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- Volume 68, Issue 6, 2020
Geophysical Prospecting - Volume 68, Issue 6, 2020
Volume 68, Issue 6, 2020
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Application of a cascading filter implemented using morphological filtering and time–frequency peak filtering for seismic signal enhancement
Authors Yanping Liu and Zhengguo YanABSTRACTInspired by the idea of the iterative time–frequency peak filtering, which applies time–frequency peak filtering several times to improve the ability of random noise reduction, this article proposes a new cascading filter implemented using mathematic morphological filtering and the time–frequency peak filtering, which we call here morphological time–frequency peak filtering for convenience. This new method will be used mainly for seismic signal enhancement and random noise reduction in which the advantages of the morphological algorithm in processing nonlinear signals and the time–frequency peak filtering in processing nonstationary signals are utilized. Structurally, the scheme of the proposed method adopts mathematic morphological operation to first preprocess the signal and then applies the time–frequency peak filtering method to ultimately extract the valid signal. Through experiments on synthetic seismic signals and field seismic data, this paper demonstrates that the morphological time–frequency peak filtering method is superior to the time–frequency peak filtering method and its iterative form in terms of valid signal enhancement and random noise reduction.
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A numerical study on deblending of land simultaneous shooting acquisition data via rank‐reduction filtering and signal enhancement applications
Authors Woodon Jeong, Constantinos Tsingas and Mohammed S. AlmubarakABSTRACTWe propose a workflow of deblending methodology comprised of rank‐reduction filtering followed by a signal enhancing process. This methodology can be used to preserve coherent subsurface reflections and at the same time to remove incoherent and interference noise. In pseudo‐deblended data, the blending noise exhibits coherent events, whereas in any other data domain (i.e. common receiver, common midpoint and common offset), it appears incoherent and is regarded as an outlier. In order to perform signal deblending, a robust implementation of rank‐reduction filtering is employed to eliminate the blending noise and is referred to as a joint sparse and low‐rank approximation. Deblending via rank‐reduction filtering gives a reasonable result with a sufficient signal‐to‐noise ratio. However, for land data acquired using unconstrained simultaneous shooting, rank‐reduction–based deblending applications alone do not completely attenuate the interference noise. A considerable amount of signal leakage is observed in the residual component, which can affect further data processing and analyses. In this study, we propose a deblending workflow via a rank‐reduction filter followed by post‐processing steps comprising a nonlinear masking filter and a local orthogonalization weight application. Although each application shows a few footprints of leaked signal energy, the proposed combined workflow restores the signal energy from the residual component achieving significantly signal‐to‐noise ratio enhancement. These hierarchical schemes are applied on land simultaneous shooting acquisition data sets and produced cleaner and reliable deblended data ready for further data processing.
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Common image gather conditioning using cycle generative adversarial networks
By G.S. O'BrienABSTRACTSeismically derived amplitude‐versus‐angle attributes along with well constraints are the base inputs into inverting seismic into subsurface properties. Conditioning the common image gathers is a common workflow in quantitative inversion and leads to a more accurate inversion product due to the removal of post‐migration artefacts. Here, we apply a neural network to condition the post‐migration gathers. The network is a cycle generative adversarial network, CycleGAN, which was designed for image‐to‐image translation. This can be considered the same problem as translating an artefact rich seismic gather to an artefact free seismic gather. To assess the feasibility of applying the network to pre‐stack conditioning, synthetic data sets were generated to train different networks for different tasks. The networks were trained to remove white noise, residual de‐multiples, gather flattening and a combination of the above for conditioning. The results show that a trained network was able remove white noise providing a more robust amplitude‐versus‐offset calculation. Another network trained using synthetic gathers with and without multiples assisted in multiple removal. However, instability around primary preservation has been observed so the network works better as a residual de‐multiple method. For gather conditioning, a network was trained with the unpaired artefact‐rich and artefact‐free training data where the artefacts included complex moveout, noise and multiples. When applied to the test data sets, the networks cleaned the artefact‐rich test data and translated complex moveout into flat gathers whilst preserving the amplitude response. Finally, two networks are applied to real data where a gather based on the well logs is used to quantify the match between the conditioned gathers and the raw gathers. The first network used synthetic data to train the network and, when applied to real data, provided a better tie with the well. The second network was trained with synthetic gathers whose properties were constrained by real seismic gathers from near the well. As anticipated, the network trained on the representative training data outperforms the network trained using the unconstrained data. However, the ability of the first network to condition the gather indicates that a sweep of networks can be trained without the need for real data and applied in a manner analogous to the way parameters are adjusted in traditional geophysical methods. The results show that the different neural networks can offer an alternative or augmentation to the existing geophysical workflow for conditioning pre‐stack seismic gathers.
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Dispersion‐relationship‐preserving seismic modelling using the cross‐rhombus stencil with the finite‐difference coefficients solved by an over‐determined linear system
Authors Guiting Chen, Yanfei Wang, Zhenli Wang and Shuyang ZhangABSTRACTFinite‐difference modeling with a cross‐rhombus stencil with high‐order accuracy in both spatial and temporal derivatives is a potential method for efficient seismic simulation. The finite‐difference coefficients determined by Taylor‐series expansion usually preserve the dispersion property in a limited wavenumber range and fixed angles of propagation. To construct the dispersion‐relationship‐preserving scheme for satisfying high‐wavenumber components and multiple angles, we expand the dispersion relation of the cross‐rhombus stencil to an over‐determined system and apply a regularization method to obtain the stable least‐squares solution of the finite‐difference coefficients. The new dispersion‐relationship‐preserving based scheme not only satisfies several designated wavenumbers but also has high‐order accuracy in temporal discretization. The numerical analysis demonstrates that the new scheme possesses a better dispersion characteristic and more relaxed stability conditions compared with the Taylor‐series expansion based methods. Seismic wave simulations for the homogeneous model and the Sigsbee model demonstrate that the new scheme yields small dispersion error and improves the accuracy of the forward modelling.
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Effective medium theory and multiple linear regression‐based velocity estimation in syn‐rift clastic sequence of the Krishna–Godavari basin, India
Authors Prabal Shankar Das, Rima Chatterjee and Sumangal DasguptaABSTRACTAn inclusion model, based on the Kuster–Toksöz effective medium theory along with Gassmann theory, is tested to forward model velocities for fluid‐saturated rocks. A simulated annealing algorithm, along with the inclusion model, effectively inverts measured compressional velocity (VP) to achieve an effective pore aspect ratio at each depth in a depth variant manner, continuously along with depth. Early Cretaceous syn‐rift clastic sediments at two different depth intervals from two wells [well A (2160–2274 m) and well B (5222–5303 m)], in the Krishna–Godavari basin, India, are used for this study. Shear velocity (VS) estimated using modelled pore aspect ratio offers a high correlation coefficient (>0.95 for both the wells) with measured data. The modelled pore aspect ratio distribution suggests the decrease in pore aspect ratio for the deeper interval, mainly due to increased effective vertical stress. The pore aspect ratio analysis in relation to total porosity and volume of clay reveals that the clay volume has insignificant influence in shaping the pore geometry in the studied intervals. An approach based on multiple linear regression method effectively predicts velocity as a linear function of total porosity, the volume of clay and the modelled pore‐space aspect ratio of the rock. We achieved a significant match between measured and predicted velocities. The correlation coefficients between measured and modelled velocities are considerably high (approximately 0.85 and 0.8, for VP and VS, respectively). This process indicates the possible influence of pore geometry along with total porosity and volume of clay on velocity.
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Prestack data enhancement with phase corrections in time‐frequency domain guided by local multidimensional stacking
Authors Andrey Bakulin, Dmitri Neklyudov and Ilya SilvestrovABSTRACTWe present a new approach to enhancing weak prestack reflection signals without sacrificing higher frequencies. As a first step, we employ known multidimensional local stacking to obtain an approximate ‘model of the signal’. Guided by phase spectra from this model, we can detect very weak signals and make them visible and coherent by ‘repairing’ corrupted phase of original data. Both presented approaches – phase substitution and phase sign corrections – show good performance on complex synthetic and field data suffering from severe near‐surface scattering where conventional processing methods are rendered ineffective. The methods are mathematically formulated as a special case of time‐frequency masking (common in speech processing) combined with the signal model from local stacking. This powerful combination opens the avenue for a completely new family of approaches for multi‐channel seismic processing that can address seismic processing of land data with nodes and single sensors in the desert environment.
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Spatially constrained attenuation compensation in the mixed domain
Authors Xiong Ma, Guofa Li, Shumei He, Hao Li and Zhewu WangABSTRACTSeismic attenuation compensation is a spectrum‐broadening technique for enhancing the resolution of non‐stationary seismic data. The single‐trace attenuation compensation algorithms ignore the prior information that the seismic reflection events are generally continuous along seismic traces, thus, the compensated result may have poor spatial continuity and low signal‐to‐noise ratio. To address this problem, we extend the single‐trace approaches to the multi‐trace algorithms and furthermore propose a multi‐trace attenuation compensation with a spatial constraint. The frequency‐space prediction filters are the key to construct this spatial regularization. We test the effectiveness of the proposed spatially constrained attenuation compensation algorithm by applying both synthetic and field data examples. Synthetic data tests indicate that the proposed multi‐trace attenuation compensation approach can provide a better compensated result than single‐trace attenuation compensation algorithm in terms of suppressing noise amplification and guaranteeing structural continuities. Field data applications further confirm its stability and practicality to improve seismic resolution.
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Data‐driven retrieval of primary plane‐wave responses
Authors Giovanni Angelo Meles, Lele Zhang, Jan Thorbecke, Kees Wapenaar and Evert SlobABSTRACTSeismic images provided by reverse time migration can be contaminated by artefacts associated with the migration of multiples. Multiples can corrupt seismic images, producing both false positives, that is by focusing energy at unphysical interfaces, and false negatives, that is by destructively interfering with primaries. Multiple prediction/primary synthesis methods are usually designed to operate on point source gathers and can therefore be computationally demanding when large problems are considered. A computationally attractive scheme that operates on plane‐wave datasets is derived by adapting a data‐driven point source gathers method, based on convolutions and cross‐correlations of the reflection response with itself, to include plane‐wave concepts. As a result, the presented algorithm allows fully data‐driven synthesis of primary reflections associated with plane‐wave source responses. Once primary plane‐wave responses are estimated, they are used for multiple‐free imaging via plane‐wave reverse time migration. Numerical tests of increasing complexity demonstrate the potential of the proposed algorithm to produce multiple‐free images from only a small number of plane‐wave datasets.
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Offset dependence of overburden time‐shifts from ultrasonic data
Authors Audun Bakk, Rune M. Holt, Andreas Bauer, Bastien Dupuy and Anouar RomdhaneABSTRACTDepletion or injection into a reservoir implies stress changes and strains in the reservoir and its surroundings. This may lead to measurable time‐shifts for seismic waves propagating in the subsurface. To better understand the offset dependence of time‐shifts in the overburden, we have systematically quantified the time‐shifts of three different overburden shales in controlled laboratory tests. These experiments may be viewed as an analogue to the time‐shifts recorded from seismic field surveys. For a range of different stress paths, defined as the ratio between the horizontal and the vertical stress changes, the changes of the P‐wave velocities in different directions were measured such that the offset dependence of time‐shifts for different stress paths could be studied. The time‐shifts are stress path dependent, which is particularly pronounced at large offsets. For all stress paths, the time‐shifts exhibit a linearly decreasing trend with increasing offset, that is, a negative offset gradient. At zero offset, for which the ray path is normal to the bedding, the time‐shifts are similar for all investigated stress paths. The isotropic stress path is associated with the smallest offset gradient of the time‐shifts. In contrast, the constant‐mean‐stress path shows the largest gradient with a flip in the polarity of the time‐shifts for the largest offsets. The separate contributions from the strain and velocity changes to the time‐shifts were also quantified. The time‐shifts for the isotropic stress path are dominated by the contribution from velocity changes at all offsets. In contrast, the strain contributes significantly to the time‐shifts at small offsets for the constant‐mean‐stress path. This shows that the offset dependence in pre‐stack seismic data may be a key to understand the changes of subsurface stresses, pore pressure and strain upon depletion or injection. To utilize this knowledge from laboratory experiments, calibrated rock physics models and correlations are needed to constrain the seismic time‐shifts and to obtain an adequately updated geological model reflecting the true anisotropic nature of the subsurface. This may have important implications for improved recovery and safety, particularly in mature fields.
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Three‐dimensional Marchenko internal multiple attenuation on narrow azimuth streamer data of the Santos Basin, Brazil
Authors Myrna Staring and Kees WapenaarABSTRACTIn recent years, a variety of Marchenko methods for the attenuation of internal multiples has been developed. These methods have been extensively tested on two‐dimensional synthetic data and applied to two‐dimensional field data, but only little is known about their behaviour on three‐dimensional synthetic data and three‐dimensional field data. Particularly, it is not known whether Marchenko methods are sufficiently robust for sparse acquisition geometries that are found in practice. Therefore, we start by performing a series of synthetic tests to identify the key acquisition parameters and limitations that affect the result of three‐dimensional Marchenko internal multiple prediction and subtraction using an adaptive double‐focusing method. Based on these tests, we define an interpolation strategy and use it for the field data application. Starting from a wide azimuth dense grid of sources and receivers, a series of decimation tests are performed until a narrow azimuth streamer geometry remains. We evaluate the effect of the removal of sail lines, near offsets, far offsets and outer cables on the result of the adaptive double‐focusing method. These tests show that our method is most sensitive to the limited aperture in the crossline direction and the sail line spacing when applying it to synthetic narrow azimuth streamer data. The sail line spacing can be interpolated, but the aperture in the crossline direction is a limitation of the acquisition. Next, we apply the adaptive Marchenko double‐focusing method to the narrow azimuth streamer field data from the Santos Basin, Brazil. Internal multiples are predicted and adaptively subtracted, thereby improving the geological interpretation of the target area. These results imply that our adaptive double‐focusing method is sufficiently robust for the application to three‐dimensional field data, although the key acquisition parameters and limitations will naturally differ in other geological settings and for other types of acquisition.
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Multi‐parameter reflection waveform inversion for acoustic transversely isotropic media with a vertical symmetry axis
Authors Yuanyuan Li and Tariq AlkhalifahABSTRACTFull waveform inversion in transversely isotropic media with a vertical symmetry axis provides an opportunity to better match the data at the near and far offsets. However, multi‐parameter full waveform inversion, in general, suffers from serious cycle‐skipping and trade‐off problems. Reflection waveform inversion can help us recover a background model by projecting the residuals of the reflected wavefield along the reflection wavepath. Thus, we extend reflection waveform inversion to acoustic transversely isotropic media with a vertical symmetry axis utilizing the proper parameterization for reduced parameter trade‐off. From a radiation patterns analysis, an acoustic transversely isotropic media with a vertical symmetry axis is better described by a combination of the normal‐moveout velocity and the anisotropic parameters η and δ for reflection waveform inversion applications. We design a three‐stage inversion strategy to construct the optimal resulting model. In the first stage, we only invert for the background by matching the simulated reflected wavefield from the perturbations of and δ with the observed reflected wavefield. In the second stage, the background and η are optimized simultaneously and the far‐offset reflected wavefield mainly contribute to their updates. We perform Born modelling to compute the reflected wavefield for the two stages of reflection waveform inversion. In the third stage, we perform full waveform inversion for the acoustic transversely isotropic media with a vertical symmetry axis to delineate the high‐wavenumber structures. For this stage, the medium is described by a combination of the horizontal velocity , η and ε instead of , η and δ. The acoustic multi‐parameter full waveform inversion utilizes the diving waves to improve the background as well as utilizes reflection for high‐resolution information. Finally, we test our inversion algorithm on the modified Sigsbee 2A model (a salt free part) and a two‐dimensional line from a three‐dimensional ocean bottom cable dataset. The results demonstrate that the proposed reflection waveform inversion approach can recover the background model for acoustic transversely isotropic media with a vertical symmetry axis starting from an isotropic model. This recovered background model can mitigate the cycle skipping of full waveform inversion and help the inversion recover higher resolution structures.
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Design considerations for using Distributed Acoustic Sensing for cross‐well seismics: A case study for CO2 storage
Authors Andreas Wuestefeld and Wolfgang WeinzierlABSTRACTDownhole monitoring with fibre‐optic Distributed Acoustic Sensing (DAS) systems offers unprecedented spatial resolution. At the same time, costs are reduced since repeated wireline surveys can be replaced by the permanent installation of comparatively cheap fibre cables. However, the single component nature of fibre data requires novel approaches when designing a monitoring project such as cross‐well seismics. At the example of the shallow CO2 injection test site in Svelvik, Norway, we model the evolution of velocity changes during CO2 injection based on rock physics theory. Different cross‐well seismic design scenarios are then considered to evaluate the best design and the limits of this method to detect containment breach. We present a series of evaluation tools to compare the effect of different well spacings for cross‐well seismic tomography. In addition to travel‐times, we also consider characteristic amplitude changes along the fibre unique to DAS strain measurements, which might add a constraint to the inversion. We also compare the effect of using helical fibres instead of classical straight fibres. We thus present a toolbox to evaluate and compare different monitoring design options for fibre optic downhole installations for cross‐well monitoring.
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Analysis of reservoir heterogeneity‐induced amplification effect on time‐lapse seismic responses of fluid substitution: A physical modelling study
Authors Yan‐Xiao He and Shangxu WangABSTRACTSeismic wave propagation through a fluid‐saturated poroelastic layer might be strongly affected by media heterogeneities. Via incorporating controlled laboratory simulation experiments, we extend previous studies of time‐lapse seismic effects to evaluate the wave scattering influence of the heterogeneous nature of porous permeable media and the associated amplification effects on 4D seismic response characteristics of reservoir fluid substitution. A physical model consisted of stratified thin layers of shale and porous sandstone reservoir with rock heterogeneities was built based on the geological data of a real hydrocarbon‐saturated reservoir in Northeast China. Multi‐surveys data of good quality were acquired by filling poroelastic reservoir layers with gas, water and oil in sequence. Experimental observations show that reservoir heterogeneity effect causes significantly magnified abnormal responses to the fluid‐saturated media. Specifically, reflection signatures of the gas‐filled reservoir are dramatically deviated from those of the liquid fluid‐filled reservoir, compared with ones of the homogeneous media. By removing the influences unrelated to reservoir property alterations, 4D seismic estimates of travel‐time and frequency‐dependent characteristic are reasonably consistent with fluid variations. Nevertheless, strong 4D amplitude difference anomalies might not correspond to the regions where fluid variations occur. We also find that 4D seismic difference attributes are evident between oil‐ and water‐filled models, whereas significant between oil‐ and gas‐filled models. Meanwhile, rock physics modelling results reveal the predicted 4D seismic differences are obviously smaller than those calculated from seismic observations. The results in this paper, therefore, implicate that the effect of a reservoir's heterogeneous nature might be beneficial for hydrocarbons detection as well as monitoring small variations in pore fluids.
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Seismoelectric numerical simulation in 2D vertical transverse isotropic poroelastic medium
Authors Munirdin Tohti, Yibo Wang, Evert Slob, Yikang Zheng, Xu Chang and Yi YaoABSTRACTSeismoelectric coupling in an electric isotropic and elastic anisotropic medium is developed using a primary–secondary formulation. The anisotropy is of vertical transverse isotropic type and concerns only the poroelastic parameters. Based on our finite difference time domain algorithm, we solve the seismoelectric response to an explosive source. The seismic wavefields are computed as the primary field. The electric field is then obtained as a secondary field by solving the Poisson equation for the electric potential. To test our numerical algorithm, we compared our seismoelectric numerical results with analytical results obtained from Pride's equation. The comparison shows that the numerical solution gives a good approximation to the analytical solution. We then simulate the seismoelectric wavefields in different models. Simulated results show that four types of seismic waves are generated in anisotropic poroelastic medium. These are the fast and slow longitudinal waves and two separable transverse waves. All of these seismic waves generate coseismic electric fields in a homogenous anisotropic poroelastic medium. The tortuosity has an effect on the propagation of the slow longitudinal wave. The snapshot of the slow longitudinal wave has an oval shape when the tortuosity is anisotropic, whereas it has a circular shape when the tortuosity is isotropic. In terms of the Thomsen parameters, the radiation anisotropy of the fast longitudinal wave is more sensitive to the value of ε, while the radiation anisotropy of the transverse wave is more sensitive to the value of δ.
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Characterization of a carbonate reservoir using elastic full‐waveform inversion of vertical seismic profile data
ABSTRACTTwo‐dimensional elastic full waveform inversion was applied to two lines extracted from a spiral three‐dimensional vertical seismic profile data acquired in an oilfield offshore, Abu Dhabi, in the United Arab Emirates. The lines were selected to be parallel and perpendicular to the plane defined by the deviated borehole. The purpose of the inversion was to derive high‐resolution elastic properties of the subsurface. After pre‐processing, the data were band‐pass filtered with a minimum frequency of 3.5 Hz and a maximum frequency of 30 Hz. A sequential inversion approach was used to mitigate non‐linearity. The pre‐processing of the data consisted in the removal of bad traces, followed by amplitude and phase corrections. High‐resolution P‐ and S‐wave velocity models that show good correlations with the available sonic logs were obtained. The results of the inversion suggest that the oilfield consists of a stack of layers with varying lithology, porosity and possibly fluid content.
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Seismoelectric and electroseismic responses to a point source in a marine stratified model
Authors Dongdong Wang, Yongxin Gao, Cheng Yao, Baozhen Wang and Mengqiang WangABSTRACTWe investigate the seismoelectric/electroseismic wavefields excited by a point source in an air/seawater/three‐layered porous medium configuration containing a hydrocarbon layer. The results show that if an explosive source for excitation is used, receivers at seafloor can record the coseismic electromagnetic fields accompanying the P, S, fluid acoustic waves and the interface responses converted from the acoustic waves at seafloor interface and from the seismic waves at the interfaces beneath the seafloor. Employing a vertical electric dipole source shows that, with the exception of the interface responses converted from electromagnetic waves at seafloor, the interface responses converted from transmitted electromagnetic waves at the interfaces beneath the seafloor can also be identified. Given that the strength of the explosive source is within excitation capability of industry air guns, the generated interface responses from the hydrocarbon layer can be detected by current electromagnetic sensors considering the low ambient noise at the seafloor. Our results demonstrate the feasibility of the seismoelectric method applied to marine hydrocarbon exploration. Electroseismic modelling results suggest that it is not practical to employ this method to prospect marine hydrocarbon layer due to the weak interface response signal, unless a much larger current is injected into seafloor.
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Deep exploration using long‐offset transient electromagnetics: interpretation of field data in time and frequency domain
Authors Wiebke Mörbe, Pritam Yogeshwar, Bülent Tezkan and Tilman HansteinABSTRACTIn the framework of the Deep Electromagnetic Soundings for Mineral Exploration project, we conducted ground‐based long‐offset transient‐electromagnetic measurements in a former mining area in eastern Thuringia, Germany. The large‐scale survey resulted in an extensive dataset acquired with multiple high‐power transmitters and a high number of electric and magnetic field receivers. The recorded data exhibit a high data quality over several decades of time and orders of magnitude. Although the obtained subsurface models indicate a strong multi‐dimensional subsurface with variations in resistivity over three orders of magnitude, the electrical field step‐on transients are well fitted using a conventional one‐dimensional inversion. Due to superimposed induced polarization effects, the transient step‐off data are not interpretable with conventional electromagnetic inversion. For further interpretation in one and two dimensions, a new approach to evaluate the long‐offset transient‐electromagnetic data in frequency domain is realized. We present a detailed workflow for data processing in both domains and give an overview of technical obstructions that can occur in one domain or the other. The derived one‐dimensional inversion models of frequency‐domain data show strong multi‐dimensional effects and are well comparable with the conventional time domain inversion results. To adequately interpret the data, a 2.5D frequency‐domain inversion using the open source algorithm MARE2DEM (Modeling with Adaptively Refined Elements for 2‐D EM) is carried out. The inversion leads to a consistent subsurface model with shallow and deep conductive structures, which are confirmed by geology and additional geophysical surveys.
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Research Note: A proposed procedure for ameliorating edge effects in magnetic data transformations
ABSTRACTReduction to pole and other transformations of total field magnetic intensity data are often challenging to perform at low magnetic latitudes, when remanent magnetization exists, and when large topographic relief exists. Several studies have suggested the use of inversion‐based equivalent source methods for performing such transformations under those complicating factors. However, there has been little assessment of the importance of erroneous edge effects that occur when fundamental assumptions underlying the transformation procedures are broken. In this work we propose a transformation procedure that utilizes magnetization vector inversion, inversion‐based regional field separation and equivalent source inversion on unstructured meshes. We investigated whether edge effects in transformations could be reduced by performing a regional separation procedure prior to equivalent source inversion. We applied our proposed procedure to the transformation of total field magnetic intensity to all three Cartesian magnetic field components using a complicated synthetic example based on a real geological scenario from mineral exploration. While the procedure performed acceptably on this test example, the results could be improved. We pose many questions regarding the various choices and control parameters used throughout the procedure, but we leave the investigation of those questions to future work.
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Volumes & issues
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Volume 72 (2023 - 2024)
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Volume 71 (2022 - 2023)
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Volume 70 (2021 - 2022)
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Volume 69 (2021)
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Volume 68 (2020)
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Volume 67 (2019)
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Volume 66 (2018)
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Volume 65 (2017)
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Volume 64 (2015 - 2016)
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Volume 63 (2015)
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Volume 62 (2014)
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Volume 61 (2013)
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Volume 60 (2012)
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Volume 59 (2011)
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Volume 54 (2006)
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Volume 53 (2005)
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Volume 52 (2004)
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Volume 47 (1999)
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Volume 35 (1987)
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Volume 30 (1982)
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