Full Waveform Inversions of Borehole Transient Electromagnetic Virtual Wave Fields and Potential Applications

2020 ◽  
Vol 25 (2) ◽  
pp. 211-222
Author(s):  
Fan Tao ◽  
Qi Zhipeng ◽  
Yan Bin ◽  
Zhao Zhao ◽  
Wang Bingchun ◽  
...  
Keyword(s):  
Wave Field ◽  
Shanxi Province ◽  
Small Scale ◽  
Detection Accuracy ◽  
Dynamic Correction ◽  
Wave Fields ◽  
Full Waveform ◽  
Transient Electromagnetic ◽  
Good Imaging ◽  
Imaging Results

The transient electromagnetic method (TEM) for boreholes uses fixed source loops to launch at excavation faces, and is able to realize the mobile reception of secondary fields in the boreholes and detections of low-resistance hazards. This method is known as high detection accuracy, due to the fact that the receiving points are close to the anomalies. However, the interpretation method for this device has not yet been perfected. The present study's goal was to realize the interpretations of boreholes TEM based on inverse transform algorithms of the TEM wave-fields and full waveform inversions. It was found that under the conditions of transient electromagnetic virtual wave-fields, the characteristics of the virtual wave-field time-distance curves of the two-dimensional device could be examined, and a corresponding dynamic correction algorithm was successfully obtained. The wave-field velocities were analyzed using an equivalent conductive plane method. Additionally, the pseudo-seismic inversions of the tunnel-borehole TEM data were realized using full waveform inversion technology. Then, the inversion results of the three-dimensional numerical simulations, flume physical simulations, and downhole field simulations were calculated. It was observed that good imaging results had been obtained for small-scale borehole radial anomalies. Finally, the proposed method was applied to the engineering practices in an underground coal mine in Shanxi Province. The practicability and effectiveness of the proposed method in the fine detection of the properties, forms, and scale of water-logged goaf roadways were successfully tested in the field. The research results indicated that the roadway-borehole transient electromagnetic detection method was complementary to the underground geophysical exploration and drilling, and could be effectively applied in the detection of water-logged goaf roadways.

Identifying Deep Saturated Coal Bed Zones in China through the Use of Large Loop TEM

2018 ◽  
Vol 23 (1) ◽  
pp. 135-142
Author(s):  
Guo-qiang Xue ◽  
Wei-ying Chen ◽  
Zhen-jun Ma ◽  
Dong-yang Hou
Keyword(s):  
Geophysical Methods ◽  
Cost Effective ◽  
Shanxi Province ◽  
Coal Bed ◽  
Detection Accuracy ◽  
Coal Beds ◽  
Large Loop ◽  
Transient Electromagnetic ◽  
Coal Deposits ◽  
The Time Domain

Most of the shallow mineral deposits of China have already been mined because of the country's fast-growing social and economic development. Consequently, the exploration and mining of deep-seated coal deposits have become alternative ways to satisfy the energy needs for both domestic and industrial use. To ensure safe mining practices and avoid the intrusion of water from the bases of coal deposits, it has become essential to investigate the distribution of deep-seated coal deposits using appropriate and cost-effective geophysical methods. For example, a coal mine located in the southern part of China's Shanxi Province is characterized by a roof of dry rocks, whereas the coal beds in this area are saturated. A new technique which uses a large loop transient electromagnetic method (hereafter referred to as a modified central loop TEM) to detect geological targets located at deeper levels in the subsurface was successfully developed and applied in this study. The detection abilities of this technique, such as the time-domain responses and depth of investigation, as well as its sensitivity to deep targets, were analyzed. This new method was successfully employed to detect the floor of a 900 m deep coal seam at the location of the saturated coal beds in Shanxi Province. Wells were drilled to confirm the results, showing that the proposed method is both applicable and convenient for future exploration purposes. TEM could potentially be used to detect geological materials located at greater depths with higher detection accuracy. [Figure: see text]

Improved SSD-assisted algorithm for surface defect detection of electromagnetic luminescence

2021 ◽  
pp. 1748006X2199538
Author(s):  
Zhenying Xu ◽  
Ziqian Wu ◽  
Wei Fan
Keyword(s):  
Defect Detection ◽  
Feature Fusion ◽  
Recognition Rate ◽  
Detection Methods ◽  
Small Scale ◽  
Detection Accuracy ◽  
Single Shot ◽  
Surface Defect Detection ◽  
Feature Pyramid ◽  
Small Feature

Defect detection of electromagnetic luminescence (EL) cells is the core step in the production and preparation of solar cell modules to ensure conversion efficiency and long service life of batteries. However, due to the lack of feature extraction capability for small feature defects, the traditional single shot multibox detector (SSD) algorithm performs not well in EL defect detection with high accuracy. Consequently, an improved SSD algorithm with modification in feature fusion in the framework of deep learning is proposed to improve the recognition rate of EL multi-class defects. A dataset containing images with four different types of defects through rotation, denoising, and binarization is established for the EL. The proposed algorithm can greatly improve the detection accuracy of the small-scale defect with the idea of feature pyramid networks. An experimental study on the detection of the EL defects shows the effectiveness of the proposed algorithm. Moreover, a comparison study shows the proposed method outperforms other traditional detection methods, such as the SIFT, Faster R-CNN, and YOLOv3, in detecting the EL defect.

Interaction of High Frequency Lamb Waves with Surface-Mount Sensor Adhesives

2013 ◽  
Vol 558 ◽  
pp. 489-500 ◽  
Author(s):  
Patrick Norman ◽  
Claire Davis ◽  
Cédric Rosalie ◽  
Nik Rajic
Keyword(s):  
Wave Field ◽  
Lamb Waves ◽  
Base Material ◽  
Adhesive Layer ◽  
Scattered Wave ◽  
Phase Lag ◽  
Wave Fields ◽  
Surface Mount ◽  
Frequency Regime ◽  
Fibre Bragg Gratings

The application of Lamb waves to damage and/or defect detection in structures is typicallyconfined to lower frequencies in regimes where only the lower order modes propagate in order to simplifyinterpretation of the scattered wave-fields. Operation at higher frequencies offers the potentialto extend the sensitivity and diagnostic capability of this technique, however there are technical challengesassociated with the measurement and interpretation of this data. Recent work by the authorshas demonstrated the ability of fibre Bragg gratings (FBGs) to measure wave-fields at frequencies inexcess of 2 MHz [1]. However, when this work was extended to other thinner plate specimens it wasfound that at these higher frequencies, the cyanoacrylate adhesive (M-Bond 200) used to attach theFBG sensors to the plate was significantly affecting the propagation of the waves. Laser vibrometrywas used to characterise the wave-field in the region surrounding the adhesive and it was found that theself-adhesive retro-reflective tape applied to aid with this measurement was also affecting the wavefieldin the higher frequency regime. This paper reports on an experimental study into the influence ofboth of these materials on the propagating wave-field. Three different lengths of retro-reflective tapewere placed in the path of Lamb waves propagating in an aluminium plate and laser vibrometry wasused to measure the wave-field upstream and downstream of the tape for a range of different excitationfrequencies. The same experiment was conducted using small footprint cyanoacrylate film samplesof different thickness. The results show that both of these surface-mount materials attenuate, diffractand scatter the incoming waves as well as introducing a phase lag. The degree of influence of thesurface layer appears to be a function of its material properties, the frequency of the incoming waveand the thickness and footprint of the surface layer relative to the base material thickness. Althoughfurther work is required to characterise the relative influence of each of these variables, investigationsto date show that for the measurement of Lamb Waves on thin structures, careful considerationshould be given to the thickness and footprint of the adhesive layer and sensor, particularly in the highfrequency regime, so as to minimise their effect on the measurement.

Full-waveform inversion with wavefield gradients

2021 ◽  
Author(s):  
Sneha Singh ◽  
Yann Capdeville ◽  
Heiner Igel ◽  
Navid Hedjazian ◽  
Thomas Bodin
Keyword(s):  
Waveform Inversion ◽  
Effective Model ◽  
Small Scale ◽  
Full Waveform Inversion ◽  
Coupling Tensor ◽  
Full Waveform ◽  
Surface Topographies ◽  
Good For ◽  
Incorrect Model

<p>Wavefield gradient instruments, such as rotational sensors and DAS systems, are becoming more and more accessible in seismology. Their usage for Full Waveform Inversion (FWI) is in sight. Nevertheless, local small-scale heterogeneities, like geological inhomogeneities, surface topographies, and cavities are known to affect wavefield gradients. This effect is in fact measurable with current instruments. For example, the agreement between data and synthetics computed in a tomographic model is often not as good for rotation as it is for displacement.</p><p>The theory of homogenization can help us understand why small-scale heterogeneities strongly affect wavefield gradients, but not the wavefield itself. It tells us that at any receiver measuring wavefield gradient, small-scale heterogeneities cause the wavefield gradient to couple with strain through a coupling tensor <strong>J</strong>. Furthermore, this <strong>J</strong> is 1) independent of source, 2) independent of time, but 3) only dependent on the receiver location. Consequently, we can invert for <strong>J</strong> based on an effective model for which synthetics fit displacement data reasonably well. Once inverted, <strong>J</strong> can be used to correct all other wavefield gradients at that receiver.</p><p>Here, we aim to understand the benefits and drawbacks of wavefield gradient sensors in a FWI context. We show that FWIs performed with rotations and strains are equivalent to that performed with displacements provided that 1) the number of data is sufficient, and 2) the receivers are placed far away from heterogeneities. In the case that receivers are placed near heterogeneities, we find that due to the effect of these heterogeneities, an incorrect model is recovered from inversion. In this case therefore, the coupling tensor <strong>J</strong> needs to be taken into account for each receiver to get rid of the effect.</p>

An introduction to seismic exploration of the Micang-Dabashan foothill belt in the Sichuan Basin

2018 ◽  
Vol 6 (4) ◽  
pp. SM39-SM50
Author(s):  
Jingbo Wang ◽  
Zhongshan Qi ◽  
Penggui Jing ◽  
Tianfa Zheng ◽  
Yanqi Li ◽  
...  
Keyword(s):  
Sichuan Basin ◽  
Oil And Gas ◽  
Seismic Exploration ◽  
Small Scale ◽  
Marine Strata ◽  
Piedmont Zone ◽  
Migration Imaging ◽  
Imaging Results ◽  
Platform Margin ◽  
The Sichuan Basin

Geologic studies indicate that the platform-margin reef-shallow facies in Permo-Triassic marine strata in the Micang-Dabashan foothill belt in the Sichuan Basin are favorable exploration targets for oil and gas exploration. However, the typical dual-complexity problem (complex surface condition and subsurface structure) brings a great challenge for seismic technology targeting of those potential oil and gas reservoirs. To overcome this problem, varieties of advanced seismic acquisition and processing methods have been used to improve the imaging quality of piedmont seismic data since 2000. Some improvements have been achieved: The reflection waves from the far offset and deep layer can be acquired in shot gathers from limestone outcropped areas, and the signal-to-noise ratio (S/N) of reflection and diffraction waves in the stack section has been enhanced significantly so as to reveal amounts of valuable geologic information. The resolution and the S/N of seismic migration imaging for the strong fold zone in marine strata have been improved partially, so that the structure of the step-fault zone and the enveloping of gypsum rock are clearer than those revealed by the old seismic section. Even so, actual drilling data demonstrate that the subsurface structures of the foothill belt are far more complex than those revealed by the current seismic imaging results. Therefore, postdrilling evaluation for the validity of seismic techniques implemented in the Nanjiang and Zhenba piedmont zone has been carried out. The results indicate that the current acquisition scheme and processing workflow cannot completely fulfill the requirements of high-precision velocity modeling and migration imaging of complex structures (such as footwalls of thrust fault and small-scale fault blocks) in the piedmont zone, especially when the rugged surface and the widespread limestone outcrop appear simultaneously. Finally, we have developed some potential needs of seismic theories and techniques in the foothill belt, including seismic wave propagation, acquisition, and processing technology.

scholarly journals Geothermal resource exploration by using Numerical simulation and comprehensive geophysical method

2021 ◽  
Author(s):  
Yang Yang ◽  
Bin Xiong ◽  
Sanxi Peng ◽  
Ibrar Iqbal ◽  
Tianyu Zhang
Keyword(s):  
Detection Efficiency ◽  
Energy Resource ◽  
Clean Energy ◽  
Shanxi Province ◽  
Geothermal System ◽  
Exploratory Research ◽  
Geothermal Resource ◽  
Geothermal Resources ◽  
Transient Electromagnetic ◽  
Resistivity Model

Abstract Geothermal energy is an important renewable clean energy resource with high development and usage potential. Geothermal resources, on the other hand, are buried deep below, and mining hazards are significant. Geophysical investigation is frequently required to determine the depth and location of geothermal resources. The Transient Electromagnetic Method (TEM) and the Controlled Source Audio Frequency Magnetotellurics (CSAMT) have the highest detection efficiency and accuracy of all electromagnetic exploration methods. This article initially explains the algorithm theory of the finite difference technique before establishing a simplified geothermal system resistivity model. Established on the simplified resistivity model, a simulation analysis of the ability of CSAMT and TEM to distinguish target body faults at different resistivities and dip angles was performed, and the effectiveness and difference of the two methods in detecting typical geothermal resource targets was verified. A complete exploratory research of CSAMT and TEM was conducted in Huairen County, Shuozhou City, Shanxi Province, China, based on theoretical analysis. Both approaches can reflect the geoelectric structure of the survey region, demonstrating the efficacy of the two methods in detecting genuine geothermal resources.

The Development of Near-source Electromagnetic Methods in China

2018 ◽  
Vol 23 (1) ◽  
pp. 115-124 ◽  
Author(s):  
Guo-qiang Xue
Keyword(s):  
High Efficiency ◽  
Academic Research ◽  
Electromagnetic Method ◽  
Detection Accuracy ◽  
Wide Field ◽  
Transient Electromagnetic Method ◽  
Transient Electromagnetic ◽  
Detection Technology ◽  
Deep Depth ◽  
Central Loop

Near-source electromagnetic technology has been developed and applied in the exploration of petroleum, metallic ore, coal, and engineering geology due to its high efficiency, high detection accuracy, and deep depth of investigation. In this paper, research and applications of the frequency-domain electromagnetic sounding method (FDEM), wide-field electromagnetic method (WFEM), modified central-loop transient electromagnetic method (TEM), and short-offset grounded-wire TEM (SOTEM) with obvious near-source characteristics, were reviewed and analyzed. From the 1960s to 1990s, the FDEM method and equipment were extensively developed in China. These methods have played important roles in the exploration of coal resources. Based on controlled source audio-frequency magnetotelluric (CSAMT) and FDEM methods, a new method has been developed by deriving a new expression to calculate apparent resistivity. This method, which is referred to as WFEM, has been studied, applied, and received great attention in China. To increase work efficiency and reduce the influence of local transverse anisotropy on the detection processes, a modified central-loop TEM detection technology based on the central loop transient electromagnetic method was developed in China. The advantages of SOTEM in near-source surveys with high resolution and increased depth detection stimulated academic research interest to further develop grounded-wire TEM techniques. [Figure: see text]

Near-Borehole Imaging Using Full-Waveform Sonic Data

2021 ◽  
Author(s):  
Hala Alqatari ◽  
Thierry-Laurent Tonellot ◽  
Mohammed Mubarak
Keyword(s):  
Seismic Data ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Full Waveform ◽  
Time Migration ◽  
Imaging Results ◽  
High Resolution Images ◽  
Recorded Data ◽  
The Impact ◽  
Processing Steps

Abstract This work presents a full waveform sonic (FWS) dataset processing to generate high-resolution images of the near-borehole area. The dataset was acquired in a nearly horizontal well over a distance of 5400 feet. Multiple formation boundaries can be identified on the final image and tracked at up to 200 feet deep, along the wellbore's trajectory. We first present a new preprocessing sequence to prepare the sonic data for imaging. This sequence leverages denoising algorithms used in conventional surface seismic data processing to remove unwanted components of the recorded data that could harm the imaging results. We then apply a reverse time migration algorithm to the data at different processing stages to assess the impact of the main processing steps on the final image.

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