中心回线瞬变电磁2.5维正演及反演研究

发布时间：2018-06-30 17:18

本文选题：瞬变电磁 + 正演　；参考：《成都理工大学》2015年硕士论文

【摘要】：瞬变电磁法作为近年来迅速发展的电磁法,因为其分辨率高,勘探深度大等优点,被广泛应用于工程,环境,水文,能源勘探等领域。但是,瞬变电磁法资料解释水平还较低,在野外应用中,基本处于一维阶段,现阶段二维以及三维反演技术还不能用于实际生产中。但是随着计算机技术的飞速发展,以及瞬变电磁智能化先进仪器的不断涌现,对瞬变电磁资料解释也提出了新的要求。因此本文针对该该问题,以瞬变电磁2.5维正反演为研究对象。瞬变电磁2.5维正反演问题,即采用三维源,二维的地电断面,与三维模型相比,只需要对截面而不是整个体积作离散处理,相对节省了计算量;与一维、二维模型相比,其又能较好的近似地质情况。而如今瞬变电磁2.5维问题的研究并不多,并且还有很多不妥善之处,主要表现在计算精度和计算速度方面,目前程度的瞬变电磁2.5维正反演暂时还不能应用到实际生产中,所以对于2.5维模拟的进一步研究是非常有意义和价值的。而中心回线法是瞬变电磁中最常用到的方法之一,在目前的理论研究却并不多,因此本文选择了瞬变电磁中心回线2.5维正反演问题为研究内容。本文从瞬变电磁的一维正演出发,对麦克斯韦方程进行推导,进行了汉克尔数数值滤波和余弦数值滤波,得到瞬变电磁一维响应式,实现了瞬变电磁的一维正演。通过对发射参数的改变了解不同发射参数下的瞬变电磁响应,其中发射线框越大,瞬变电磁响应的衰减就越慢,早期的时间也就越长,随着发射电流的增大,瞬变电磁响应的幅值也线性增大。通过建立各种地电模型,从而了解瞬变电磁响应规律,其中包括D型,G型以及H型。在瞬变电磁2.5维正演方面,从麦克斯韦方程出发,对瞬变电磁2.5维问题中异常体偏微分方程的定解问题,变分问题,边界问题等进行了详细的推导。在这其中着重的分析了几个关键性问题:拉普拉斯变换,傅里叶变换,非走向分量的计算。使用了非结构化网格这一工具,对异常区网格以及在测点附近进行了局部的加密处理,大幅度的降低了网格单元数和节点数,从而减少了不必要的节点计算。通过该非结构网格剖分方法可以实现对复杂模型的剖分,使得瞬变电磁2.5维正演的应用范围得到很好的扩展。建立K型和H型两种模型,并进行了瞬变电磁2.5维正演有限元的计算,将计算结果与同样模型的解析解进行了比较,可以知道有限元解和解析解,它们的误差很小,说明本文的2.5维有限元解的可行性和有效性。利用瞬变电磁2.5维正演有限元算法分别对直立低阻板状体和低阻圆柱体,两个低阻圆柱体同时存在这三个模型进行了模拟,直立低阻板状体,在板状体两边出现极大值,板状体处呈现极小值;低阻圆柱体体模拟中,圆柱体处时,各测道出现了明显的对称,并且出现了圆柱体顶的单峰异常;两个低阻圆柱体同时存在,当扩散到两个圆柱体处时,出现了对称的两个极大值,在极大值中间存在极小值。在反演方面,首先是一维反演,利用二等分全区视电阻率算法进行“烟圈”快速反演,并设置各种模型进行了反演,总结出了该反演方法具有反演速度快,反演的电阻率剖面能够大致的描述出地下地质分布的特点。对于瞬变电磁法的2.5维反演,本文提出以烟圈反演结果和测区地质信息做为得到初始模型,也就是利用烟圈反演作为2.5反演的参考,并通过人为的对反演结果与2.5维正演模型进行对比,即人机联合反演,实现瞬变电磁2.5反演。该方法具有一定的可行性。
[Abstract]:As an electromagnetic method developed rapidly in recent years, transient electromagnetic method has been widely used in engineering, environment, hydrology, energy exploration and other fields because of its high resolution and deep exploration depth. However, the data interpretation level of transient electromagnetic method is still low. In the field application, the base is in one dimensional stage, and the two dimensional and three dimensional inversion techniques are also used in the present stage. It can not be used in actual production. However, with the rapid development of computer technology and the continuous emergence of transient electromagnetic intelligent advanced instruments, new requirements for transient electromagnetic data interpretation are also put forward. Therefore, this paper takes the 2.5 dimensional forward inversion of transient electromagnetic as the research object for the problem. The problem of transient electromagnetic 2.5 dimensional positive inversion is adopted. The three-dimensional source and two-dimensional geoelectric section, compared with the three-dimensional model, only need to discretize the cross section instead of the whole volume, and save the amount of calculation relatively. Compared with one dimension and two dimensional model, it can be better approximate to the geological condition. But there are not much research on the 2.5 dimension of the transient electromagnetic problem, and there are still a lot of improper points. In terms of calculation precision and calculation speed, the present degree of 2.5 dimensional transient electromagnetic inversion can not be applied to actual production, so it is very meaningful and valuable for the further study of the 2.5 dimensional simulation. And the central loop method is one of the most commonly used methods in transient electromagnetic. In this paper, the 2.5 dimensional positive inversion problem of the transient electromagnetic center loop is selected as the research content. In this paper, the Maxwell equation is derived from one dimension forward of the transient electromagnetic field, and the numerical filtering of Hankel number and the cosine numerical filtering are carried out to obtain the one-dimensional response of the transient electromagnetic. The number of changes in the transient electromagnetic response under different emission parameters is understood. The larger the emitter frame, the slower the attenuation of the transient electromagnetic response and the longer the early time. With the increase of the emission current, the amplitude of the transient electromagnetic response is also increased linearly. By establishing various electric models, the transient electromagnetic response law is understood, in which the envelope is known. D, G and H type. In the 2.5 dimensional forward transient electromagnetic field, starting from the Maxwell equation, the definite solution to the partial differential equation of the anomalous body, the variational problem and the boundary problem in the 2.5 dimensional transient electromagnetic problem are derived in detail. In this, several key problems are emphatically analyzed: Laplasse transform, Fourier transform, and non The unstructured grid is used as a tool. The mesh of the anomaly area and the local encryption processing near the test point are processed. The number of grid cells and the number of nodes are reduced greatly, and the unnecessary node calculation is reduced. The dissection of the complex model can be realized by the unstructured mesh generation method. The application range of the 2.5 dimensional forward electromagnetic field is well extended. Two models of K and H are established and the 2.5 dimensional forward finite element of transient electromagnetic is calculated. The calculation results are compared with the analytical solutions of the same model. The finite element solution and the analytical solution can be known. Their error is very small, and the 2.5 dimensional finite element solution of this paper is explained. The 2.5 dimensional forward finite element algorithm is used to simulate the vertical and low resistance cylinder and the low resistance cylinder, and the two low resistance cylinders are simulated simultaneously with the three models. The erect low resistance plate, the maximum value on both sides of the plate, the minimum in the plate body, and the circle in the low resistance cylinder body. When the column is located, there are obvious symmetry in each channel, and there is a single peak anomaly of the top of the cylinder. Two low resistance cylinders exist simultaneously. When the two cylinders are spread, there are two maximum values of symmetry and there is a minimum in the middle of the maximum value. In the inverse aspect, the first one is one dimensional inversion, and the two equal division all region apparent resistivity. The algorithm performs fast inversion of "smoke circle" and sets up various models for inversion. It is concluded that the inversion method has fast inversion speed, and the inversion resistivity profile can describe the characteristics of underground geological distribution roughly. For 2.5 dimensional inversion of transient electromagnetic method, this paper presents the result of the inversion of the smoke circle and the geological information of the measured area. To the initial model, it is to use the inversion of the smoke loop as the reference of the 2.5 inversion, and compare the inversion results with the 2.5 dimensional forward model, that is, the joint inversion of the man machine, and the inversion of the transient electromagnetic 2.5 is realized. This method is feasible.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.325

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