导电性对地面核磁共振信号的影响研究

与其它勘探方法相比,核磁共振(NuclearMagneticResonance,缩写NMR)的方法是直接勘探地下水中NMR信号的唯一有效方法,该信号的初始振幅决定了含水层深度及自由水的含量。但在实际工作中,大地导电性对含水地层中的NMR信号有直接影响,使得同样脉冲矩条件下,勘探深度有变化。为了评价大地(岩石)导电性对勘探深度的影响,建立了一个地面找水模型,对NMR信号进行数值模拟。仿真结果表明,NMR信号的振幅可以评价含水地层的结构,但大地导电性的增强将导致勘探深度的降低。

INFLUENCE INVESTIGATION OF EARTH ELECTRICAL CONDUCTIVITY ON SURFACE NMR SIGNALS

The advantage of the surface nuclear magnetic resonance (NMR) method compared to other geophysical methods in the field of groundwater investigation is of the ability to measure NMR signal directly from the water molecules. The initial amplitude of the signal corresponds to the location and amount of free water in the aquifers. In the practical application, the earth electrical conductivity of the field may effect the NMR signal. In order to estimate the effect of the conductivity of the ground, a numerical simulation of the NMR signal is conducted. The result of simulation indicates that formation of the aquifers can be estimated by the amplitude of the NMR signal, and the NMR measurements are, however, also sensitive to earth electrical conductivity which causes the decrease of exploration depth.