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核磁共振找水是目前唯一能够直接探测地下水的地球物理方法,本文在weichman等人改进的核磁共振理论的基础上,应用经典的Chave算法对含有贝塞尔函数的积分核进行积分,求得了地下磁场和垂直激发场的空间分布。通过计算地下垂直激发场的椭圆极化率,验证了垂直激发场的椭圆极化效应,发现当地下电导率较大时椭圆极化效应将导致垂直激发场严重畸变;地下垂直激发场的正旋和逆旋分量显示了椭圆极化效应对核磁共振找水激发和接收上的不同影响,发射线圈和接收线圈间的延迟相位揭示了相位延迟效应的存在性及其相关性质。将以上理论应用到共圈模式下的核磁共振找水响应函数中,得到了地下氢核的扳倒角、地面核磁共振找水核函数和单一含水层模型的响应曲线,发现椭圆极化效应和相位延迟效应将导致核磁共振找水响应发生明显改变,因此对核磁共振找水理论和实际研究考虑椭圆极化效应是十分必要的。
Nuclear magnetic resonance to find water is the only geophysical method that can directly detect groundwater. Based on the improved NMR theory of weichman et al., This paper integrates the integral kernel containing Bessel function by the classical Chave algorithm and obtains the underground Spatial distribution of magnetic field and vertical excitation field. The elliptic polarization of the vertical excitation field is verified by calculating the elliptic polarization of the vertical excitation field. It is found that the elliptical polarization of the vertical excitation field will cause serious vertical excitation when the conductivity is low. And the anti-spin component show the different effects of elliptic polarization on the excitation and reception of NMR water. The phase delay between the transmitting coil and the receiving coil reveals the existence of the phase delay effect and its related properties. The above theory is applied to find the water response function of NMR in the common-lap mode, and the response curve of the underground hydrogen nucleus chamfering angle, the ground-based nuclear magnetic resonance finding water core function and the single aquifer model is obtained. It is found that the elliptic polarization effect Phase delay effect will lead to a significant change in NMR response to find the water, so looking for the NMR theory and practical research to consider the elliptic polarization effect is very necessary.