磁法与大地电磁法数据二维联合反演研究

发布时间：2018-01-31 14:29

本文关键词： 二维联合反演交叉梯度磁法反演大地电磁反演　出处：《中国地质大学(北京)》2015年硕士论文　论文类型：学位论文

【摘要】：传统的物探方法包括重力,磁法,电法,测井,地震,放射性六种,每种方法都通过对单一的物性反演来进行对地质体的推断解释。联合反演是指通过同时反演多种地球物理数据,在反演过程中加入岩石物性关系来求得同一地质体的反演方法,是一种不同于单一的地球物理反演的新方法。联合反演法不再从单一物性角度观测地质体,而是通过岩石的物性和几何参数之间的相互关系来同时反演地下构造,它不仅能够克服单一反演方法的局限性,还能减少反演过程中的多解性,是地球物理反演发展的必然方向。通过对近年来国际上主流的地球物理联合反演方法的学习和分析,并且考虑到大地电磁反演中用到了磁化率这一物性信息,本文对磁法和大地电磁法的数据二维联合反演进行了相关研究。首先,分别对磁法的正反演和大地电磁的正反演做了基础性的研究工作。磁法方面,使用求取解析解的方法求取磁异常,反演使用光滑约束和对数障碍法。反演过程采用了新的目标函数,目标函数不只包括数据拟合差,还包括模型的光滑度及对数项,这样不仅减少了磁法反演中的多解性,还回避了利用高斯牛顿法反演磁化率时出现的磁化率为负值的问题。大地电磁方面,使用有限差分法求取大地电磁正演响应,反演的目标函数中同样加入了模型光滑度,增加目标函数对模型的约束,使用共轭梯度法进行计算,大大提高了运算效率,减少了运算时间。其次,本文基于交叉梯度理论(GallardoMeju,2004),实现了磁法与大地电磁数据的二维联合反演研究,并考虑了磁化率对大地电磁正反演的影响,在联合反演的同时,将磁法反演出的磁化率模型代入到大地电磁反演中。在联合反演过程中,采用五点中心差分格式对目标函数中的交叉梯度项进行离散化,加大交叉梯度项对模型边界的约束,提高了反演的可信度。最后,利用上述程序,设计理论模型进行联合反演计算。反演结果表明,利用交叉梯度方法耦合大地电磁中的电阻率参数和磁法勘探中的磁化率参数,使得在联合反演过程中两种物性参数相互约束,获得的反演结果与常规单一方法的反演结果相比更加准确可靠,从而验证了磁法和大地电磁法数据二维联合反演的有效性和正确性。
[Abstract]:Traditional geophysical methods include gravity, magnetic method, electrical method, logging, earthquake, radioactivity six kinds. Each method uses a single physical inversion to infer and interpret geological bodies. Joint inversion refers to simultaneous inversion of multiple geophysical data. It is a new method which is different from the single geophysical inversion method to obtain the inversion method of the same geological body by adding the physical relation of rock in the inversion process. The joint inversion method no longer observes the geological body from the angle of the single physical property. It can not only overcome the limitation of the single inversion method, but also reduce the multi-solution in the inversion process. It is the inevitable direction of the development of geophysical inversion. Through the study and analysis of the international mainstream geophysical joint inversion method in recent years, the magnetization information is used in magnetotelluric inversion. In this paper, two dimensional joint inversion of magnetotelluric and magnetotelluric data is studied. Firstly, the forward inversion of magnetotelluric method and forward inversion of magnetotelluric method are studied respectively. The magnetic anomaly is obtained by using the analytical solution, and the smooth constraint and logarithmic obstacle method are used in the inversion. A new objective function is used in the inversion process, and the objective function includes not only the fitting error of the data. It also includes the smoothness and logarithm of the model, which not only reduces the multi-solvability in the magnetic inversion, but also avoids the problem of negative magnetic susceptibility when using Gao Si Newton method to inverse the magnetic susceptibility. The forward magnetotelluric response is obtained by using the finite difference method. The model smoothness is also added to the object function of the inversion, and the constraint of the objective function to the model is increased, and the conjugate gradient method is used to calculate it. The computational efficiency is greatly improved and the operation time is reduced. Secondly, this paper bases on the theory of cross gradient and Gallardo Mejuan 2004). The joint inversion of magnetotelluric data and magnetotelluric data is realized, and the influence of magnetization on magnetotelluric inversion is considered. The magnetization model which is inverse by magnetic method is added to magnetotelluric inversion. In the process of joint inversion, the cross-gradient term in the objective function is discretized by the five-point central difference scheme. The reliability of the inversion is improved by increasing the constraint of the cross gradient term on the boundary of the model. Finally, the theoretical model is designed to carry out the joint inversion calculation using the above program. The inversion results show that. The cross-gradient method is used to couple the resistivity parameters in magnetotelluric field and the magnetic susceptibility parameters in magnetotelluric exploration, which makes the two physical parameters constrain each other in the process of joint inversion. The obtained inversion results are more accurate and reliable than those of the conventional single method, which verifies the validity and correctness of the two-dimensional joint inversion of magnetotelluric and magnetotelluric data.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.2;P631.325

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