核磁共振与瞬变电磁三维联合解释方法  

Three-dimensional joint interpretation of nuclear magnetic resonance and transient electromagnetic data

作　　者：李貅[1] 刘文韬[1] 智庆全 赵威[1] 

机构地区：[1]长安大学地质工程与测绘学院,西安710054 [2]中国地质科学院地球物理地球化学勘查研究所,河北廊坊065000

出　　处：《地球物理学报》2015年第8期2730-2744,共15页Chinese Journal of Geophysics

基　　金：国家重点基础研究发展计划项目(973项目)(2013CB036002);国家重大科研设备研制项目(ZDYZ2012-1-05-04);国家自然科学基金重点项目(51139004)联合资助

摘　　要：传统核磁共振地下含水量解释多采用基于均匀半空间或层状导电模型的一维反演,分层给出地下含水信息.然而,这些方法忽略了地下复杂电阻率分布信息对结果的影响,也不能很好地反映局部三维含水构造.本文从三维电介质中核磁共振响应的正演理论出发,提出首先利用瞬变电磁数据进行基于等效导电平面法的快速电阻率成像,然后将成像结果作为核磁共振三维反演的电性模型,进行联合解释.激发磁场的分布采用有限元法直接求解,通过引入伪δ源实现电流源的加载,并强加散度条件排除了三维磁场模拟中"弱解"的影响.针对核磁共振灵敏度矩阵的病态性和数据中存在的干扰信号,提出考虑罚项的非线性拟合目标函数,利用线性化方法进行核磁共振反演.模型数据表明该方法能较准确反映地下三维含水构造,实测算例进一步证明了方法的有效性.本研究将促使核磁共振方法在岩溶、裂隙水、孤立水体等复杂水文地质条件及隧道、矿井灾害水源探测等方面得到有效应用.The traditional interpretation methods of nuclear magnetic resonance（NMR）usually use 1Dinversion based on homogeneous half space or layered conductive earth model and the information of water amount in each layer will be derived.However,these methods usually ignore the influence of the inhomogeneous underground conductivity to the interpretation results.Meanwhile,these results are easily restricted to local water-bearing structures.For the purpose of avoiding the problems aforementioned,a novel joint interpretation method combining transient electromagnetic（TEM）and NMR data is proposed in this paper,which provides an effective and practical interpretation method for the detection of complex hydrogeological conditions.This paper proposes a novel joint interpretation method combining transient electromagnetic（TEM）and NMR data based on the forward modeling theory of NMR method in 3Dconductive media.Firstly,a fast resistivity image is derived from floating plate interpretation results ofTEM data.Afterwards,the resistivity imaging data will be used as the electrical model in 3D NMR inversion.The distribution of transmitting magnetic field is calculated by FE method directly.The transmitting current source is loaded by introducing apseudo-delta source,and the influence of＂weak solution＂in three dimensional simulation of magnetic field is eliminated by a force introduction of divergence condition.In order to improve the illness of sensitivity matrix and eliminate the noise,a non-linear fitting objective function considering the penalty terms is proposed and the linearized inversion method is used in the inversion process.The results of homogenous half-space model show that solutions of excitation magnetic field are almost the same as FEM solutions and digital filtering solutions and the influence of＂weak solution＂is eliminated.Results of the distribution of the NMR kernel function in different conductive models show that：（1）The background conductive of a model affects the distribution of the ke

关 键 词：核磁共振 瞬变电磁 等效导电平面 三维联合解释 

分 类 号：P631[天文地球—地质矿产勘探]