The seismic images produced by pre-stack depth migration show more accurate subsurface structures than time images, resulting in a growing need for depth-domain inversion. However, due to the strong non-stationarity exhibited by depth-domain seismic data, time-domain inversion methods based on the convolutional model cannot be directly applied in the depth domain. To address this issue, we have developed a method for extracting a depth-variant seismic wavelet, which is then combined with a non-stationary convolutional model to enable direct inversion of the depth-domain acoustic impedance. First, we extend the Morlet wavelet to the depth domain and propose an orthogonal matching pursuit spectral decomposition method using the depth-domain Morlet wavelet. We then investigate the waveforms and wavenumber spectra similarities between the depth-domain Morlet wavelet and depth-domain Ricker wavelet and extract depth-variant Ricker wavelets from the depth-wavenumber spectrum. We add a depth-domain impedance trend constraint to the conventional basis pursuit inversion to enhance the lateral continuity of the inversion results. Then, we attain direct inversion of the depth-domain acoustic impedance. Tests of synthetic and field data demonstrate that the proposed method achieves high-accuracy inversion results while maintaining high computational efficiency, highlighting our approach's effectiveness and strong reservoir characterization potential.
{"title":"A depth-variant seismic wavelet extraction method for basis pursuit inversion with impedance trend constraint","authors":"R. Cai, Chengyu Sun, Zhen’an Yao, Shizhong Li","doi":"10.1190/geo2023-0255.1","DOIUrl":"https://doi.org/10.1190/geo2023-0255.1","url":null,"abstract":"The seismic images produced by pre-stack depth migration show more accurate subsurface structures than time images, resulting in a growing need for depth-domain inversion. However, due to the strong non-stationarity exhibited by depth-domain seismic data, time-domain inversion methods based on the convolutional model cannot be directly applied in the depth domain. To address this issue, we have developed a method for extracting a depth-variant seismic wavelet, which is then combined with a non-stationary convolutional model to enable direct inversion of the depth-domain acoustic impedance. First, we extend the Morlet wavelet to the depth domain and propose an orthogonal matching pursuit spectral decomposition method using the depth-domain Morlet wavelet. We then investigate the waveforms and wavenumber spectra similarities between the depth-domain Morlet wavelet and depth-domain Ricker wavelet and extract depth-variant Ricker wavelets from the depth-wavenumber spectrum. We add a depth-domain impedance trend constraint to the conventional basis pursuit inversion to enhance the lateral continuity of the inversion results. Then, we attain direct inversion of the depth-domain acoustic impedance. Tests of synthetic and field data demonstrate that the proposed method achieves high-accuracy inversion results while maintaining high computational efficiency, highlighting our approach's effectiveness and strong reservoir characterization potential.","PeriodicalId":55102,"journal":{"name":"Geophysics","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139957217","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Thomas Højland Lorentzen, M. A. Kass, Johanna Scheer, Soňa Tomaškovičová, Anders Vest Christiansen, Pradip Kumar Maury, T. Ingeman‐Nielsen
This paper analyzes a continuous near-surface transient electromagnetic (TEM) survey on permafrost, around Ilulissat in western Greenland, an area characterized by continuous saline permafrost. The TEM data is severely affected by induced polarization (IP) effects, causing a large range of decay shapes. We identify seven unique decay shapes: “oversteepened”, ”sign-change“, ”all-negative”, “double-sign-change”, “no apparent IP”, “flat-spot”, and “positive-nonmonotonic”, of which the last two have not previously been identified in the scientific literature. A clear spatial dependency of the decay shapes is observed. Inversion of the data is carried out using a Cole-Cole model which poses a highly nonunique inversion problem with an extreme starting model dependency. A series of inversion and forward modeling experiments demonstrate these challenges, and show that a low-resistivity and highly chargeable layer with time constant ([Formula: see text]) values between [Formula: see text] and[Formula: see text] and frequency exponent (C) values above 0.74 is needed to fit the data used in the inversion experiment. Forward modeling further shows that low [Formula: see text] and high C values are needed to reproduce the observed flat-spot and positive-nonmonotonic decay shapes. Based on these observations, we attribute the IP effects to the orientational polarization of ice in the soil column. This mechanism allows for low-resistivity, high-chargeability layers due to partially frozen saline sediments; a combination which is difficult to explain by the IP mechanisms traditionally considered. Based on forward modeling of a realistic structural model of a layered sediment pack over dipping bedrock, we are able to reproduce all the observed decay shapes. This model provides a consistent framework for qualitative interpretation of the entire data set, and evidence for the presence of saline deposits in the central parts of the sedimentary basins.
本文分析了在格陵兰西部伊卢利萨特周围对永久冻土进行的连续近地表瞬变电磁（TEM）勘测，该地区的特点是存在连续的盐碱永久冻土。TEM 数据受到诱导极化（IP）效应的严重影响，导致衰减形状范围很大。我们发现了七种独特的衰减形状："过度陡峭"、"符号变化"、"全负"、"双符号变化"、"无明显 IP"、"平点 "和 "正-非单调"，其中后两种以前在科学文献中从未发现过。衰减形状具有明显的空间依赖性。使用科尔-科尔模型对数据进行反演，这是一个高度非唯一的反演问题，具有极端的起始模型依赖性。一系列反演和前向建模实验证明了这些挑战，并表明需要一个时间常数（[公式：见正文]）值介于[公式：见正文]和[公式：见正文]之间、频率指数（C）值高于 0.74 的低电阻率和高电荷层才能适合反演实验中使用的数据。前向建模进一步表明，需要低[式：见正文]和高 C 值来重现观测到的平斑和正非单调衰减形状。根据这些观测结果，我们将 IP 效应归因于土壤柱中冰的定向极化。这种机制允许部分冻结的盐沉积物产生低电阻率、高电荷率层；传统的 IP 机制很难解释这种组合。基于对倾斜基岩上的层状沉积物群的现实结构模型的前向建模，我们能够再现所有观测到的衰减形状。该模型为整个数据集的定性解释提供了一个一致的框架，并为沉积盆地中部存在盐渍沉积提供了证据。
{"title":"Exploring the challenges of interpreting near-surface towed TEM data on saline permafrost","authors":"Thomas Højland Lorentzen, M. A. Kass, Johanna Scheer, Soňa Tomaškovičová, Anders Vest Christiansen, Pradip Kumar Maury, T. Ingeman‐Nielsen","doi":"10.1190/geo2023-0221.1","DOIUrl":"https://doi.org/10.1190/geo2023-0221.1","url":null,"abstract":"This paper analyzes a continuous near-surface transient electromagnetic (TEM) survey on permafrost, around Ilulissat in western Greenland, an area characterized by continuous saline permafrost. The TEM data is severely affected by induced polarization (IP) effects, causing a large range of decay shapes. We identify seven unique decay shapes: “oversteepened”, ”sign-change“, ”all-negative”, “double-sign-change”, “no apparent IP”, “flat-spot”, and “positive-nonmonotonic”, of which the last two have not previously been identified in the scientific literature. A clear spatial dependency of the decay shapes is observed. Inversion of the data is carried out using a Cole-Cole model which poses a highly nonunique inversion problem with an extreme starting model dependency. A series of inversion and forward modeling experiments demonstrate these challenges, and show that a low-resistivity and highly chargeable layer with time constant ([Formula: see text]) values between [Formula: see text] and[Formula: see text] and frequency exponent (C) values above 0.74 is needed to fit the data used in the inversion experiment. Forward modeling further shows that low [Formula: see text] and high C values are needed to reproduce the observed flat-spot and positive-nonmonotonic decay shapes. Based on these observations, we attribute the IP effects to the orientational polarization of ice in the soil column. This mechanism allows for low-resistivity, high-chargeability layers due to partially frozen saline sediments; a combination which is difficult to explain by the IP mechanisms traditionally considered. Based on forward modeling of a realistic structural model of a layered sediment pack over dipping bedrock, we are able to reproduce all the observed decay shapes. This model provides a consistent framework for qualitative interpretation of the entire data set, and evidence for the presence of saline deposits in the central parts of the sedimentary basins.","PeriodicalId":55102,"journal":{"name":"Geophysics","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140445149","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Parsimonious Refraction Interferometry (PRI) is a useful technique for generating dense virtual traveltimes when the seismic survey is performed with sparse acquisition geometry. However, PRI has limitations in accurately calculating the traveltimes of direct and diving waves, leading to inaccurate velocity structures when applying the first-arrival traveltime tomography (FATT). To address this issue, we propose an improved approach using a deep learning (DL) network called U-Net. We first examine the feasibility of the proposed algorithm analytically through the traveltime interpretation of a simple model. Then, the U-Net model is trained on various datasets to learn the relationship between PRI results and actual traveltimes. Subsequently, the trained network corrects the traveltime errors of the PRI results. As a result, we can obtain accurate first-arrival traveltimes using only two shot gathers without additional information such as infilled shots. The proposed technique enables virtual traveltime corrections, allowing for improved FATT results, even in cases where dense shots are difficult to deploy. Numerical results demonstrate that the proposed method can achieve comparable accuracy to picked traveltime data, indicating its high effectiveness in increasing the resolution of FATT results. The proposed approach maximizes the cost-saving benefits of PRI and can be advantageous in obtaining high-resolution FATT results when dense shot geometry is unavailable.#xD;
准折射干涉测量法（PRI）是一种有用的技术，可在地震勘探采用稀疏采集几何时生成密集的虚拟行波时间。然而，PRI 在精确计算直达波和潜波的旅行时间方面存在局限性，导致在应用首次到达旅行时间层析（FATT）时速度结构不准确。为解决这一问题，我们提出了一种使用深度学习（DL）网络（U-Net）的改进方法。我们首先通过对一个简单模型的旅行时间解释，分析检验了所提算法的可行性。然后，在各种数据集上训练 U-Net 模型，学习 PRI 结果与实际旅行时间之间的关系。随后，经过训练的网络会修正 PRI 结果的旅行时间误差。因此，我们只需使用两个镜头采集即可获得精确的首次到达旅行时间，而无需填充镜头等附加信息。所提出的技术可实现虚拟旅行时间校正，从而改进 FATT 结果，即使在难以部署高密度镜头的情况下也是如此。数值结果表明，所提出的方法可以达到与采到的旅行时间数据相当的精度，这表明它在提高 FATT 结果的分辨率方面非常有效。所提出的方法最大限度地发挥了 PRI 节省成本的优势，在没有高密度射电几何图形的情况下，也有利于获得高分辨率的 FATT 结果；
{"title":"Improving Parsimonious Refraction Interferometry through U-Net-based Correction of First-Arrival Traveltimes","authors":"Ganghoon Lee, Sukjoon Pyun","doi":"10.1190/geo2023-0435.1","DOIUrl":"https://doi.org/10.1190/geo2023-0435.1","url":null,"abstract":"Parsimonious Refraction Interferometry (PRI) is a useful technique for generating dense virtual traveltimes when the seismic survey is performed with sparse acquisition geometry. However, PRI has limitations in accurately calculating the traveltimes of direct and diving waves, leading to inaccurate velocity structures when applying the first-arrival traveltime tomography (FATT). To address this issue, we propose an improved approach using a deep learning (DL) network called U-Net. We first examine the feasibility of the proposed algorithm analytically through the traveltime interpretation of a simple model. Then, the U-Net model is trained on various datasets to learn the relationship between PRI results and actual traveltimes. Subsequently, the trained network corrects the traveltime errors of the PRI results. As a result, we can obtain accurate first-arrival traveltimes using only two shot gathers without additional information such as infilled shots. The proposed technique enables virtual traveltime corrections, allowing for improved FATT results, even in cases where dense shots are difficult to deploy. Numerical results demonstrate that the proposed method can achieve comparable accuracy to picked traveltime data, indicating its high effectiveness in increasing the resolution of FATT results. The proposed approach maximizes the cost-saving benefits of PRI and can be advantageous in obtaining high-resolution FATT results when dense shot geometry is unavailable.#xD;","PeriodicalId":55102,"journal":{"name":"Geophysics","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140444053","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Natural fractures in oil and gas reservoirs are a crucial factor that cannot be ignored, as they significantly influence the reservoir's petrophysical properties and hydrocarbon development. A horizontal transversely isotropic (HTI) medium composed of a single fracture set in an isotropic background is a typical anisotropic medium. Meanwhile, the shear wave splitting (SWS) is a sensitive response of such anisotropic media, resulting in the generation of fast and slow shear waves. The normal and tangential fracture weaknesses are crucial parameters that characterize the anisotropy of fractured media. We proposed an inversion method for fracture weakness based on three-component vertical seismic profiling (3CVSP) data. Firstly, assuming weak anisotropy and an HTI medium containing single fracture set, we derived a first-order linear approximation of the travel times of the converted fast and slow shear waves (PS1- and PS2-waves) with respect to fracture weakness parameters in the phase velocity domain. By solving for the horizontal projection of the slowness vector, approximate equations of the travel times of the PS1- and PS2-waves were converted from phase velocity domain to the group velocity domain. Furthermore, we devised an inversion workflow consisting of three primary steps: 1. pre-processing the VSP data to derive the travel times and azimuth of the HTI medium; 2. constructing a forward model with undetermined fracture weakness parameters; 3. following the establishment of the objective function, conducting the inversion for the fracture weakness parameters. We demonstrated the reliability of the method through numerical examples and synthetic 3CVSP data. The inversion errors are primarily influenced by the azimuth angle, with minimal influence from the receiver depth. Furthermore, a collective set of inverted results derived from all geophones are more stable and accurate than individual geophones. The application to actual 3CVSP data further confirmed the effectiveness of our approach.
{"title":"Inversion of Fracture Weakness Parameters Based on the 3CVSP Data?Part I: HTI Media Composed of A Single Fracture Set in the Isotropic Background Media","authors":"Yuyong Yang, Alexey Stovas, Qiaomu Qi, Huailai Zhou","doi":"10.1190/geo2023-0539.1","DOIUrl":"https://doi.org/10.1190/geo2023-0539.1","url":null,"abstract":"Natural fractures in oil and gas reservoirs are a crucial factor that cannot be ignored, as they significantly influence the reservoir's petrophysical properties and hydrocarbon development. A horizontal transversely isotropic (HTI) medium composed of a single fracture set in an isotropic background is a typical anisotropic medium. Meanwhile, the shear wave splitting (SWS) is a sensitive response of such anisotropic media, resulting in the generation of fast and slow shear waves. The normal and tangential fracture weaknesses are crucial parameters that characterize the anisotropy of fractured media. We proposed an inversion method for fracture weakness based on three-component vertical seismic profiling (3CVSP) data. Firstly, assuming weak anisotropy and an HTI medium containing single fracture set, we derived a first-order linear approximation of the travel times of the converted fast and slow shear waves (PS1- and PS2-waves) with respect to fracture weakness parameters in the phase velocity domain. By solving for the horizontal projection of the slowness vector, approximate equations of the travel times of the PS1- and PS2-waves were converted from phase velocity domain to the group velocity domain. Furthermore, we devised an inversion workflow consisting of three primary steps: 1. pre-processing the VSP data to derive the travel times and azimuth of the HTI medium; 2. constructing a forward model with undetermined fracture weakness parameters; 3. following the establishment of the objective function, conducting the inversion for the fracture weakness parameters. We demonstrated the reliability of the method through numerical examples and synthetic 3CVSP data. The inversion errors are primarily influenced by the azimuth angle, with minimal influence from the receiver depth. Furthermore, a collective set of inverted results derived from all geophones are more stable and accurate than individual geophones. The application to actual 3CVSP data further confirmed the effectiveness of our approach.","PeriodicalId":55102,"journal":{"name":"Geophysics","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140451076","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wang Hao, Shengqing Xiong, Li Fei, Wanyin Wang, Feng Bin, Jifeng Zhang, Yang Min
The airborne transient electromagnetic (ATEM) method is a geophysical exploration technique that offers several advantages, including rapid exploration, minimal interference from complex terrains, dense data sampling, and environmental friendliness. However, the full-frequency time-domain secondary field signal acquisition of ATEM is susceptible to various electromagnetic interferences, resulting in noise in the collected data. This noise complicates subsequent processing and interpretation. To address this issue, we have developed a one-dimensional minimum-curvature difference equation with unequal spacing based on the minimum-curvature differential equations. Through research, we propose an ATEM noise-suppression method based on multiple single-step and multiple superposition-step implicit iterative formats. In addition, we have investigated the convergence of explicit and implicit iterative schemes via Fourier spectrum analysis, and proved that the implicit iterative schemes converge. This method effectively suppresses noise in both synthetic and real ATEM data during processing. Our results show that the minimum-curvature method is particularly effective in suppressing sferic and Gaussian noises in ATEM data. As a result, our proposed method provides high-quality and reliable ATEM data for further data processing and interpretation. Moreover, the minimum-curvature method is also capable of suppressing noise in ground and groundspace transient electromagnetic data, as well as magnetotelluric data noise. Therefore, this method exhibits a wide range of potential applications.
{"title":"Noise Suppression of ATEM Data using Minimum Curvature Method","authors":"Wang Hao, Shengqing Xiong, Li Fei, Wanyin Wang, Feng Bin, Jifeng Zhang, Yang Min","doi":"10.1190/geo2022-0107.1","DOIUrl":"https://doi.org/10.1190/geo2022-0107.1","url":null,"abstract":"The airborne transient electromagnetic (ATEM) method is a geophysical exploration technique that offers several advantages, including rapid exploration, minimal interference from complex terrains, dense data sampling, and environmental friendliness. However, the full-frequency time-domain secondary field signal acquisition of ATEM is susceptible to various electromagnetic interferences, resulting in noise in the collected data. This noise complicates subsequent processing and interpretation. To address this issue, we have developed a one-dimensional minimum-curvature difference equation with unequal spacing based on the minimum-curvature differential equations. Through research, we propose an ATEM noise-suppression method based on multiple single-step and multiple superposition-step implicit iterative formats. In addition, we have investigated the convergence of explicit and implicit iterative schemes via Fourier spectrum analysis, and proved that the implicit iterative schemes converge. This method effectively suppresses noise in both synthetic and real ATEM data during processing. Our results show that the minimum-curvature method is particularly effective in suppressing sferic and Gaussian noises in ATEM data. As a result, our proposed method provides high-quality and reliable ATEM data for further data processing and interpretation. Moreover, the minimum-curvature method is also capable of suppressing noise in ground and groundspace transient electromagnetic data, as well as magnetotelluric data noise. Therefore, this method exhibits a wide range of potential applications.","PeriodicalId":55102,"journal":{"name":"Geophysics","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139958560","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Marine vibrators are increasingly being recognized as a viable alternative to seismic airguns for ocean-bottom acquisition due to their ability to generate more low-frequency content and their less adverse impact on marine wildlife. However, their use introduces processing challenges, such as the Doppler effect and time-dependent source-receiver offsets, which are negligible in conventional airgun acquisition. In addition, the time-varying nature of the sea surface during the multi-second acquisition time introduces further challenges for processing and inversion. To accurately account for source motion and time-varying sea surface effects in seismic data processing, we develop a reliable and robust numerical modeling tool. We use a mimetic finite-difference method in a generalized coordinate system to model the full acoustic wavefield triggered by a moving source in the presence of a time-varying sea surface. Our approach uses a time- and space-dependent coordinate transformation, which tracks the source movement and conforms to the irregular time-varying sea surface, to map an irregular physical domain in Cartesian coordinates to a regular computational domain in generalized coordinates. We formulate this coordinate transformation such that both coordinate systems conformally match below the ocean-bottom level. Numerical examples demonstrate that this approach is accurate and stable, even for an unrealistically exaggerated sea state. This computational tool is not limited to modeling, but could also be used to develop advanced processing techniques for marine vibrator data, such as imaging and inversion.
{"title":"Modeling acoustic wavefields from moving sources in the presence of a time-varying free surface","authors":"Khalid Almuteri, Jeffrey Shragge, Paul Sava","doi":"10.1190/geo2023-0527.1","DOIUrl":"https://doi.org/10.1190/geo2023-0527.1","url":null,"abstract":"Marine vibrators are increasingly being recognized as a viable alternative to seismic airguns for ocean-bottom acquisition due to their ability to generate more low-frequency content and their less adverse impact on marine wildlife. However, their use introduces processing challenges, such as the Doppler effect and time-dependent source-receiver offsets, which are negligible in conventional airgun acquisition. In addition, the time-varying nature of the sea surface during the multi-second acquisition time introduces further challenges for processing and inversion. To accurately account for source motion and time-varying sea surface effects in seismic data processing, we develop a reliable and robust numerical modeling tool. We use a mimetic finite-difference method in a generalized coordinate system to model the full acoustic wavefield triggered by a moving source in the presence of a time-varying sea surface. Our approach uses a time- and space-dependent coordinate transformation, which tracks the source movement and conforms to the irregular time-varying sea surface, to map an irregular physical domain in Cartesian coordinates to a regular computational domain in generalized coordinates. We formulate this coordinate transformation such that both coordinate systems conformally match below the ocean-bottom level. Numerical examples demonstrate that this approach is accurate and stable, even for an unrealistically exaggerated sea state. This computational tool is not limited to modeling, but could also be used to develop advanced processing techniques for marine vibrator data, such as imaging and inversion.","PeriodicalId":55102,"journal":{"name":"Geophysics","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140449214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Since the appearance of wave-equation migration, many have tried to improve the resolution and effectiveness of this technology. Least-squares wave-equation migration is one of those attempts that tries to fill the gap between the migration assumptions and reality in an iterative manner. However, these iterations do not come cheap. A proven solution to limit the number of least-squares iterations is to correct the gradient direction within each iteration via the action of a preconditioner that approximates the Hessian inverse. However, the Hessian computation, or even the Hessian approximation computation, in large-scale seismic imaging problems involves an expensive computational bottleneck, making it unfeasible. Therefore, we propose an efficient computation of the Hessian approximation operator, in the context of one-way wave-equation migration (WEM) in the space-frequency domain. We build the Hessian approximation operator depth by depth, considerably reducing the operator size each time it is calculated. We prove the validity of our proposed method with two numerical examples. We then extend our proposal to the framework of full-wavefield migration, which is based on WEM principles but includes interbed multiples. Finally, this efficient preconditioned least-squares full-wavefield migration is successfully applied to a dataset with strong interbed multiple scattering.
{"title":"Efficient Preconditioned Least-Squares Wave-Equation Migration","authors":"Siamak Abolhassani, D. J. Verschuur","doi":"10.1190/geo2023-0048.1","DOIUrl":"https://doi.org/10.1190/geo2023-0048.1","url":null,"abstract":"Since the appearance of wave-equation migration, many have tried to improve the resolution and effectiveness of this technology. Least-squares wave-equation migration is one of those attempts that tries to fill the gap between the migration assumptions and reality in an iterative manner. However, these iterations do not come cheap. A proven solution to limit the number of least-squares iterations is to correct the gradient direction within each iteration via the action of a preconditioner that approximates the Hessian inverse. However, the Hessian computation, or even the Hessian approximation computation, in large-scale seismic imaging problems involves an expensive computational bottleneck, making it unfeasible. Therefore, we propose an efficient computation of the Hessian approximation operator, in the context of one-way wave-equation migration (WEM) in the space-frequency domain. We build the Hessian approximation operator depth by depth, considerably reducing the operator size each time it is calculated. We prove the validity of our proposed method with two numerical examples. We then extend our proposal to the framework of full-wavefield migration, which is based on WEM principles but includes interbed multiples. Finally, this efficient preconditioned least-squares full-wavefield migration is successfully applied to a dataset with strong interbed multiple scattering.","PeriodicalId":55102,"journal":{"name":"Geophysics","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140451118","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Ishizu, T. Kasaya, T. Goto, Katsuaki Koike, W. Siripunvaraporn, H. Iwamoto, Y. Kawada, Jun-Ichiro Ishibashi
Deep-sea massive sulfide deposits formed by hydrothermal fluid circulation are potential metal resources. They can exist not only as mound manifestations on the seafloor (seafloor massive sulfides) but also as embedded anomalies buried beneath the seafloor (embedded massive sulfides). The distribution of embedded massive sulfides is largely unknown, despite their expected high economic value. Recent drilling surveys have revealed a complex model suggesting embedded massive sulfides coexist beneath seafloor massive sulfides. In the coexisting case, geophysical methods are required to distinguish and map both seafloor and embedded massive sulfides for accurate resource estimation. Marine controlled-source electromagnetic (CSEM) methods are useful for mapping massive sulfides as they exhibit higher electrical conductivity compared to the surrounding host rock. However, CSEM applications capable of distinguishing and mapping both massive sulfides are lacking. We employ a towed electric dipole transmitter with two types of receivers: stationary ocean bottom electric (OBE) and short-offset towed receivers. This combination utilizes differences in sensitivity: the towed receiver data are sensitive to seafloor massive sulfides and the stationary OBE receiver data are sensitive to embedded massive sulfides. Our synthetic data example demonstrates that the combined inversion of towed and OBE data can recover resistivities and positions of both massive sulfides more accurately than the existing inversion methods using individual applications. We perform the combined inversion of measured CSEM data obtained from the middle Okinawa Trough. The inversion models demonstrate that a combined inversion can map the location and shape of embedded massive sulfides identified during drilling more accurately than the inversion of individual datasets.
由热液循环形成的深海块状硫化物矿床是潜在的金属资源。它们不仅可以以海底土丘的形式存在（海底块状硫化物），也可以以埋藏在海底下的嵌入式异常点的形式存在（嵌入式块状硫化物）。尽管嵌入式块状硫化物具有很高的经济价值，但其分布情况在很大程度上仍不为人所知。最近的钻探勘测揭示了一个复杂的模型，表明嵌入式块状硫化物与海底块状硫化物共存。在共存的情况下，需要采用地球物理方法来区分海底块状硫化物和内蕴块状硫化物并绘制地图，以进行准确的资源估算。海洋可控源电磁（CSEM）方法可用于绘制块状硫化物地图，因为与周围的主岩相比，块状硫化物具有更高的导电性。然而，目前还缺乏能够区分和绘制两种块状硫化物的 CSEM 应用。我们采用了拖曳式电偶极子发射器和两种类型的接收器：固定海底电（OBE）和短偏移拖曳接收器。这种组合利用了灵敏度上的差异：拖曳式接收器数据对海底块状硫化物敏感，而固定式 OBE 接收器数据对嵌入式块状硫化物敏感。我们的合成数据示例表明，与现有的单独应用反演方法相比，拖曳数据和 OBE 数据的组合反演能更准确地恢复两种块状硫化物的电阻率和位置。我们对冲绳海槽中部的 CSEM 测量数据进行了组合反演。反演模型表明，与单个数据集的反演相比，组合反演能更准确地绘制出钻探过程中发现的嵌入式块状硫化物的位置和形状。
{"title":"A marine controlled-source electromagnetic application using towed and seafloor-based receivers capable of mapping both seafloor and embedded massive sulfides","authors":"K. Ishizu, T. Kasaya, T. Goto, Katsuaki Koike, W. Siripunvaraporn, H. Iwamoto, Y. Kawada, Jun-Ichiro Ishibashi","doi":"10.1190/geo2023-0389.1","DOIUrl":"https://doi.org/10.1190/geo2023-0389.1","url":null,"abstract":"Deep-sea massive sulfide deposits formed by hydrothermal fluid circulation are potential metal resources. They can exist not only as mound manifestations on the seafloor (seafloor massive sulfides) but also as embedded anomalies buried beneath the seafloor (embedded massive sulfides). The distribution of embedded massive sulfides is largely unknown, despite their expected high economic value. Recent drilling surveys have revealed a complex model suggesting embedded massive sulfides coexist beneath seafloor massive sulfides. In the coexisting case, geophysical methods are required to distinguish and map both seafloor and embedded massive sulfides for accurate resource estimation. Marine controlled-source electromagnetic (CSEM) methods are useful for mapping massive sulfides as they exhibit higher electrical conductivity compared to the surrounding host rock. However, CSEM applications capable of distinguishing and mapping both massive sulfides are lacking. We employ a towed electric dipole transmitter with two types of receivers: stationary ocean bottom electric (OBE) and short-offset towed receivers. This combination utilizes differences in sensitivity: the towed receiver data are sensitive to seafloor massive sulfides and the stationary OBE receiver data are sensitive to embedded massive sulfides. Our synthetic data example demonstrates that the combined inversion of towed and OBE data can recover resistivities and positions of both massive sulfides more accurately than the existing inversion methods using individual applications. We perform the combined inversion of measured CSEM data obtained from the middle Okinawa Trough. The inversion models demonstrate that a combined inversion can map the location and shape of embedded massive sulfides identified during drilling more accurately than the inversion of individual datasets.","PeriodicalId":55102,"journal":{"name":"Geophysics","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139958775","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lele Zhang, Yang Zhao, Lu Liu, Fenglin Niu, Wei Wu, Chuangyang Wang, Hengyu Tang, Jingming Li, J. Zuo, Yi Yao, Yixin Wang
Optical fiber-based distributed acoustic sensing (DAS) technology has been a popular seismic acquisition tool due to its easy deployment, wide bandwidth, and dense sampling. However, the sensitivity of straight optical fiber to only single-axis strain presents challenges in fully characterizing multi-components seismic wavefields, making it difficult to use these data in elastic reverse time migration (ERTM). The helical-winding fiber receives projecting signals projected onto the fiber from all seismic strain field components and has the potential to reconstruct those strain components for ERTM imaging. Here we give detailed mathematical principles of helical fiber-based DAS with crucial parameters such as pitch angle, gauge length and rotating angle. At least six points of DAS responses are required in one or several winding periods to rebuild the strain fields within the seismic wavelength. The projecting matrix of conventional regular helical-winding fiber is singular and ill-conditioned, which results in computation challenges for the inverse of the Hessian matrix for strain component reconstruction. To tackle this problem, we develop a non-regular variant-pitch angle winding configuration for helical fiber. Our winding design is validated using the rank and condition number of the projecting matrix, which is proven as an important tool in the reconstruction of the original seismic strains. The recovered strain components from the DAS response are then used to backward propagate receiver wavefields in ERTM with an efficient P/S decoupled approach. To sum up, we develop a novel winding design of helical fiber to recover the strain fields, and then propose an efficient 3D anisotropic P/S wave-mode decomposition method for generating vector P- and S-wavefields during their propagation. Both methods are applied to build an anisotropic DAS-ERTM workflow for producing PP- and PS- images. Two synthetic examples demonstrate the effectiveness of our approach.
基于光纤的分布式声学传感（DAS）技术因其易于部署、带宽宽、采样密集等优点而成为一种流行的地震采集工具。然而，直光纤只对单轴应变敏感，这给全面描述多成分地震波场带来了挑战，使这些数据难以用于弹性反向时间迁移（ERTM）。螺旋缠绕光纤可接收投射到光纤上的所有地震应变场分量的投射信号，并有可能为 ERTM 成像重建这些应变分量。在此，我们给出了基于螺旋光纤的 DAS 的详细数学原理，其中包括俯仰角、轨距长度和旋转角度等关键参数。在一个或多个绕组周期内，至少需要六个点的 DAS 响应，才能重建地震波长内的应变场。传统常规螺旋缠绕光纤的投影矩阵是奇异和条件不良的，这给应变分量重建的赫塞斯矩阵逆计算带来了挑战。为解决这一问题，我们开发了一种非规则变距角螺旋光纤缠绕结构。我们的缠绕设计利用投影矩阵的秩和条件数进行了验证，该矩阵被证明是重建原始地震应变的重要工具。然后，从 DAS 响应中恢复的应变分量可用于在 ERTM 中通过高效的 P/S 解耦方法反向传播接收波场。总之，我们开发了一种新颖的螺旋光纤缠绕设计来恢复应变场，然后提出了一种高效的三维各向异性 P/S 波模分解方法，用于在传播过程中生成矢量 P 波场和 S 波场。这两种方法都被用于建立各向异性 DAS-ERTM 工作流程，以生成 PP 和 PS 图像。两个合成实例证明了我们方法的有效性。
{"title":"Strain field reconstruction from helical-winding fiber distributed acoustic sensing and its application in anisotropic elastic reverse time migration","authors":"Lele Zhang, Yang Zhao, Lu Liu, Fenglin Niu, Wei Wu, Chuangyang Wang, Hengyu Tang, Jingming Li, J. Zuo, Yi Yao, Yixin Wang","doi":"10.1190/geo2023-0354.1","DOIUrl":"https://doi.org/10.1190/geo2023-0354.1","url":null,"abstract":"Optical fiber-based distributed acoustic sensing (DAS) technology has been a popular seismic acquisition tool due to its easy deployment, wide bandwidth, and dense sampling. However, the sensitivity of straight optical fiber to only single-axis strain presents challenges in fully characterizing multi-components seismic wavefields, making it difficult to use these data in elastic reverse time migration (ERTM). The helical-winding fiber receives projecting signals projected onto the fiber from all seismic strain field components and has the potential to reconstruct those strain components for ERTM imaging. Here we give detailed mathematical principles of helical fiber-based DAS with crucial parameters such as pitch angle, gauge length and rotating angle. At least six points of DAS responses are required in one or several winding periods to rebuild the strain fields within the seismic wavelength. The projecting matrix of conventional regular helical-winding fiber is singular and ill-conditioned, which results in computation challenges for the inverse of the Hessian matrix for strain component reconstruction. To tackle this problem, we develop a non-regular variant-pitch angle winding configuration for helical fiber. Our winding design is validated using the rank and condition number of the projecting matrix, which is proven as an important tool in the reconstruction of the original seismic strains. The recovered strain components from the DAS response are then used to backward propagate receiver wavefields in ERTM with an efficient P/S decoupled approach. To sum up, we develop a novel winding design of helical fiber to recover the strain fields, and then propose an efficient 3D anisotropic P/S wave-mode decomposition method for generating vector P- and S-wavefields during their propagation. Both methods are applied to build an anisotropic DAS-ERTM workflow for producing PP- and PS- images. Two synthetic examples demonstrate the effectiveness of our approach.","PeriodicalId":55102,"journal":{"name":"Geophysics","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139960986","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Exploration seismology based on moving sources like high-speed trains has attracted increasingly great attention. It is important task to perform near-surface seismic imaging and inversion using moving sources. In this context, an accurate and efficient forward-modeling engine for moving sources is crucial. We initially consider a single moving point source. To implement the numerical simulation in terms of a moving point source, two aspects need to be considered: (1) the numerical discretization strategy of the seismic-wave equation and (2) the discrete representation of the moving point source. For the 3D heterogeneous elastic-wave equation, we propose an improved frequency-domain average-derivative numerical method (ADM) by introducing the weighted average of four sets of grid points for the mass-acceleration term. Due to the numerical discretization template, the continuously moving point source is discretized as a series of fixed sources located at different grid points and excited at different times. The corresponding discrete representation of spatio-temporal variation is given by modifying the right-hand side of the resulting linear system of equations. A numerical experiment in a 3D homogeneous half-space model validates the higher computational accuracy of the improved ADM and the feasibility of the numerical simulation scheme for a moving point source. Furthermore, we test the performance of the moving-point-source numerical simulation scheme in the 3D heterogeneous overthrust model. The successful implementation of the 3D frequency-domain numerical simulation for a moving point source establishes a foundation for subsequent practical applications of moving sources in seismic imaging, to be performed in the future.
{"title":"An improved 27-point frequency-domain elastic-wave average-derivative method with applications to a moving point source","authors":"Hao Wang, Jingbo Chen","doi":"10.1190/geo2023-0257.1","DOIUrl":"https://doi.org/10.1190/geo2023-0257.1","url":null,"abstract":"Exploration seismology based on moving sources like high-speed trains has attracted increasingly great attention. It is important task to perform near-surface seismic imaging and inversion using moving sources. In this context, an accurate and efficient forward-modeling engine for moving sources is crucial. We initially consider a single moving point source. To implement the numerical simulation in terms of a moving point source, two aspects need to be considered: (1) the numerical discretization strategy of the seismic-wave equation and (2) the discrete representation of the moving point source. For the 3D heterogeneous elastic-wave equation, we propose an improved frequency-domain average-derivative numerical method (ADM) by introducing the weighted average of four sets of grid points for the mass-acceleration term. Due to the numerical discretization template, the continuously moving point source is discretized as a series of fixed sources located at different grid points and excited at different times. The corresponding discrete representation of spatio-temporal variation is given by modifying the right-hand side of the resulting linear system of equations. A numerical experiment in a 3D homogeneous half-space model validates the higher computational accuracy of the improved ADM and the feasibility of the numerical simulation scheme for a moving point source. Furthermore, we test the performance of the moving-point-source numerical simulation scheme in the 3D heterogeneous overthrust model. The successful implementation of the 3D frequency-domain numerical simulation for a moving point source establishes a foundation for subsequent practical applications of moving sources in seismic imaging, to be performed in the future.","PeriodicalId":55102,"journal":{"name":"Geophysics","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140481993","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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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