半航空电磁探测方法技术创新思考

最新的成矿理论研究和深部定位预测结果均表明我国大陆2000 m深部蕴藏着潜力巨大的矿产资源,为在辽阔的国土面积上实现大深度、高精度、广覆盖地球物理探测,开展半航空电磁探测方法与技术研究显得十分必要.本文总结了国内外半航空电磁法的发展现状,重点围绕方法与装备技术等问题进行讨论,并对近年来的最新成果,如:时频协同探测、半航...     

Electrical and electromagnetic borehole measurements: A review

Electrical and electromagnetic geophysical techniques have reached a high level of technological sophistication since they were first used in boreholes less than one hundred years ago. Borehole logging-the detailed determination of rock and fluid properties adjacent to the borehole, and borehole geophysics-extending the range of geophysical investigation large distances away from the borehole, are essential for exploration, assessment and production of earth resources, as well as for fundamental studies of the earth. Borehole electrical and electromagnetic methods incorporate 17 decades of the electromagnetic spectrum, from 1000-s geomagnetic studies, through resistivity and permittivity measurements, to high-resolution resistivity imaging, NMR and optical spectroscopy.     

长白山天池火山岩浆系统分析

针对外媒报道长白山天池火山在近2年内有可能喷发的言论,在长白山天池火山区布测了一条长度约为103 km的二维大地电磁测深观测剖面,对火山区深部电性结构进行探测研究.由于研究区内不明来源的电磁干扰非常强,对数据采用了远参考处理、Robust处理、Rhoplus分析、张量阻抗分解和基于一维层状介质电阻率与相位互算方法等先进处理技术,获取到一批在强干扰区质量较为可靠的电磁数据,利用数据计算分析了长白山天池火山区二维构造走向和感应矢量特征,采用NLCG二维反演技术对资料进行了二维反演解释,并将反演结果与前人探测结果进行了对比分析.探测结果表明:在天池火山口下方存在明显的直立型岩浆通道,岩浆通道在下方约5~8 km位置形成关闭;在火山口下方往北方向附近,在埋深位置约7 km深处存在一个明显的低阻异常体,电阻率小于10 Ωm,且与岩浆通道对接,推测其可能是地表浅部发育的岩浆囊;在长白山山门附近C07-C09号测点之间和C04-C05号测点之间,在埋深约7~17 km深处发现近直立型低阻带,低阻带与下方低阻体直接相连,推测低阻带内赋存有活动的岩浆;随着埋深的增加,从天池火山口南部约20 km位置往北方向,在埋深13~30 km之间壳内广泛发育明显的低阻异常体,推测其可能是活动的岩浆囊.反演结果与前人探测结果整体电性特征相似,但又局部不同.     

Geophysical techniques to aquifer locating and monitoring for industrial zones in North Hanoi, Vietnam

Geophysical methods were applied for hydrogeological targets in many countries including Vietnam. This paper presents results of using complex geophysical techniques as well as 2D electrical resistivity imaging (ERI), vertical electrical sounding (VES), very low frequency (VLF), and seismic refraction for geological structure investigation for locating the aquifers and assessing the hydrogeological conditions for groundwater potential in industrial zones of North Hanoi, Vietnam. The locations of two aquifers are determined by their depth and thickness on the basis of resistivity and seismic velocity values which were proved by stratifications of three boreholes to 40–60 m of depth on the study area. There are connections from surface water to shallow aquifer by hydraulic windows, as follows from VLF data. The deeper aquifer can be considered as a potential groundwater supply, but the water level is descending in time, as shown by hydrological monitoring. However, with careful use and by reducing sources of pollution, groundwater can continue to be an important natural resource for future.     

New methods of controlled-source electromagnetic detection in China

As an important branch of geophysical exploration method, the electromagnetic method with artificial source has advanced rapidly in the past decade. These methods are classified as airborne electromagnetic method, ground-air electromagnetic method, ground electromagnetic method, and marine electromagnetic method. Over the years, researchers in China have made significant improvement to the fundamental theory, forward modeling and inverse for series of electromagnetic detection methods. Conversely, significant progress was made in the development of corresponding equipment. The researched techniques and their developed equipment have been successfully utilized to detect underground targets as deep as 10 km.However, there is increasing need for deep resources exploration, urban subsurface study, and prediction, monitoring and detection of geological hazards. To meet the increasing need and catch up with the advanced international level of exploration technologies and developed equipment, there is urgent necessity and requirement to continue developing geophysical methods and the corresponding equipment.     

层状各向异性介质海洋可控源电磁场灵敏度计算及特征分析

海洋可控源电磁（CSEM）方法已广泛应用于地质构造研究以及海底资源探测,但其在各向异性地层中的分辨能力依然不明确.灵敏度分析是一种分析电磁场对探测目标分辨能力的有效方法,传统的地球物理反演方法也需要精确计算电磁场关于地下介质电阻率的灵敏度.在模拟和解释海洋CSEM资料时,地球物理数值模拟常在笛卡尔直角坐标系下进行,且通常假定发射源为理想的水平电偶极源.然而,在实际的海洋可控源电磁勘探作业中,由于海水运动等影响,发射源可能会发生旋转和倾斜等.复杂姿态的电偶极源可通过计算并矢量叠加三个正交方向发射源分量的电磁场以获得总电磁场,因此需三个正交方向电偶源电磁场的计算方法.本文推导了笛卡尔直角坐标系下,电阻率垂直各向异性介质中三个正交方向电偶极源电磁场表达式,并详细导出了电磁场分量关于各向异性电导率的灵敏度解析表达式.通过与各向同性算法对比,验证了本文所提出灵敏度计算方法的正确性;模拟了不同方向电偶源情况下地电模型的灵敏度并分析其特征.计算结果表明,薄层将显著影响地下介质各向异性电阻率的灵敏度分布,垂直电偶源对海底地层各向异性电阻率的分辨能力高于水平电偶源,通过反演各向异性率间接恢复低灵敏度的各向异性电阻率值是一个可行的反演策略.

     

高频电磁测深在地下热水勘探中的应用

高频电磁测深法是一种利用天然高频电磁场作为场源的电磁勘探方法,具有高分辨率和相对直流电法较深的勘探深度的特点,特别适合中浅层地热和地下水勘探。本文介绍了一个应用高频电磁测深评价地下热水资源的一个成功实例。野外数据采集采用了高频电磁测深系统MT-U5A,采用远参考技术,以保证数据采集质量。高频电磁测深资料二维反演成像处理结果较好地描述了地下热水的空间分布范围,为查明该区的地下热水的来源提供了较有利的证据。     

A comparison of helicopter-borne electromagnetics in frequency- and time-domain at the Cuxhaven valley in Northern Germany

Two different airborne electromagnetic methods were applied in the same area: the frequency-domain helicopter-borne electromagnetic (HEM) system operated by the Federal Institute for Geosciences and Natural Resources, Germany, and the time-domain SkyTEM system of the HydroGeophysics Group at the University of Aarhus, Denmark. For verification of and comparison with the airborne methods, ground-based transient electromagnetics and 2-D resistivity surveying were carried out. The target of investigation was the Cuxhaven valley in Northern Germany, which is a significant local groundwater reservoir. The course of this buried valley was revealed by drillings and the shape was determined by reflection seismics at several cross sections.We applied electrical and electromagnetic methods to investigate the structure of the valley filling consisting of gravel, sand, silt and clay. The HEM survey clearly outlines a shallow conductor at about 20m depth and a deeper conductor below 40m depth inside the valley. This is confirmed by 2-D resistivity surveying and a drilling. The thickness of the deeper conductor, however, is not revealed due to the limited investigation depth of the HEM system. The SkyTEM survey does not resolve the shallow conductor, but it outlines the thickness of the deeper clay layer inside the valley and reveals a conductive layer at about 180m depth outside the valley. The SkyTEM results are very consistent with ground-based transient electromagnetic soundings.Airborne electromagnetic surveying in general has the advantage of fast resistivity mapping with high lateral resolution. The HEM system is cost-efficient and fast, but the more expensive and slower SkyTEM system provides a higher depth of investigation. Ground-based geophysical surveys are often more accurate, but they are definitively slower than airborne surveys. It depends on targets of interest, time, budget, and manpower available by which a method or combination of methods will be chosen. A combination of different methods is useful to obtain a detailed understanding of the subsurface resistivity distribution.     

金属矿地球物理勘探技术与设备:回顾与进展

地球物理勘探技术是深部矿产资源勘查的主要技术手段.长期以来,我国地球物理勘查技术和仪器严重依赖国外进口,国产勘查技术无论仪器设备,还是方法、软件尚不能满足日益增长的深部矿产勘查需求."十二五"国家高技术研究发展计划（863计划）资源环境技术领域设立了"深部矿产资源勘探技术"重大项目,以提高深部矿产资源探测的深度、精度、分辨率和抗干扰能力为目标,研发高精度重磁探测技术、电法及电磁探测技术、地震探测、钻探和井中探测技术和装备.经过4年的攻关研究,突破了高精度微重力传感器、铯光泵磁场传感器、宽带感应式电磁传感器等10余项关键技术;研发、完善和升级了地面高精度数字重力仪、质子磁力仪、大功率伪随机广域电磁探测系统、分布式多参数电磁探测系统等18套勘探地球物理仪器设备;创新和完善了20余项勘探地球物理数据处理、正反演方法,研发和完善了2套适合金属矿数据处理及解释的大型软件系统,和8套其他专用软件系统,大幅度提升了我国地球物理勘探技术水平.本文旨在介绍项目取得的主要成果,首先回顾我国地球物理勘探技术的发展历程,然后再重点介绍"深部矿产资源勘探技术"重大项目取得的主要成果和进展,最后对发展我国地球物理勘探技术提出作者的看法和建议.     

冻土区天然气水合物各向异性储层的AMT响应特征

陆域天然气水合物通常发育于冻土层下方破碎带和岩层裂隙处,其储层会表现明显电性各向异性特征.音频大地电磁法（AMT）能有效探测陆域水合物储藏范围,且不易受高阻冻土层的压制和干扰,可用于陆域天然气水合物探测研究.本文采用AMT对角各向异性二维正演方法,对多种陆域天然气水合物各向异性储层模型及相关参数进行了模拟试算,分析其视电阻率和相位响应特征.结果表明AMT能清晰显示各向异性储层空间位置和分布情况,并对储层的水合物饱和度变化以及储层数量等特征都有所反映.天然气水合物电性各向异性模拟研究为这一新型潜力能源的勘查工作提供了新的思路.

     

海洋天然气水合物可控源电磁法的响应特征:一维正演模拟

We discuss the feasibility of using controlled-source electromagnetic （CSEM） in the frequency domain for prospecting marine gas hydrates. Based on the Ocean Drilling Program （ODP） Leg 164 log data, we have established several 1-D resistivity models which have different gas hydrate concentrations. Meanwhile, we analyzed the electromagnetic response of marine gas hydrates in the frequency domain based on these models. We also studied the relationship between electrical field magnitude or phase and parameters such as receiver-transmitter distance and frequency. Our numerical modeling results provide us with a quantitative reference for exploration and resource evaluation of marine gas hydrates.     

Sensitivity and inversion of marine electromagnetic data in a vertically anisotropic stratified earth

The controlled‐source electromagnetic (CSEM) and magnetotelluric method (MT) are two techniques that can be jointly used to explore the resistivity structure of the earth. Such methods have, in recent years, been applied in marine environments to the exploration and appraisal of hydrocarbons. In many situations the electric properties of the earth are anisotropic, with differences between resistivity in the vertical direction typically much higher than those in the horizontal direction. In cases such as this, the two modes of the time‐harmonic electromagnetic field are altered in different ways, implying that the sensitivity to the earth resistivity may vary significantly from one particular resistivity component (scalar, horizontal or vertical) to another, depending on the measurement configuration (range, azimuth, frequency or water depth). In this paper, we examine the sensitivity of the electromagnetic field to a vertically anisotropic earth for a typical set of configurations, compare inversion results of synthetic data characterizing a vertically anisotropic earth obtained using the isotropic and anisotropic assumptions and show that correctly accounting for anisotropy can prevent artefacts in inversion results.     

煤及煤层气储层导电特性研究综述与展望

随着人类对天然气资源需求的剧增,煤层气勘探开发已备受业界重视.煤层气勘探开发的诸多技术均移植于常规天然气.常规天然气储层的含气饱和度与电阻率间具有良好的相关性.对于煤层气储层,煤层含气量与电阻率间是否具有相关性、其影响因素主要有哪些,对电阻率预测煤层含气量至关重要.本文翔实调研了国内外煤及煤层气储层导电性研究的相关文献,系统总结了煤体结构、煤的变质程度、温度及水分等对煤体导电性的影响特征,并细致梳理了含气煤储层吸附和解吸过程中电阻率变化规律.系统总结得知,现有研究成果多集中在煤体导电性的研究方面,煤层含气量与煤储层导电性间的内在定量关系尚不清晰.借助于煤岩样标定电阻率测井,进而来分煤阶、分煤体结构来研究煤层气储层导电性是本领域发展的趋势.     

Groundwater exploration using integrated geophysical techniques

The integrated approach to solving complicated geological, hydrological and environmental problems is now widely used in geophysics. Among all the geophysical methods, electrical and electromagnetic techniques are the most popular in groundwater exploration due to the close relationship between electrical conductivity and some hydrogeological properties of the aquifer (e.g. porosity, clay content, mineralization of the groundwater and degree of water saturation). Case histories presented here show that by proper combination of different techniques such as conventional direct current (DC) resistivity as well as the more advanced electromagnetic (EM) methods and the most recent nuclear magnetic resonance (NMR) tomography, the reliability of interpretation as compared to that typical for the individual methods can be significantly improved.     

高密度电法与瞬变电磁法在戈壁区找水的联合应用

为准确掌握地下水资源的动态变化,有效支撑生态环境的可持续发展,在新疆哈密某矿集区利用高密度电法与瞬变电磁法联合进行物探勘查,对地下含水层与隔水层进行预判。经验证,高密度电法与瞬变电磁法的组合,有效指导水文钻探施工,为同类地质条件下物探手段的选取和应用提供参考。     

Method for continuous monitoring of electrical rock resistivity

This paper presents the main results of developing a method for continuous monitoring of rock resistivity. The method uses continuous electromagnetic radiation of man-made or natural origin as a sounding signal. Underground electrical antennas are used as sensors. The physical basis of this method is the dependence of rock resistivity on the degree of fluid saturation, which changes under mechanical stress variations in geological media.     

海洋拖曳式水平电偶源数值模拟与电场接收机研制

海洋天然气水合物资源调查中,电磁法已成为地震勘探最有效的补充手段之一,而我国海洋水合物电磁探测中的拖曳式电场接收机此前是空白.本文从方法原理、仪器设备和海洋试验等方面,对海洋拖曳式水平电偶极-偶极方法进行研讨.建立三维电阻率模型,进行数值模拟,讨论收发距、发射频率、拖曳装置离海底高度等参数与电场异常响应的关系,针对特定模型给出了最佳观测参数以指导仪器硬件设计与海洋测试.在此基础上,采用高级嵌入式计算机的智能化控制、前端低噪声斩波放大、高精度同步采集等技术,研制了由拖体、承压舱、采集电路、低噪声电场传感器等组成的海洋拖曳式水平轴向电场接收机,其系统噪声达到2 nV/√HZ@(1~100Hz).将自主研制的电场接收机用于国内首次拖曳式电偶极-偶极方法的海洋试验与评估,并对海试资料进行了处理与分析.研究结果表明,所研发的仪器达到了设计指标,能够用于海洋天然气水合物调查.     

STUDY ON THE ELECTRICAL STRUCTURE OF THE ANQIU AND JUXIAN ELECTROMAGNETIC STATIONS IN THE TANLU FAULT ZONE

The Yishu fault zone is one of the branch faults of the Tanlu fault zone in its central part. Moderate and strong earthquakes occurred in the Yishu fault zone repeatedly. Due to its complex structure, the Yishu fault zone attracts much attention from earthquake researches. The Anqiu and Juxian electromagnetic stations in Shandong Province locate near the Anqiu-Juxian Fault and Changyi-Dadian Fault, which are branches of the Yishu fault zone, respectively. Geoelectric field and geomagnetic field observation were carried out in these two stations. The Wudi electromagnetic station is in the west of Tanlu fault zone in the Jidong-Bohai block and 230km from Anqiu electromagnetic station. This paper firstly describes the crustal structure near the electromagnetic stations by using magnetotelluric(MT)method. By processing the data carefully, we obtain the MT data in good quality near the stations. The MT data of each electromagnetic station and its nearby area suggests that the electrical structure and geological structure of the station are comparable. This paper applied 1-D and 2-D inversion for MT data and obtained the crustal electrical structure model beneath the Anqiu and Juxian seismic station. The shallow electrical structure from the MT method was compared with the results of symmetrical quadrupole electrical sounding. The model suggests that the electrical structure beneath the Anqiu and Juxian electromagnetic stations is complex and shows the feature of block boundary. The Wudi electromagnetic station is located inside a basin, the crustal structure shows layered feature typical for the stable blocks. Beneath the Anqiu electromagnetic station, there is a 1km-thick relative low resistivity layer in the shallow crust and a high resistivity body beneath it with a depth of 13km. There is a high resistivity structure in the crust beneath the Juxian electromagnetic station. The crustal structures are divided into two different parts by Anqiu-Juxian Fault and Changyi-Dadian Fault, respectively. More conductive layers appear to the west of the two faults. Plenty of fluid possibly exists within the conductive body to the west of Changyi-Dadian Fault, which plays important role in the earthquake generation. There is a relative low resistivity layer in the crust within 1~2km beneath the Wudi electromagnetic station. Beneath the relatively low resistivity layer, a relatively high resistivity layer extends to a depth of around 15km, and the resistivity value decreases with the increase of depth. The electrical resistivity model suggests the seismic activity of the Yishu fault zone around the Anqiu and Juxian electromagnetic stations should be taken into account seriously, and monitoring and research on it need to be strengthened. The results of this paper provide a certain reference value for the crustal structure research to similar stations.     

CARACTERES DE ĽONDE ELECTROMAGNETIQUE DE SURFACE ENGENDREE PAR UN DIPOLE MAGNETIQUE *

The electromagnetic field radiated from a magnetic dipole lying on the ground is considered, in the extremely low frequency range (DC to 20 000 Hertz). Theoretical and experimental data are given on the characteristics of the surface wave (vanishing wave) generated at the air-ground interface, in the case of an homogeneous subsurface. The case of a subsurface with electrical resistivity varying with depth is considered. It is shown how the above-mentioned characteristics may be applied in the quantitative investigation of the electrical resistivity of the subsurface as a function of depth, in a method using the measurements on the ground of all the components of the radiated field: horizontal electrical components, vertical and horizontal magnetic components.     

Interpretation of magnetic resonance soundings in rocks with high electrical conductivity

Magnetic resonance sounding (MRS) is an electromagnetic method designed for groundwater investigations. MRS can be applied not only for studying fresh-water aquifers, but also in areas where intrusion of saline water is rendering the subsurface electrically conductive. In the presence of rocks with a high electrical-conductivity attenuation and a phase shift of the MRS signal may influence the efficiency of the MRS method. We investigated the performance of MRS for allowing us to propose a procedure for interpreting MRS data under these conditions. For numerical modeling, we considered a subsurface with a resistivity between 0.5 and 10 Ω m. The results show that the depth of investigation with MRS depends upon the electrical conductivity of groundwater and surrounding rocks, on the depth of the saline water layer, and on the amount of fresh water above the saline water. For interpreting MRS measurements, the electrical conductivity of the subsurface is routinely measured with an electrical or electromagnetic method. However, due to the equivalence problem, the result obtained with these methods may be not unique. Hence, we investigated the influence of the uncertainty in conductivity distribution provided by transient electromagnetic measurements (TEM) on MRS results. It was found that the uncertainty in TEM results has an insignificant effect on MRS.