磁共振与瞬变电磁空间约束联合反演方法研究

The shortage of water resources seriously constrains the economic development of Western China. Nevertheless, the fissure water and karst water in the complicated stratum increase the difficulty of exploration. The method of Magnetic Resonance Sounding (MRS) has the advantages of determining the subsurface water qualitatively and quantitatively, which is an effective means in the exploration of water resources. However, being restricted to the acquirement of conductivity, terrain and adjacent point parameters, the traditional inversion method is facing bottleneck in the interpretation of non-layered water detection. By taking into account of all the factors of terrain, conductivity and continuity, a set of space constrained joint inversion algorithms for MRS and Transient Electromagnetic method (TEM) is proposed in this project. Via designing the rotation coefficient matrix to create the inclination model, the geomagnetic field direction parameter can be introduced into the MRS inversion process. We then study the QT inversion theory of MRS, which can be combined with the resistivity distribution acquired by the TEM technology. Referring to the key problems of objective function construction, and weight coefficient selection, as well as regularization factor determination, the joint inversion algorithms of MRS and TEM are studied intensively. Furthermore,based on the spacial correlations of the adjacent points and the preconditioned conjugate gradient method, the space constrained joint inversion algorithm is provided, which consequently avoided the problem of non-uniqueness of the inversion results. Finally, the inversion algorithm is verified and improved by the real data. The implementation of this project will lay a significant foundation of science and technology for the exploration of water resources in Western China.

水资源短缺严重制约我国西部经济发展，而复杂地质环境中赋存的裂隙水、岩溶水增加了勘探难度。地面磁共振测深具备定性定量分析地下水的优势，但常规反演受限于电阻率、地形参数、相邻测点信息的有效获取，在非层状水准确解释中面临瓶颈。 本项目综合考虑地势起伏、地层电性以及大地模型连续变化等因素，提出磁共振与瞬变电磁空间约束联合反演方法。设计旋转系数矩阵建立探测倾角模型，将地磁场方向参数引入磁共振反演。研究全部采集时间下磁共振数据反演理论，结合瞬变电磁技术得到的电阻率分布，针对目标函数构建、权系数选取、正则化因子确定等关键问题，深入探索磁共振与瞬变电磁联合反演方法。基于相邻测点空间范围内的关联性，攻克预处理共轭梯度大型矩阵计算技术，实现联合反演的空间约束，解决孤立测点反演的多解性问题。最后，通过实测数据验证并完善所提出的反演方法。 本项目的实施将为我国西部水资源勘察提供有力的科技支撑。

水资源短缺严重制约我国西部经济发展，而复杂地质环境中赋存的裂隙水、岩溶水增加了勘探难度。地面磁共振测深具备定性定量分析地下水的优势，但常规反演受限于电阻率、地形参数、相邻测点信息的有效获取，使其在非层状水准确解释中面临瓶颈。.本项目综合考虑了地势起伏、地层电性以及大地模型连续变化等因素，提出了磁共振与瞬变电磁空间约束联合反演方法。设计了旋转系数矩阵建立探测倾角模型，将地磁场方向参数，即地磁倾角、地磁偏角、坡体倾角和剖面倾角引入旋转系数矩阵参与磁共振反演，为复杂地形的含水层准确解释提供了坚实的理论依据。.利用全部采集时间下的磁共振探测数据，结合瞬变电磁技术实时更新地下电阻率分布信息，构建联合反演目标函数，以相邻测点地下结构应具备空间连续性为依据，在反演目标函数中加入模型参数空间约束矩阵，加强探测空间地质结构和含水模型连续性，实现视电阻率、层厚度、含水量、弛豫时间的光滑连续约束，解决了孤立测点反演的多解性问题。.研究了快速磁共振正演计算方法，加快迭代收敛速度，解决传统数值积分方法引起的求解效率低的问题，结合预处理共轭梯度大型矩阵计算技术，使得多个接收线圈的磁共振与瞬变电磁全体数据集参与反演过程，实现了海量数据快速反演。.理论模型仿真试验和多处实际野外案例的反演结果表明，磁共振与瞬变电磁空间约束联合反演方法能够有效抑制多解性并排除多余异常体，增强地下空间结构反演结果的连续性和可靠性，减小观测数据噪声对反演结果的影响。本项目于内蒙古正镶白旗北部阿拉坦嘎达苏苏木境内开展总面积约200平方公里的水源地勘探工作，实现了对地下水的定向定位勘察，解决了当地居民的缺水问题；并于安徽省黄山市歙县金川乡合丰村探测长为200m的滑坡带，为排除地质灾害隐患做出重要贡献。本项目的实施将为我国西部水资源勘察提供有力的科技支撑。