Journal articles: 'EM inversion'

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Zhang, Zhiyi, Partha S. Routh, Douglas W. Oldenburg, David L. Alumbaugh, and Gregory A. Newman. "Reconstruction of 1-D conductivity from dual‐loop EM data." GEOPHYSICS 65, no. 2 (March 2000): 492–501. http://dx.doi.org/10.1190/1.1444743.

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Inversions of electromagnetic data from different coil configurations provide independent information about geological structures. We develop a 1-D inversion algorithm that can invert data from the horizontal coplanar (HC), vertical coplanar, coaxial (CA), and perpendicular coil configurations separately or jointly. The inverse problem is solved by minimizing a model objective function subject to data constraints. Tests using synthetic data from 1-D models indicate that if data are collected at a sufficient number of frequencies, then the recovered models from individual inversions of different coil systems can be quite similar. However, if only a limited number of frequencies are available, then joint inversion of data from different coils produces a better model than the individual inversions. Tests on 3-D synthetic data sets indicate that 1-D inversions can be used as a fast and approximate tool to locate anomalies in the subsurface. Also for the test example presented here, the joint inversion of HC and CA data over a 3-D conductivity provided a better model than that produced by the individual inversion of the data sets.

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Um, Evan Schankee, Michael Commer, and Gregory A. Newman. "A strategy for coupled 3D imaging of large-scale seismic and electromagnetic data sets: Application to subsalt imaging." GEOPHYSICS 79, no. 3 (May 1, 2014): ID1—ID13. http://dx.doi.org/10.1190/geo2013-0053.1.

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Offshore seismic and electromagnetic (EM) imaging for hydrocarbons can require up to tens of millions of parameters to describe the 3D distribution of complex seabed geology and relevant geophysical attributes. The imaging and data volumes for such problems are enormous. Descent-based methods are the only viable imaging approach, where it is often challenging to manage the convergence of stand-alone seismic and EM inversion experiments. When a joint seismic-EM inversion is implemented, convergence problems with descent-based methods are further aggravated. Moreover, resolution mismatches between seismic and EM pose another challenge for joint inversion. To overcome these problems, we evaluated a coupled seismic-EM inversion workflow and applied it to a set of full-wave-seismic, magnetotelluric (MT) and controlled-source electromagnetic (CSEM) data for subsalt imaging. In our workflow, we address disparate resolution properties between seismic and EM data by implementing the seismic inversion in the Laplace domain, where the wave equation is transformed into a diffusion equation. The resolution of seismic data thus becomes comparable to that of EM data. To mitigate the convergence problems, the full joint seismic-EM inverse problem is split into manageable components: separate seismic and EM inversions and an intermediate step that enforces structural coupling through a cross-gradient-only inversion and resistivity-velocity crossplots. In this workflow, stand-alone seismic and MT inversion are performed first. The cross-gradient-only inversion and the crossplots are used to precondition the resistivity and velocity models for subsequent stand-alone inversions. By repeating the sequence of the stand-alone seismic, MT, and cross-gradient-only inversions along with the crossplots, we introduce the seismic structural information into the resistivity model, and vice versa, significantly improving the salt geometry in both resistivity and velocity images. We conclude that the improved salt geometry can then be used to precondition a starting model for CSEM inversions, yielding significant improvement in the resistivity images of hydrocarbon reservoirs adjacent to the salt.

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Wilson, Glenn A., Art Raiche, Fred Sugeng, and Robert G. Ellis. "Practical 3D EM Inversion." ASEG Extended Abstracts 2007, no. 1 (December 1, 2007): 1. http://dx.doi.org/10.1071/aseg2007ab165.

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Hu, Wenyi, Aria Abubakar, and Tarek M. Habashy. "Joint electromagnetic and seismic inversion using structural constraints." GEOPHYSICS 74, no. 6 (November 2009): R99—R109. http://dx.doi.org/10.1190/1.3246586.

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We have developed a frequency-domain joint electromagnetic (EM) and seismic inversion algorithm for reservoir evaluation and exploration applications. EM and seismic data are jointly inverted using a cross-gradient constraint that enforces structural similarity between the conductivity image and the compressional wave (P-wave) velocity image. The inversion algorithm is based on a Gauss-Newton optimization approach. Because of the ill-posed nature of the inverse problem, regularization is used to constrain the solution. The multiplicative regularization technique selects the regularization parameters automatically, improving the robustness of the algorithm. A multifrequency data-weighting scheme prevents the high-frequency data from dominating the inversion process. When the joint-inversion algorithm is applied in integrating marine controlled-source electromagnetic data with surface seismic data for subsea reservoir exploration applications and in integrating crosswell EM and sonic data for reservoir monitoring and evaluation applications, results improve significantly over those obtained from separate EM or seismic inversions.

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Ogunbo, Jide Nosakare, Guy Marquis, Jie Zhang, and Weizhong Wang. "Joint inversion of seismic traveltime and frequency-domain airborne electromagnetic data for hydrocarbon exploration." GEOPHYSICS 83, no. 2 (March 1, 2018): U9—U22. http://dx.doi.org/10.1190/geo2017-0112.1.

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Geophysical joint inversion requires the setting of a few parameters for optimum performance of the process. However, there are yet no known detailed procedures for selecting the various parameters for performing the joint inversion. Previous works on the joint inversion of electromagnetic (EM) and seismic data have reported parameter applications for data sets acquired from the same dimensional geometry (either in two dimensions or three dimensions) and few on variant geometry. But none has discussed the parameter selections for the joint inversion of methods from variant geometry (for example, a 2D seismic travel and pseudo-2D frequency-domain EM data). With the advantage of affordable computational cost and the sufficient approximation of a 1D EM model in a horizontally layered sedimentary environment, we are able to set optimum joint inversion parameters to perform structurally constrained joint 2D seismic traveltime and pseudo-2D EM data for hydrocarbon exploration. From the synthetic experiments, even in the presence of noise, we are able to prescribe the rules for optimum parameter setting for the joint inversion, including the choice of initial model and the cross-gradient weighting. We apply these rules on field data to reconstruct a more reliable subsurface velocity model than the one obtained by the traveltime inversions alone. We expect that this approach will be useful for performing joint inversion of the seismic traveltime and frequency-domain EM data for the production of hydrocarbon.

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Guo, Zhenwei, Hefeng Dong, and Åge Kristensen. "Image-guided regularization of marine electromagnetic inversion." GEOPHYSICS 82, no. 4 (July 1, 2017): E221—E232. http://dx.doi.org/10.1190/geo2016-0130.1.

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Marine electromagnetic (EM) inverse methods have recently been rapidly developed for offshore exploration. However, inverted resistivity results with low resolution are provided by the EM method. To improve this quality of the results, we have developed an image-guided regularization method for inversion of the marine EM data. The method incorporates seismic constraints into EM inversion. Information is extracted from seismic/geologic images and consists of the metric tensor field and sampling on the geologic structure. In addition to the regularization, geologic horizons picked from the seismic images and samplings on the structure can be used to generate an irregular sparse mesh. Compared with an unstructured regular dense mesh, a coherence-based irregular sparse mesh can reduce computational costs. Furthermore, image-guided regularization represents an improvement compared with traditional regularization that are structurally based on seismic images by following geologic features more closely and handling anomalies better. We have determined that image-guided regularization improves the results of EM inversions with irregular sparse meshes. The image-guided regularized inversion can be applied to marine controlled-source electromagnetic (CSEM) data and magnetotelluric (MT) data, and it can be used for joint inversion of CSEM and MT data. Regarding its application to real data, image-guided inversion was successfully applied to CSEM data on the Troll area, using an anisotropic model.

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Xie, Ganquan, Jianhua Li, and Feng Xie. "Advanced GILD EM Modeling And Inversion." PIERS Online 1, no. 1 (2005): 105–9. http://dx.doi.org/10.2529/piers041206094200.

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Ruan, Baiyao, and Youxue Wang. "New Topography Inversion Using EM Field." PIERS Online 1, no. 1 (2005): 79–83. http://dx.doi.org/10.2529/piers111504202500.

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Cho, In-ky, and Kyoung-chan Ahn. "Underground EM 1D Modeling and Inversion." Journal of the Korean Society of Mineral and Energy Resources Engineers 58, no. 5 (October 1, 2021): 464–74. http://dx.doi.org/10.32390/ksmer.2021.58.5.464.

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Ellis, Robert G., and Ian N. MacLeod. "Quasi3D Inversion of Airborne EM Data." ASEG Extended Abstracts 2015, no. 1 (December 2015): 1–4. http://dx.doi.org/10.1071/aseg2015ab099.

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Yin, Changchun, and Greg Hodges. "Simulated annealing for airborne EM inversion." GEOPHYSICS 72, no. 4 (July 2007): F189—F195. http://dx.doi.org/10.1190/1.2736195.

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The traditional algorithms for airborne electromagnetic (EM) inversion, e.g., the Marquardt-Levenberg method, generally run only a downhill search. Consequently, the model solutions are strongly dependent on the starting model and are easily trapped in local minima. Simulated annealing (SA) starts from the Boltzmann distribution and runs both downhill and uphill searches, rendering the searching process to easily jump out of local minima and converge to a global minimum. In the SA process, the calculation of Jacobian derivatives can be avoided because no preferred searching direction is required as in the case of the traditional algorithms. We apply SA technology for airborne EM inversion by comparing the inversion with a thermodynamic process, and we discuss specifically the SA procedure with respect to model configuration, random walk for model updates, objective function, and annealing schedule. We demonstrate the SA flexibility for starting models by allowing the model parameters to vary in a large range (far away from the true model). Further, we choose a temperature-dependent random walk for model updates and an exponential cooling schedule for the SA searching process. The initial temperature for the SA cooling scheme is chosen differently for different model parameters according to their resolvabilities. We examine the effectiveness of the algorithm for airborne EM by inverting both theoretical and survey data and by comparing the results with those from the traditional algorithms.

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Xie, G. Q., J. Li, L. Xie, and F. Xie. "A GL Metro Carlo EM Inversion." Journal of Electromagnetic Waves and Applications 20, no. 14 (January 2006): 1991–2000. http://dx.doi.org/10.1163/156939306779322756.

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Chelyadina, Natalya, Natalya Pospelova, Mark Popov, Ludmila Smyrnova, Irina Kharchuk, and Vitaliy Ryabushko. "SEX INVERSION IN CULTIVATED MUSSELS MYTILUS GALLOPROVINCIALIS LAM. (CRIMEA, BLACK SEA) UNDER INFLUENCE OF EXTERNAL ENVIRONMENTAL FACTORS." Ecologica Montenegrina 19 (September 13, 2018): 26–31. http://dx.doi.org/10.37828/em.2018.19.3.

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In the last decade, there has been a shift in the sex ratio of the mussel Mytilus galloprovincialis in the Black Sea towards increase of males. In modern literature, focus is mainly on mechanisms of sex inheritance in mussels and hormonal regulation of the reproduction, and there is no information on sex inversion in M. galloprovincialis under the influence of environmental factors. The goal of this work is to establish the fact of sex change in mussels cultivated near the coast of Crimea under the influence of some external environmental factors. We establish that mussels change sex from female to male, but some specimens become hermaphrodites, with their fraction reaching 13%. Under unfavorable environmental conditions, mussel females change sex, and their mortality rises up to 69%. In water areas subject to anthropogenic impact, the proportion of sex inversion in the mollusks may be as high as 58%. The influence of various adverse environmental factors on sex inversion in mussel females is unequal, and its strength decreases in the following order: diesel fuel > hypoxia > anionic detergents > starvation.

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Zhang, Z., and J. Xiao. "Inversions of surface and borehole data from large‐loop transient electromagnetic system over a 1‐D earth." GEOPHYSICS 66, no. 4 (July 2001): 1090–96. http://dx.doi.org/10.1190/1.1487056.

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Large‐loop electromagnetic (EM) systems that measure transient EM (TEM) data on the surface or in boreholes have shown increased application in exploration geophysics. Accurate interpretation of borehole TEM data is necessary to discover deep hidden targets that cannot be detected with surface systems. However, the inversion of borehole TEM data has not been fully addressed. In this paper, we study the propagation of the TEM field from a large‐loop EM borehole system inside a layered earth and develop a new inversion algorithm to reconstruct layered conductivity structures from large‐loop TEM data measured with both surface and borehole configurations. The magnetic field and sensitivities are first computed in the frequency domain and are then transformed into the time domain where the inversion is performed. The surface data have a higher S/N ratio at early time channels, while the borehole data have a higher S/N ratio at late time channels. Consequently, the surface data can be inverted to better resolve shallow structures, and the borehole data can be used to better detect deep structures. The merits of joint inversions of borehole and surface data are explored. We test our inversion algorithm using numeric examples.

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Brodie, Ross, and Malcolm Sambridge. "A holistic approach to inversion of frequency-domain airborne EM data." GEOPHYSICS 71, no. 6 (November 2006): G301—G312. http://dx.doi.org/10.1190/1.2356112.

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We have developed a holistic method for simultaneously calibrating, processing, and inverting frequency-domain airborne electromagnetic data. A spline-based, 3D, layered conductivity model covering the complete survey area was recovered through inversion of the entire raw airborne data set and available independent conductivity and interface-depth data. The holistic inversion formulation includes a mathematical model to account for systematic calibration errors such as incorrect gain and zero-level drift. By taking these elements into account in the inversion, the need to preprocess the airborne data prior to inversion is eliminated. Conventional processing schemes involve the sequential application of a number of calibration corrections, with data from each frequency treated separately. This is followed by inversion of each multifrequency sample in isolation from other samples.By simultaneously considering all of the available information in a holistic inversion, we are able to exploit interfrequency and spatial-coherency characteristics of the data. The formulation ensures that the conductivity and calibration models are optimal with respect to the airborne data and prior information. Introduction of interfrequency inconsistency and multistage error propagation stemming from the sequential nature of conventional processing schemes is also avoided. We confirm that accurate conductivity and calibration parameter values are recovered from holistic inversion of synthetic data sets. We demonstrate that the results from holistic inversion of raw survey data are superior to the output of conventional 1D inversion of final processed data. In addition to the technical benefits, we expect that holistic inversion will reduce costs by avoiding the expensive calibration-processing-recalibration paradigm. Furthermore, savings may also be made because specific high-altitude zero-level observations, needed for conventional processing, may not be required.

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Zhang, Bo, Changchun Yin, Yunhe Liu, Xiuyan Ren, Vikas C. Baranwal, and Bin Xiong. "3D inversion of large-scale frequency-domain airborne electromagnetic data using unstructured local mesh." GEOPHYSICS 86, no. 5 (August 4, 2021): E333—E342. http://dx.doi.org/10.1190/geo2020-0243.1.

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Airborne electromagnetic (AEM) methods have been more and more widely used in mineral exploration, environmental and engineering studies, and ground water investigation. However, compared with ground-based electromagnetic (EM) methods, such as magnetotelluric or controlled-source EM, AEM methods generally produce large amounts of data, which leads to very costly 3D EM inversions. We have developed a new 3D AEM inversion scheme based on the finite-element method and unstructured tetrahedral local meshes. This is different from the traditional local mesh method in that the traditional method uses regular cuboids for 3D AEM inversions, whereas our scheme uses irregular tetrahedral meshes that can easily accommodate the topography and complex underground structure. Moreover, because we create our local mesh by extracting from part of the global model mesh, the relationship between the local and global meshes is straightforward, so we can easily create a projection of the Jacobian matrix between global and local meshes and rapidly construct the global Jacobian matrix for 3D EM inversions. After formulating the boundary value problem based on the finite-element method, we verify the accuracy of our modeling algorithm by checking against the semianalytical solution for a homogeneous half-space model, and we test our inversion algorithm by running inversions on synthetic and survey data collected over Vesterålen, Norway. The numerical experiments demonstrate that our method can model the AEM responses at high accuracy and recover the subsurface main resistivity structures from synthetic and field data.

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Li, Jianhua, Ganquan Xie, and Feng Xie. "New Stochastic AGLID EM Modeling and Inversion." PIERS Online 2, no. 5 (2006): 490–94. http://dx.doi.org/10.2529/piers051007192902.

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Davis, Aaron, and Juerg Hauser. "Blocking borehole conductivity logs at the resolution of above-ground electromagnetic systems." GEOPHYSICS 85, no. 2 (March 1, 2020): E67—E77. http://dx.doi.org/10.1190/geo2019-0095.1.

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Borehole conductivity logs provide an in situ measurement of the electrical conductivity of the subsurface. Despite the measurements being a proxy for the true earth structure, they are often used as ground truth when inferring subsurface electrical conductivity boundaries between lithologies. Borehole conductivity measurements are therefore commonly used to plan and benchmark electromagnetic (EM) surveys and to establish the credibility of a given inversion technique. A consequence of the diffusion physics of EM prospecting is that not all subsurface features present in a conductivity log can be resolved by an EM system, nor can they be recovered by a subsequent inversion. Quantification of the ability of an EM system to determine layer boundaries in the subsurface is therefore an issue meriting investigation. We have developed a reversible-jump Markov chain Monte Carlo (RJMCMC) method to segment borehole conductivity logs at the scale recoverable by a given EM system as the foundation for an objective comparison between the inversion results and conductivity logs. A common consequence of RJMCMC inversions for EM problems is that few layers are required to fit the data. Similarly, we find that a borehole log blocked at the scale sensed by an EM system consists of a limited number of segments. Segmentation of borehole conductivity logs is determined by the physics of EM prospecting and by factors such as base frequency, number of gates, system geometry, and noise levels. For a survey line intersecting a borehole near Carnarvon, Western Australia, we see that different inversion schemes result in images of the subsurface that are consistent with a borehole conductivity log segmented according to the mechanics of the EM system and accounting for the physics of EM prospecting.

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Schaller, Andreas, Rita Streich, Guy Drijkoningen, Oliver Ritter, and Evert Slob. "A land-based controlled-source electromagnetic method for oil field exploration: An example from the Schoonebeek oil field." GEOPHYSICS 83, no. 2 (March 1, 2018): WB1—WB17. http://dx.doi.org/10.1190/geo2017-0022.1.

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Controlled-source electromagnetic (CSEM) data are sensitive to the subsurface resistivity distribution, but 3D inversion results are ambiguous, and in-depth interpretation is challenging. Resolution and sensitivity analysis as well as the influence of noise on resolution have been used to quantify 3D inversion performance. Based on these numerical studies, a land-based CSEM survey was designed and carried out at the Schoonebeek oil field, the Netherlands. The acquired data were processed and subsequently inverted for the resistivity distribution. The 1D and 3D inversion of horizontal electric-field data show the reservoir at the right depth, matching well-log data without using a priori knowledge about the actual reservoir depth. We used a 1D model with fine layering as a starting model for 3D inversion. Synthetic data inversions and sensitivity tests demonstrate that resistive or conductive bodies inside the reservoir zone may be well-detectable with our limited acquisition geometry. Spatial variations in the reservoir resistivity are visible in the measured data and after inversion by assuming good knowledge of the background resistivity distribution. The reservoir resistivity and size, however, have to be interpreted with care considering the intrinsically low resolution of electromagnetic (EM) which is further reduced by manmade EM noise.

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Clegg, Nigel, Endre Eriksen, Kevin Best, Ingeborg Tøllefsen, Artur Kotwicki, and David Marchant. "Mapping Complex Injectite Bodies With Multiwell Electromagnetic 3D Inversion Data." Petrophysics – The SPWLA Journal of Formation Evaluation and Reservoir Description 62, no. 1 (February 1, 2021): 109–21. http://dx.doi.org/10.30632/pjv62n1-2021a7.

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Electromagnetic (EM) inversion processing of ultradeep resistivity data has advanced from one dimensional (1D) to three dimensional (3D). These advances have helped improve the geological complexity that can be imaged and provide additional reservoir information. The large depth of investigation (DOI) of ultradeep LWD EM tools means that distant boundaries might not be detected by any other sensor in the tool string, making it difficult to verify the results. As inversion results represent a model of the subsurface resistivity distribution and not a direct measurement, it is important to have high confidence in the results. Directly comparing the component data measured by the tool to the modeled component data from the inversion across multiple frequencies provides confidence in the resultant model where the data have a close fit. However, as measurement sensitivities decrease with distance, there is potential for non-uniqueness, generating a model that is geologically unrealistic. Increased confidence can be achieved with independent verification of the model. This paper details results from a trilateral well in an injectite reservoir wherein the sand distribution was expected to be complex. The 1D inversions showed the vertical distribution of the sand, but the results were sometimes distorted by lateral resistivity variations. The 3D inversion of the data allowed the lateral resistivity variations to be resolved. These results can be corroborated by direct comparison with azimuthal resistivity images. Additionally, the laterals all diverged from the same main bore and remained close together initially in an area containing major sand injectites. The 3D inversions from two of the wells overlap and define similarly shaped structures, providing confidence in the 3D inversion model. In complex geobodies, such as the injectites described, significant lateral variation in the reservoir distribution is expected, which is not captured by 1D inversion. Understanding the shape of these structures and their potential connectivity using 3D inversion provides a major increase in reservoir understanding that is critical to completion design.

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Hoversten, G. M., G. A. Newman, H. F. Morrison, E. Gasperikova, and John‐Inge Berg. "Reservoir characterization using crosswell electromagnetic inversion: A feasibility study for the Snorre field, North Sea." GEOPHYSICS 66, no. 4 (July 2001): 1177–89. http://dx.doi.org/10.1190/1.1487064.

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The spatial resolution of a commercially available crosswell electromagnetic (EM) system is demonstrated using models derived from three time steps from a reservoir simulation of the Snorre field in the North Sea. The numerical simulation of the Snorre field waterflood shows that crosswell EM field measurements provide high sensitivity to changes in the reservoir over time. This sensitivity is achieved by combining the reservoir geometry derived from surface 3‐D seismic interpretation, reservoir conductivities at well locations, and constrained EM inversion of the reservoir’s electrical conductivity. Inversions of 2‐D and 3‐D numerical models show that the changes in electrical conductivity attributable to changes in water saturation can be quantitatively mapped as a function of time. The inversions provide smooth estimates of the spatial variation of reservoir electrical conductivity that can discriminate between the level of water saturation at different stages of the waterflood. Inversions performed on 2‐D data show that for the Snorre example, 3%–5% Gaussian random noise (depending on the model) can be added without a significant degradation in the inverse models. Two‐dimensional inversions of the full 3‐D data in the Snorre example can map the vertical average electrical conductivity within the reservoir in the interwell region almost as well as when the model is two dimensional (constant in strike direction). The effect of 3‐D structure does not seriously degrade 2‐D inversion in the Snorre example‐even between wells that lie in a line parallel to structure. A series of 2‐D inversions where various constraints and starting models are used demonstrates the importance of incorporating a priori information in the form of starting models and restricting the inversion domain to the reservoir zone. These tests show that totally unconstrained, smooth inversions of the interwell volume provide very limited quantitative information. However, when the reservoir geometry is constrained by seismic data and starting models are provided by linear interpolation of conductivities at well locations, the reservoir’s vertical average electrical conductivity can be predicted to within a few percent by 2‐D inversion. The snorre field consists of a full‐scale reservoir with interwell spacings that exceed 1 km where previous work has demonstrated the applicability of crosswell EM in shallow reservoirs with well separations on the order of 100 m. The simulations show that, given current transmitter and receiver technology, the magnetic fields could be measured in the Snorre field in steel‐cased wells separated from the transmitter by up to 725 m.

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McMillan, Michael S., and Douglas W. Oldenburg. "Cooperative constrained inversion of multiple electromagnetic data sets." GEOPHYSICS 79, no. 4 (July 1, 2014): B173—B185. http://dx.doi.org/10.1190/geo2014-0029.1.

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We evaluated a method for cooperatively inverting multiple electromagnetic (EM) data sets with bound constraints to produce a consistent 3D resistivity model with improved resolution. Field data from the Antonio gold deposit in Peru and synthetic data were used to demonstrate this technique. We first separately inverted field airborne time-domain EM (AEM), controlled-source audio-frequency magnetotellurics (CSAMT), and direct current resistivity measurements. Each individual inversion recovered a resistor related to gold-hosted silica alteration within a relatively conductive background. The outline of the resistor in each inversion was in reasonable agreement with the mapped extent of known near-surface silica alteration. Variations between resistor recoveries in each 3D inversion model motivated a subsequent cooperative method, in which AEM data were inverted sequentially with a combined CSAMT and DC data set. This cooperative approach was first applied to a synthetic inversion over an Antonio-like simulated resistivity model, and the inversion result was both qualitatively and quantitatively closer to the true synthetic model compared to individual inversions. Using the same cooperative method, field data were inverted to produce a model that defined the target resistor while agreeing with all data sets. To test the benefit of borehole constraints, synthetic boreholes were added to the inversion as upper and lower bounds at locations of existing boreholes. The ensuing cooperative constrained synthetic inversion model had the closest match to the true simulated resistivity distribution. Bound constraints from field boreholes were then calculated by a regression relationship among the total sulfur content, alteration type, and resistivity measurements from rock samples and incorporated into the inversion. The resulting cooperative constrained field inversion model clearly imaged the resistive silica zone, extended the area of interpreted alteration, and also highlighted conductive zones within the resistive region potentially linked to sulfide and gold mineralization.

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Tuncer, Volkan, Martyn J. Unsworth, Weerachai Siripunvaraporn, and James A. Craven. "Exploration for unconformity-type uranium deposits with audiomagnetotelluric data: A case study from the McArthur River mine, Saskatchewan, Canada." GEOPHYSICS 71, no. 6 (November 2006): B201—B209. http://dx.doi.org/10.1190/1.2348780.

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Unconformity-type deposits supply a significant amount of the world’s uranium and consist of uranium that is generally codeposited with graphite in a fault zone. The low resistivity of the graphite produces a significant contrast in electrical resistivity, which can be located with electromagnetic (EM) methods. The Athabasca Basin in Western Canada hosts significant uranium deposits, and exploration in deeper parts of the basin has required the application of new EM methods. This paper presents an evaluation of the audiomagnetotelluric (AMT) exploration method at the McArthur River mine in the Athabasca Basin. AMT data were collected at 132 stations on a grid, and two-dimensional (2D) and three-dimensional (3D) inversions were used to generate resistivity models. These models showed two major results: (1) a significant conductor coincident with a major basement fault (P2) and the uranium deposits (this conductor begins at the unconformity at a depth of [Formula: see text] and extends to a depth of at least three km) and (2) a resistive halo which might be caused by the silicification associated with mineralization. However, synthetic inversions showed that this halo could be an artifact of smoothing function in the inversion scheme. The 2D inversions were validated by synthetic inversions, comparison with the 3D inversion models, and correlation with well-log information. 3D AMT forward modeling showed that strong 3D effects are not present in the AMT impedance data. Induction vectors showed more evidence of complexity, but the inclusion of these data in the inversion improved subsurface resolution.

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Schultz, G., and C. Ruppel. "Inversion of inductive electromagnetic data in highly conductive terrains." GEOPHYSICS 70, no. 1 (January 2005): G16—G28. http://dx.doi.org/10.1190/1.1852775.

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Despite the increasing use of controlled-source frequency-domain EM data to characterize shallow subsurface structures, relatively few inversion algorithms have been widely applied to data from real-world settings, particularly in high-conductivity terrains. In this study, we develop robust and convergent regularized, least-squares inversion algorithms based on both linear and nonlinear formulations of mutual dipole induction for the forward problem. A modified version of the discrepancy principle based on a priori information is implemented to select optimal smoothing parameters that simultaneously guarantee the stability and best-fit criteria. To investigate the problems of resolution and equivalence, we consider typical layered-earth models in one and two dimensions using both synthetic and observed data. Synthetic examples show that inversions based on the nonlinear forward model more accurately resolve subsurface structure, and that inversions based on the linear forward model tend to drastically underpredict high conductivities at depth. Inversions of actual field data from well-characterized sites (e.g., National Geotechnical Experimentation Site; sand-dominated coastal aquifer in the Georgia Bight) are used to test the applicability of the model to terrains with different characteristic conductivity structure. A comparison of our inversion results with existing cone-penetrometer and downhole-conductivity data from these field sites demonstrates the ability of the inversions to constrain conductivity variations in practical applications.

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Purnamasari, Anastasia Neni Candra. "Metode Inversi AVO Simultan untuk Mengetahui Sebaran Hidrokarbon Formasi Baturaja, Lapangan "Wine”, Cekungan Sumatra Selatan." Jurnal Offshore: Oil, Production Facilities and Renewable Energy 1, no. 1 (July 13, 2017): 26. http://dx.doi.org/10.30588/jo.v1i1.239.

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Data seismik 3D (CDP gather) pada daerah penelitian dilakukan proses inversi prestack yaitu inversi AVO simultan untuk mengetahui sebaran hidrokarbon. Data seismik 3D terbentang dengan jangkauan inline 1003-1302 dan xline 5002-5300. Metode inversi AVO simultan dilakukan dengan data masukan berupa angle stack yang diinversi secara bersama-sama (simultan) untuk menghasilkan impedansi-P, impedansi-S dan densitas. Dari hasil inversi impedansi-P dan inversi impedansi-S didapatkan nilai lambda-rho dan mu-rho sebagai hasil turunannya. Kisaran nilai hasil inversi impedansi-P, impedansi-S, densitas, lambda-rho dan mu-rho pada porous limestone formasi Baturaja yaitu nilai impedansi-P sekitar 11000-13500 m/s*g/cc, nilai impedansi-S sekitar 6500-7400 m/s*g/cc, nilai densitas sekitar 2,52-2,6 g/cc, nilai lambda-rho sekitar 36-70 Gpa*g/cc dan nilai mu-rho sekitar 41-59 Gpa*g/cc. Berdasarkan map slice hasil inversi impedansi-P, map slice hasil inversi impedansi-S, map slice hasil inversi densitas, map slice hasil inversi lambda-rho dan map slice hasil inversi mu-rho dapat diketahui area persebaran hidrokarbon pada formasi Baturaja. Persebaran hidrokarbon berada di sekitar sumur TT.3D seismic data (CDP gather) in the study area was carried out a prestack inversion process, namely simultaneous AVO inversion to determine the distribution of hydrocarbons. 3D seismic data stretches with inline range 1003-1302 and xline 5002-5300. Simultaneous AVO inversion method is done with input data in the form of angle stack which is inverted together (simultaneously) to produce P-impedance, S-impedance and density. From the results of P-impedance inversion and S-impedance inversion, the values of lambda-rho and mu-rho are derived as a result of their derivatives. The range of values of P-impedance inversion, S-impedance, density, lambda-rho and mu-rho in porous limestone formation i.e. the P-impedance value around 11000-13500 m/s*g/cc, the S-impedance value around 6500-7400 m/s*g/cc, the density value around 2.52-2.6 g/cc, the lambda-value rho around 36-70 Gpa*g/cc and your value around 41-59 Gpa*g/cc. Based on the P-impedance inversion map slice, S-impedance inversion map slice, density inversion map slice, lambda-rho inversion map slice and mu-rho inversion map slice can be known the area of hydrocarbon distribution in the Baturaja formation. Hydrocarbon spread is around the TT well.

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26

Raiche, Art. "Practical 3D airborne EM inversion in complex terranes." ASEG Extended Abstracts 2004, no. 1 (December 2004): 1–4. http://dx.doi.org/10.1071/aseg2004ab118.

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Raiche, Art, Fred Sugeng, and Glenn Wilson. "Practical 3D EM inversion – the P223F software suite." ASEG Extended Abstracts 2007, no. 1 (December 1, 2007): 1–5. http://dx.doi.org/10.1071/aseg2007ab114.

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Scholl, C., and F. Miorelli. "Otze - Airborne EM Inversion on Unstructured Model Grids." ASEG Extended Abstracts 2018, no. 1 (December 2018): 1–7. http://dx.doi.org/10.1071/aseg2018abm2_2e.

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Scholl, Carsten, and Federico Miorelli. "Airborne EM inversion on vertically unstructured model grids." Exploration Geophysics 51, no. 1 (October 1, 2019): 108–21. http://dx.doi.org/10.1080/08123985.2019.1668239.

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Jung, Hyun-Key. "Loop-loop EM Inversion for a Conducting Sphere." Journal of the Korean Society of Mineral and Energy Resources Engineers 51, no. 5 (October 1, 2014): 696–704. http://dx.doi.org/10.12972/ksmer.2014.51.5.696.

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Song, Xiaoqian, Maokun Li, Fan Yang, Shenheng Xu, and Aria Abubakar. "Three-Dimensional Joint Inversion of EM and Acoustic Data Based on Contrast Source Inversion." IEEE Journal on Multiscale and Multiphysics Computational Techniques 5 (2020): 28–36. http://dx.doi.org/10.1109/jmmct.2020.2974677.

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Gascón. "La vida es sueño Reimagined: Inversion, Mimicry, and Communitas in Teatro Inverso’s Rosaura (2018)." Comedia Performance 17, no. 1 (2020): 25. http://dx.doi.org/10.5325/comeperf.17.1.0025.

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Noh, Kyubo, Seokmin Oh, Soon Jee Seol, and Joongmoo Byun. "3D sequential inversion of frequency-domain airborne electromagnetic data to determine conductive and magnetic heterogeneities." GEOPHYSICS 83, no. 5 (September 1, 2018): E357—E369. http://dx.doi.org/10.1190/geo2017-0668.1.

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We have developed two inversion workflows that sequentially invert conductivity and susceptibility models from a frequency-domain controlled-source electromagnetic data set. Both workflows start with conductivity inversion using electromagnetic (EM) kernel and out-of-phase component data, which is mainly sensitive to conductivity, and then we adopt the susceptibility inversion using in-phase component data. The difference between these two workflows is in the susceptibility inversion algorithm: One uses an EM kernel and a conductivity model as the input model; the other uses a magnetostatic kernel and a conductivity model to generate the appropriate input data. Because the appropriate input data for magnetostatic inversion should not contain the EM induction effect, the in-phase induction effect is simulated through the conductivity model obtained by inverting out-of-phase data and subtracting them from observed in-phase data to generate an “induction-subtracted” in-phase data set that becomes input data for magnetostatic inversion. For magnetostatic inversion, we used a linear magnetostatic kernel to enable rapid computation. Then, we applied the two inversion workflows to a field data set of a DIGHEM survey, and we successfully reconstructed the conductivity and susceptibility models from each workflow using two zones within the data sets, in which conductive and susceptible anomalies were present. One important finding is that the susceptibility inversion results obtained from two different workflows are very similar to each other. However, computational time can be significantly saved with linear magnetostatic inversion. We found out how the results of the conductivity and susceptibility models could be well-imaged using a sequential inversion workflow and also how magnetostatic inversion could be used efficiently for airborne EM data inversion.

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Liu, Yunhe, and Changchun Yin. "3D inversion for multipulse airborne transient electromagnetic data." GEOPHYSICS 81, no. 6 (November 2016): E401—E408. http://dx.doi.org/10.1190/geo2015-0481.1.

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Multipulse airborne transient electromagnetic (ATEM) systems transmit one high-power pulse and one low-power pulse containing more high-frequency EM signals. Such systems have better near-surface resolutions while maintaining the depth of exploration of other conventional systems. ATEM systems are especially suitable for geologic mapping and mineral exploration. The inversion of multipulse ATEM data has been mainly limited to 1D modeling, which is not suitable for complex underground structures. We have investigated an algorithm for 3D multipulse ATEM data inversion based on direct Gauss-Newton optimization with quite-fast convergence. The forward problems were solved in the frequency-domain based on the secondary scattered electrical field equation, and then the inverse Fourier transform and the convolution with transmitting waveform were applied to calculate the arbitrary waveform response and sensitivity matrix in the time domain. To optimize the number of computations and memory, we further used an EM “footprint” concept in our inversions to reduce the forward model size and sparse the sensitivity matrix. The inversion results of synthetic data showed that our 3D algorithm is very effective for inverting the multipulse data with results combining advantageous resolutions of different transmitting pulses. Finally, we applied our algorithm to invert real survey data obtained at McMurray, Alberta, Canada, to further test its effectiveness.

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Wilt, M. J., and J. P. Williams. "Layered model inversion of central-loop EM soundings near a geological contact." Exploration Geophysics 20, no. 2 (1989): 71. http://dx.doi.org/10.1071/eg989071.

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Central-loop time-domain EM is a widely used method for depth sounding due to its relative insensitivity to lateral changes in conductivity. Near a geological contact, however, this method produces distortions which are not easily distinguished from the layered-model response that is sought by inversion. In this paper we examine this problem for a simple two-dimensional model. Central-loop TDEM data were collected over a vertically dipping quarter-space model using a scale model system developed at U C Berkeley. Both vertical and horizontal magnetic field measurements were made within 250m radius loop transmitters with soundings spaced from 50 to 200m apart along a profile orthogonal to the contact. The sounding data from individual stations were then fitted to layered models using a standard least squares algorithm and the resulting layered models were plotted as a pieced-together cross-section. For the vertical field data the contact effect appears as a loss in field strength at lag times that depend on the distance from the contact and the conductivity of the quarter-space. At stations more distant from the edge the fields are reduced only at later times, whereas closer to the contact the effect shifts to earlier times and increases in magnitude. The layered model inversions seem to interpret this distortion as a fictitious resistive layer that grows more shallow and more resistive as the contact is approached. For stations within one loop radius of the contact the entire sounding is affected and the layered model inversions show little similarity to the true section. The scale model data also indicate that horizontal magnetic fields in the centre of the loop are diagnostic of the contact effect. These data may be used to determine which parts of a sounding may be confidently used for inversions. We have empirically found that for values of the TDEM tipper (Hx/Hz) greater than 0.5 the layered-models produce unreliable results.

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Wang, Xuan, Jinsong Shen, and Zhigang Wang. "3D general-measure inversion of crosswell EM data using a direct solver." Journal of Geophysics and Engineering 18, no. 1 (February 2021): 124–33. http://dx.doi.org/10.1093/jge/gxab001.

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Abstract We present a three-dimensional (3D) general-measure inversion scheme of crosswell electromagnetic (EM) data in the frequency domain with a direct forward solver. In the forward problem, we discretised the EM Helmholtz equation by the staggered-grid finite difference (SGFD) scheme and solved it using the Intel MKL PARDISO direct solver. By applying a direct solver, we simultaneously solved the multisource forward problems at a given frequency. In the inversion, we integrated a general measure of data misfit and model constraints with linearised least-squares inversion. We reconstructed a model with blocky features by selecting the appropriate measure parameters and model constraints. We used the adjoint equation method to explicitly calculate the Jacobian matrix, which facilitated the determination of an appropriate initial value for the regularisation coefficient in the objective function. We illustrated the inversion scheme using synthetic crosswell EM data with a general measure, the L2 norm, and, specifically, two mixed norms.

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Unsworth, Martyn J., Xinyou Lu, and M. Don Watts. "CSAMT exploration at Sellafield: Characterization of a potential radioactive waste disposal site." GEOPHYSICS 65, no. 4 (July 2000): 1070–79. http://dx.doi.org/10.1190/1.1444800.

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The long term disposal of radioactive waste in an underground repository requires the detailed geological evaluation of a potential site. Owing to their inherent sensitivity to the presence of fluids in rocks, electromagnetic (EM) methods have an important role in this assessment. Controlled‐source EM techniques are especially useful in strong anthropogenic noise environments such as industrial locations. However the complexity of modeling and inversion can limit the quantitative interpretation of controlled‐source EM data. A potential radioactive waste disposal site at Sellafield in Great Britain has been investigated using a variety of EM exploration techniques. Controlled‐source audio‐frequency magnetotelluric (CSAMT) data have given the best subsurface information in an environment that has a high level of cultural noise. One‐dimensional inversions of the Sellafield CSAMT data were found to be inadequate; 2.5-D forward modeling and inversion were used to interpret the data. The resulting resistivity models show good agreement with well log data collected at the site. These resistivity models show the presence of a large zone of hypersaline groundwater extending 1 km inland towards the potential repository and indicate the effect of faults on the hydrogeology.

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Franks. "Mental Inversion, Modernist Aesthetics, and Disability Exceptionalism in Olive Moore's Spleen." Journal of Modern Literature 38, no. 1 (2014): 107. http://dx.doi.org/10.2979/jmodelite.38.1.107.

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Hoad. "English Literary Sexology: Translations of Inversion, 1860-1930, by Heike Bauer." Victorian Studies 52, no. 4 (2010): 657. http://dx.doi.org/10.2979/vic.2010.52.4.657.

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Deleersnyder, Wouter, David Dudal, and Thomas Hermans. "Novel Airborne EM Image Appraisal Tool for Imperfect Forward Modeling." Remote Sensing 14, no. 22 (November 14, 2022): 5757. http://dx.doi.org/10.3390/rs14225757.

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Full 3D inversion of time-domain Airborne ElectroMagnetic (AEM) data requires specialists’ expertise and a tremendous amount of computational resources, not readily available to everyone. Consequently, quasi-2D/3D inversion methods are prevailing, using a much faster but approximate (1D) forward model. We propose an appraisal tool that indicates zones in the inversion model that are not in agreement with the multidimensional data and therefore, should not be interpreted quantitatively. The image appraisal relies on multidimensional forward modeling to compute a so-called normalized gradient. Large values in that gradient indicate model parameters that do not fit the true multidimensionality of the observed data well and should not be interpreted quantitatively. An alternative approach is proposed to account for imperfect forward modeling, such that the appraisal tool is computationally inexpensive. The method is demonstrated on an AEM survey in a salinization context, revealing possible problematic zones in the estimated fresh–saltwater interface.

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Teixeira, Joana. "Será a interface sintaxe-discurso necessariamente um locus de opcionalidade em L2? O caso da inversão locativa em inglês L2." Revista da Associação Portuguesa de Linguística, no. 3 (September 29, 2017): 347–86. http://dx.doi.org/10.26334/2183-9077/rapln3ano2017a19.

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This study investigates the acquisition of locative inversion in L1 European Portuguese (EP) – L2 English and L1 French – L2 English. Its purpose is to test two opposing hypotheses on the end-state of L2 acquisition at the syntaxdiscourse interface: the Interface Hypothesis (IH) and the L1+input Hypothesis (LIH). The former proposes that the syntax-discourse/pragmatics interface is a locus of residual, but permanent, optionality, because L2 speakers are less than optimally efficient at integrating syntactic and contextual information in real-time language use as a by-product of bilingualism. The latter, in contrast, sustains that structures at this interface generate problems at highly advanced levels of proficiency iff their properties are different in the L1 and the L2 and the evidence available in the input is not transparent (e.g., because the structure is rare). By administering 2 untimed drag and drop tasks, 2 speeded acceptability judgement tasks and 1 syntactic priming task to a total of 80 participants, we tested, on the one hand, the type of intransitive verb allowed in locative inversion and, on the other, the type of discourse context in which this inversion is admitted. The results disconfirm the LIH and confirm (most of) the IH’s predictions.

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42

Li, Jianhua, Ganquan Xie, Michael Oristaglio, Lee Xie, and Feng Xie. "A 3D-2D AGILD EM Modeling and Inversion Imaging." PIERS Online 3, no. 4 (2007): 423–29. http://dx.doi.org/10.2529/piers060907233117.

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43

Viezzoli, Andrea, Gianluca Fiandaca, Esben Auken, Anders V. Christiansen, and Simonetta Sergio. "Constrained inversion of IP parameters from Airborne EM data." ASEG Extended Abstracts 2013, no. 1 (December 2013): 1–4. http://dx.doi.org/10.1071/aseg2013ab274.

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Björnemo, Erik, and Joel Skogman. "Probabilistic analysis of EM data sensitivity and inversion accuracy." ASEG Extended Abstracts 2015, no. 1 (December 2015): 1–4. http://dx.doi.org/10.1071/aseg2015ab292.

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Macnae, James, Ken Witherly, and Tim Munday. "3D EM Inversion: an Update on Capabilities and Outcomes." Preview 2012, no. 159 (August 2012): 24–27. http://dx.doi.org/10.1071/pvv2012n159p24.

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Liu, Yun-He, Chang-Chun Yin, Xiu-Yan Ren, and Chang-Kai Qiu. "3D parallel inversion of time-domain airborne EM data." Applied Geophysics 13, no. 4 (December 2016): 701–11. http://dx.doi.org/10.1007/s11770-016-0581-x.

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Gao, Zong-Hui, Chang-Chun Yin, Yan-Fu Qi, Bo Zhang, Xiu-Yan Ren, and Yong-Chao Lu. "Transdimensional Bayesian inversion of time-domain airborne EM data." Applied Geophysics 15, no. 2 (June 2018): 318–31. http://dx.doi.org/10.1007/s11770-018-0684-7.

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Mashayekh, Hamidreza, Loukas F. Kallivokas, and John L. Tassoulas. "Parameter Estimation in Layered Media Using Dispersion-Constrained Inversion." Journal of Engineering Mechanics 144, no. 11 (November 2018): 04018099. http://dx.doi.org/10.1061/(asce)em.1943-7889.0001527.

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Sasaki, Yutaka, Jung-Ho Kim, and Seong-Jun Cho. "Multidimensional inversion of loop-loop frequency-domain EM data for resistivity and magnetic susceptibility." GEOPHYSICS 75, no. 6 (November 2010): F213—F223. http://dx.doi.org/10.1190/1.3503652.

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Electromagnetic (EM) induction measurements are affected by resistivity and magnetic susceptibility. Thus, inverting EM data for resistivity alone can give misleading models if susceptible effects are strong. An inversion algorithm is presented to simultaneously recover multidimensional distributions of resistivity and susceptibility from various types of loop-loop frequency-domain EM data. The algorithm adopts a staggered-grid finite-difference method for the 3D forward solutions and computes the sensitivities with respect to resistivity and susceptibility from the forward solutions using the reciprocity principle. The algorithm is tested on synthetic data sets from ground-based small-loop, airborne, and Slingram EM surveys. It is shown that the simultaneous inversion of the small-loop EM data collected at a singleheight is unstable and likely to produce unreliable susceptibility models because the effect of susceptibility is nearly independent of the frequency. However, if the data are obtained for multiple heights or different loop configurations, simultaneous inversion can produce more reliable susceptibility and resistivity models even if the data are contaminated by offset errors. It is also shown that although the simultaneous inversion of airborne EM data is relatively stable, adding data obtained at different heights helps to increase the reliability of the resistivity and susceptibility models. Among the loop-loop EM methods discussed here, the Slingram method is relatively insensitive to susceptibility anomalies and thus cannot be used to recover the susceptibility distribution via inversion even if the data are obtained using different loop configurations.

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Zhang, Yong C., Ce Liu, and Liang C. Shen. "An iterative algorithm for conductivity image reconstruction from crosswell EM measurements." GEOPHYSICS 61, no. 4 (July 1996): 987–97. http://dx.doi.org/10.1190/1.1444047.

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An efficient iterative modeling and inversion algorithm is developed to reconstruct conductivity images using data obtained from crosswell electromagnetic measurements. The forward modeling uses a distorted Born approximation, in which cylindrical conductivity distributions are considered to be deviations from a 1-D background conductivity. The inversion algorithm employs a constrained optimization method to achieve maximum stability when noise is present. Both synthetic and field‐measured data are inverted in this paper. The method developed starts with an estimated homogeneous formation and reconstructs a 1-D conductivity image; the 2-D image reconstruction uses the reconstructed 1-D image as the initial input in the inversion process. Conductivity tomographs of two synthetic models and of the Devine Test Site are presented. The operating frequency used in the examples is 512 Hz and a range of [Formula: see text] is imaged. The images reconstructed for the tested cases show a satisfactory agreement with the known geological properties.

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Journal articles on the topic 'EM inversion'

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