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1.
The development of crosshole seismic tomography as an imaging method for the subsurface has been hampered by the scarcity of real data. For boreholes in excess of a few hundred metres depth, crosshole seismic data acquisition is still a poorly developed and expensive technology. A partial solution to this relative lack of data has been achieved by the use of an ultrasonic seismic modelling system. Such ultrasonic data, obtained in the laboratory from physical models, provide a useful test of crosshole imaging software. In particular, ultrasonic data have been used to test the efficacy of a convolutional back-projection algorithm, designed for crosshole imaging. The algorithm is described and shown to be less susceptible to noise contamination than a Simultaneous Iterative Reconstruction Technique (SIRT) algorithm, and much more computationally efficient. 相似文献
2.
The integration of geophysical data into the subsurface characterization problem has been shown in many cases to significantly improve hydrological knowledge by providing information at spatial scales and locations that is unattainable using conventional hydrological measurement techniques. In particular, crosshole ground-penetrating radar (GPR) tomography has shown much promise in hydrology because of its ability to provide highly detailed images of subsurface radar wave velocity, which is strongly linked to soil water content. Here, we develop and demonstrate a procedure for inverting together multiple crosshole GPR data sets in order to characterize the spatial distribution of radar wave velocity below the water table at the Boise Hydrogeophysical Research Site (BHRS) near Boise, Idaho, USA. Specifically, we jointly invert 31 intersecting crosshole GPR profiles to obtain a highly resolved and consistent radar velocity model along the various profile directions. The model is found to be strongly correlated with complementary neutron porosity-log data and is further corroborated by larger-scale structural information at the BHRS. This work is an important prerequisite to using crosshole GPR data together with existing hydrological measurements for improved groundwater flow and contaminant transport modeling. 相似文献
3.
在简述了全息成象的一般原理, 并讨论了全息成象应用于钻孔电波勘探的物理基础之后, 着重介绍了多重全息图的概念及其合成成象技术.指明了对钻孔电波勘探的多次定点观测曲线和多次同步观测曲线, 可利用多重全息图及合成成象技术进行联合处理, 以提高分辨力和成象质量.并证明这相当于接收天线阵和发射天线阵依次聚焦在每一成象点上的双聚焦扫描成象的过程.文中对双孔透射法和单孔反射法都进行了讨论, 并给出了相应的计算公式;然后讨论了资料处理中的几个问题, 如发射点象的干扰及其消除、透射全息的屏蔽区问题、水平同步成象时的双象问题等, 并同时介绍了用衍射点模型进行计算机模拟的结果。最后给出了对水槽模型试验资料的处理结果和野外资料的试算结果. 相似文献
4.
井间电磁（EM）成像系统的技术目标是实现井间电学特性的直接测量,并提供井间电阻率的二维及三维图像.从1997年开始,胜利油田与美国EMI公司合作,开展了EM技术的应用与研究,主要是通过大型、系统的现场试验,在大井间距的条件下,进一步验证仪器的性能,进行油藏研究的适用性和可行性分析;以系统的现场实测数据为依据,加快成像处理方法和软件的开发;开展穿透金属套管井的EM试验,探讨金属套管条件下的电阻率成像方法。两年来,利用EMI提供的XBH2000型测量系统,对胜利油田典型的低电阻率砂泥岩剖面,成功地进行了3对井、10个井次的试验。试验证明了仪器性能的可靠,取得了测量重复性好、系统完整的井间EM数据.并反演得到电阻率成像,在分析井间油气分布和油层开采动态方面,取得了良好的地质效果. 相似文献
5.
平面波偏移是一种面炮偏移方法,相对于常规逐炮偏移,其具有较高的计算效率.然而常规平面波偏移方法成像精度低,且成像时会产生串扰噪音.为此,本文在实现常规平面波偏移算法基础上,引入反演思想实现了基于静态平面波编码的最小二乘偏移理论方法及处理流程,在优化算法基础上对平层模型和复杂砂砾断块模型进行了成像测试并与其他成像策略进行对比.研究结果表明:基于时移编码的平面波最小二乘偏移能有效抑制低频成像噪音和串扰噪音,补偿中深部成像能量,是一种较为有效的保幅成像策略. 相似文献
6.
Crosshole ground penetrating radar (GPR) tomography has been widely used and has the potential to improve the obtained subsurface models due to its high spatial resolution compared to other methods. Recent advances in full-waveform inversion of crosshole GPR data show that higher resolution images can be obtained compared to conventional ray-based GPR inversion because it can exploit all information present in the observed data. Since the first application of full-waveform inversion on synthetic and experimental GPR data, the algorithm has been significantly improved by extending the scalar to a vectorial approach, and changing the stepped permittivity and conductivity update into a simultaneous update. Here, we introduce new normalized gradients that do not depend on the number of sources and receivers which enable a comparison of the gradients and step lengths for different crosshole survey layouts. An experimental data set acquired at the Boise Hydrogeophysics Research Site is inverted using different source–receiver setups and the obtained permittivity and conductivity images, remaining gradients and final misfits are compared for the different versions of the full-waveform inversion. Moreover, different versions of the full-waveform inversion are applied to obtain an overview of all improvements. Most improvements result in a reducing final misfit between the measured and synthetic data and a reducing remaining gradient at the final iteration. Regions with relatively high remaining gradient amplitudes indicate less reliable inversion results. Comparison of the final full-waveform inversion results with Neutron–Neutron porosity log data and capacitive resistivity log data show considerably higher spatial frequencies for the logging data compared to the full-waveform inversion results. To enable a better comparison, we estimated a simple wavenumber filter and the full-waveform inversion results show an improved fit with the logging data. This work shows the potential of full-waveform inversion as an advanced method that can provide high resolution images to improve hydrological models. 相似文献
7.
Two particular sources of distortion, which may be encountered when applying tomographic imaging techniques to crosshole seismic data, have been investigated. Errors in survey locations of the shots and receivers can produce significant distortions in the images obtained. A simple method for solving simultaneously for the velocity field and shot and receiver location errors is presented and applied to synthetic and real data. Reflection and refraction of rays at velocity interfaces may produce poor density and angular coverage of the rays within the region of interest. It is shown that the effect of the velocity field on the ray coverage can significantly affect the resolution in the velocity image, even if ray bending is taken into account. One consequence of this effect is that, in some cases, little improvement in image quality is achieved by using curvi-ray rather than straight-ray inversion techniques, despite the occurrence of pronounced ray bending. 相似文献
8.
9.
对于裂缝、溶蚀孔洞发育的碳酸盐岩缝洞储层,如何从测井资料中提取裂缝、溶蚀孔洞信息是评价储层有效性的关键问题.为了从电成像测井静态图像上准确地分割出清晰的裂缝、溶蚀孔洞子图像进而提取其参数信息,本文提出了一种基于小波变换模极大值图像分割技术的电成像测井资料缝洞面孔率提取方法.以钮扣电极电导率曲线为对象,先消除井壁凹凸不平导致的地层背景噪声的影响,利用小波变换模极大值图像分割方法得到包含裂缝和溶蚀孔洞目标的子图像,根据子图像提取裂缝-孔洞总面孔率、裂缝面孔率、孔洞面孔率等信息.本文利用塔里木盆地奥陶系碳酸盐岩地层的电成像测井数据提取了缝洞面孔率参数,还利用同井岩心CT扫描图像计算的平均缝洞面孔率、双侧向电阻率、常规测井资料三孔隙度模型计算的相对连通缝洞孔隙度进行了对比,并进行了试油验证.对比表明,电成像测井裂缝-孔洞总面孔率、裂缝面孔率、孔洞面孔率与岩心CT扫描图像平均缝洞面孔率、双侧向电阻率、相对连通缝洞孔隙度、试油结果均有较好的一致性.这一方面验证了采用本文方法提取的裂缝-孔洞总面孔率、裂缝面孔率、孔洞面孔率的合理性,另一方面表明所提取参数可用于指示缝洞型碳酸盐岩储层的渗透性和有效性. 相似文献
10.
A tomographic imaging technique combined with coherence inversion is proposed for constructing a near-surface model from refraction events. A model obtained from coherence inversion serves as a good background model for the tomographic reconstruction. A simultaneous iterative reconstruction technique (SIRT) algorithm was used for this purpose. This is a simple algorithm and can be easily adapted to irregular acquisition geometry and limited angular aperture. Using synthetic data it was shown that the proposed procedure can be used for determination of local velocity anomalies in a shallow subsurface. The technique was also tested on a real data set. 相似文献
11.
We present the chain of time‐reverse modeling, image space wavefield decomposition and several imaging conditions as a migration‐like algorithm called time‐reverse imaging. The algorithm locates subsurface sources in passive seismic data and diffractors in active data. We use elastic propagators to capitalize on the full waveforms available in multicomponent data, although an acoustic example is presented as well. For the elastic case, we perform wavefield decomposition in the image domain with spatial derivatives to calculate P and S potentials. To locate sources, the time axis is collapsed by extracting the zero‐lag of auto and cross‐correlations to return images in physical space. The impulse response of the algorithm is very dependent on acquisition geometry and needs to be evaluated with point sources before processing field data. Band‐limited data processed with these techniques image the radiation pattern of the source rather than just the location. We present several imaging conditions but we imagine others could be designed to investigate specific hypotheses concerning the nature of the source mechanism. We illustrate the flexible technique with synthetic 2D passive data examples and surface acquisition geometry specifically designed to investigate tremor type signals that are not easily identified or interpreted in the time domain. 相似文献
12.
Tatiana Pertuz Alireza Malehmir Jordan Bos Bojan Brodic Yinshuai Ding Richard de Kunder Paul Marsden 《Geophysical Prospecting》2022,70(1):79-94
A prototype electromagnetic vibrator, referred to here as E-Vib, was upgraded and developed for broadband hardrock and mineral exploration seismic surveys. We selected the iron oxide mine in Blötberget, central Sweden, for a test site in 2019 for the newly developed E-Vib because of the availability of earlier seismic datasets (from 2015 to 2016) for verification of its performance for hardrock imaging purposes. The two-dimensional data acquisition consisted of a fixed geometry with 550 receiver locations spaced at every 5 m, employing both cabled and wireless seismic recorders, along an approximately 2.7 km long profile. The E-Vib operated at every second receiver station (i.e. 10 m spacing) with a linear sweep of 2–180 Hz and with a peak force of 7 kN. The processing workflow took advantage of the broadband signal generated by the E-Vib in this challenging hardrock environment with varying ground conditions. The processed seismic section shows a set of reflections associated with the known iron oxide mineralization and a major crosscutting reflection interpreted to be from a fault system likely to be crosscutting the mineralization. The broadband source data acquisition and subsequent processing helped to improve signal quality and resolution in comparison with the earlier workflows and data where a drophammer seismic source was used as the seismic source. These results suggest new possibilities for the E-Vib source for improved targeting in hardrock geological settings. 相似文献
13.
We have developed an algorithm that allows crosshole georadar amplitude data contaminated with systematic errors to be tomographically inverted. The effects of the errors, which may due to variable antenna-borehole coupling, the groundwater table, and 3-D heterogeneities in the vicinity of one or more boreholes, are included in a series of transmitter and receiver amplitude-correction factors. Tests with synthetic georadar sections demonstrate that the new approach is capable of producing reliable attenuation information, even when large systematic errors are present in the amplitude data. Standard inversions of crosshole georadar data acquired within a highly complex alpine rock glacier yield distorted tomograms. In contrast the new approach results in geologically useful images. 相似文献
14.
While seismic imaging for crustal and mantle structures has traditionally relied on surface wave and refraction data, the use of reflection data for crustal-scale targets has been largely limited to the common midpoint (CMP) stack techniques. The rapid increase in the number of seismograph array deployments in recent years in crustal and mantle seismology has reached a level such that a re-examination of the imaging techniques is becoming necessary. In this paper we show the advantage of prestack depth imaging for crustal reflection studies, based on data from two reflection surveys of the Los Angeles Regional Seismic Experiment (LARSE) to map faults and crustal-scale structures. Our analysis indicates that the quality of the previous images of these surveys is limited by the CMP stack technique. For comparison, we present here depth images of the same LARSE data using wave equation prestack depth imaging and a tomographic velocity model based on first arrivals of the LARSE surveys and local earthquakes. Our new images are considerably improved over previous images in terms of resolution and reflector continuity. The new images show reflectors throughout the crust and suggest truncations in the Moho associated with the San Andreas Fault. A series of bright reflector segments, which are associated with the San Gabriel and San Andreas faults have been identified and might represent reflections from the fault zones. Our results suggest that the presence of high noise level, strong lateral velocity heterogeneity and wide angle geometry argue for, rather than against, the use of prestack depth imaging over the simple CMP stack techniques. As demonstrated in this study, it is now viable to conduct prestack depth imaging of crustal reflection data using a velocity model based on earthquake first arrivals thanks to the dense acquisition deployment. 相似文献
15.
In seismic migration, it is important to sample a range of dips around the local structural dip at each image point. Meaningful images are obtained only where this condition holds. For cross-hole seismic reflection surveys, the distribution of dips sampled at each image point is controlled principally by the survey geometry, including source and receiver array lengths and their element spacings. Using a real data set as an example, we show how survey geometry can limit imaging capability close to the boreholes and even in the middle of the section between the boreholes. At the processing stage, effective removal of direct waves and accurate estimation of the velocity field are essential for optimizing image quality. For migration, we propose a generalized Berryhill (GB) scheme which is based on the Kirchhoff integral and takes into account both the near-field and far-field terms. This should improve the ability to image close to source and receiver arrays, provided that the element spacing in the nearby array is small enough. 相似文献
16.
A fast imaging technique is developed to deduce the spatial conductivity distribution in the earth from low-frequency (> 1 MHz) cross-well electromagnetic measurements. A sinusoidally oscillating, vertically orientated, magnetic dipole employed as a source, and it is assumed that the scattering bodies are azimuthally symmetric about the source dipole axis. The use of this model geometry reduces the 3D vector problem to a more manageable 2D scalar form. Additional efficiency is obtained by using the Born series approximation which is derived from nonlinear integral equations that account for the scattered magnetic fields generated by inhomogeneities embedded in a layered earth. Stabilization of the inversion problem is accomplished through the use of bounding constraints and a regularization method which results in a smooth model that fits the data to the desired noise level. The applicability of cross-well electromagnetics for imaging and monitoring changes caused by subsurface processes has been tested by simulating plumes of conductive fluid with 2D models. The images that result from inverting these synthetic data indicate that the vertical resolution of the method is better than the horizontal, increasing the noise decreases the image resolution, and incorporating a priori knowledge in the form of positivity constraints improves the results. Although higher operating frequencies are usually associated with better resolution, frequencies as low as 100 Hz can produce acceptable images in simulated oilfield environments. The imaging scheme has been applied to data collected during a salt-water injection experiment at the Richmond Field Station test site in Richmond, California. Both the data and the resulting images clearly reveal the presence of the plume and indicate that it is migrating towards the north-northwest rather than spreading symmetrically about the injection well. Applying the imaging code to synthetic data generated by a 3D sheet model verifies the interpretation of these results. 相似文献
17.
Sinem Yavuz Roman Pevzner Sofya Popik Konstantin Tertyshnikov Todd Wood Michelle C. Robertson Julia Correa Barry Freifeld 《Geophysical Prospecting》2022,70(1):108-120
Time-lapse seismic is one of the main methods for monitoring changes in reservoir conditions caused by production or injection of fluids. One approach to time-lapse seismic is through permanent reservoir monitoring, whereby seismic sources and/or receivers are permanently deployed. Permanent reservoir monitoring can offer a more cost-effective and environmentally friendly solution than traditional campaign-based surveys that rely on temporarily deployed equipment while facilitating more frequent measurements. At the CO2CRC Otway Project, surface orbital vibrators were coupled to a buried geophone array to form a permanent reservoir monitoring system. These are fixed position seismic sources that provide both P and S waves using induction motor-driven eccentric masses. After an initial injection of CO2 in February 2016, five months of continuous seismic data were acquired, and reflection imaging was used to assess the system performance. Analysis of the data showed the effects of weather variations on the near-surface conditions and the sweep signatures of surface orbital vibrators. Data processing flows of the continuous data was adapted from Vibroseis four-dimensional data processing flows. Ground roll proved a significant challenge to data processing. In addition, variations in the surface wave pattern were linked to major rainfall events. For the appraisal of surface orbital vibrators in imaging, a Vibroseis four-dimensional monitor survey data with similar geometry was also processed. Surface orbital vibrators are observed to be reliable sources with a potential to provide a repeatable signal, especially if the ground roll should fall outside the target window of interest. To guide future permanent reservoir monitoring applications, a repeatability analysis was performed for the various key data processing steps. 相似文献
18.
Li-Li Yan Bing-Jie Cheng Tian-Ji Xu Ying-Ying Jiang Zhao-Jun Ma Jian-Ming Tang 《应用地球物理》2018,15(1):57-68
Anisotropy correction is necessary during the processing of converted PSwave seismic data to achieve accurate structural imaging, reservoir prediction, and fracture detection. To effectively eliminate the adverse effects of S-wave splitting and to improve PSwave imaging quality, we tested methods for pre-stack migration imaging and anisotropic correction of PS-wave data. We based this on the propagation rules of seismic waves in a horizontal transverse isotropy medium, which is a fractured medium model that reflects likely subsurface conditions in the field. We used the radial (R) and transverse (T) components of PS-wave data to separate the fast and slow S-wave components, after which their propagation moveout was effectively extracted. Meanwhile, corrections for the energies and propagation moveouts of the R and T components were implemented using mathematical rotation. The PS-wave imaging quality was distinctly improved, and we demonstrated the reliability of our methods through numerical simulations. Applying our methods to three-dimensional and three-component seismic field data from the Xinchang-Hexingchang region of the Western Sichuan Depression in China, we obtained high-quality seismic imaging with continuous reflection wave groups, distinct structural features, and specific stratigraphic contact relationships. This study provides an effective and reliable approach for data processing that will improve the exploration of complex, hidden lithologic gas reservoirs. 相似文献
19.
Iterative migration velocity analysis is computationally expensive, where most of the computation time is used for generating prestack depth images. By using a reduced form of Kirchhoff migration, denoted as wave path migration, we can significantly speed up the depth imaging process and reduce the entire velocity analysis expense accordingly. Our results with 2D synthetic and field data show that wave path migration velocity analysis can efficiently improve the velocity model and the wave path migration velocity analysis updated velocity correlates well with that from the Kirchhoff migration velocity analysis. The central processing unit comparison shows that, for a 2D synthetic and field data set, wave path migration velocity analysis is six times faster than Kirchhoff migration velocity analysis. This efficiency should be even greater for 3D data. 相似文献
20.
《Journal of Applied Geophysics》2007,61(1):16-38
Unstable rocky slopes are major hazards to the growing number of people that live and travel though mountainous regions. To construct effective barriers to falling rock, it is necessary to know the positions, dimensions and shapes of structures along which failure may occur. To investigate an unstable mountain slope distinguished by numerous open fracture zones, we have taken advantage of three moderately deep (51.0–120.8 m) boreholes to acquire geophysical logs and record single-hole radar, vertical radar profiling (VRP) and crosshole radar data. We observed spallation zones, displacements and borehole radar velocity and amplitude anomalies at 16 of the 46 discontinuities identified in the borehole optical televiewer images. The results of the VRP and crosshole experiments were disappointing at our study site; the source of only one VRP reflection was determined and the crosshole velocity and amplitude tomograms were remarkably featureless. In contrast, much useful structural information was provided by the single-hole radar experiments. Radar reflections were recorded from many surface and borehole fracture zones, demonstrating that the strong electrical property contrasts of these features extended some distance into the adjacent rock mass. The single-hole radar data suggested possible connections between 6 surface and 4 borehole fractures and led to the discovery of 5 additional near-surface fracture zones. Of particular importance, they supplied key details on the subsurface geometries and minimum subsurface lengths of 8 of the 10 previously known surface fracture zones and all of the newly discovered ones. The vast majority of surface fracture zones extended at least 40–60 m into the subsurface, demonstrating that their depth and surface dimensions are comparable. 相似文献