第 9 卷增刊 2000 年9 月( 37.-43)CT理论与应用研究 CTTheor y andAppl i cationsV 01 .9, St甲 plement Sept ,2000 Surface Nuclear Magnetic Induction System and Its Application in HydrogeologicalInvestigationsPan Y uling“andJeanBERNARD) I)China Universi妙ofGeosciences,Wuhan,430074,China 2)IRIS inst ruments,Odeans,60074 5060,FranceNuclear Magnetic Resonance isthe onlynon-invasive methodwhich directly studies ground- water reservoirs f r om surface measurements.At present,in the world only such countries as Russia,France.Germany and ChinapossessNUMISsystem.Method Principle is:Hydrogen atoms ofwater are energized by pulse of alter n ative current at the proper f r equency(Larmor frequency),t r ansmitted into a loop laid on the ground-The magnetic field they produce in retur n is measured and analyzed for vaviours energizing pulse moment (intensit y Xdurations), The NUMISP “ systemallows the directdetectionof groundwater thgouthmeasurements of the relaxation magnetic f i eld pr o duced by Hydrogen protons f r om grou n dwater af t er they were energized by acurrentintoalooplaidonthegr ound. NUMISO components The systemconsists of two conver t er units powered by two 12 V bat t eries,two turning units for optimizing the excitation energy,a t r ansmitter-rereceiver unit for pulse generation andmeasurement,a wir e loopusedbothas a t r ansmittingand a receiving antenna and aPCcomputerfor thecont r ol of thewholesystem,andfordataprocessingandinterpretation. NUMIS“main features:NUMISP is animprovedoriginal NUMISandhas highoutput power(maximum outputs:450A,4000V),high receiver sensitivit y (measured signal in nV)and PC cont r ol. NUMIS“ isamodularequipment designedfortoallowmeasurements atremotelocations,as eachcomponent ofthesystemweights25kgmless,makingit one man portable. The Tx/Rx unit is the core of the system.It ensures the pr o duction of the energizing pu l ses at the Larmor frequencyalsothe measurementof theNMRresponse with filtering,amplification and analog digital conversion, The PCcomputerreceivesrawdata ,then processes,displays and stores themforfu rther interpretation. ThetwoDC/DC conven er units arerequiredfor a maximuminvestigation depth of 150mto energezise the 150mside square loop(600mtotal length). However, if an investigation of 100mis suf f icientoneconvener unito吻 is requiredwith 100msidesquareloop供 00mtotal length). Thetwo tuning unitsmust beusedat lower magnetic labtudes (for an Earthsfield lower t han 31000nTwith the 150mside square loop,or37000nT with the I00m side square loop),while one tuning unit only isneededatmediumandhigher labtudes. NUMISP isequippedwithsof t waresofmeasurements,signal collect cont rol andinterpreta- tion.With thesof t wares canbe measuredsignalampl itude,signal decay time andsig n al phase.The inte印 retationof measurementspermitstoestimatethewatercontent andthemeanporesizeofeach layer at depth.These parameters are used to deter m ine the prospects of a gr o undwater reservoir before drilling. Application ofNUN I I SP - in hydrogeologicalinvestigations WithNUMISP canberesolvedalotofhydr ogeologicalproblems Example 1 In Yongan area,Hubei province,karst water has been detected in thr e e NMR soun ding points.Resultsof interpr e tation show:in givenar e athere aretwo aquifers,the first one is located at 23-42m depth,water content 2-6%,decay time 40-192 ms;the second one (main aquofer) at 75- 100mdepth, water content 2-5%, Tz=218-230.6ms.In theareakarstwater isfound,quality of the water isgood,day output mor e than 1000m.V01.9CTTheor y andApplicationsE: ample 2 In St-Cyr-en-Val,France,karst water has been detectedsatisfactor y results obtained throughat measurements.The karst wateris located inandt W 0layers.The 五 rst one content 6 %， 几 =120ms;andthe second one at 28-51m dep氏wateris at 5-15 m content 11 %， 叮=230ms. WithNMR . method of detectinggroundwater can beobtainedsatisfactor y geological results, th e r e fo re ,th em e th o d h a sa g o o d fuA y ln taaA A A *颧其 在 水 文 地 质 调 查 工 作 中 的 应 用 研 究 潘玉玲JeanBERNARD I 中国地质大学地球物理系， 武汉， 430074, E-mail:ftangcug.edu.cn 2IRIS 公司，法国，奥尔良 ， 60074 5060正-n ail:irisinsibm.net)摘要: 本文概要介绍了地面核磁共振找水方法的原理和世界上最新的直接探查地下水的仪器设备一 一地面核磁感应系统的特点，并以实例说明了NMR 找水方法的应用效果，提出了 关于提高NUMIS 系统 抗干扰能力、完善解释方法、研制系列仪器等方面的建议。 1地面核磁共振找水方法原理概述 地面核磁共振 (NuclearMagneticResonance， 缩写为NMR) 找 水方 法， 又称地面NMR 测 深。 该 方 法应用核 磁感 应系 统 (Nuclear Magnetic Induction System, 缩写为NUMIS) 实 现对地下水资源的探测。地面 NMR 找水方法利用了不同物质原子核弛豫性质差异产生的 NMR 效应。即利用了水中氢核 (质子) 的弛豫 特性差异， 在地面上利用核磁共振找水仪， 观测、研究在地层中水质子产生的核磁共振信号的变化规律，进而探测地下水。 核磁共振是一个基于原子核特性的 物理现象，系指具有核子顺磁性的物质选择性地吸 收电 磁能量(11 。从理论上讲，应用 NMR 技术的唯一条件是所研究物质的原子核磁矩不为 零。水中氢核具有核子顺磁性，其磁矩不为零。 氢核是地层中具有核子顺磁性物质中丰度 最高、 磁旋比最大的核子。 在稳定地磁场的作用下， 氢核象陀螺一样绕地磁场方向旋进 (见 图1 )，其旋进频率 (拉摩尔频率) 与地磁场强度和原子核的磁旋比有关。氢核在地磁场作 用下，处在一定的能级上。如果以具有拉摩尔频率的交变磁场对地下水中的质子进行激发， 则使原子核能级间产生跃迁，即产生核磁共振。为此，通常向铺在地面上的线圈中供入频 率为拉摩尔频率的交变电流，在地中形成的交变磁场激发下，使地下水中氢核形成宏观磁 矩。这一宏观磁矩在地磁场中 产生旋进运动，其旋进频率为氢核所特有。在切断电流脉冲 后，用同一线圈拾取由不同激发脉冲矩激发产生的 NMR 信号，该信号的强弱直接与水中 质子的数量有关. 即 NMR 信号的幅值与所探测空间内自由 水含量成正比，因此构成了一 种直接找水技术，形成了地面核磁共振找水方法 (