张量CSAMT三维主轴各向异性正反演研究

发布时间：2018-09-12 20:27

【摘要】：地球物理电磁法勘探领域发展至今,从最初的直接定性解释,已经发展到可以较为精确的定量分析。这其中,正反演技术的飞速发展为这种变化起到了巨大的作用。首先正演技术,从上世纪的积分方程法,逐步发展到三维有限差分法,此外自适应有限元的应用,也开始显现出模拟复杂地形的巨大优势。而在反演技术上,尽管存在陷入局部极小的问题,但大量的实践证明当前的反演技术在一定程度上能较好的完成勘探需要。在实际应用中,还有许多因素严重影响电磁法勘探的观测数据,首先是强烈的起伏地形,其次就是可能存在严重的各向异性。除了这两个问题外,在部分区域还存在磁导率、极化率等参数的强烈影响。当前电磁法勘探正在逐一研究这些问题,期望能做到更加精确可靠的解释。本文的研究重点就是在可控源音频大地电磁法(Controlled Source Audio-Frequency Magnetotelluric Methods) 里,引入电阻率各向异性参数。严格意义的各向异性参数是任意各向异性,即任意方向都是不同的。尽管这种方式更符合实际情况,但在目前的反演领域里,是无法反演的。因此在本文的研究中将各向异性简化为主轴各向异性,在一定程度上虽然降低了可靠性,但也同时为反演极大的降低了多解性。从这个角度上来说,也是在目前理论体系下,做到了相对最优化。确立了这个研究思路后,本文选用三维交错网格有限差分作为正演算子,该方法容易实现,且运算效率高,是目前地球物理内广泛应用的正演技术。在实现了 CSAMT三维主轴各向异性正演后,进行了正演分析的研究,结果表明采用张量源作为发射源,其多分量数据能尽可能的识别各向异性参数。进一步的,本文选用了有限内存拟牛顿法(LBFGS)与非线性共轭梯度法(NLCG)作为反演研究手段,首先完成了张量CSAMT三维各向同性反演研究。研究结果表明,不考虑场源效应而直接用大地电磁进行反演,深部反演结果不可信,同时张量CSAMT的反演结果分辨率也明显高于标量CSAMT,此外本文同时还进行了 LBFGS与NLCG的反演效果与效率的对比研究。最后,本文的各向异性反演理论试算还证明,忽略各向异性直接进行各向同性反演,会给最终的反演带来很多假异常,严重影响最终的解释。
[Abstract]:The rapid development of forward and inversion techniques has played an important role in this change. First of all, forward modeling techniques, from the integral equation method in the last century, have gradually developed to the three-dimensional finite difference method. The application of adaptive finite element method has also begun to show great advantages in simulating complex terrain. In inversion technology, although there is a problem of falling into local minima, a large number of practices have proved that the current inversion technology can better fulfill exploration needs to a certain extent. In practical application, there are still many factors seriously affecting electromagnetic prospecting. In addition to these two problems, there are also strong effects of permeability and polarizability in some areas. Currently, electromagnetic exploration is studying these problems one by one, hoping to achieve more accurate and reliable interpretation. The emphasis is on introducing resistivity anisotropy parameters into the Controlled Source Audio-Frequency Magnetotelluric Method. Strictly speaking, the anisotropy parameters are arbitrary anisotropy, i.e. all directions are different. In this paper, the anisotropy is simplified as the principal axis anisotropy, which reduces the reliability to a certain extent, but also greatly reduces the multiplicity of solutions for the inversion. In this paper, three-dimensional staggered grid finite difference method is chosen as forward operator. This method is easy to implement and has high computing efficiency. It is a widely used forward technique in geophysics at present. Furthermore, the finite-memory quasi-Newton method (LBFGS) and the nonlinear conjugate gradient method (NLCG) are selected as the inversion methods. First, the three-dimensional isotropic inversion of tensor CSAMT is completed. The results show that the magnetotelluric inversion is carried out directly without considering the field source effect, and the deep inversion is carried out. The inversion results of tensor CSAMT are not credible, and the resolution of tensor CSAMT is obviously higher than that of scalar CSAMT. In addition, the inversion effects and efficiency of LBFGS and NLCG are compared. Finally, the theoretical calculation of anisotropic inversion in this paper also proves that the inversion results will be the final inversion band if the anisotropy is ignored. There are many false anomalies which seriously affect the final interpretation.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P631.325

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