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1

Grey wolf optimization-based variational mode decomposition for magnetotelluric data combined with detrended fluctuation analysis

Zhang Xian, Li Diquan, Li Jin, Li Yong

Acta Geophysica

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2022

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Vol. 70, no 1

111--120

EN

We present a magnetotelluric data denoising method that uses grey wolf optimization to optimize variational mode decomposition and combines it with detrended fluctuation analysis. First, envelope entropy is selected as the fitness function for grey wolf optimization and is used to determine the number of modes K and the penalty factor, which are the key parameters of the variational mode decomposition method. Then, the optimized variational mode decomposition method is used to decompose magnetotelluric data. Finally, the scaling exponent in detrended fluctuation analysis is used to determine the corresponding intrinsic mode function components to superimpose and reconstruct the useful magnetotelluric data. Extensive experiments and thorough analyses are performed on the synthetic data and field data. The results of the proposed method are compared with the results of the remote reference, variational mode decomposition, variational mode decomposition and matching pursuit, variational mode decomposition and detrended fluctuation analysis methods; the proposed method can improve the denoising performance and reliability of low-frequency magnetotelluric data. The reconstructed data are closer to the natural magnetotelluric data. The satisfactory performance in the results verifies the effectiveness of the design and optimization method.

2

An effective estimate for selecting the regularization parameter in the 3D inversion of magnetotelluric data

Ghaedrahmati Reza, Moradzadeh Ali, Moradpouri Farzad

Acta Geophysica

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2022

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Vol. 70, no 2

609--621

EN

The magnetotelluric (MT) inverse problem is a nonlinear and strongly ill-posed problem. Therefore, to avoid the problem of non-uniqueness of response, this problem is mainly solved by Tikhonov regularization method. The purpose of this study is to present a suitable method for selecting the regularization parameters in the 3D MT inverse problem, with regard to the accuracy and speed of the inversion. In this research, the regularization parameter is simply estimated in each iteration of inversion as the ratio of the data misfit to sum of the data misfit and model norm in the pre-iteration. This scheme is applied in the well-known 3D inversion algorithm, WSInv3DMT, instead of the discrepancy principle method. The accuracy of this scheme is assessed by performing the inversion on synthetic models and real data. Results from the inversion for the synthetic and real data indicate that the data misfit and the model norm are reduced with an acceptable rate during the inversion operation. The inverse model has been smoothly converged to an appropriate model and that unrealistic structures have not been included in the model. The results also show that estimation of the regularization parameter by the discrepancy principle method and continuing the inversion to achieve the target data misfit may lead to the production of a model with non-realistic structures, while in the proposed scheme the inversion has not encountered this problem and it converges to an appropriate model after fewer iterations of inversion. In addition, the results show that the time consumed for the inversion of a set of real data with 41 stations and 16 measurement frequencies would decrease up to 27 percent compared to the time devoted for inverting the same set of data by the discrepancy principle method. Also the inversion does not deviate toward unrealistic models and it closely converges to the model of real geological structures.

3

2D inversion of magnetotelluric data using deep learning technology

Liao Xiaolong, Shi Zeyu, Zhang Zhihou, Yan Qixiang, Liu Pengfei

Acta Geophysica

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2022

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Vol. 70, no 3

1047--1060

EN

The inverse problem of magnetotelluric data is extremely difficult due to its nonlinear and ill-posed nature. The existing gradient-descent approaches for this task surface from the problems of falling into local minima and relying on reliable initial models, while statistical-based methods are computationally expensive. Inspired by the excellent nonlinear mapping ability of deep learning, in this study, we present a novel magnetotelluric inversion method based on fully convolutional networks. This approach directly builds an end-to-end mapping from apparent resistivity and phase data to resistivity anomaly model. The implementation of the proposed method contains two stages: training and testing. During the training stage, the weight sharing mechanism of fully convolutional network is considered, and only the single anomalous body model samples are used for training, which greatly shortens the modeling time and reduces the difficulty of network training. After that, the unknown combinatorial anomaly model can be reconstructed from the magnetotelluric data using the trained network. The proposed method is tested in both synthetic and field data. The results show that the deep learning-based inversion method proposed in this paper is computationally efficient and has high imaging accuracy.

4

Integrated magnetotelluric and seismic investigation of Cenozoic graben structure near Obrzycko, Poland

Cygal Adam, Stefaniuk Michał, Kret Anna

Acta Geophysica

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2021

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Vol. 69, no. 2

711--723

EN

This article presents the results of an integrated interpretation of measurements made using Audio-Magnetotellurics and Seismic Refection geophysical methods. The obtained results were used to build an integrated geophysical model of shal low subsurface cover consisting of Cenozoic deposits, which then formed the basis for a detailed lithological and tectonic interpretation of deeper Mesozoic sediments. Such shallow covers, consisting mainly of glacial Pleistocene deposits, are typical for central and northern Poland. This investigation concentrated on delineating the accurate geometry of Obrzycko Cenozoic graben structure flled with loose deposits, as it was of great importance to the acquisition, processing and interpretation of seismic data that was to reveal the tectonic structure of the Cretaceous and Jurassic sediments which underly the study area. Previously, some problems with estimation of seismic static corrections over similar grabens flled with more recent, low-velocity deposits were encountered. Therefore, a novel approach to estimating the exact thickness of such shallow cover consisting of low-velocity deposits was applied in the presented investigation. The study shows that some alternative geophysical data sets (such as magnetotellurics) can be used to signifcantly improve the imaging of geological structure in areas where seismic data are very distorted or too noisy to be used alone

5

Geophysical depth to basement research in the SW sector of the Santa Lucía Basin, southern Uruguay

Corbo-Camargo Fernando, Ramos Julián, Rodríguez Pablo, De los Santos Jorge

Acta Geophysica

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2021

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Vol. 69, no. 4

1287--1296

EN

The Santa Lucía River Basin Trough is located in the southern sector of the Eastern Republic of Uruguay and has an area of almost 6,000 km2 . In this work, the depth to the basement in the SW sector of the Santa Lucia Basin (SLB) was determined, using geophysical methods of exploration. The interest of exploring this geological basin is to determine its depth, recognizing the possible existence of deep aquifers, and the feasibility of hydrothermalism. For this reason were acquired, processed, inverted, and interpreted 10 magnetotelluric (MT) soundings. A 3D inversion based on the ModEM code was performed, and a 2D inversion (NLCG) of the invariant determinant along a profle that crosses the study area was carried out; their comparison yields similar resistivity and structural models results. The resistivity modeling was complemented with a Bouguer anomaly map created from a gravimetric database of 157 stations. Our geophysical results indicate that the Santa Lucia trough deepens toward the E-NE, reaching sedimentary thicknesses that may exceed 950 m. Outside the studied sector, its depth increases according to the gravity minimum, toward the NE of the area. Therefore, sandy or deep fractured episodes could harbor hot springs, whose temperature, considering the normal geothermal gradient of 30 °C/km, would approximately be in the range of 36–40 °C.

6

Estimation of electrical resistivity using artifcial neural networks: a case study from Lublin Basin, SE Poland

Ważny Jakub, Stefaniuk Michał, Cygal Adam

Acta Geophysica

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2021

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Vol. 69, no. 2

631--642

EN

Artifcial neural networks method (ANNs) is a common estimation tool used for geophysical applications. Considering borehole data, when the need arises to supplement a missing well log interval or whole logging-ANNs provide a reliable solution. Supervised training of the network on a reliable set of borehole data values with further application of this network on unknown wells allows creation of synthetic values of missing geophysical parameters, e.g., resistivity. The main assumptions for boreholes are: representation of similar geological conditions and the use of similar techniques of well data collection. In the analyzed case, a set of Multilayer Perceptrons were trained on fve separate chronostratigraphic intervals of borehole, considered as training data. The task was to predict missing deep laterolog (LLD) logging in a borehole representing the same sequence of layers within the Lublin Basin area. Correlation between well logs data exceeded 0.8. Subsequently, magnetotelluric parametric soundings were modeled and inverted on both boreholes. Analysis showed that congenial Occam 1D models had better ftting of TM mode of MT data in each case. Ipso facto, synthetic LLD log could be considered as a basis for geophysical and geological interpretation. ANNs provided solution for supplementing datasets based on this analytical approach.

7

Assessment and recognition of pre and co seismic electromagnetic signatures from magnetotelluric data: a case study from Koyna–Warna seismoactive region, India

Vijaya Kumar P. V., Rawat Vishal S., Patro Prasanta K., Gupta A. K., Babu Narendra

Acta Geophysica

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2021

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Vol. 69, no. 1

1--15

EN

Continuously monitored magnetotelluric (MT) time series data were used to identify the short-term earthquake co-seismic and pre-seismic electromagnetic phenomenon. The co-seismic behavior of the MT time series data recorded at 15 Hz sampling frequency is analyzed for the earthquake that occurred on November 24, 2007, of Mw =4.6. The wavelet analysis of the MT time series data shows signifcant enhancement at 3–6 Hz frequency band in the scalogram during the earthquake in comparison with pre- and post-time. The signifcant enhancement in the scalogram is related to the onset of the main shock of the earthquake. In this paper, we have also shown the precursory signatures of several earthquake magnitudes (Mw) ranging from 3.9 to 4.9 and the focal depth extending from 5 to 10 km mainly dominated by normal and strike-slip faulting. The spectral polarization ratio technique was implemented on these events to identify the precursory signatures. A few days before the earthquake, a signifcant anomaly was identifed for most of the earthquakes using this technique. This prominent anomaly is correlated with Dst index, which provides information about the ionosphere and magnetosphere responses in the presence of the solar wind and interplanetary magnetic feld. We inferred the unusual behavior prior to the earthquake is related to the precursory signature, but not related to the solar-terrestrial efect. The complex tectonic settings in the study region suggest that both electrokinetic and seismic dynamo mechanisms are the probable mechanisms playing an important role in generation of co- and pre-seismic electromagnetic signals.

8

Magnetotelluric sounding evidence of development of nappes in the Tuolai Sag, Yin-E Basin

Penghui Zhang, Hui Fang, Xiaobo Zhang, Yaoyang Zhang, Haihong Xu, Yan Peng, Yongzhen Yuan

Acta Geophysica

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2020

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Vol. 68, no. 1

91--104

EN

To explore the tectonic framework and features of stratigraphic distribution in the Tuolai Sag, Yin-E Basin, a 47-km-long magnetotelluric (MT) sounding measurement was performed around Well MAZD1 in the sag. During feld data acquisition, a remote reference technique was used to ensure data quality, with apparent resistivity and phase curves of all measuring points obtained using the Fourier transform, power spectrum selection, robust estimation and other methods. After MT data processing, dimensionality analysis and the degree of two-dimensional deviation indicated that the study area had the dimensionality needed for two-dimensional inversion. The major electrical axis in the sag was determined, using a multipoint–multifrequency point statistical imaging technique, to be in the WNW direction. Within the constraints of the resistivity log data for Well MAZD1, inversion results for TE and TM models were compared, after which the TM model, which corresponded well to geological conditions, was selected for conducting the nonlinear conjugate gradient method inversion and a reliable resistivity model was fnally obtained. Based on regional petrophysical properties, resistivity logging, and near-well bathymetric data, the electrical characteristics of diferent formations within the sag were obtained and a set of low-resistance clastic rock identifed in the lower Carboniferous strata. Based on an integrated analysis of the regional surface geology, tectonic setting, and depositional environment, and within the constraints of gravity to ft with electrical structure, a tectonic framework of two subsags sandwiched by an uplift is proposed for the Tuolai Sag. The scale of the northern subsag is large, with development of pre-Carboniferous nappe as well as of Carboniferous–Permian strata within the lower part of the nappe. The southern subsag is small and flled mainly with Carboniferous–Permian strata.

9

Effective denoising of magnetotelluric (MT) data using a combined wavelet method

Ling Zhenbao, Wang Peiyuan, Wan Yunxia, Li Tonglin

Acta Geophysica

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2019

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Vol. 67, no. 3

813--824

EN

Noise interference, especially from human noise, seriously affects the quality of magnetotelluric (MT) data. Strong human noise distorts the apparent resistivity curve, known as the near-source effect, causing poor reliability of MT data inversion. Based on analyzing the frequency characteristics of human noise resulting from the surrounding environment, a new waveletbased denoising method is proposed for both synthetic and real MT data in this paper. The new technique combines multiresolution analysis with a wavelet threshold algorithm based on Bayes estimation and has a remarkable effect on denoising at all band frequencies. The multi-resolution analysis method was employed to reduce long-period noise, and a wavelet threshold algorithm was used to eliminate strong high-frequency noise. In this research, the improved algorithm was assessed via simulated experiments and field measurements with regard to the reduction in human noises. This study demonstrates that the new denoising technique can increase the signal-to-noise ratio by at least 112% and provides an extensive analysis method for mineral resource exploration.

10

Zastosowanie badań geofizycznych do rozpoznawania warunków geologicznych otoczenia złoża hydrogeotermalnego w masywie krystalicznym w rejonie Lądka-Zdroju

Stefaniuk M., Ostrowski C., Sada M., Cygal A.

Technika Poszukiwań Geologicznych

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2017

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R. 56, nr 2

131--146

PL

Rejon Lądka Zdroju jest od kilkuset lat znany z występowania i wykorzystywania ciepłych źródeł. Złoże wód geotermalnych występuje tutaj w specyficznych warunkach geologicznych charakterystycznych dla obszaru sudeckiego. Ma ono charakter szczelinowy i występuje w warunkach naporowych. Rozwój Uzdrowiska spowodował potrzebę lepszego rozpoznania złoża hydrogeotermalnego i jego geologicznego otoczenia. W ramach zrealizowanego programu badań wykonane zostały również badania geofizyczne zorientowane na rozpoznanie ogólnych warunków geologicznych złoża i jego otoczenia. Zastosowane zostały metody: magnetyczna, grawimetryczna i geotermiczna, profilowania VLF, sondowania i profilowania elektrooporowe oraz ciągłe profilowania magnetotelluryczne. W ramach prezentowanej pracy wykonany został przegląd wcześniejszych badań geofizycznych oraz wykonano reinterpretację danych magnetotellurycznych z włączeniem interpretacji danych grawimetrycznych. Reinterpretacja obejmowała przegląd prac pomiarowych, weryfikację procedur i wyników przetwarzania danych pomiarowych oraz została zweryfikowana i rozszerzona interpretacja krzywych sondowań w tym inwersyjne modelowania dwuwymiarowe. Badania te pozwoliły na wyinterpretowanie stref uskokowych, wykrycie anomalii temperaturowych i w bardzo ograniczonym stopniu rozpoznanie przestrzenne szczelinowych poziomów wodonośnych.

EN

The Lądek-Zdrój area has been known for several hundred years as a place of occurrence and use of hot springs. A hydrogeothermal reservoir occur there in specific geological conditions characteristic for Sudetes area. The reservoir is of a fracture type and occurs in artesian conditions. The development of the Health Resort caused the need for the better recognition of the hydrogeothermal reservoir and its geological vicinity. The carried out investigation program included, among others, a geophysical survey for the recognition of general geological conditions of the reservoir and its vicinity. The magnetic, gravity and surface geothermic methods were applied as well as VLF profiling, resistivity profiling and soundings and continuous magnetotelluric profiling. The review of the earlier geophysical surveys and reinterpretation of the magnetotelluric data including gravity data were made within the framework of the presented paper. The reinterpretation works a included review of data acquisition, the verification of procedures and results of data processing as well as verification and an extended interpretation of the sounding curves with use of inverse 2D modeling. As results of the survey tectonic zones were interpreted and temperature anomalies were discovered and, within a limited range, space recognition of the fractured aquifer horizons was made.

11

Geofizyczne monitorowanie procesu podziemnego zgazowania węgla brunatnego

Wojciechowski K.

Zeszyty Naukowe Instytutu Gospodarki Surowcami Mineralnymi i Energią PAN

|

2016

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nr 93

75--82

PL

Z powodu bezszybowego dostępu do złoża skuteczne przeprowadzenie procesu podziemnego zgazowania węgla brunatnego wymaga ciągłego monitorowania geofizycznego. Odpowiada ono za identyfikację położenia frontu zgazowania, modelowanie powstałej kawerny, określenie wpływu gazogeneratora na warstwy nadkładu i osiadanie terenu, jak również pomaga w wykryciu przypuszczalnych ucieczek gazu. Należy wspomnieć, że środowisko naukowe nie wypracowało optymalnego i standaryzowanego systemu monitorowania procesu podziemnego zgazowania węgla brunatnego. Niniejszy artykuł skupia się na wyborze metody obserwacji zjawiska zgazowania dopasowanej do warunków geologicznych towarzyszących polskim węglom brunatnym. Rozpatrywana technologia zgazowania dedykowana jest przede wszystkim pozabilansowym, zawodnionym i zapiaszczonym pokładom węgla brunatnego, występującym w sąsiedztwie utworów ilastych, które za zadanie mają stanowić izolację dla planowanego georeaktora. Wybór metody opiera się na charakterystycznych warunkach panujących w okolicy gazogeneratora, które wywołują lokalne anomalie geofizyczne. Warunki te to przede wszystkim oddziaływanie termiczne gazogeneratora, które wpływa na przewodnictwo elektryczne, porowatość, przepuszczalność, gęstość, czy prędkość rozchodzenia się fal. W efekcie jako najbardziej perspektywiczną metodę wybrano tomografię elektrooporową, która umożliwia niemalże automatyczne monitorowanie procesu. Zaproponowano również metodykę prowadzenia badań, dopasowaną do najbardziej perspektywicznych technologii podziemnego zgazowania węgla brunatnego.

EN

Effective implementation of the brown coal underground gasification process requires continuous geophysical monitoring due to the shaft free access to deposits. Geophysical monitoring is responsible for identifying the gasification front location, modeling formed caverns, determining the impact of the gasifier at layers of overburden and subsidence, as well as helping to detect possible gas escapes. It should be noted that the scientific community did not develop optimal and standardized systems of brown coal underground gasification monitoring. This paper is focused on selecting the gasification monitoring method adapted to the geological conditions accompanying the Polish brown coals. The considered gasification technology is primarily dedicated to off-balance sheet, water-logged and gritty decks of brown coal, occurring near the loams designed to provide insulation for the planned gasifier. The method choice is based on the specific conditions prevailing in the gasifier area, which cause local geophysical anomalies. These conditions are primarily the thermal impact of gasifier which affects the electrical conductivity, porosity, permeability, density, and the waves propagation speed. As a result, electrical resistivity tomography was chosen as the most perspective method which allows for an almost automatic monitoring process, thus it allows the gasifier’s impact on the surroundings to be observed at a relatively low cost. The research methodology, adapted to the most promising technology of brown coal underground gasification was also proposed.

12

Pareto Joint Inversion of 2D Magnetotelluric and Gravity Data – Towards Practical Applications

Miernik K., Bogacz A., Kozubal A., Danek T., Wojdyła M.

Acta Geophysica

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2016

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Vol. 64, no. 5

1655--1672

EN

In this paper, a Pareto inversion based global optimization approach, to obtain results of joint inversion of two types of geophysical data sets, is formulated. 2D magnetotelluric and gravity data were used for tests, but presented solution is flexible enough to be used for combination of any kind of two or more target functions, as long as misfits can be calculated and forward problems solved. To minimize dimensionality of the solution, space and introduce straightforward regularization Sharp Boundary Interface (SBI) method was applied. As a main optimization engine, Particle Swarm Optimization (PSO) was used. Synthetic examples based on a real geological model were used to test proposed approach and show its usefulness in practical applications.

13

Kompleksowa interpretacja sejsmiczna i geoelektryczna w poszukiwaniu i rozpoznawaniu złóż rud miedzi typu stratoidalnego położonych na znacznych głębokościach

Niedbał M., Kwaśny L., Zielińska A., Farbisz J., Wojdyła M., Sito Ł.

Cuprum : czasopismo naukowo-techniczne górnictwa rud

|

2015

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nr 4

5--25

PL

Do rozpoznania złoża rud miedzi Radwanice-Gaworzyce na monoklinie przedsudeckiej wykorzystano kilka metod geofizycznych, m.in. sejsmikę refleksyjną 2D, magnetotellurykę i polaryzację wzbudzoną (IP). W rezultacie otrzymano m.in. morfologię spągu cechsztynu wraz z interpretacją tektoniki oraz rozkład polaryzowalności i oporności strefy złożowej. Rozkłady anomalii otrzymanych parametrów geofizycznych były przedmiotem kompleksowej interpretacji, w wyniku której zostały wyznaczone granice ciała rudnego, w znacznym stopniu pokrywające się z granicą pomiędzy strefą redukcyjną i utlenioną. Interesująca ze złożowego punktu widzenia jest metoda polaryzacji wzbudzonej, wykorzystująca zdolność minerałów siarczkowych do polaryzacji pod wpływem impulsu prądu elektrycznego. Przetestowano kilka wariantów metodycznych, wybierając dwa najbardziej efektywne dla określonych warunków zalegania mineralizacji rudnej, oparte na pomiarach układem ekwatorialnym oraz gradientu środkowego. Planowane dalsze prace badawcze na modelach litologiczno-mineralnych oraz w i nad wyrobiskami górniczymi mają potwierdzić skuteczność zastosowanych metod do ilościowej oceny mineralizacji rudnej oraz planowania eksploatacji górniczej. Jednak już na podstawie wykonanych badań można stwierdzić, że kompleksowe pomiary geofizyczne wspomagają efektywne pla-nowanie prac poszukiwawczo-rozpoznawczych.

EN

A number of geophysical methods were used, e.g. 2D reflexive seismics, magnetotellurics and induced polarization (IP), to study the Radwanice-Gaworzyce deposit in the Sudeten monocline. This allowed obtaining a morphology of Zechstein [mine stone] thill, tectonic interpretation as well as polarity distribution and deposit zone resistance. The resulting distribution of geophysical parameter anomalies was comprehensively analysed to allow marking ore-bearing body boundaries were found to overlap to a large extent with the boundary of the reductive zone. The polarisation method is very interesting to a deposit researcher, as it uses the ability of sulphide minerals to polarize under an electric impulse. A number of different methodological variants, based on central gradient measurements and using the equatorial system, were tested to select the two most effective for the specific conditions of ore mineralization. Further research work has been planned on lithological and mineral models as well as in and above mining workings in order to confirm the adequacy of the methods applied in the quantitative assessment of ore mineralisation and mining exploitation planning. Based only on the research now in progress, it is already possible to state that comprehensive geophysical measurements help in works related to search and detection.

14

Increased resolution of subsurface parameters from 1D magnetotelluric modeling

Shireesha M., Harinarayana T.

Acta Geophysica

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2013

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Vol. 61, no. 3

569--582

EN

In electric and electromagnetic techniques, it is well known that the principle of equivalence poses a problem in the interpretation of subsurface layers. This means the inversion problem can provide the conductivity-thickness product more confidently than the individual parameters - conductivity and thickness - separately. The principle of equivalence corresponds to the middle layer in a three-layer earth structure. In order to resolve this problem, we have touched upon the different formulae of apparent resistivity proposed by earlier workers considering the real and imaginary parts of the impedance tensor and designed a new formula to compute apparent resistivity for different models. We observed that the application of our new formula for apparent resistivity using the combination of real and imaginary parts of the impedance has a better resolution as compared to earlier conventional formulae of apparent resistivity. These results have been demonstrated through both forward and inverse modeling schemes.

15

Próba wykorzystania sieci neuronowych w kompleksowej interpretacji danych elektromagnetycznych na przykładzie złoża Grabownica

Mastej W.

Geologia / Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie

|

2011

|

T. 37, z. 1

157-173

PL

W pracy przedstawiono próbę zastosowania metody rozpoznawania obrazów z użyciem sztucznych sieci neuronowych w kompleksowej interpretacji danych z sondowań magnetotellurycznych AMT (Audio-frequency Magnetotellurics) i CSAMT (Controlled Source Audio-frequency Magnetotellurics) ze złoża ropy i gazu Grabownica (dipol podłużny i poprzeczny względem linii profili pomiarowych). Obiektami klasyfikacji były pionowe pasy z przekrojów magnetotellurycznych, o szerokości 50 m, utworzone na bazie siatek interpolacyjnych. Strukturę obiektów formalnie niestrukturalnych wymuszono częściowo poprzez ich podział na: przypowierzchniową, wysokooporową strefę do 200 m n.p.m., strefę niskooporowych utworów uszczelniających oraz słabych maksimów - kominów dyfuzyjnych, od 200 do -100 m n.p.m. i najniższą, wysokooporową strefę złoża. Prawidłowe wskazanie rzeczywistych stref złożowych na bazie informacji pochodzących z często niejasnych i rozbieżnych między sobą obrazów z przekrojów magnetotellurycznych, świadczą o przydatności tej metody. Wskazano także dwie nieznane strefy złożowe w NE części przekroju G4 i w SW części przekroju G2.

EN

The paper presents an attempt to apply the pattern recognition method using artificial neural networks in integrated interpretation of the magnetotelluric data AMT (Audio-frequency Magnetotellurics) and CSAMT (Controlled Source Audio-frequency Magnetotellurics), acquired from the Grabownica oil and gas deposit (longitudinal and transversal dipole in relation to measurement profile lines). Vertical belts of magnetotelluric cross-sections, each 50 m wide, obtained from interpolation grids, were the objects of classification. The structure of formally non-structural objects was partly imposed through division into: near-surface high-resistivity zone, to 200 m a.s.l., low-resistivity screens and week maxima - diffusion chimneys, from 200 to -100 m a.s.l., and the lowest, high-resistivity deposit zone. The usefulness of the method was proven by correct identification of real deposit zones based on data often coming from ambiguous and incompatible magnetotelluric cross-sections. In addition, two unknown deposit zones were discovered in NE part of cross-section G4 and SW part of cross-section G2.

16

Metody elektromagnetyczne w prospekcji naftowej

Stefaniuk M.

Geologia / Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie

|

2011

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T. 37, z. 1

5-36

PL

Nasycenie węglowodorami powoduje anomalne zmiany własności fizycznych ośrodka geologicznego i pomierzonych pól geofizycznych, pozwalające na wykrywanie i rozpoznawanie złóż ropy naftowej i gazu ziemnego. Kompleksy złożowe charakteryzują się podwyższeniem oporności o 1-4 rzędy wielkości względem otoczenia. Kontrasty pojawiają się na granicy dolnej złoża pomiędzy skałą zbiornikową nasyconą zmineralizowaną wodą złożową i nasyconą węglowodorami oraz na jego granicy górnej z niskooporowymi, uszczelniającymi skałami ilastymi. Na granicy pomiędzy ropą naftową i wodą złożową pojawia się ponadto radykalny kontrast zdolności do polaryzacji elektrycznej ośrodka, wzbudzonej przez przepływ prądu. Pośrednim wskaźnikiem obecności złoża węglowodorów jest przypowierzchniowa strefa mineralizacji siarczkowej związana z dyfuzją węglowodorów, zmieniająca właściwości magnetyczne i polaryzowalność ośrodka. Prezentowane przykłady pochodzą ze strefy karpackiego złoża ropnego "Grabownica" oraz złoża gazowego "Rudka" w zapadlisku przedkarpackim.

EN

Hydrocarbons saturating rocks give rise to anomalous changes in physical properties of geological medium and measured geophysical fields, thus allowing discovering and recognizing of oil and gas fields. Deposit complexes are characterized by resistivity increased by 1-4 orders of magnitude. Resistivity contrast appear at the lower boundary of deposit, between reservoir rock saturated with mineralized water and saturated with hydrocarbons, as well as at the upper boundary with low-resistivity sealing clayey rocks. Moreover, a contrast of environment's ability to electric polarization induced by electric current flow appears at the boundary between hydrocarbons and formation water. The indirect indicator of a hydrocarbon deposit is the near-surface zone of sulfide mineralization connected with the hydrocarbon diffusion, which modifies magnetic properties and electric polarization ability of the medium. Examples of investigations made in the zone of the Carpathian oil field "Grabownica" and gas field "Rudka" in the Carpathian Foredeep are presented.

17

Interpretacja złożonych struktur geologicznych z wykorzystaniem prostych i inwersyjnych modelowań pola magnetotellurycznego

Wojdyła M., Stefaniuk M.

Geologia / Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie

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2011

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T. 37, z. 1

113-140

PL

W pracy przedstawiono ogólne założenia jedno- i dwuwymiarowych modelowań prostych i odwrotnych (inwersyjnych) pola magnetotellurycznego. Opisano metodykę interpretacji danych magnetotellurycznych, w tym analizę wymiarowości środka geoelektrycznego oraz jej wpływ na dobór odpowiedniego modelu interpretacyjnego. Na przykładzie polowych danych magnetotellurycznych (AMT i CSAMT) zarejestrowanych w rejonie złoża węglowodorów Grabownica pokazano wpływ modelu startowego na wynik końcowy inwersji 2D. Drugim analizowanym złożem było złoże ropy naftowej Łodyna. Skupiono się na analizie możliwości wyinterpretowania na drodze inwersji 1D i 2D cienkich, pionowych warstw, jakimi w przybliżeniu można to złoże aproksymować. Wskazano na różnice w odwzorowaniu budowy geologicznej w zależnooeci od polaryzacji interpretowanych krzywych (TE mode lub TM mode) oraz zaproponowano zoptymalizowaną metodykę interpretacji.

EN

General assumptions of 1D and 2D modeling and inversion were presented in this paper. Methodology of magnetotelluric data interpretation was described including analysis of dimensionality of geoelectrical medium and its influence on choosing the proper interpretation model. Relations between initial model and final results of inversion were shown based on magnetotelluric (AMT and CSAMT) data from Grabownica oil and gas field. The second example was from the Lodyna oil field. A possibility of interpretation of thin vertical layers, which can approximate the Lodyna field by 1D and 2D MT inverse procedures was analyzed. Dependences between final geological models and MT curve type (TE mode or TE mode) taken to interpretation were shown. Finally, methodology of interpretation was proposed.

18

Application of Kalman Filter to Noise Reduction in Multichannel Data

Leśniak A., Danek T., Wojdyła M.

Schedae Informaticae

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2009

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Vol. 17/18

63-73

EN

The results of application of multichannel Kalman filtering to reduction of uncorrelated noise in magnetotelluric recordings are discussed in this article. Magnetotelluric method of Earth structure recognition is shortly presented together with the its most popular measurement method called the remote reference method. The basic theory of nonstationar, discrete Kalman filter and its implementation to multichannel magnetotelluric data recorded in multi-site experiment are also discussed with details. The practical examples of Kalman filter application to the real 2D and 3D data illustrate the merits of presented technique.

19

Wybrane problemy magnetotellurycznych i grawimetrycznych badań strukturalnych we wschodniej części polskich Karpat

Stefaniuk M., Ostrowski C., Targosz P., Wojdyła M.

Geologia / Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie

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2009

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T. 35, z. 4/1

7-46

PL

W artykule przedstawione zostały wybrane rezultaty najnowszych badań magnetotellurycznych i grawimetrycznych wykonanych we wschodniej części Karpat polskich. Zreinterpretowane zostały wyniki regionalnych badań magnetotellurycznych wykonanych wzdłuż dwóch profili: Maniów - Przemyśl i Radoszyce - Przemyśl z wykorzystaniem najnowszych procedur inwersji 1D i 2D. W ramach prac interpretacyjnych przeanalizowana została dokładność określenia położenia granic opornościowych. Opracowane zostały przekroje oporności zawierające główne wyinterpretowane granice litologiczne i strefy tektoniczne. Zweryfikowane zostały modele budowy geologicznej wzdłuż profili: Szczawne - Kuźmina i Jaśliska - Brzozów za pomocą modelowań pola siły ciężkości. Oszacowane zostały korelacyjne zależności pomiędzy prędkościami średnimi fali sejsmicznej i wartościami anomalii rezydualnych siły ciężkości. Na podstawie uzyskanych równań regresji skonstruowano regionalne mapy prędkości średnich.

EN

Selected results of recent magnetotelluric and gravity investigations made in eastern part of the Polish Carpathians were presented in the paper. Results of regional magnetotelluric survey made along two profiles: Maniów - Przemyśl and Radoszyce - Przemyśl were reinterpreted with the use of state-of-the-art 1D and 2D inversion procedures. The accuracy of the evaluation of a depth of interpreted resistivity boundaries was analysed in the framework of interpretation works. Resistivity cross-sections including main interpreted lithological boundaries and tectonic zones were made. Geological models along profiles: Szczawne - Kuźmina and Jaśliska - Brzozów were verified with the use of gravity force modelling. Correlation dependences between average velocities of seismic wave and values of residual anomalies of gravity force were evaluated. Regional maps of average velocities were constructed based on obtained regression equations.

20

Zastosowanie metody magnetotellurycznych profilowań ciągłych w badaniach strukturalnych

Stefaniuk M., Czerwiński T., Klityński W., Wojdyła M.

Geologia / Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie

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2008

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T. 34, z. 1

43-68

PL

Przedmiotem artykułu są przykłady zastosowania magnetotellurycznych profilowań ciągłych do badań strukturalnych w zróżnicowanych warunkach geologicznych. Dwa spośród przedstawionych przykładów odnoszą się do rozpoznawania struktury allochtonu fliszowego w polskich Karpatach Zewnętrznych oraz jego podłoża. Przykłady z obszaru sudeckiego przedstawiają wykorzystanie magnetotellurycznych profilowań ciągłych do rozpoznawania stref tektonicznych w utworach krystalicznych oraz związanych z nimi stref filtracji wód mineralnych i termalnych. Przykład rozpoznania struktury wysadu solnego pochodzi z rejonu centralnej części wału środkowopolskiego. W strefie platformowej, w rejonie Pomorza Wschodniego, wykonano badania w celu rozpoznania kompleksów geologicznych położonych poniżej silnie ekranującego energię sprężystą horyzontu utworów ewaporatowych cechsztynu. Przedstawiono metodykę badań, rezultaty interpretacji geofizycznej i niektóre aspekty interpretacji geologicznej.

EN

The paper presents case studies of the continuous magnetotelluric profiling applied to structural studies under varied geological conditions. Two applications refer to identifying of allochthonous flysch structure and its basement in the Polish Outer Carpathians. The case studies from the Sudetes Mts. present the application of the continuous magnetotelluric profiling to identify tectonic zones in crystalline rock complexes and accompanying filtration zones of mineral and thermal waters. A case of a salt dome that was identified by means of the MT investigations in the central part of the Mid-Polish Ridge is also presented. At the platform-type zone of the East Pomerania, the MT investigations were carried out to recognize geological complexes resting beneath the evaporate Zechstein horizon that screened the elastic energy. The methodology of the MT investigations and results of geophysical interpretation and some aspects of geological interpretation of MT data are presented.