共查询到20条相似文献，搜索用时 937 毫秒
1.
Mining,Environmental, Petroleum,and Engineering Industry Applications of Electromagnetic Techniques in Geophysics 总被引：6，自引：1，他引：5
Electromagnetic (EM) techniques are extremely important as a direct detection geophysical tool utilized in the base metal
industry. They were developed in countries such as Canada, whose thin conductive weathering overburden did not hamper the
penetration of EM signals and enabled exploration to depths on the order of 300 m. As a result, EM techniques were used widely
in North America and Scandinavia for many years before they became common in countries with a thick conductive overburden,
such as Australia. The 1980s and 1990s have seen the use of EM methods move from anomaly finding to mapping, as well as the
development of better, faster and more accurate computer modelling algorithms. A review of EM papers, for the years 1998 to
2002, showed that most dealt with EM techniques as mapping tools. Airborne, ground and marine EM techniques are still being
developed, as are data processing and interpretation software. The advent of robust 2-D and 3-D computer modelling and inversion
algorithms has led to the acceptance of EM methods as a mapping tool for many environmental and petroleum industry applications,
a trend which is expected to increase. 相似文献
2.
在前人工作的基础上,本文推导了电导率任意各向异性介质的海洋可控源电磁三维谱元法正演方程.采用一次场/二次场分离算法结合混合阶矢量基函数,可以有效避免源点的奇异性的影响,从而提高数值解的精度.采用任意六面体单元离散研究区域,有利于模拟复杂地形和地电结构.利用不完全LU分解的Induced Dimension Reduction(IDR(s))迭代算法求解线性方程组,有效地提高了求解的效率.设计典型的地电模型进行正演计算,并将计算结果与有限元解进行对比,对比结果表明本文提出的基于混合阶矢量基函数的海洋可控源电磁三维谱元数值模拟算法是正确的、有效的.本文算法具有良好的通用性,可推广用于电导率呈任意各向异性的陆地电磁、井中电磁等数值模拟研究. 相似文献
3.
P. Kaikkonen 《Surveys in Geophysics》1986,8(3):301-337
Recent activity in important approximate methods used in numerical electromagnetic (EM) modeling is reviewed. Comparisons between the results obtained by different numerical methods and between analytical and numerical solutions are presented. The importance of 3D modeling and thin sheet approximations are pointed out.This review also considers and summarizes studies of characteristic dimensions in three topics: source fields, numerical modeling and physical phenomena in the earth and interpretation. The skin depth (i.e., generally the attenuation) of the EM energy is considered to be the most important and fundamental characteristic dimension. 相似文献
4.
Numerical Modelling in Geo-Electromagnetics: Advances and Challenges 总被引：11，自引：0，他引：11
Ralph-Uwe Börner 《Surveys in Geophysics》2010,31(2):225-245
During the last decade, tremendous advances have been observed in the broad field of numerical modelling for geo-electromagnetic
applications. This trend received support due to increasing industrial needs, mainly caused by hydrocarbon and ore exploration
industry. On the other hand, the increasing reliability and accuracy of data acquisition techniques further spurs this development.
In this review, we will focus on advances and challenges in numerical modelling in geo-electromagnetics. We review recent
developments in the discrete solution of the 3-D induction problem in the time and frequency domains. Particularly, advantages
and disadvantages of the common numerical techniques for solving partial differential equations such as the Finite Difference
and Finite Element methods will be considered. 相似文献
5.
A Review Of Environmental Applications Of Quasi-Stationary Electromagnetic Techniques 总被引：2，自引：0，他引：2
Bülent Tezkan 《Surveys in Geophysics》1999,20(3-4):279-308
Electromagnetic (EM) techniques are the most commonly used geophysical methods in mineral exploration. However, the use of EM measurements for environmental and engineering applications like the detection of contaminant plumes or the exploration of waste sites is relatively new.The reason for the success of the application of EM methods to environmental problems lies in the variation of conductivity caused by different geometry of pore fluids and clay contents in rocks, and by the presence of organic and inorganic contaminants.Many EM methods/instruments used for mapping near surface geology exist and nowadays they play a central role in environmental geophysics. In general, these methods can be classified in two blocks: EM methods using a plane wave source of excitation and EM methods using a controlled source like a magnetic dipole or a loop source. The Very Low Frequency (VLF, VLF-R) and Radiomagnetotelluric (RMT) methods are chosen as representative methods for plane wave techniques, while horizontal loop EM methods operating in low induction numbers (EM31, EM34) and Transient Electromagnetic methods (TEM) are chosen as representatives of magnetic dipole or loop source techniques. Basic principles, advantages and disadvantages of each technique as well as their connection to specific environmental problems will be discussed.Different successful applications of these methods are reported in the literature. However, this review will focus on three major subjects: waste site exploration, detection of contaminated earth layers, and groundwater exploration. Case histories are presented illustrating the suitability of EM methods for solving such problems. 相似文献
6.
L.A. Tabarovsky M.M. Goldman M.B. Rabinovich K.-M. Strack 《Journal of Applied Geophysics》1996,35(4):261-284
Understanding, using, or eliminating three-dimensional (3-D) effects in electromagnetic methods of geophysics are critical requirements. Numerous achievements in 3-D modeling sometimes give the impression that they are widely available today in geophysical practice. This is not necessarily true. Existing 3-D modeling packages prove that we know how to perform 3-D modeling. However, the computer resources and costs involved make the practical application of 3-D EM modeling in geophysical applications very limited.A practical compromise, or even alternative, is represented by 2.5-D modeling characterized by the use of a 3-D source in a 2-D medium. This combination allows one to mathematically describe the related boundary value problem as a sequence of independent two-dimensional problems. The typical technique leading to such a split formulation is Fourier analysis. That is why the individual terms of a split solution are often referred to as harmonics.Although each independent problem is two-dimensional, the algorithmic implementation of finite differences or integral equations for the higher harmonics has some specific features not present in the classical 2-D cases. In this paper, a hybrid scheme consisting of a combination of the finite difference technique with the integral equation approach for transient fields is described. Evaluation of algorithm accuracy is presented and a transient logging technique application is considered. The algorithm is fast and easily implemented on a personal computer 相似文献
7.
Controlled-Source Electromagnetic Approaches for Hydrocarbon Exploration and Monitoring on Land 总被引：4，自引：1，他引：3
Rita Streich 《Surveys in Geophysics》2016,37(1):47-80
Electromagnetic methods that utilize controlled sources have been applied for natural resource exploration for more than a century. Nevertheless, concomitant with the recent adoption of marine controlled-source electromagnetics (CSEM) by the hydrocarbon industry, the overall usefulness of CSEM methods on land has been questioned within the industry. Truly, there are few published examples of land CSEM surveys carried out completely analogously to the current marine CSEM standard approach of towing a bipole source across an array of stationary receivers, continuously transmitting a low-frequency signal and interpreting the data in the frequency domain. Rather, different sensitivity properties of different exploration targets in diverse geological settings, gradual advances in theoretical understanding, acquisition and computer technology, and different schools in different parts of the world have resulted in a sometimes confusing multitude of land-based controlled-source EM surveying approaches. Here, I aim to review previous and present-day approaches, and provide reasoning for their diversity. I focus on surface-based techniques while excluding airborne EM and well logging and on applications for hydrocarbon exploration. Attempts at the very demanding task of using onshore controlled-source EM for reservoir monitoring are shown, and the possible future potential of EM monitoring is discussed. 相似文献
8.
Applied Mathematics in EM Studies with Special Emphasis on an Uncertainty Quantification and 3-D Integral Equation Modelling 总被引：1，自引：0，他引：1
Despite impressive progress in the development and application of electromagnetic (EM) deterministic inverse schemes to map the 3-D distribution of electrical conductivity within the Earth, there is one question which remains poorly addressed—uncertainty quantification of the recovered conductivity models. Apparently, only an inversion based on a statistical approach provides a systematic framework to quantify such uncertainties. The Metropolis–Hastings (M–H) algorithm is the most popular technique for sampling the posterior probability distribution that describes the solution of the statistical inverse problem. However, all statistical inverse schemes require an enormous amount of forward simulations and thus appear to be extremely demanding computationally, if not prohibitive, if a 3-D set up is invoked. This urges development of fast and scalable 3-D modelling codes which can run large-scale 3-D models of practical interest for fractions of a second on high-performance multi-core platforms. But, even with these codes, the challenge for M–H methods is to construct proposal functions that simultaneously provide a good approximation of the target density function while being inexpensive to be sampled. In this paper we address both of these issues. First we introduce a variant of the M–H method which uses information about the local gradient and Hessian of the penalty function. This, in particular, allows us to exploit adjoint-based machinery that has been instrumental for the fast solution of deterministic inverse problems. We explain why this modification of M–H significantly accelerates sampling of the posterior probability distribution. In addition we show how Hessian handling (inverse, square root) can be made practicable by a low-rank approximation using the Lanczos algorithm. Ultimately we discuss uncertainty analysis based on stochastic inversion results. In addition, we demonstrate how this analysis can be performed within a deterministic approach. In the second part, we summarize modern trends in the development of efficient 3-D EM forward modelling schemes with special emphasis on recent advances in the integral equation approach. 相似文献
9.
反射地震勘探中的偏移成像技术是获取地下介质构造形态最有效的手段之一.在叠前深度域偏移方法中,目前工业界采用的方法包括基于射线理论的波动方程积分解法和基于波动理论的微分波动方程单程波解法,这两类方法难以处理地震波横向速度变化剧烈的高陡倾角构造成像问题.近年来勘探地震学研究领域发展起来的叠前逆时偏移采用了双程波求解微分波动方程的算法,这种方法具有相位准确、不受介质横向速度变化和高陡倾角构造的影响、成像精度高、可以利用回转波正确成像等优点,从理论上弥补了当前工业界常规地震偏移所面临的成像缺陷.然而,叠前逆时偏移成像方法从理论走向实用尚需解决如下问题:计算速度和数据存储空间的节省、初始速度模型的建立、震源子波的选择、数值模型边界条件的定义和假像的消除等等.对于计算速度和存储量大的问题,随着计算机硬件的快速发展,将会不断得到改善,同时可以采取一些计算技术和存储策略来加以缓解.本文主要针对初始速度模型的建立、震源子波的选择、数值模型边界条件的定义和假像的消除这些因素,利用简单模型进行了分析.对于反射波造成的传播路径上的假像,给出了一种振幅补偿滤波方法.对勘探地球物理学界给出的SEG/EAGE二维盐丘模型、Marmousi模型和本研究设计的崎岖海底模型进行了叠前逆时偏移成像,均取得了较好的成像效果. 相似文献
10.
George R. Jiracek 《Surveys in Geophysics》1990,11(2-3):163-203
11.
K. M. Strack 《Surveys in Geophysics》2014,35(1):157-177
For hydrocarbon applications, seismic exploration is the workhorse of the industry. Only in the borehole, electromagnetic (EM) methods play a dominant role, as they are mostly used to determine oil reserves and to distinguish water from oil-bearing zones. Throughout the past 60 years, we had several periods with an increased interest in EM. This increased with the success of the marine EM industry and now electromagnetics in general is considered for many new applications. The classic electromagnetic methods are borehole, onshore and offshore, and airborne EM methods. Airborne is covered elsewhere (see Smith, this issue). Marine EM material is readily available from the service company Web sites, and here I will only mention some future technical directions that are visible. The marine EM success is being carried back to the onshore market, fueled by geothermal and unconventional hydrocarbon applications. Oil companies are listening to pro-EM arguments, but still are hesitant to go through the learning exercises as early adopters. In particular, the huge business drivers of shale hydrocarbons and reservoir monitoring will bring markets many times bigger than the entire marine EM market. Additional applications include support for seismic operations, sub-salt, and sub-basalt, all areas where seismic exploration is costly and inefficient. Integration with EM will allow novel seismic methods to be applied. In the borehole, anisotropy measurements, now possible, form the missing link between surface measurements and ground truth. Three-dimensional (3D) induction measurements are readily available from several logging contractors. The trend to logging-while-drilling measurements will continue with many more EM technologies, and the effort of controlling the drill bit while drilling including look-ahead-and-around the drill bit is going on. Overall, the market for electromagnetics is increasing, and a demand for EM capable professionals will continue. The emphasis will be more on application and data integration (bottom-line value increase) and less on EM technology and modeling exercises. 相似文献
12.
2-D Versus 3-D Magnetotelluric Data Interpretation 总被引：6，自引：0，他引：6
In recent years, the number of publications dealing with the mathematical and physical 3-D aspects of the magnetotelluric method has increased drastically. However, field experiments on a grid are often impractical and surveys are frequently restricted to single or widely separated profiles. So, in many cases we find ourselves with the following question: is the applicability of the 2-D hypothesis valid to extract geoelectric and geological information from real 3-D environments? The aim of this paper is to explore a few instructive but general situations to understand the basics of a 2-D interpretation of 3-D magnetotelluric data and to determine which data subset (TE-mode or TM-mode) is best for obtaining the electrical conductivity distribution of the subsurface using 2-D techniques. A review of the mathematical and physical fundamentals of the electromagnetic fields generated by a simple 3-D structure allows us to prioritise the choice of modes in a 2-D interpretation of responses influenced by 3-D structures. This analysis is corroborated by numerical results from synthetic models and by real data acquired by other authors. One important result of this analysis is that the mode most unaffected by 3-D effects depends on the position of the 3-D structure with respect to the regional 2-D strike direction. When the 3-D body is normal to the regional strike, the TE-mode is affected mainly by galvanic effects, while the TM-mode is affected by galvanic and inductive effects. In this case, a 2-D interpretation of the TM-mode is prone to error. When the 3-D body is parallel to the regional 2-D strike the TE-mode is affected by galvanic and inductive effects and the TM-mode is affected mainly by galvanic effects, making it more suitable for 2-D interpretation. In general, a wise 2-D interpretation of 3-D magnetotelluric data can be a guide to a reasonable geological interpretation. 相似文献
13.
A. V. Kuvshinov 《Surveys in Geophysics》2008,29(2):139-186
Electromagnetic induction in the Earth’s interior is an important contributor to the near-Earth magnetic and electric fields.
The oceans play a special role in this induction due to their relatively high conductivity which leads to large lateral variability
in surface conductance. Electric currents that generate secondary fields are induced in the oceans by two different processes:
(a) by time varying external magnetic fields, and (b) by the motion of the conducting ocean water through the Earth’s main
magnetic field. Significant progress in accurate and detailed predictions of the electric and magnetic fields induced by these
sources has been achieved during the last few years, via realistic three-dimensional (3-D) conductivity models of the oceans,
crust and mantle along with realistic source models. In this review a summary is given of the results of recent 3-D modeling
studies in which estimates are obtained for the magnetic and electric signals at both the ground and satellite altitudes induced
by a variety of natural current sources. 3-D induction effects due to magnetospheric currents (magnetic storms), ionospheric
currents (Sq, polar and equatorial electrojets), ocean tides, global ocean circulation and tsunami are considered. These modeling
studies demonstrate that the 3-D induction (ocean) effect and motionally-induced signals from the oceans contribute significantly
(in the range from a few to tens nanotesla) to the near-Earth magnetic field. A 3-D numerical solution based on an integral
equation approach is shown to predict these induction effects with the accuracy and spatial detail required to explain observations
both on the ground and at satellite altitudes.
On leave from Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation, Russian Academy of Sciences, 142190
Troitsk, Moscow region, Russia. 相似文献
14.
Iv. M. Varentsov 《Surveys in Geophysics》1983,6(1-2):55-78
The main results obtained during the last 5–8 yr in the solution of forward and inverse problems of 3D induction studies are summarized. The up-to-date status of 3D modelling is presented and prospective improvements in the formulation and numerical solution of forward problems are discussed. Approximate techniques and practical aspects of 3D modelling are specially considered. The general scheme of 3D interpretation of electromagnetic geophysical observations is outlined and realistic formalized approaches to solving 3D inverse problems, namely direct inversion and formalized model fitting, are studied. 相似文献
15.
Groundwater exploration using integrated geophysical techniques 总被引：1，自引：0，他引：1
The integrated approach to solving complicated geological, hydrological and environmental problems is now widely used in geophysics. Among all the geophysical methods, electrical and electromagnetic techniques are the most popular in groundwater exploration due to the close relationship between electrical conductivity and some hydrogeological properties of the aquifer (e.g. porosity, clay content, mineralization of the groundwater and degree of water saturation). Case histories presented here show that by proper combination of different techniques such as conventional direct current (DC) resistivity as well as the more advanced electromagnetic (EM) methods and the most recent nuclear magnetic resonance (NMR) tomography, the reliability of interpretation as compared to that typical for the individual methods can be significantly improved. 相似文献
16.
适用于近地表(2000m以内)勘探的频率域电磁法主要有音频大地电磁法(audio-frequency magnetotellurics,AMT),无线电大地电磁法(radio-magnetotellurics,RMT),可控源音频大地电磁法(controlled source audiofrequency magnetotellurics,CSAMT),广域电磁法(Wide Field Electromagnetic Method,WFEM).本文拟从最新的数据采集技术、数据处理技术、正反演算法、实例等四个方面,论述适用于浅部勘探的AMT,RMT,CSAMT和WFEM方法的国内外最新进展,总结目前AMT,RMT,CSAMT和WFEM方法遇到的困难,对潜在的发展方向提出建议.综述表明:(1)张量测量、多站阵列、多站叠加可提高AMT、RMT和CSAMT数据的质量.利用近区数据WFEM法可获得良好的效果.国产与国外仪器在质量方面的差距正在逐步缩小.(2)数学形态滤波技术、Hilbert-Huang变换等可有效分离出有用的数据,局部畸变仍然是亟待解决的难题,需要更为深入的研究.(3)矢量有限元与非结构网格的出现大幅度提高了有限元处理复杂电磁问题模拟的精度与应用范围,成为目前电磁正演的首选工具.完全非线性反演算法仍然局限于1D、2D问题,共轭梯度法和高斯牛顿算法等为解决3D问题的发展趋势.地质约束的引入和多数据联合反演可以减小反演的非唯一性.各向异性的反演为目前反演研究的热点之一.(4)野外数据解释的正确性严重依赖于对地下结构先期的维性判别,在2D特性不明显、3D特性明显时,需要采用3D进行反演解释. 相似文献
17.
Doug Oldenburg 《Surveys in Geophysics》1990,11(2-3):231-270
This paper explores some of the newer techniques for acquiring and inverting electromagnetic data. Attention is confined primarily to the 2d magnetotelluric (MT) problem but the inverse methods are applicable to all areas of EM induction. The basis of the EMAP technique of Bostick is presented along with examples to illustrate the efficacy of that method in structural imaging and in overcoming the deleterious effects of near-surface distortions of the electric field. Reflectivity imaging methods and the application of seismic migration techniques to EM problems are also explored as imaging tools. Two new approaches to the solution of the inverse problem are presented. The AIM (Approximate Inverse Mapping) inversion of Oldenburg and Ellis uses a new way to estimate a perturbation in an iterative solution which does not involve linearization of the equations. The RRI (Rapid Relaxation Inverse) of Smith and Booker shows how approximate Fréchet derivatives and sequences of 1d inversions can be used to develop a practical inversion algorithm. The overview is structured to provide insight about the latest inversion techniques and also to touch upon most areas of the inverse problem that must be considered to carry out a practical inversion. These include model parameterization, methods of calculating first order sensitivities, and methods for setting up a linearized inversion. 相似文献
18.
19.
《Advances in water resources》2005,28(5):523-539
Most available numerical methods face problems, in the presence of variable topographies, due to the imbalance between the source and flux terms. Treatments for this problem generally work well for structured grids, but most of them are not directly applicable for unstructured grids. On the other hand, despite of their good performance for discontinuous flows, most available numerical schemes (such as HLL flux and ENO schemes) induce a high level of numerical diffusion in simulating recirculating flows. A numerical method for simulating shallow recirculating flows over a variable topography on unstructured grids is presented. This mass conservative approach can simulate different flow conditions including recirculating, transcritical and discontinuous flows over variable topographies without upwinding of source terms and with a low level of numerical diffusion. Different numerical tests cases are presented to show the performance of the scheme for some challenging problems. 相似文献
20.
Kerry Key 《Surveys in Geophysics》2012,33(1):135-167
The past decade has been a period of rapid growth for marine electromagnetic (EM) methods, predominantly due to the industrial
adoption and promotion of EM as a valuable tool for characterizing offshore hydrocarbon reservoirs. This growth is illustrated
by a database of marine EM publications spanning from the early developments in the 1960’s to the present day; while over
300 peer-reviewed papers on marine EM have been published to date, more than half of these papers have been published within
the last decade. This review provides an overview of these recent developments, covering industrial and academic use of marine
EM for resource exploration and tectonic investigations, ranging from acquisition technology and modeling approaches to new
physical and geological insights learned from recent data sets. 相似文献