Institute of Geophysics and Geomatics,China University of Geosciences (Wuhan),Wuhan　 430074,China

在煤矿的开采过程中,巷道突水事故严重地威胁着人民的生命和财产安全。核磁共振技术由于具有直接找水的特点,被我国一些专家学者提出将其应用于巷道的超前探水工作之中。但是,由于巷道核磁共振超前探测方法与传统的地面核磁共振方法(SNMR)相比,其施工环境和线圈装置都发生了巨大的变化,许多方法技术、理论,包括探测的距离都需要重新作一定的分析。根据核磁共振超前探测方法的特点,分析讨论了地磁场强度、地磁倾角、地层电阻率、巷道方向、线圈参数等自然和人为控制因素对超前探测距离的影响。研究结果表明,探测距离会因地理位置不同而出现较大的变化。电阻率值虽然对超前探测的距离有较大的影响,但主要集中在电阻率极低区域,当电阻率值大于100Ω·m时,地层电阻率的变化对探测距离的影响并不明显。巷道的朝向不同虽然会影响核磁共振激发场的垂直磁场分布形态,但是由于大脉冲矩时较远区域的一维核函数值相差不大,所以不同的巷道方向对于探测距离的影响并不大。最后,通过引入线圈的有效面积概念,把线圈大小和匝数对探测距离的影响简化为有效面积对探测距离的影响。只要保持激发和接收线圈的有效面积相等,超前探测距离就不会发生改变。

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.

PAN Jianwei,HUANG Xueming,HONG Tao,et al. Analyzing the influencing factors of exploration distance of NMR advanced detection [J]. Journal of China Coal Society,2018,43(2):507-518.