引入倾向约束的大地电磁法二维反演研究

发布时间：2018-06-07 07:31

本文选题：模型约束项 + 先验信息　；参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：大地电磁法是一种高效的地球物理勘探方法,经多年的发展,该方法理论体系逐渐完善,而且不断引进新的数学计算方法,故大地电磁法的应用空间愈加广泛。目前在油气勘查、地热资源勘探和金属矿产勘查中大地电磁法都有广阔的发挥空间,实践证明该方法是一种不可或缺的地球物理勘查方法,有必要对其进行更加深层次的学习与研究。大地电磁法的目标函数由数据拟合项及模型约束项组成。在目标函数中,数据拟合项控制反演所得结果的正演响应与理论模型的正演响应之间差值在一个可接受的范围内;模型约束项控制模型光滑约束,此外,该项还能够改变反演结果中的异常形态,其灵活多变,可以在其中添加多种先验信息。本论文主要介绍了通过修改模型约束项来引入倾角信息、界面信息,充分地利用了先验信息已到达改善反演结果的目的。地质体一般具有清晰的走向或倾角信息,有必要建立一种新的目标函数来将这些信息加入到电磁法反演中。用一个旋转矩阵对水平方向及垂直方向导数做旋转运算,使得其导数方向可以任意改变。将这个旋转矩阵代入到模型约束项中创建一个新的目标函数,使得新目标函数可以在结构体的走向或者倾角方向上起到拉伸的作用。本文在大地电磁法二维的情况下讨论了该方法,列举了理论模型及实测数据加以验证,对比新方法与普通方法的反演结果,证明新方法的有效性。在地球物理勘探方法中,地震勘探对界面信息比较敏感,可以通过反射波划分地下界面信息。本论文建立一种新的目标函数将界面信息引入到电磁法反演中,分别采用了添加交叉梯度项进行分区域反演及修改拉普拉斯算子控制边界导数这两种方法,令新的目标函数可以更加准确地划分地层界面。在大地电磁法二维的情况下,建立理论模型以及实测数据分别对改进后的算法进行验证分析,证明该方法的正确性。引入倾角信息、界面信息这两种方法都取得了良好的效果,说明在反演中先验信息的引入是至关重要的,通过引入先验信息可以减弱反演多解性、改善反演结果。
[Abstract]:Magnetotelluric method is an efficient geophysical exploration method. With the development of many years, the theoretical system of this method has been gradually improved and a new mathematical calculation method has been introduced, so the application space of magnetotelluric method has become more and more extensive. At present, magnetotelluric method is widely used in oil and gas exploration, geothermal resources exploration and metal mineral exploration. It has been proved by practice that this method is an indispensable geophysical exploration method. It is necessary to carry on the deeper level study and research to it. The objective function of magnetotelluric method consists of data fitting term and model constraint term. In the objective function, the difference between the forward response of the inversion result and the forward response of the theoretical model is within an acceptable range, and the model constraint term controls the smooth constraint of the model, in addition, the difference between the forward response of the inversion result and the forward response of the theoretical model is within an acceptable range. This method can also change the abnormal shape in the inversion result, and it can add a variety of prior information to it. This paper mainly introduces the introduction of inclination information and interface information by modifying the constraint terms of the model, and makes full use of the prior information to improve the inversion results. Geological bodies generally have clear information of strike or inclination, so it is necessary to establish a new objective function to add these information to electromagnetic inversion. A rotation matrix is used to rotate the horizontal and vertical derivatives so that the derivative direction can be changed arbitrarily. The rotation matrix is added to the constraint term of the model to create a new objective function so that the new objective function can stretch in the direction of structure direction or inclination. This paper discusses the magnetotelluric method under the condition of two-dimensional magnetotelluric method, enumerates the theoretical model and the measured data to verify it, compares the inversion results of the new method with the common method, and proves the validity of the new method. In geophysical exploration, seismic exploration is sensitive to interface information and can be divided into underground interface information by reflection wave. In this paper, a new objective function is established to introduce the interface information into the electromagnetic inversion. Two methods are used to inverse the boundary derivatives by adding the cross gradient terms and modifying the Laplace operator to control the boundary derivatives. The new objective function can be used to divide the stratigraphic interface more accurately. In the case of two dimensional magnetotelluric method, the theoretical model and the measured data are established to verify and analyze the improved algorithm, and the correctness of the method is proved. The introduction of dip information and interface information shows that the introduction of prior information is very important in inversion. The introduction of prior information can weaken the multi-solution of inversion and improve the inversion results.
【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】：2017
【分类号】：P631.325

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