Analyzing the influencing factors of exploration distance of NMR advanced detection

In coal mining,water inrush disaster is a kind of geological hazard which seriously threatens the lives of miners. Because of its selective sensitivity to water molecules,some researchers have proposed that the nuclear magnet- ic resonance (NMR) method should be used to detect the water in front of a tunnel-face. However,compared with the traditional surface nuclear magnetic resonance ( SNMR) method,the working environment and the loop configuration of NMR advanced detection are very different. It is necessary to reanalyze its exploration distance. According to the characteristics of NMR advanced detection method,the influencing factors such as geomagnetic field intensity,geomag- netic inclination,resistivity,loop configuration and tunnel azimuth which can affect the exploration distance had been analyzed. The results revealed that the exploration distance would be different when the geographical location is changed. Even the resistivity of the stratum also had a great influence on exploration distance,but it is mainly appeared in low resistivity range. When the resistivity value exceeded 100 Ω·m,the change of resistivity almost didn’ t affect the exploration distance. The simulation results revealed that although the difference of tunnel azimuth would cause the change of distribution of vertical magnetic field. However,because the 1D kernel values of far distance just had little difference. The influence caused by different tunnel azimuth is not significant. At last,by using the definition of effec- tive area,the influences come from the loop sizes and turns had been simplified into the influence of effective area. It had been found that when the effective areas of transmitter-loop and receiver-loop were remained the same,the explo- ration distance would not be changed.