magnetization is symmetrical with the excitation angle and positive with the T₂ spectrum's amplitude when the excitation angle is less than 90°. In additional, the refocusing angle has no clear influence on the NMR response. The phase angle of the excitation pulse is inversely correlated with the echo amplitude and can be neglected when the value is lower than 15°. The phase angle of the refocusing pulse causes the zig-zag phenomenon, but the response of the even echoes is not disturbed. Moreover, the influence of the pulse duration should not be neglected at higher values, particularly for the mesopore. The simulation results are helpful for the design and optimization of the pulse sequence, and the data manipulation of the measured signals.

我们开发了一种数值模拟算法，以基于Carr-Purcell-Meiboom-Gill（CPMG）脉冲序列和Bloch方程探索多孔介质的核磁共振（NMR）响应。模拟了两个代表性孔隙在不同脉冲特性（包括激发角，重聚焦角，相角以及脉冲持续时间）下的磁化矢量的演化过程，以了解NMR弛豫信号。结果表明，归一化磁化强度与激发角对称，对T ₂正磁化。激发角小于90°时光谱的振幅。另外，重聚焦角度对NMR响应没有明显的影响。激励脉冲的相位角与回波幅度成反比，并且当该值小于15°时可以忽略不计。重聚焦脉冲的相角会引起锯齿形现象，但是偶数回波的响应不会受到干扰。此外，在较高值时，尤其对于中孔，不应忽略脉冲持续时间的影响。仿真结果有助于脉冲序列的设计和优化，以及对被测信号的数据处理。