综合物探技术识别地震反射异常体属性

埋藏在6000m以下的地震反射异常体是礁体还是火成岩体？或者是海底滑塌体？在高质量重磁电资采集的基础上，通过对研究区域内的地层岩石物性细致研究，利用CEMP资料界面约束二维反演、重磁力异常剥离技术和LCT重磁力地震联合反演解释技术细致研究了异常体的物性参数，从密度、磁化率、电阻率、速度等多种特征推测判断了深层异常体地质属性，为钻井部署提供了间接依据。     

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.     

Seismic attenuation tomography in frequency domain and its application to engineering

Seismic tomography is a new geophysical technique being developed to meet the needs of mining and engineering projects. Attenuation tomography, as one kind of seismic tomography technique, is a powerful prospecting tool for determining structure defaults such as fault, broken zone, and hidden voids, but it has been little discussed up to now. Its principle and applications are presented in detail. Attenuation tomography technology includes the following main points. First, on the basis of spectrum analysis to each seismic record, geometric correction is conducted, then common source parameters are introduced into common shot records in order to keep absorption effect of the geological media separate from source spectrum influence. Finally, an equation set is obtained which consists of absorption coefficients, common source parameters and energy field data observed. This technique can be employed together with velocity tomography to provide more evidence for engineering and geological diagnosis. Its applications to exploration of mineral and engineering have led to satisfactory results.     

基于交叉梯度交替结构约束的二维地震走时与全通道直流电阻率联合反演

在利用不同的地球物理勘探方法对地下复杂介质成像时,因观测系统的非完备性及数据本身对某些岩石物性的不敏感性,单独成像的结果存在较大的不确定性和不一致性.对于地震体波走时成像与直流电阻率成像,均面临着成像阴影区问题.对于地震走时成像,地震射线对低速区域覆盖较差形成阴影区,造成低速区域分辨率降低.对于电阻率成像,电场线在高阻区域分布较少,造成高阻区域分辨率较低.为了提高地下介质成像的精度,Gallado和Meju(2003)提出了基于交叉梯度结构约束的联合地球物理成像方法.在要求不同的物性模型拟合各自对应的数据同时,模型之间的结构要求一致,即交叉梯度趋于零.为了更有效地实现基于交叉梯度的结构约束,我们提出了一种新的交替结构约束的联合反演流程,即交替反演不同的数据而且在反演一种数据时要求对应的模型与另一个模型结构一致.新的算法能够更容易地把单独的反演系统耦合在一起,而且也更容易建立结构约束和数据拟合之间的平衡.基于新的联合反演流程,我们测试了基于交叉梯度结构约束的二维跨孔地震走时和直流电阻率联合成像.合成数据测试表明,我们提出的交替结构约束流程能够很好地实现基于交叉梯度结构约束的联合成像.与单独成像结果相比,地震走时和全通道电阻率联合成像更可靠地确定了速度和电阻率异常.     

露天煤矿地下水电磁探测与类型判别

为准确确定露天煤矿地下水分布与类型,根据不同赋存条件电磁差异,基于磁场强度与电阻率参数进行异常划分与类型判别。以新疆某露天煤矿为例,采用高精度磁法通过磁异常强度确定烧变岩边界,并采用高密度电法和瞬变电磁法通过电阻率圈定低阻异常区,结合异常响应差异分别推断地下水分布范围与赋存类型。地面钻探验证探测成果的准确性。结果表明:露天煤矿烧变岩水与砂岩裂隙水电磁响应差异明显,基于磁场强度与电阻率的双参数综合电磁法能准确圈定其分布范围,并判别其赋存类型。     

Electrical resistivity and seismic refraction tomography to detect buried cavities

Near‐surface cavities can pose serious hazards to human safety, especially in highly urbanized town centres. The location of subsurface voids, the estimation of their size and the evaluation of the overburden thickness are necessary to assess the risk of collapse. In this study, electrical resistivity tomography (ERT) and seismic refraction tomography data are integrated in a joint interpretation process for cavity location in the city of Rome. ERT is a well established and widely employed method for cavity detection. However, additional information provided by seismic refraction tomography is capable of eliminating some potential pitfalls in resistivity data interpretation. We propose that the structure of the cavities defined by ERT can be used as a base to optimize seismic refraction tomography investigations within the framework of a joint interpretation process. Data integration and the insertion of a priori information are key issues for reducing the uncertainties associated with the inversion process and for optimizing both acquisition procedures and computation time. Herein, the two geophysical methods are tested on both synthetic and real data and the integration of the results is found to be successful in detecting isolated cavities and in assessing their geometrical characteristics. The cavity location inferred by geophysical non‐invasive methods has been subsequently confirmed by direct inspection.     

Improved imaging of a karst aquifer using focused source electromagnetic and differentially normalized method: a qualitative analysis

Geophysical investigations using conventional techniques applied to groundwater exploration can often present strong limitations involving high financial costs, complex acquisition logistics and high ambiguity in results. Dispersion of the electric current flow, induced polarization) effects, cultural noises and shallow lateral heterogeneities represent the main problems faced by geoelectric methods in these types of surveys. Moreover, elements such as intrusions and mineralization at different depths may be responsible for signal attenuation as well as high resistivity in unsaturated zones and complex three-dimensional formations or clayey zones cause variations in the electric current. The focused source electromagnetic and differentially normalized method approaches can help to solve some these issues. Aiming at a higher signal-to-noise ratio, the focused source electromagnetic method and approaches of the differentially normalized method, first applied to petroleum exploration, are tested on a groundwater target, in a karst environment sectioned by a diabase dyke. We performed the processing and analysis on real IP resistivity profiling data acquired with two-way dipole-dipole array, guided by magnetic data acquired on the same profile, mapping a diabase dyke. The inversion of focused source electromagnetic method/differentially normalized method was not performed, instead that we converted the induced polarization–resistivity data to a differential signal to qualitatively prove the presence of aquifer. Joint interpretation of focused source electromagnetic method curves and inverted two-dimensional induced polarization–resistivity sections allowed for precise delineation of a conductive zone associated with the karst aquifer, le magnetics allowed for the definition of a neighbour dyke. The techniques have great potential in the aid of groundwater exploration, contributing substantially to the reduction of interpretation ambiguity. Focused source electromagnetic method/differentially normalized method/ approaches show that a simple linear combination of the conventional geoelectric data is able to remove the geological noise and provide the vertical focusing of the electric current.     

地震作用下横断层地质金属成矿带电法找矿成果研究

深部矿产资源勘探是未来勘探的必然趋势.地震作用下的横断层地质构造对金属矿、 能源矿等矿产资源的分布具有重要影响,拥有较大的找矿潜力.对于地震作用下横断层地质等条件复杂的场合,采用高密度电阻率法、 激发极化法和可控源音频大地电磁法等单一电法勘探可能存在找矿效果不佳的问题,有必要研究更为有效的找矿技术方法.首先阐述了激发极化法、CSAMT法等电法勘探的基本内容和各自优缺点;然后,在分析地震作用下横断层地质特征的基础上,研究并提出了基于激发极化法和CSAMT的综合找矿法.基于激发极化法和CSAMT的综合找矿法能有效反映地下地电差异,在大深度范围有效反应地电断面电阻、 极化率参数,互相校正验证;结合已有地质物探资料,推断地下异常,提高横断层的金属矿产勘探效率和效果.将本文的研究成果应用于某横断层地质区域的金属矿勘探实践,取得了良好的勘探效果.实践表明本文所提方法有效、 可行.     

EXAMPLES OF RESOLUTION IMPROVEMENT IN GEOELECTRICAL SOUNDINGS APPLIED TO GROUNDWATER INVESTIGATIONS1

One simulation and two field examples from New Jersey illustrate resolution improvement in geoelectrical soundings applied to groundwater exploration. Layered-earth parameter resolution is derived from data obtained with the commonly used methods of resistivity, induced polarization (IP) and transient electromagnetic (TEM) soundings. Resolution improvement is achieved by simultaneous inversion of two or more data sets and by constraining parameters of the inverse problem. A quantitative analysis showing the contribution of IP data to the resolution of geo-electric sections is presented. Simultaneous inversion of simple IP data with conventional resistivity and resistivity-TEM data sets resulted in improved parameter resolution. IP data improved resolution in three ways: (1) by decoupling correlated layered-earth parameters, (2) by adding information to a geological interpretation about a second physical property, namely chargeability, and (3) by increasing the electrical information available.     

地面磁共振与瞬变电磁横向约束联合反演方法研究

大地电阻率分布信息是影响磁共振地下水探测反演结果准确性的重要因素.在众多电磁法勘探技术中,瞬变电磁法具有高分辨率、高效率和大探测深度等优势,能准确探测地下几百米范围内的电阻率分布信息.因此磁共振与瞬变电磁联合解释方法具有重要意义.然而,利用单一测点拼接的磁共振与瞬变电磁联合解释方法进行模拟二维反演时存在解释结果不唯一,容易出现错误异常体等问题,尤其在复杂地质情况下,同一测线上相邻测点探测结果连续性差,解释结果偏离实际.基于此,本文提出磁共振与瞬变电磁横向约束联合反演方法（Laterally Constrained Inversion,简称LCI）,重点引入外推积分法（quadrature with extrapolation,简称QWE）,解决了传统正演过程中基于直接数值积分方法引起的求解效率低的问题,保证了联合反演方法的顺利实施,进而以相邻测点地下结构应具备连续性为依据,引入横向约束反演思想,通过在联合反演目标函数中加入相邻测点间各模型参数约束矩阵,提高磁共振解释结果准确性,加强探测剖面地质结构和含水模型连续性.经过理论模型证实,本文提出的LCI方法能有效提高传统一维反演结果的稳定性和唯一性.最后,对安徽黄山野外实际探测数据进行横向约束联合反演,验证了磁共振与瞬变电磁LCI联合反演方法的实用性.本文的研究成果将为磁共振与瞬变电磁空间约束联合反演奠定基础.     

地震岩石物理研究进展

地震岩石物理(Seismic Rock Physics)是研究岩石物理性质与地震响应之间关系的一门学科,旨在通过研究不同温度压力条件下岩性、孔隙度、孔隙流体等对岩石弹性性质的影响,分析地震波传播规律,建立各岩性参数、物性参数与地震速度、密度等弹性参数之间的关系.本文主要论述了半个多世纪以来,国内外地震岩石物理在岩石、流体基础研究、烃类检测等方面取得的主要进展,并分析目前国内岩石物理的研究现状、存在的问题、最新研究动向及展望.     

A few case histories of subsurface imaging with EMAP as an aid to seismic processing and interpretation1

The electromagnetic array profiling (EMAP) exploration method can be combined with a direct one-dimensional inversion process for conversion to depth to produce a subsurface resistivity cross-section. This cross-section may then be interpreted in parallel with a seismic cross-section to enhance the prediction of rock type and structure. In complex thrust environments and areas of shallow carbonate rocks, the EMAP method is often used to provide additional data either to help the seismic processor and/or to aid the seismic interpretation. In particular, the electromagnetic (EM) data can be used to build an independent seismic velocity file for depth migration. Three EMAP test areas in the western United States are used to demonstrate such a use of EMAP as an expioration tool. The first shows how a velocity file is estimated from resistivity data for seismic depth migration processing in a complex thrust environment. In the second example, the method is applied in layer-cake geology with high seismic velocity rocks at the earth's surface. The third example is another complex thrust environment, but in this case the velocity file derived from the resistivity data is used for stacking the seismic data.     

Characterisation of glacial sediments using geophysical methods for groundwater source protection

A sequence of glacial and alluvial deposits overlying the Cretaceous Chalk in Eastern England was characterised using two geophysical techniques: electrical resistivity imaging and electromagnetic (EM) induction. Extensive geological data were available from trenching and boreholes. Synthetic modelling of the electrical resistivity imaging technique was undertaken to identify its limitations and to optimise survey design. The EM induction method provided a quick and cost-effective reconnaissance technique for identifying large-scale lateral variation in lithology, and for siting resistivity profiles and further boreholes. The resistivity imaging technique provided detailed information on the vertical continuity of permeable units, and was able to identify permeable pathways through the sequence. Certain limitations in detecting thin sand or gravel layers underlying electrically conductive clay were seen in both the synthetic and field data. Nevertheless, the study shows that knowledge of these limitations allows interpretation for the purpose of groundwater vulnerability assessment, given that an appropriate amount of invasive investigation has been conducted.     

用地震反射波定量解释煤层厚度的方法

一、引言 工业可采煤层厚度一般为1.5m,如何从地震资料上准确圈定1m厚的煤层边界、并定量解释煤层厚度、准确计算地质储量,国外一些学者研究了薄层地震反射波的动力学特征与薄层厚度的关系后,得出了不同的薄层垂直分辨率标准,Widess用零相位子波作实验时,发现当薄层厚度为λ/8(λ是地震子波的主波长)时,反射波形正好是入射波的导数,并可直观地鉴别顶底反射;Kallweit利用可控震源研究了薄层响应的频谱后,提出了分辨地震波的极限为1/(1.4f)(f为地震子波的上限频率),经主频换算后,此     

Characterisation of glacial sediments using geophysical methods for groundwater source protection

A sequence of glacial and alluvial deposits overlying the Cretaceous Chalk in Eastern England was characterised using two geophysical techniques: electrical resistivity imaging and electromagnetic (EM) induction. Extensive geological data were available from trenching and boreholes. Synthetic modelling of the electrical resistivity imaging technique was undertaken to identify its limitations and to optimise survey design. The EM induction method provided a quick and cost-effective reconnaissance technique for identifying large-scale lateral variation in lithology, and for siting resistivity profiles and further boreholes. The resistivity imaging technique provided detailed information on the vertical continuity of permeable units, and was able to identify permeable pathways through the sequence. Certain limitations in detecting thin sand or gravel layers underlying electrically conductive clay were seen in both the synthetic and field data. Nevertheless, the study shows that knowledge of these limitations allows interpretation for the purpose of groundwater vulnerability assessment, given that an appropriate amount of invasive investigation has been conducted.     

三维可视化在CSAMT勘探中的应用

CSAMT法是一种强有力的地球物理勘探手段,具有测量迅速、探测深度大、信噪比高等优点,已被广泛应用于金属矿、油气田、地下水、以及地热田的勘探中.在CSAMT勘探资料解释方面,传统的二维电阻率断面很难清晰、直观地揭示3D(三维)地电结构的分布特征,为此应加强3D可视化应用技术的研究.本文详细的介绍了3D可视化的建模过程,将3D构造的建模分为空间曲面剖分、空间曲面拟合插值、空间曲面拓扑关系生成、3D结构网格剖分、属性建模等过程.并以一个CSAMT勘探实例,展现出3D可视化方法技术的突出优势.三维可视化可以多角度、多层面展现地下3D电性结构的分布特征,使我们更加清晰、直观地了解3D地质体的空间范围与几何形态.     

电阻率层析成像法在辽阳活断层探测中的应用

电阻率层析成像法是近年来迅速发展起来的地球物理新技术,目前逐渐成为工程物探中的主要方法。在辽阳市地震活断层与地震危险性评价研究中运用该方法取得了良好的效果。通过在目标区布设探测剖面,辅以浅层地震,地质钻探,可以准确地探测断层的几何结构和物理特征,为辽阳市活断层探测与地震危险性评价研究提供准确可靠的物探依据。     

地热地球物理勘探新进展

地热作为一种清洁能源具有巨大的开发潜力,将在我国的经济发展中起到巨大的作用.在传统的热水型地热开发的基础上,国际上非常重视热干岩(Enhanced Geothermal)型地热的勘探开发.在这两类地热勘查和开发中,地球物理方法具有非常重要的作用.本文从地热系统的目标体岩石的地球物理性质出发,分析岩石的地球物理性质与温度、压力和含水量等影响因素的关系.例如随着温度的升高,岩石会出现去磁、电阻率降低、密度降低、弹性波速度也现明显降低等现象.进而分析地球物理方法应用到具体的地热勘查地质-地球物理异常模型.结合国际上21世纪以后的新方法技术,分析了重磁、电、地震方法在利用由于岩石温度的升高而出现的特殊地球物理现象,并应用于地热勘探.通过国内外实例介绍了各种地球物理勘探方法在地热勘查中成功应用,为进一步提高我国地热勘查水平,提供一些参考.     

矿井瞬变电磁法超前探测合成孔径成像研究

在矿井瞬变电磁超前探测数据处理和解释中,为了更好地识别巷道前方含水体电性分界面,利用扩散场与波动场间的函数关系,将矿井瞬变电磁法超前探测中瞬变电磁波场转换为拟地震波场,实现波场转换.同时,为了解决波场转换后信号幅值偏弱,以增加信噪比利于解释,利用雷达的合成孔径方法对波场转换后的拟地震信号进行相关叠加处理.将矿井瞬变电磁法巷道超前探测的同一测点不同探测方向的数据作为孔径数据进行合成孔径成像,以突出弱异常而提高信噪比,结合应用实例验证了方法的效果.研究表明,矿井瞬变电磁法合成孔径成像方法能够提高电性界面信息的信噪比和界面几何分辨率,对矿井瞬变电磁法精细超前探测含水构造具有重要的理论意义和应用价值.     

Trans‐dimensional Bayesian inversion of controlled‐source electromagnetic data in the German North Sea

This paper presents the first controlled‐source electromagnetic survey carried out in the German North Sea with a recently developed seafloor‐towed electrical dipole–dipole system, i.e., HYDRA II. Controlled‐source electromagnetic data are measured, processed, and inverted in the time domain to estimate an electrical resistivity model of the sub‐seafloor. The controlled‐source electromagnetic survey targeted a shallow, phase‐reversed, seismic reflector, which potentially indicates free gas. To compare the resistivity model to reflection seismic data and draw a combined interpretation, we apply a trans‐dimensional Bayesian inversion that estimates model parameters and uncertainties, and samples probabilistically over the number of layers of the resistivity model. The controlled‐source electromagnetic data errors show time‐varying correlations, and we therefore apply a non‐Toeplitz data covariance matrix in the inversion that is estimated from residual analysis. The geological interpretation drawn from controlled‐source electromagnetic inversion results and borehole and reflection seismic data yield resistivities of ～1 Ωm at the seafloor, which are typical for fine‐grained marine deposits, whereas resistivities below ～20 mbsf increase to 2–4 Ωm and can be related to a transition from fine‐grained (Holocene age) to unsorted, coarse‐grained, and compacted glacial sediments (Pleistocene age). Interface depths from controlled‐source electromagnetic inversion generally match the seismic reflector related to the contrast between the different depositional environments. Resistivities decrease again at greater depths to ～1 Ωm with a minimum resistivity at ～300 mbsf where a seismic reflector (that marks a major flooding surface of late Miocene age) correlates with an increased gamma‐ray count, indicating an increased amount of fine‐grained sediments. We suggest that the grain size may have a major impact on the electrical resistivity of the sediment with lower resistivities for fine‐grained sediments. Concerning the phase‐reversed seismic reflector that was targeted by the survey, controlled‐source electromagnetic inversion results yield no indication for free gas below it as resistivities are generally elevated above the reflector. We suggest that the elevated resistivities are caused by an overall decrease in porosity in the glacial sediments and that the seismic reflector could be caused by an impedance contrast at a thin low‐velocity layer. Controlled‐source electromagnetic interface depths near the reflector are quite uncertain and variable. We conclude that the seismic interface cannot be resolved with the controlled‐source electromagnetic data, but the thickness of the corresponding resistive layer follows the trend of the reflector that is inclined towards the west.