A Design Scheme of Receiving System of Small-Diameter Nuclear Magnetic Resonance Logging Tool

Obtaining the information of shallow surface hydrogeological parameters is of great significance to the study of the groundwater cycle, the development and utilization of groundwater, and the protection of groundwater. Nuclear magnetic resonance (NMR) technology is the only method among all geophysical methods that can directly qualitatively and quantitatively measure groundwater content and evaluate aquifer reservoirs. The emergence of small-diameter NMR logging tools provides a powerful tool for the evaluation of shallow surface hydrogeological parameters. However, the low signal-to-noise ratio (SNR) of the NMR signal is still an important factor restricting the development of such instruments. In this article, we propose a design scheme for the receiving system of a small-diameter NMR logging tool. Its main design purpose is to improve the SNR of the receiving signal. The receiving system mainly includes an integrated differential coil, MOSFET-based duplexer, series LCR signal processing circuit, and ultralow noise lithium battery power. To verify the effect of the receiving system we designed, a sand sample moisture content test experiment has been conducted. The experimental results show that the NMR logging system can measure the water content accurately and reflect the distribution of porosity of the sample. The comparison with other small-diameter NMR logging systems shows that the receiving system we designed has a good receiving effect and is close to the level of commercial equipment. Finally, we expect such instruments to play an important role in the evaluation of pollution on the shallow surface.