Fagen Pei, Xuben Wang, H. Fang, Dashuang He, Meixing He, B. Du, Peng-hui Zhang, Xiaojiang Wang
The Muli permafrost area is the only midlatitude permafrost area where natural gas hydrates (NGHs) have been drilled. Although a series of achievements has been obtained in studies on NGH accumulation conditions in the permafrost area, related studies on gas hydrate stability zones, gas sources and groundwater are still controversial and need further work. Based on geophysical, geological and geochemical data, this paper systematically elaborates the main NGH accumulation conditions in the Muli area in terms of the pressure‒temperature stability conditions, fault structure, gas composition, gas source, reservoir characteristics, groundwater distribution and topographic characteristics. The results show that the thicknesses of the NGH stability zone range from 491.0 m to 962.7 m. The fault structure can provide a pathway for hydrocarbon gas migration from deep to NGH stability zones, in which thrust faults can prevent the upwards migration of gas by sealing it below the hanging wall block. Rock fractures in the NGH stability zone can not only be gas migration channels but also serve as a reservoir space for NGH accumulation. The hydrocarbon gas of NGHs shows multiple origins and is mainly composed of oil‒associated gas. The formation of frost mounds related to the overpressured gas ejection caused by NGH decomposition may imply the existence of NGHs. Synthetically, similarities and differences in NGH accumulation conditions between the Muli permafrost area and other high‒latitude permafrost areas are proposed, and the “regression” NGH accumulation pattern in the Muli area is constructed. The study results can enrich theoretical knowledge of terrestrial NGH accumulation, and provide scientific guidance for NGH exploration in mid-latitude permafrost areas.
木里永久冻土区是唯一一个钻探天然气水合物(ngh)的中纬度永久冻土区。虽然多年冻土区天然气水合物成藏条件的研究取得了一系列成果，但天然气水合物稳定带、气源和地下水的相关研究仍存在争议，需要进一步开展工作。根据物探、地质、地球化学等资料，从压温稳定条件、断裂构造、气成分、气源、储层特征、地下水分布、地形特征等方面系统阐述了木里地区天然气水合物的主要成藏条件。结果表明:天然气水合物稳定带厚度范围为491.0 m ~ 962.7 m;断裂构造为油气从深部向天然气水合物稳定带运移提供了通道，其中逆冲断裂通过将油气封闭在上盘块体下方，阻止了油气向上运移。天然气水合物稳定区内岩石裂缝既是天然气运移的通道，也是天然气水合物成藏的储集空间。天然气水合物烃类气成因多样，以油气伴生气为主。天然气水合物分解引起的超压气体喷射引起的霜丘的形成可能暗示了天然气水合物的存在。综合分析木里多年冻土区天然气水合物成藏条件与其他高纬多年冻土区天然气水合物成藏条件的异同，构建木里地区天然气水合物“回归”成藏模式。研究成果可以丰富陆相天然气水合物成藏理论知识，为中纬度多年冻土区天然气水合物勘探提供科学指导。
{"title":"Accumulation conditions and patterns of natural gas hydrate in the Muli permafrost area, northeastern margin of the Qinghai‒Tibet Plateau, NW China","authors":"Fagen Pei, Xuben Wang, H. Fang, Dashuang He, Meixing He, B. Du, Peng-hui Zhang, Xiaojiang Wang","doi":"10.1093/jge/gxad036","DOIUrl":"https://doi.org/10.1093/jge/gxad036","url":null,"abstract":"The Muli permafrost area is the only midlatitude permafrost area where natural gas hydrates (NGHs) have been drilled. Although a series of achievements has been obtained in studies on NGH accumulation conditions in the permafrost area, related studies on gas hydrate stability zones, gas sources and groundwater are still controversial and need further work. Based on geophysical, geological and geochemical data, this paper systematically elaborates the main NGH accumulation conditions in the Muli area in terms of the pressure‒temperature stability conditions, fault structure, gas composition, gas source, reservoir characteristics, groundwater distribution and topographic characteristics. The results show that the thicknesses of the NGH stability zone range from 491.0 m to 962.7 m. The fault structure can provide a pathway for hydrocarbon gas migration from deep to NGH stability zones, in which thrust faults can prevent the upwards migration of gas by sealing it below the hanging wall block. Rock fractures in the NGH stability zone can not only be gas migration channels but also serve as a reservoir space for NGH accumulation. The hydrocarbon gas of NGHs shows multiple origins and is mainly composed of oil‒associated gas. The formation of frost mounds related to the overpressured gas ejection caused by NGH decomposition may imply the existence of NGHs. Synthetically, similarities and differences in NGH accumulation conditions between the Muli permafrost area and other high‒latitude permafrost areas are proposed, and the “regression” NGH accumulation pattern in the Muli area is constructed. The study results can enrich theoretical knowledge of terrestrial NGH accumulation, and provide scientific guidance for NGH exploration in mid-latitude permafrost areas.","PeriodicalId":54820,"journal":{"name":"Journal of Geophysics and Engineering","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43289555","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this study, the efficiency of estimating the model parameters of sheet-shaped single and multiple-sources of the self-potential (SP) anomaly using the Differential Search algorithm (DSA) was investigated. First of all, noise-free and noisy synthetic anomalies were calculated for a single sheet-shaped source, and its model parameters were estimated by DSA. The DSA inversion was also done for a model consisting of three inclined sheets. In order to test the effectiveness of the method, the same processes were repeated with a more conventional algorithm, PSO, and the solutions of both methods were compared. The results of synthetic anomaly analyses have shown that DSA can predict the parameters as accurately as PSO. Then, both algorithms were also applied to two field SP anomalies (Surda and Beldih) that have been evaluated by different algorithms in the literature. The source of the Surda anomaly is modelled as one sheet, whereas the source model of the Beldih anomaly is assumed to consist of three sheets. The five model parameters for each model were estimated using both algorithms and it is determined that they are in good agreement with the findings of the previous studies. The contribution of the regional background anomaly to the synthetic and field anomalies was also included and regional coefficients were estimated. Finally, it can be concluded that DSA can solve the source parameters without the need for the initial values required in conventional iterative inversion methods and is an efficient and promising algorithm for determining the parameters of SP sources.
{"title":"Estimating model parameters from SP anomaly of sheet-shaped sources using Differential Search and Particle Swarm Optimization Algorithms","authors":"Ş. Özyalın, Petek Sındırgı","doi":"10.1093/jge/gxad037","DOIUrl":"https://doi.org/10.1093/jge/gxad037","url":null,"abstract":"\u0000 In this study, the efficiency of estimating the model parameters of sheet-shaped single and multiple-sources of the self-potential (SP) anomaly using the Differential Search algorithm (DSA) was investigated. First of all, noise-free and noisy synthetic anomalies were calculated for a single sheet-shaped source, and its model parameters were estimated by DSA. The DSA inversion was also done for a model consisting of three inclined sheets. In order to test the effectiveness of the method, the same processes were repeated with a more conventional algorithm, PSO, and the solutions of both methods were compared. The results of synthetic anomaly analyses have shown that DSA can predict the parameters as accurately as PSO. Then, both algorithms were also applied to two field SP anomalies (Surda and Beldih) that have been evaluated by different algorithms in the literature. The source of the Surda anomaly is modelled as one sheet, whereas the source model of the Beldih anomaly is assumed to consist of three sheets. The five model parameters for each model were estimated using both algorithms and it is determined that they are in good agreement with the findings of the previous studies. The contribution of the regional background anomaly to the synthetic and field anomalies was also included and regional coefficients were estimated. Finally, it can be concluded that DSA can solve the source parameters without the need for the initial values required in conventional iterative inversion methods and is an efficient and promising algorithm for determining the parameters of SP sources.","PeriodicalId":54820,"journal":{"name":"Journal of Geophysics and Engineering","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48886527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Correction: Seismic profile denoising based on common-reflection-point gathers using convolution neural networks","authors":"","doi":"10.1093/jge/gxad027","DOIUrl":"https://doi.org/10.1093/jge/gxad027","url":null,"abstract":"","PeriodicalId":54820,"journal":{"name":"Journal of Geophysics and Engineering","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45176191","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The transient electromagnetic method (TEM) is a geophysical exploration method that can efficiently acquire subsurface electrical parameters. For airborne, towed, and other mobile platforms TEM systems, large data volumes, and the traditional one-dimensional denoising method with low efficiency and low signal-to-noise ratio (SNR) of late-time are the main bottlenecks limiting its reliable application. To address this problem, this paper proposes a neural network structure suitable for two-dimensional (2D) TEM data processing. The proposed structure combines a classical convolutional neural network denoising autoencoder with a gated recurrent neural network autoencoder, called the CNN-GRU dual autoencoder (CG-DAE). This method can directly input 2D TEM response data as images into the network for processing, which greatly improves data processing efficiency compared to single-time-channel processing. The simulation experiments verified the effectiveness of CG-DAE. After using CG-DAE denoising, the SNR of the late-time (0.2 ms∼1 ms) signals is improved to nearly 29 dB, the 2D anomaly layer position is clear, and the relative error (RE) between the denoised data and the corresponding clean data is less than 1.41%, while the RE of the late-time signals can be reduced to 3.68%. The proposed method can lay the foundation for fast processing of TEM data based on mobile platforms such as airborne and towed.
瞬变电磁法是一种能够有效获取地下电性参数的物探方法。对于机载、拖曳等移动平台TEM系统来说，数据量大、传统的一维去噪方法效率低、后期信噪比低是限制其可靠应用的主要瓶颈。为了解决这一问题，本文提出了一种适用于二维透射电镜数据处理的神经网络结构。该结构结合了经典卷积神经网络去噪自编码器和门控递归神经网络自编码器，称为CNN-GRU双自编码器(CG-DAE)。该方法可以直接将TEM二维响应数据作为图像输入到网络中进行处理，与单时间通道处理相比，大大提高了数据处理效率。仿真实验验证了CG-DAE的有效性。采用CG-DAE去噪后，后期(0.2 ms ~ 1 ms)信号的信噪比提高到接近29 dB, 2D异常层位置清晰，去噪后的数据与对应的干净数据的相对误差(RE)小于1.41%，而后期信号的相对误差(RE)可降至3.68%。该方法可为机载、拖曳等移动平台上瞬变电磁法数据的快速处理奠定基础。
{"title":"CG-DAE: A noise suppression method for two-dimensional transient electromagnetic data based on deep learning","authors":"Shengbao Yu, Yihan Shen, Yang Zhang","doi":"10.1093/jge/gxad035","DOIUrl":"https://doi.org/10.1093/jge/gxad035","url":null,"abstract":"\u0000 The transient electromagnetic method (TEM) is a geophysical exploration method that can efficiently acquire subsurface electrical parameters. For airborne, towed, and other mobile platforms TEM systems, large data volumes, and the traditional one-dimensional denoising method with low efficiency and low signal-to-noise ratio (SNR) of late-time are the main bottlenecks limiting its reliable application. To address this problem, this paper proposes a neural network structure suitable for two-dimensional (2D) TEM data processing. The proposed structure combines a classical convolutional neural network denoising autoencoder with a gated recurrent neural network autoencoder, called the CNN-GRU dual autoencoder (CG-DAE). This method can directly input 2D TEM response data as images into the network for processing, which greatly improves data processing efficiency compared to single-time-channel processing. The simulation experiments verified the effectiveness of CG-DAE. After using CG-DAE denoising, the SNR of the late-time (0.2 ms∼1 ms) signals is improved to nearly 29 dB, the 2D anomaly layer position is clear, and the relative error (RE) between the denoised data and the corresponding clean data is less than 1.41%, while the RE of the late-time signals can be reduced to 3.68%. The proposed method can lay the foundation for fast processing of TEM data based on mobile platforms such as airborne and towed.","PeriodicalId":54820,"journal":{"name":"Journal of Geophysics and Engineering","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43534884","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the exploration of unconventional oil and gas reservoirs, single-well acoustic imaging has become an important technique to detect geophysical structures around the borehole. In this study, we propose a simple method to calculate the total reflection wavefields of pressure and displacement for single-well imaging (SWI) with eccentric monopole or dipoles. To calculate the pressure at the eccentric site for incident waves with different angles of incidence and azimuth, reciprocity is applied to the radiation from the eccentric monopole source and the far-field forces generating the waves corresponding to the incident waves. Displacement solutions are derived by calculating the gradient of the pressure fields. When considering eccentric monopole or dipole sources for an inclined reflector outside the borehole, reciprocity is again used to derive the total reflection waves, including the same type of waves (P-P/SV-SV/SH- SH) and the converted waves (P- SV/SV-P). The analytical results agree well with the reference solutions of the 3D finite difference time-domain method, illustrating the validation of the method. The analysis shows that the pressure amplitude in the eccentric position is greater than that in the borehole axis, proving that the eccentric monopole can increase the weak amplitude of reflection waves. We also simulate the wavefields for the acoustic imaging model for eccentric monopole and dipoles. The results show that the pressure and displacement wavefields in the eccentric position are sensitive to the azimuth angle of the reflector, proving that SWI with eccentric logging tools is capable of identifying the azimuth angle.
{"title":"A simple method for fast simulation of total reflection waves of single-well imaging with eccentric tools","authors":"Jiaqi Xu, Hengshan Hu, B. Han","doi":"10.1093/jge/gxad034","DOIUrl":"https://doi.org/10.1093/jge/gxad034","url":null,"abstract":"\u0000 In the exploration of unconventional oil and gas reservoirs, single-well acoustic imaging has become an important technique to detect geophysical structures around the borehole. In this study, we propose a simple method to calculate the total reflection wavefields of pressure and displacement for single-well imaging (SWI) with eccentric monopole or dipoles. To calculate the pressure at the eccentric site for incident waves with different angles of incidence and azimuth, reciprocity is applied to the radiation from the eccentric monopole source and the far-field forces generating the waves corresponding to the incident waves. Displacement solutions are derived by calculating the gradient of the pressure fields. When considering eccentric monopole or dipole sources for an inclined reflector outside the borehole, reciprocity is again used to derive the total reflection waves, including the same type of waves (P-P/SV-SV/SH- SH) and the converted waves (P- SV/SV-P). The analytical results agree well with the reference solutions of the 3D finite difference time-domain method, illustrating the validation of the method. The analysis shows that the pressure amplitude in the eccentric position is greater than that in the borehole axis, proving that the eccentric monopole can increase the weak amplitude of reflection waves. We also simulate the wavefields for the acoustic imaging model for eccentric monopole and dipoles. The results show that the pressure and displacement wavefields in the eccentric position are sensitive to the azimuth angle of the reflector, proving that SWI with eccentric logging tools is capable of identifying the azimuth angle.","PeriodicalId":54820,"journal":{"name":"Journal of Geophysics and Engineering","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46913867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Chuantong Ruan, Fei Li, J. Ba, J. Carcione, Chun-ping Wu
Deep carbonate reservoirs are subject to in-situ conditions of high temperature and high pressure. We consider six water-saturated dolomite specimens from these reservoirs and perform ultrasonic experiments to obtain the P- and S-wave waveforms and velocities at different pressure and temperature conditions. The P-wave attenuation is estimated with the spectral-ratio method. The results show that with the increase of temperature, the velocities slightly decrease and attenuation increases. At effective pressures less than 40 MPa, the P-wave velocities increase sharply with pressure, and then approximately linearly at higher pressures, while attenuation decreases gradually with pressure. The crack porosity as a function of pressure is obtained from the experimental data. The P-wave velocities decrease with this porosity while attenuation has an opposite behaviour. Then, a multiscale poroelasticity model considering micro-, meso- and macro-scale fluid-flow mechanisms is proposed, to analyze the effects of the fluid properties, temperature, and crack content on the wave responses. The model results agree well with the experimental data at different pressures, which provides a theoretical basis for the analysis of broadband wave velocity dispersion and attenuation phenomena of carbonate reservoirs and underground porous media in general.
{"title":"Effects of temperature and pressure on the wave responses of deep carbonate reservoirs","authors":"Chuantong Ruan, Fei Li, J. Ba, J. Carcione, Chun-ping Wu","doi":"10.1093/jge/gxad033","DOIUrl":"https://doi.org/10.1093/jge/gxad033","url":null,"abstract":"\u0000 Deep carbonate reservoirs are subject to in-situ conditions of high temperature and high pressure. We consider six water-saturated dolomite specimens from these reservoirs and perform ultrasonic experiments to obtain the P- and S-wave waveforms and velocities at different pressure and temperature conditions. The P-wave attenuation is estimated with the spectral-ratio method. The results show that with the increase of temperature, the velocities slightly decrease and attenuation increases. At effective pressures less than 40 MPa, the P-wave velocities increase sharply with pressure, and then approximately linearly at higher pressures, while attenuation decreases gradually with pressure. The crack porosity as a function of pressure is obtained from the experimental data. The P-wave velocities decrease with this porosity while attenuation has an opposite behaviour. Then, a multiscale poroelasticity model considering micro-, meso- and macro-scale fluid-flow mechanisms is proposed, to analyze the effects of the fluid properties, temperature, and crack content on the wave responses. The model results agree well with the experimental data at different pressures, which provides a theoretical basis for the analysis of broadband wave velocity dispersion and attenuation phenomena of carbonate reservoirs and underground porous media in general.","PeriodicalId":54820,"journal":{"name":"Journal of Geophysics and Engineering","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44859523","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the following research, traditional and modern spatial prediction techniques are applied in the analysis of water quality, evidencing a new approach that allows the modeling of a hydrogeological system in the central area of Boyacá, Colombia. The objective is to determine the quality status of groundwater for human consumption. In the process, spatial predictions were made based on frequent methods (Kriging - Cokriging) and Bayesian methods (R-INLA SPDE) as an alternative to MCMC methods that require a large computational cost. From the application of these methods, a comparison is made by statistical tests that determine the goodness of adjustment of the predictions. The interest is based on the implementation of future more robust, economic and scientific solutions, particularly for hydrogeological data and this way properly manage water resources. Finally, the vulnerability of the aquifers is analyzed with the DRASTIC method, which takes into account the surrounding media of the aquifers through the variables Depth (D), Net Recharge (R), Type of Aquifer (A), Soil (S), Topography (T), Impact of the vadose zone (I) and Hydraulic conductivity (C)
{"title":"Hydrogeological spatial modelling: A comparison between frequentist and Bayesian statistics","authors":"Jason M Romero, Daniel C Salazar, Carlos E. Melo","doi":"10.1093/jge/gxad023","DOIUrl":"https://doi.org/10.1093/jge/gxad023","url":null,"abstract":"\u0000 In the following research, traditional and modern spatial prediction techniques are applied in the analysis of water quality, evidencing a new approach that allows the modeling of a hydrogeological system in the central area of Boyacá, Colombia. The objective is to determine the quality status of groundwater for human consumption. In the process, spatial predictions were made based on frequent methods (Kriging - Cokriging) and Bayesian methods (R-INLA SPDE) as an alternative to MCMC methods that require a large computational cost. From the application of these methods, a comparison is made by statistical tests that determine the goodness of adjustment of the predictions. The interest is based on the implementation of future more robust, economic and scientific solutions, particularly for hydrogeological data and this way properly manage water resources. Finally, the vulnerability of the aquifers is analyzed with the DRASTIC method, which takes into account the surrounding media of the aquifers through the variables Depth (D), Net Recharge (R), Type of Aquifer (A), Soil (S), Topography (T), Impact of the vadose zone (I) and Hydraulic conductivity (C)","PeriodicalId":54820,"journal":{"name":"Journal of Geophysics and Engineering","volume":"1 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"61719043","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hang Yang, Wangsheng Cheng, Z. Qi, H. Cao, Xiu Li, N. Sun, Jie Ma
The coal goaf areas are the main cause of accidents involving water intrusion in coal mines. The ground collapse caused by water intrusion in goaf areas pose major threats to further coal mining. As the conventional ground-based transient electromagnetic method is difficult to perform due to the hilly terrain in the Loess Plateau. In this study, a ground-airborne transient electromagnetic method for detecting coal goaf areas on the Loess Plateau was presented. First, a numerical model was built using the geological data of the study area. The TEM responses of the coal goaf area were determined by forward modeling. Then, the high-precision wavefield transformation method was applied to image the forward model. It was found that compared with the apparent resistivity definition method, the results of the high-precision wavefield transformation method more accurately represented the subsurface structures and the volume effect was avoided. Finally, the high-precision time sweep wavefield imaging method was applied to process the field data. The results revealed that the high-precision wavefield imaging method was able to accurately determine the locations of the goaf areas. In addition, the upper and lower interfaces of the strata and the goaf areas were clearly identified.
{"title":"Goaf area detection using high-precision wavefield imaging method of ground-airborne transient electromagnetics","authors":"Hang Yang, Wangsheng Cheng, Z. Qi, H. Cao, Xiu Li, N. Sun, Jie Ma","doi":"10.1093/jge/gxad028","DOIUrl":"https://doi.org/10.1093/jge/gxad028","url":null,"abstract":"\u0000 The coal goaf areas are the main cause of accidents involving water intrusion in coal mines. The ground collapse caused by water intrusion in goaf areas pose major threats to further coal mining. As the conventional ground-based transient electromagnetic method is difficult to perform due to the hilly terrain in the Loess Plateau. In this study, a ground-airborne transient electromagnetic method for detecting coal goaf areas on the Loess Plateau was presented. First, a numerical model was built using the geological data of the study area. The TEM responses of the coal goaf area were determined by forward modeling. Then, the high-precision wavefield transformation method was applied to image the forward model. It was found that compared with the apparent resistivity definition method, the results of the high-precision wavefield transformation method more accurately represented the subsurface structures and the volume effect was avoided. Finally, the high-precision time sweep wavefield imaging method was applied to process the field data. The results revealed that the high-precision wavefield imaging method was able to accurately determine the locations of the goaf areas. In addition, the upper and lower interfaces of the strata and the goaf areas were clearly identified.","PeriodicalId":54820,"journal":{"name":"Journal of Geophysics and Engineering","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45500775","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Many rocks often have the electrical anisotropy property that produces quite different responses from the electrical isotropic rocks. We applied an advanced modeling method to calculate the apparent resistivity responses over an anisotropic target in a homogenous isotropic backgound and an isotropic target embedded in different anisotropic host rocks. We demonstrated comprehensive modeling experiments to characterize the responses of surface pole-pole surveys to the buried targets in different geological backgrounds, which vary in the principal resistivities and Euler angles of the targets or the host rocks. Our modeling results show that: (1) the location of current injection controls the apparent resistivity images in value and shape; (2) almost circle-contours or more or less elongated contours appear in the apparent resistivity images for the anisotropic targets; (3) the isotropic target embedded in the anisotropic host rock generates some radial patterns from the current injection point; (4) the anisotropy strike angles can be obtained from the symmetry axis of the apparent resistivity contours;.(5) multiple locations of current injections throughout the detection region are necessary for the surface pole-pole survey to avoid misleading data interpretation.
{"title":"3D pole-pole responses of buried anisotropic targets and various anisotropic backgrounds in direct-current resistivity survey","authors":"Fengqun Ma, H. Tan, Wenxin Kong, Depeng Zhu","doi":"10.1093/jge/gxad030","DOIUrl":"https://doi.org/10.1093/jge/gxad030","url":null,"abstract":"\u0000 Many rocks often have the electrical anisotropy property that produces quite different responses from the electrical isotropic rocks. We applied an advanced modeling method to calculate the apparent resistivity responses over an anisotropic target in a homogenous isotropic backgound and an isotropic target embedded in different anisotropic host rocks. We demonstrated comprehensive modeling experiments to characterize the responses of surface pole-pole surveys to the buried targets in different geological backgrounds, which vary in the principal resistivities and Euler angles of the targets or the host rocks. Our modeling results show that: (1) the location of current injection controls the apparent resistivity images in value and shape; (2) almost circle-contours or more or less elongated contours appear in the apparent resistivity images for the anisotropic targets; (3) the isotropic target embedded in the anisotropic host rock generates some radial patterns from the current injection point; (4) the anisotropy strike angles can be obtained from the symmetry axis of the apparent resistivity contours;.(5) multiple locations of current injections throughout the detection region are necessary for the surface pole-pole survey to avoid misleading data interpretation.","PeriodicalId":54820,"journal":{"name":"Journal of Geophysics and Engineering","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44877540","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Full waveform inversion is a methodology that determines high-resolution parameters. The widely used L2-norm misfit function has local minima if the low wavenumber components are not accurate. Suffering from cycle skipping problem, the solution of waveform inversion will be trapped in the local minima. Dynamic time warping aims to find an optimal alignment between two signals, which is a more robust measure to avoid cycle-skipping challenges. However, the discontinuity makes the conventional dynamic time warping distance unsuitable for waveform inversion. We introduce a soft dynamic time warping distance as the misfit function, which is differentiable that inverted solution can converge to the accurate global minimum. We compare the convexity of the L2-norm and soft dynamic time warping distance and show that the soft dynamic time warping distance has a wider convexity range with different time shift and amplitudes. It can alleviate the half-wavelength limitation of the conventional L2-norm. We calculate the gradient using the automatic differentiation technique and the minibatch strategy and then analyze the alignment paths of different smooth parameters. A significant smooth parameter γ makes the Soft-DTW distance tending to the L2-norm, which generates new local minima. We recommend a small smooth parameter to ensure the convexity of the Soft-DTW distance. Numerical examples show that the soft dynamic time warping can effectively reconstruct the deep velocity parameters of the BG Compass and Marmousi models with noise robustness and lower dependence on the initial model.
{"title":"Robust full-waveform inversion based on automatic differentiation and differentiable dynamic time warping","authors":"Y. Liu, Jie Tang, Zhengwei Tang, Chengyu Sun","doi":"10.1093/jge/gxad029","DOIUrl":"https://doi.org/10.1093/jge/gxad029","url":null,"abstract":"\u0000 Full waveform inversion is a methodology that determines high-resolution parameters. The widely used L2-norm misfit function has local minima if the low wavenumber components are not accurate. Suffering from cycle skipping problem, the solution of waveform inversion will be trapped in the local minima. Dynamic time warping aims to find an optimal alignment between two signals, which is a more robust measure to avoid cycle-skipping challenges. However, the discontinuity makes the conventional dynamic time warping distance unsuitable for waveform inversion. We introduce a soft dynamic time warping distance as the misfit function, which is differentiable that inverted solution can converge to the accurate global minimum. We compare the convexity of the L2-norm and soft dynamic time warping distance and show that the soft dynamic time warping distance has a wider convexity range with different time shift and amplitudes. It can alleviate the half-wavelength limitation of the conventional L2-norm. We calculate the gradient using the automatic differentiation technique and the minibatch strategy and then analyze the alignment paths of different smooth parameters. A significant smooth parameter γ makes the Soft-DTW distance tending to the L2-norm, which generates new local minima. We recommend a small smooth parameter to ensure the convexity of the Soft-DTW distance. Numerical examples show that the soft dynamic time warping can effectively reconstruct the deep velocity parameters of the BG Compass and Marmousi models with noise robustness and lower dependence on the initial model.","PeriodicalId":54820,"journal":{"name":"Journal of Geophysics and Engineering","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47956570","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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