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electromagnetic monitoring with local mesh for time-lapse monitoring of hydraulic fracturing

JOURNAL OF APPLIED GEOPHYSICS 2023年 212卷

作者： Zhang, Zihao Liu, Jianxin Guo, Rongwen Kouadio, Kouao Laurent Zhan, Shaoquan Li, Aiyong Liu, Rong Cent South Univ Sch Geosci & Info Phys Changsha Hunan Peoples R China Cent South Univ Key Lab Nonferrous Resources & Geol Hazard Detect Changsha Hunan Peoples R China Team 814 East China Nonferrous Met Geol Explorat B Zhenjiang Peoples R China Cent South Univ Sch Geosci & Info Phys Changsha Hunan Peoples R China

The controlled-source electromagnetic method (CSEM) is a useful tool for monitoring underground fluid movement due to hydraulic fracturing. To understand the characteristics of time-lapse monitoring, an efficient three dimensional(3D) forward modeling is a premise. However, 3D finite element method (FEM) employs the normal mesh that applies fine grids to model the whole sensitive area, resulting in a large degree of freedom (DOF) of the equation that is associated with expensive computation cost. Moreover, time-lapse monitoring requires continual expensive calculations, which lead even an unacceptable computational burden. Inspired by the fact that during the hydraulic fracturing, the resistivity changes occur in a limited domain, we propose a method called as the FEM with local mesh, which is based on secondary field equation to model the EM field perturbation due to hydraulic fracture, and uses fine grids on the fracturing area with resistivity change and as large grids as possible to represent other areas without resistivity change. Therefore, the DOF can be reduced significantly. The numerical tests demonstrate that our method is accurate and has only 10% of the DOF of conventional method.

关键词： Hydraulic fracturing Monitoring controlled-source electromagnetic method Modeling

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A synthetic aperture for land controlled-source electromagnetic surveys

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JOURNAL OF APPLIED GEOPHYSICS 2020年第0期174卷 103945-000页

作者： Zhang, Jifeng Huang, Rihua Feng, Bing Changan Univ Sch Geol Engn & Geomat Dept Geophys Xian 710054 Peoples R China Zhenhai Urban Planning & Survey Res Inst Ningbo Ningbo 315200 Peoples R China

A controlled-source electromagnetic method with a synthetic aperture is proposed to improve the ability to detect a deep target body in the subsurface. First, we deduced the formulas of three-dimensional diffusion equations in the frequency domain, and gave the expression of synthetic aperture of the controlled-source electromagnetic array. An amplitude weighting coefficient, a phase shift coefficient, and a synthetic aperture range are selected based on model tests, and then, the optimum value of the error range is determined. A typical geo-electrical model is established, and the electric response, the normalized amplitude of the background field, and the apparent resistivity with and without a synthetic aperture are compared. The results show that a synthetic aperture can focus electromagnetic energy and enhance the electromagnetic response of the target body. This is beneficial when extracting weak anomaly information for a deep geo-electrical body, especially for a resistive target object. Finally, we apply the synthetic aperture to field data for gold ore in northern China, and the amplitude of a deep resistive anomaly is strengthened. This demonstrates that our method can be effectively applied to real field data processing using a synthetic aperture. (C) 2020 Elsevier B.V. All rights reserved.

关键词： Synthetic aperture controlled-source electromagnetic method Deep exploration Weak information extraction

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controlled-source electromagnetic signal detection using a hybrid deep learning model: Convolutional and long short-term memory neural networks

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Computers & Geosciences 2025年 204卷

作者： Yecheng Liu Diquan Li Jin Li Yanfang Hu Zijie Liu Xian Zhang School of Geosciences and Info-Physics Central South University Changsha 410083 China Key Laboratory of Metallogenic Prediction of Non-Ferrous Metals and Geological Environment Monitor Ministry of Education Central South University Changsha 410083 China Hunan Provincial Key Laboratory of Intelligent Computing and Language Information Processing College of Information Science and Engineering Hunan Normal University Changsha 410081 China Hunan Provincial Key Laboratory of Finance & Economics Big Data Science and Technology School of Information Technology and Management Hunan University of Finance and Economics Changsha 410205 China

controlled-source electromagnetic (CSEM) method using a periodic transmitted signal source suppresses random noise by superimposing and averaging the recorded signal over multiple periods. However, it still faces great challenges in strong interference environments. Here we present a CSEM signal detection method based on a hybrid architecture of convolutional neural network (CNN) and long short-term memory neural network (LSTM). Our method improves the quality of the recorded signal by filtering out all the noise periods and retaining the useful signal periods. The core lies in combining the spatial feature extraction capability of CNN with the time series modeling capability of LSTM, which can deeply excavate the feature differences between noise and CSEM useful signal. Meanwhile, a classification model of signal and noise is constructed using a large-scale training dataset. This hybrid model exhibits superior performance compared to other deep learning models such as CNN or LSTM. Also, we propose a novel signal detection mechanism that not only maintains the periodicity of CSEM signal, but also greatly enhances processing efficiency. The results of synthetic and measured data demonstrate that our method can obtain useful signals from CSEM data containing different noise types and significantly improve the quality of sounding curves. In particular, our method is useful for CSEM signal detection in strong interference.

关键词： controlled-source electromagnetic method Deep learning Noise Signal detection

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Three-Dimensional Borehole-to-Surface electromagnetic Resistivity Anisotropic Forward Simulation Based on the Unstructured-Mesh Edge-Based Finite Element method

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Applied Sciences 2025年第10期15卷 5307-5307页

作者： Baiwu Chen Hui Cao Mingchun Chen Ruolong Ma Sihao Wang College of Geophysics Chengdu University of Technology Chengdu 610059 China Geomathematics Key Laboratory of Sichuan Province Chengdu 610059 China Key Laboratory of Earth Exploration and Information Techniques (Chengdu University of Technology) Ministry of Education Chengdu University of Technology Chengdu 610059 China Sinopec Geophysical Corporation Beijing 100013 China Yellow River Engineering Consulting Co. Ltd. Zhengzhou 450003 China

Geophysics is a discipline that studies the properties of subsurface media using physical methods, among which electromagnetic methods have long been an important technical approach in resource exploration. The anisotropy of resistivity in underground media objectively exists in electromagnetic exploration. However, most borehole-to-surface electromagnetic methods (BSEMs) currently process and interpret data based on the assumption of isotropy, which can lead to misinterpretations of observational data in regions where an isotropy is significant. To address this, we propose a 3D edge-based finite element method on unstructured meshes for simulating resistivity anisotropy in BSEMs. A principal-axis anisotropic tensor is introduced to model anisotropy, and the vertical-line transmitter is transformed into an equivalent set of point sources, enabling efficient computation. The accuracy and effectiveness of the proposed numerical algorithm are validated through comparisons with the solutions from Dipole1D and MARE2D. Furthermore, a comparative analysis of reservoir dynamic monitoring under isotropic and anisotropic conditions using the same model reveals that the relative errors in amplitude and phase exceed 40%, and anisotropy must be adequately considered in reservoir monitoring with borehole-to-surface electromagnetic methods. For reservoir models with varying extraction rates, this study further examines the influence of a transmitter’s position on the electromagnetic response characteristics in anisotropic reservoir dynamic monitoring. The results indicate that effective monitoring cannot be achieved when the transmitter is located above the reservoir; however, when the transmitter is positioned below the reservoir, the borehole-to-surface electromagnetic method can significantly enhance the monitoring of reservoir dynamics.

关键词： finite-length vertical-line source geological resource exploration three-dimensional numerical modeling controlled-source electromagnetic method

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Crustal Cracks and Frozen Flow in Oceanic Lithosphere Inferred From Electrical Anisotropy

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GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 2019年第12期20卷 5979-5999页

作者： Chesley, Christine Key, Kerry Constable, Steven Behrens, James MacGregor, Lucy Columbia Univ Lamont Doherty Earth Observ Palisades NY 10964 USA Univ Calif San Diego Scripps Inst Oceanog La Jolla CA 92093 USA Edinburgh Geosci Advisors Ltd Edinburgh Midlothian Scotland

Geophysical observations of anisotropy in oceanic lithosphere offer insight into the formation and evolution of tectonic plates. Seismic anisotropy is well studied but electrical anisotropy remains poorly understood, especially in the crust and uppermost mantle. Here we characterize electrical anisotropy in 33 Ma Pacific lithosphere using controlled-source electromagnetic data that are highly sensitive to lithospheric azimuthal anisotropy. Our data reveal that the crust is similar to 18-36 times more conductive in the paleo mid-ocean ridge direction than the perpendicular paleo-spreading direction, while in the uppermost mantle conductivity is similar to 29 times higher in the paleo-spreading direction. We propose that the crustal anisotropy results from subvertical porosity created by ridge-parallel normal faulting during extension of the young crust and thermal stress-driven cracking from cooling of mature crust. The magnitude of uppermost mantle anisotropy is consistent with recent experimental results showing strong electrical anisotropy in sheared olivine, suggesting its paleo-spreading orientation results from sub-Moho mantle shearing during plate formation.

关键词： electrical anisotropy controlled-source electromagnetic method oceanic lithosphere plate hydration sheared olivine polarization ellipse

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Robust data processing of noisy marine controlled-source electromagnetic data using independent component analysis

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EXPLORATION GEOPHYSICS 2018年第1期49卷 21-29页

作者： Imamura, Naoto Goto, Tada-nori Kasaya, Takafumi Machiyama, Hideaki Oregon State Univ Coll Earth Ocean & Atmospher Sci 104 CEOAS Adm Bldg Corvallis OR 97331 USA Kyoto Univ Grad Sch Engn Nishikyo Ku C1-2-16 Kyotodaigaku Katsura Kyoto 6158540 Japan Japan Agcy Marine Earth Sci & Technol JAMSTEC Res & Dev Ctr Earthquake & Tsunami 2-15 Natsushima Yokosuka Kanagawa 2370061 Japan JAMSTEC Res & Dev Ctr Submarine Resources 2-15 Natsushima Yokosuka Kanagawa 2370061 Japan

Data processing techniques are often used to estimate the noise-free response of marine controlled-source electromagnetic (CSEM) data and magnetotelluric transfer functions. We have implemented a new CSEM data processing scheme that uses a robust method based on independent component analysis (ICA) to extract interpretable datasets from noisy marine CSEM data. We applied the data processing scheme to signals from a new CSEM observation system comprising a remotely operated vehicle (ROV) and an ocean bottom electromagnetometer (OBEM). These datasets were obtained around the Iheya North hydrothermal field, Okinawa Trough, Japan. The observation system allows a small-scaleCSEMsurvey to be conducted in areas of steep topography, such as hydrothermal fields, because the ROV can deploy the OBEM at the exact observation site. The results show that the coherent and environment noise that exists in the raw time series is reduced sufficiently by ICA processing. It makes interpretation of the resulting electric field data possible. The results also show that the processed data has a higher signal-to-noise ratio in the middle-to-high-frequency band than the data without ICA. The normalised spectrum, obtained by normalising the observed data from the hydrothermal area, indicates that a conductive anomaly exists in the near-offset area around the OBEM. We apply 2D inversion to the electric field data and find that a low resistivity body exists beneath the OBEM and 50 m offset from the OBEM. This resistivity structure is consistent with images taken by the ROV that show characteristic organisms in hydrothermal seepage around the OBEM site.

关键词： controlled-source electromagnetic method hydrothermal vent independent component analysis Okinawa Trough robust data processing

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controlled-source electromagnetic data processing based on gray system theory and robust estimation

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Applied Geophysics 2017年第4期14卷 570-580,622页

作者： Mo Dan Jiang Qi-Yun Li Di-Quan Chen Chao-Jian Zhang Bi-Ming and Liu Jia-Wen School of Geosciences and Info-physics Central South University Changsha 410083 China Key Laboratory of Metallogenie Prediction of Nonferrous Metals and Geological Environment Monitoring （Central South University） Ministry of Education Changsha 410083 China.

We propose a novel method that combines gray system theory and robust M-estimation method to suppress the interference in controlled-source electromagnetic data. We estimate the standard deviation of the data using a gray model because of the weak dependence of the gray system on data distribution and size. We combine the proposed and threshold method to identify and eliminate outliers. Robust M-estimation is applied to suppress the effect of the outliers and improve the accuracy. We treat the M-estimators of the preserved data as the true data. We use our method to reject the outliers in simulated signals containing noise to verify the feasibility of our proposed method. The processed values are observed to be approximate to the expected values with high accuracy. The maximum relative error is 3.6676%, whereas the minimum is 0.0251%. In processing field data, we observe that the proposed method eliminates outliers, minimizes the root-mean-square error, and improves the reliability of controlled-source electromagnetic data in follow-up processing and interpretation.

关键词： controlled-source electromagnetic method gray system theory robust M-estimates

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Three-dimensional inversion of CSEM data: Water leak detection using a small-loop EM method

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JOURNAL OF APPLIED GEOPHYSICS 2014年第0期102卷 134-144页

作者： Noh, Kyubo Chung, Yonghyun Seol, Soon Jee Byun, Joongmoo Uchida, Toshihiro Hanyang Univ Dept Nat Resources & Geoenvironm Engn Seoul 133791 South Korea Natl Inst Adv Ind Sci & Technol Tsukuba Ibaraki Japan

electromagnetic (EM) data sets were acquired using ground-based small-loop electromagnetic (EM) sensors over an artificially constructed sandy ground in Tsukuba, Japan, for three conditions of water saturation. The research aim was to evaluate the imaging capability of the geophysical method for detecting a water leak. Because the sensitivity analysis showed a considerable three-dimensional (3D) distribution of sensitivity around the source-receiver location, 3D inversion was applied to the field data sets. We used an accurate 3D controlled-source electromagnetic (CSEM) inversion algorithm, which adopted an edge-based finite element method as a forward scheme. To obtain the best inversion strategy for our field data and for the selection of the optimal regularization method, 3D inversion was applied to synthetic data sets prior to the inversion of the field data;the synthetic data sets were based on synthetic resistivity models used to simulate the three water-saturation phases of the real test site. Based on the results of sensitivity analysis, different regularization methods were systematically tested and the inversion results were qualitatively analyzed. For our monitoring scenario, the best performance was achieved by combining spatially varying regularization parameters, structural constraints, and the reference model method. The reference model parameters were derived from the less ill-posed model, instead of the main target model, which allowed for more accurate imaging of the main region of interest. This optimal inversion strategy was applied to the test-site field data. The water leak was successfully visualized by small-loop EM data, with systematic application of a priori information as constraints. (c) 2014 Elsevier B.V. All rights reserved.

关键词： controlled-source electromagnetic method Small-loop EM method Inversion Regularization Monitoring

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Application of the Joint MT-CSEM Inversion Algorithm for Field Data Interpretation

Application of the Joint MT-CSEM Inversion Algorithm for Fie...

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2010 IEEE International Symposium Antennas and Propagation/CNC-USNC/URSI Radio Science Meeting

作者： Li, M. Abubakar, A. Liu, J. Habashy, Tarek M. Schlumberger Doll Res Ctr Cambridge MA 02139 USA

ISBN: (纸本)9781424449682

In offshore hydrocarbon explorations, both the magnetotelluric (MT) method and the controlled-source electromagnetic (CSEM) method have been widely used. The MT method uses the electromagnetic fields due to natural sources that can be modeled by using plane waves. It has a relatively large depth of investigation and can be effectively used to obtain rough conductivity estimate of the subsurface. On the other hand, the CSEM method measures the field generated by a low-frequency electric dipole that is towed by a ship at several tens of meters above the seabed. The CSEM data are mainly sensitive to resistive objects, which makes it capable of providing useful information of the locations and shapes of hydrocarbon reservoirs. It is well known that MT and CSEM data provide complementary information: MT may provide information on the background conductivity structures, while CSEM may identify resistive targets (hydrocarbon reservoirs). Constable and Weiss also pointed out the practical importance of MT data: The same receivers can collect both CSEM and MT data, hence MT data come at a very low cost since they can be recovered from time series data when the CSEM source is turned off.

关键词： controlled-source electromagnetic method data analysis electric dipole electric field measurement electric moments electromagnetic fields electromagnetic fields field data interpretation geophysics computing hydrocarbon reservoirs hydrocarbon reservoirs hydrological techniques inverse problems joint MT-CSEM inversion algorithm magnetotelluric method magnetotellurics offshore hydrocarbon explorations rough conductivity estimation rough surfaces

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