地面核磁共振找水三维有限元数值模拟  

Three-dimensional finite element numerical simulation for surface nuclear magnetic resonance

作　　者：任志平[1,2] 李貅[1] 赵威[1] 智庆全 刘磊[1] 

机构地区：[1]长安大学地质工程与测绘学院,西安710054 [2]西安石油大学电子工程学院,西安710065

出　　处：《地球物理学进展》2016年第3期1152-1157,共6页Progress in Geophysics

基　　金：国家自然科学基金项目(41174160);国家重点基础研究发展计划(2013CB036002)项目;陕西省自然科学基础研究项目(2013JQ5010)联合资助

摘　　要：针对地下含水体结构复杂,一维模型难以准确描述含水体分布特征的问题,建立了三维核磁共振响应模型,结合回线源条件下核磁共振的响应表达式,推导了频率域三维磁场分布方程与边界条件,应用有限元法实现了正演计算,并对算法的正确性进行了验证.在此基础上分析了含水体参数变化对磁共振响应的影响,结果表明:核磁共振具有测深功能,增大发射脉冲矩可以有效提高勘探深度;与响应振幅相比,各测点曲线之间的差异更能反映含水体位置的变化;对于浅层含水体,电阻率的变化对响应曲线初始振幅的影响较大.三维核磁共振的响应研究对复杂环境下核磁共振找水应用具有重要的参考价值.One-dimensional model is difficult to accurately describe the distribution characteristics of underground water for the complex structure. In this paper, a three-dimensional nuclear magnetic resonance（ NMR） response model is established. Combing with the expression of NMR with the loop source, three-dimensional magnetic field equations and boundary conditions in frequency domain are deduced. The finite element method is applied to calculate the forward modeling and the correctness of the algorithm is verified and then the effects of water parameters on the NMR response are analyzed. Numerical simulation shows that NMR can detect the depth of aquifer and the excitation pulse moment is help to increase the detecting depth. Comparing with the response amplitude,the difference between the monitoring points curve is more suitable for reflecting the variation of aquifer position. Shallow aquifer resistivity has more influence on the initial signal amplitude,the higher of the water resistivity,the larger of the maximum of the initial amplitude will be. The research will provide the necessary reference for complex structure groundwater investigation with NMR.

关 键 词：核磁共振 找水 三维 有限元 

分 类 号：P631[天文地球—地质矿产勘探]