共查询到19条相似文献，搜索用时 171 毫秒
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地电体对频率域电磁波激发源的响应为电磁感应和激电效应的综合响应.传统CSAMT法进行数据正反演时认为大地介质电阻率是与频率无关的实数,而实际上因为激电效应,地下可极化体的电阻率是一个与频率相关的复数.为推进二者总体响应研究,并扩展激电法的应用范围,同时提高电磁法勘探的精度,本文基于Dias模型,以复电阻率代替不考虑地电体极化效应的直流电阻率,对CSAMT场源一维层状模型进行了正演模拟,为提取CSAMT信号中所含激电信息提供理论基础.结果表明,考虑激电参数后,视电阻率及相位响应曲线出现明显异常（包括远场、过渡场、近场）;极化前后振幅比值异常峰值、相位差值异常峰值可直观体现激电异常;异常峰值与极化层层厚、埋深以及电阻率变化有连续的对应关系.认为从频率域电磁法信号中提取激电信息有乐观的前景. 相似文献
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可控源电磁法(CSEM)的正演模拟与反演解释中常忽略激电介质的影响.本文基于电磁三维正反演开源平台ModEM,分别开展了陆地CSEM三维正反演以及考虑激电介质的陆地CSEM三维正演研究,并与一维模型解析解对比验证了三维计算的准确性.数值模拟结果显示,模型含激电效应与不含激电效应的电场E_x频率响应差异明显,激电效应会导致电场E_x幅值减小、相位增加,且对E_x的影响程度与激电异常体的频谱特性及观测的收发距均相关.合成数据的陆地CSEM反演结果显示,数据中含激电效应会使得反演出的异常体在深度、规模和电阻率值上都与真实异常体存在较大偏差,忽略观测数据中的激电效应会明显影响观测的准确性.本文研究表明当陆地CSEM三维观测资料中包含激电效应时,有必要考虑其影响. 相似文献
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《地球物理学进展》2017,(2)
复电阻率法(CR)又称为频谱激电法(SIP),是一种重要的激电分支方法,在矿产勘查中应用非常广泛.然而,在实际的频谱激电野外观测资料中,总是会受到不同程度的电磁耦合效应的影响.因此,研究同时存在激发极化效应和电磁效应的复电阻率性质,对频谱激电法的实际数据处理具有一定的参考价值.本文首先在均匀半空间条件下,进行了复电阻率法的正演模拟.分析了频率、收发距的改变对视电阻率和视相位的影响.然后在有低阻异常体存在情况下,同时采用三维积分方程法和三维有限差分法,研究了不同条件下视电阻率和视相位的变化.最后,根据对正演模拟结果的分析,总结出不同程度的电磁耦合效应对视电阻率及视相位的影响规律,为准确分析异常提供了依据. 相似文献
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地-井方位激电观测异常特征研究 总被引：1，自引：0，他引：1
为系统了解地-井方位激电异常特征,利用有限单元法对地-井方位激电观测在立方体、板状体等典型地电异常体上的响应进行正演计算,分析了异常体位置、方位距离等变化对观测的影响规律,讨论了地形、钻孔本身对地-井方位观测的影响等.研究结果表明地-井方位观测是探测井旁和井底盲矿体行之有效的方法,利用不同方位上的异常曲线特征,遵循异常场定性分析和"先井口、后其它方位"的分析方法,可大致确定异常体的电性特征和空间展布;地形和钻孔本身对地-井方位观测的影响主要集中在浅部区域. 相似文献
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基于伪随机发射的半航空频率域电磁测深方法具有信号强、采集速度快、成本低廉的勘探优势,近年来得到迅速发展,实际应用取得了较好的勘探效果．本文针对该领域在2.5D数值模拟中存在的一些核心问题．采用有限单元数值方法,分析讨论了电偶源加载方式、网格剖分、边界处理、观测区域、以及感应磁场随收发距和频率的分布特征．模型计算表明,采用均匀网格剖分、增加吸收边界条件能够提高有限单元法模拟精度．发现电偶极场源和长导线场源产生的感应磁场三分量Hx、Hy、Hz的场值在距离地面20 m的空气中具有如下特征：(1)当场源为电偶极源时,Hy对异常不敏感,而Hx和Hz及其转换的视电阻率异常特征明显,Hx在低阻体上方表现为“高阻特征”,且低频段特征比高频段特征明显;Hz的异常比较复杂,在AB偶极源中垂线两侧的异常会出现“对称特征”：左侧的低阻体特征为“先低后高”,右侧的低阻体为“先高后低”,左侧的高阻体特征为“先低后高”,右侧的高阻体为“先高后... 相似文献
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利用有限单元法对水下激发极化测深进行数值模拟以研究其异常特征和适用条件.水下的电阻率测深和激电测深均可对水底地质体进行近距离探测,提高探测分辨率.而水底地形对视电阻率测深的影响很大.水底极化体有限元正演模拟的结果表明,水底地形对激发极化测深结果没有影响.采用水下激发极化法进行地质体探测是可行、有效的.通过计算不同水体和水底岩石电阻率对视极化率幅值的影响发现,水体电阻率是影响水下极化率测深的主要因素.由于海水的电阻率过低,观测视极化率异常微弱而不适合开展水下激电工作. 相似文献
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在使用电偶极发射源的可控源电磁法(CSEM)勘探中,发射源的方位、长度、形状等对观测数据有重要的影响,然而现有的大部分三维数值模拟方法没有全面地将这些因素考虑进来,很多都只能应对非常简单的场源形态,例如单一方位的点电偶极子,这有可能显著降低模拟结果的准确性.本文实现了基于交错网格有限体积(FV)离散的海洋CSEM三维正演算法,能够模拟形态相对复杂的场源,包括任意方位的有限长直导线和弯曲导线发射源.该算法使用一次场/二次场方法,只需对二次场使用FV法求解,避免了场源的奇异性问题;一次场的计算为一维正演问题,使用准解析法求解,并且只要在计算一次场时考虑复杂的场源形态便可以实现同样场源的三维正演.通过与一维理论模型的解析解对比验证了三维程序的准确性,并针对三维理论模型进行了一系列正演测试,初步考察了场源形态对三维正演结果的影响. 相似文献
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Oziel Souza de Araújo Eduardo Chemas Hindi Augustinho Rigoti Fábio Henrique Rigoti 《Geophysical Prospecting》2019,67(7):1965-1976
Geophysical investigations using conventional techniques applied to groundwater exploration can often present strong limitations involving high financial costs, complex acquisition logistics and high ambiguity in results. Dispersion of the electric current flow, induced polarization) effects, cultural noises and shallow lateral heterogeneities represent the main problems faced by geoelectric methods in these types of surveys. Moreover, elements such as intrusions and mineralization at different depths may be responsible for signal attenuation as well as high resistivity in unsaturated zones and complex three-dimensional formations or clayey zones cause variations in the electric current. The focused source electromagnetic and differentially normalized method approaches can help to solve some these issues. Aiming at a higher signal-to-noise ratio, the focused source electromagnetic method and approaches of the differentially normalized method, first applied to petroleum exploration, are tested on a groundwater target, in a karst environment sectioned by a diabase dyke. We performed the processing and analysis on real IP resistivity profiling data acquired with two-way dipole-dipole array, guided by magnetic data acquired on the same profile, mapping a diabase dyke. The inversion of focused source electromagnetic method/differentially normalized method was not performed, instead that we converted the induced polarization–resistivity data to a differential signal to qualitatively prove the presence of aquifer. Joint interpretation of focused source electromagnetic method curves and inverted two-dimensional induced polarization–resistivity sections allowed for precise delineation of a conductive zone associated with the karst aquifer, le magnetics allowed for the definition of a neighbour dyke. The techniques have great potential in the aid of groundwater exploration, contributing substantially to the reduction of interpretation ambiguity. Focused source electromagnetic method/differentially normalized method/ approaches show that a simple linear combination of the conventional geoelectric data is able to remove the geological noise and provide the vertical focusing of the electric current. 相似文献
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D.C. FRASER 《Geophysical Prospecting》1981,29(4):639-651
Dipole-dipole induced polarization (IP) data are displayed typically as multi-level profiles, or as contours on vertical sectional plots referred to as pseudo-sections. The dipole-dipole array tends to yield IP anomalies in which the most anomalous values are displaced laterally from the source body. The data patterns are fairly interpretable on pseudo-sections or on multi-level profiles but are sufficiently complex to discourage the contouring of the data in plan. A method was developed for the presentation of dipole-dipole IP data on a contour map. The method consists of a simple averaging of data which can be performed manually if desired. It yields a single output value per station which reflects all levels of the pseudo-section, and is suitable for contouring in plan. The advantage of the technique is that it provides a quantitative picture of IP anomalies in their background or regional setting. 相似文献
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中心回线装置是瞬变电磁勘探中最常用的装置之一.中心回线装置的视电阻率一般从回线中心点场的公式出发导出.在现场实际施工中,为提高工作效率,把发射回线中部三分之一的区域作为观测范围.通过对场分布特征的分析研究表明,与中心点相比,观测区边缘处的感应电动势数值偏离达15%~25%,这与广泛存在于华北型煤系中赋存深度为400~1000 m的陷落柱、导水小断层等引起的异常相比,已经不可忽略.大定源回线公式可以准确地表示任意场点的感应电动势,由此导出视电阻率无边缘效应影响;观测按照中心回线方式并保持在近区进行,可使感应电动势和视电阻率之间的转换简单而直接.理论和实际应用结果表明,这些措施进一步提高了瞬变电磁探测中心回线方法的探测精度.在有上覆低阻屏蔽层的情况下,对埋深500~700 m的陷落柱给出了明显的异常反映,并被井下掘进所验证. 相似文献
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The induced polarization (IP) in rocks and minerals is of significance to the marine controlled-source electromagnetic (CSEM) field. We propose an adaptive finite-element algorithm for the 2.5D frequency-domain forward modeling of marine CSEM that considers the induced polarization. The geoelectrical model is discretized using an unstructured triangular elemental grid that accommodates the complex topography and geoelectrical structures. We use the Cole–Cole model to describe the IP and develop a complex resistivity forward modeling algorithm. We compare the simulation results with published 1D model results and subsequently calculate the electromagnetic field for variable azimuth sources, IP parameters, and topography. Finally, we analyze the IP effect on the marine CSEM field and show that IP of oil reservoirs and topography affects the marine CSEM electromagnetic field. 相似文献
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Jianping Xiang N.B. Jones Daizhan Cheng F.S. Schlindwein 《Geophysical Prospecting》2002,50(6):565-576
The problem of discrimination between a valid induced polarization (IP) response and electromagnetic (EM) coupling effects is considered and an effective solution is provided. First, a finite dimensional approximation to the Cole‐Cole model is investigated. Using the least‐squares approach, the parameters of the approximate model are obtained. Next, based on the analysis of overvoltage, a finite dimensional structure of the IP model is produced. Using this overvoltage‐based structure, a specific finite dimensional approximation of the Cole‐Cole model is proposed. Summarizing the analysis of the finite dimensional IP model, it is concluded that the proposed IP model, which fits the field data much better than the traditional Cole‐Cole model, is essentially an RC‐circuit. From a circuit‐analysis point of view, it is well known that an electromagnetic effect can be described by an RL‐circuit. The simulation results on experimental data support this conception. According to this observation, a new method to discriminate between a valid IP response and EM coupling effects is proposed as follows: (i) use a special finite dimensional model for IP–EM systems; (ii) obtain the parameters for the model using a least‐squares approach; (iii) separate RC‐type terms and RL‐type terms – the first models the IP behaviour, the latter represents the EM part. Simulation on experimental data shows that the method is very simple and effective. 相似文献
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The article discusses the excitation of transient induced polarization responses using current and voltage sources. The first method has found a wide application in induced polarization surveys and—directly or indirectly—in the theory of the induced polarization method. Typically, rectangular current pulses are injected into the earth via grounding electrodes, and decaying induced polarization voltage is measured during the pauses between pulses. In this case, only the secondary field is recorded in the absence of the primary field, which is an important advantage of this method. On the other hand, since the current injected into the ground is fully controlled by the source, this method does not allow studying induced polarization by measuring the current in the transmitter line or associated magnetic field. When energising the earth with voltage pulses, the measured quantity is the transient induced polarization current. In principle, this method allows induced polarization studies to be done by recording the transmitter line current, the associated magnetic field, or its rate of change. The decay of current in a grounded transmitter line depends not only on the induced polarization of the earth but also on the polarization of the grounding electrodes. This problem does not occur when induced polarization transients in the earth are excited inductively. A grounded transmitter line is a mixed‐type source; hence, for a purely inductive excitation of induced polarization transients, one should use an ungrounded loop, which is coupled to the earth solely by electromagnetic induction. 相似文献
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A. KEELI 《Geophysical Prospecting》1978,26(1):202-213
It has been shown that for a polarizable layer as a transmission medium there is an indirect proportionality between the frequency effect (fe) in induced polarization (IP) and the wave number of the electrical induced field. Making use of this relationship for a two layered earth a polarization transform function has been obtained. Since the mathematical expression for the polarization transform function is the same as that of the resistivity transform function, it is possible to make direct interpretation for IP frequency effect field curves. Thus, AA or QQ type resistivity sequences can be interpreted from induced polarization response of a horizontally stratified earth without resistivity extrema. A depth factor has been defined in order to obtain the true depth using the apparent depth. In this way, some electromagnetic effects between horizontal layers with different polarizabilities can partly be eliminated. 相似文献