基于逆重复m序列的岩矿石标本电性参数测量方法研究

岩矿石标本电性参数实验中,常使用一个或者多个频率激励的变频法测量电阻率,存在观测效率低、可用信息少、抗干扰能力弱等实际问题.本文将变频法改进为伪随机电流信号法进行观测,提出激励场源使用逆重复m序列伪随机电流信号的观测方法,推导出抑制工频干扰的参数选取条件,进而针对岩矿石标本电性参数实验中激励场源的特殊要求,详细分析了观测系统中信号产生与接收面临的问题,并给出了解决方法:采用高驱动能力设计及阻抗匹配技术解决岩矿石标本电阻率分布跨度大(n×10ⁿ×10⁶Ωm)导致的发送端驱动能力不足以及接收端阻抗不匹配等问题;采用系统频率响应校正技术修正系统存在的观测误差;采用高频微弱信号产生与拾取的相关技术,保证电流密度处于岩矿石标本的线性响应区间,避免非线性效应,实现宽频率分布范围观测(10-3~10⁴kHz).采用所研发的可编码、高精度、小电流(10^-6A)、连续可调输出的精密电流源,使用阻容模型进行实验测试,结果表明:(1)该方法可在10^-3~10⁴Hz频带内产生90个有效测量频点,可满足频带宽、频点密、压制工频干扰的观测要求;(2)实验中恒流源输出稳定,不同负载下直流输出稳定性误差小于0.5%,精度满足实验中对输出电流的要求;(3)标定后测量误差小于0.5%,系统具有较高的观测精度与抗干扰能力;(4)与变频法相比观测效率提高2.3倍.通过该方法开发的观测装置可有效提高工作效率和抗干扰能力,提高观测数据的准确性,适用于各种类型岩矿石标本电性参数观测工作.     

斜入射平面电磁波的视电阻率及其影响

传统的大地电磁法及音频大地电磁法都假设平面电磁波垂直入射地球表面,且忽略位移电流的影响.实际中,电磁波并不总是垂直入射地球表面,在某些情况下,位移电流也不可忽略.本文以新的方式推导了全电流条件下平面电磁波倾斜入射层状介质表面时的波阻抗公式,分析了位移电流、入射角、磁导率以及介电常数对TE和TM模式视电阻率之间相对差别的影响.结果表明:电磁波垂直入射地球表面时,TE和TM模式视电阻率相等,该特性与位移电流大小、磁导率和介电常数变化无关.当位移电流可忽略时,TE和TM模式视电阻率相等,该特性与入射角、磁导率和介电常数变化无关.当电磁波倾斜入射且位移电流不可忽略时,TE和TM模式视电阻率不相等,两者的差别随位移电流和入射角的增大而增大且与磁导率和介电常数有关.一般地,当位移电流超过传导电流的5%时,其影响就不可忽略.因此,实际数据处理及反演解释中,对特殊地质条件或频率很高时,应考虑位移电流、入射角、磁导率以及介电常数对TE和TM两种视电阻率模式之间差异的影响,否则可能得不到正确的结论.     

高频电磁波传播速度在水及淤积砂土中影响因素实验研究

水及淤积土中电磁波传播速度是实现水上探地雷达(GPR)探测数据准确时深转换的关键因素.论文基于探地雷达实测结果分析了水温、盐度、浊度对水中电磁波速的影响和粒径组成、含水量变化对砂土介电常数(电磁波速)的影响,建立了淤积砂土介电常数模型并给出了相应速度计算方法.研究表明水中电磁波速主要受水体盐度影响,随盐度增大而指数减小.淤积砂土介电常数符合Looyenga模型,现场探测时可根据土样三相体积比确定土体介电常数,进而确定土体电磁波速,实现GPR数据时深准确转换.     

多层电磁波测井反演

针对轴对称二维非均匀介质地层,以两接收线圈的相位差和幅度比为附加条件,建立了反演地层介电常数和电导率的电磁波测井反演数学模型．针对反问题的不适定性,利用正则化方法建立了反演的选代法．为克服层位较多时整体反演在存贮量、计算量等方面的问题,考虑了一种每次反演一个目的层的多层反演方案,并针对6层和10层模型进行了数值模拟．模拟结果表明,以相位差和幅度比为测井响应来反演介质电性参数是可行的,并适合于薄层解释,但对多层模型不能采用整体反演．     

便携式岩矿石样本电性测量仪信号发生器研制

对岩矿石样本进行电性测量,能够进一步约束地球物理探测数据的解释结果,进而提升矿产勘探的精度和准确度.为能对极低(10Ω级)还是极高阻抗(10 MΩ级)的岩矿石样本都能进行精确和有效测量,本团队自主设计了CannySIP测量系统.但该系统存在仪器较为笨重、功耗高、且测量过程较为繁琐的问题.为解决这些问题,本文以CannySIP测量系统小型化和便携化为驱动,设计一种小尺寸,低功耗的板卡级信号发生器.该信号发生器支持通过SPI总线发送频率控制字的方式来配置频率的输出,因此频率控制高效简单.本信号发生器设计了恒压和恒流两种工作模式.这两种工作模式都支持频率可任意配置,幅值可五档配置,其中恒压五档为10 V、1 V、100 mV、10 mV和1 mV,恒流五档为10 mA、1 mA、100μA、10μA和1μA.不管是恒压还是恒流,五个档位跨度均较宽,因此能很好地实现对极低或极高阻抗的岩矿石样本进行非失真激励.此外,本信号发生器的尺寸较小,接口标准统一,功耗较低,所以适合便携式岩矿石样本电性测量仪内部集成,以提供激励信号．     

煤层开采覆岩破坏的层析成像研究

用电磁波层析技术对邵武煤矿煤层开采后的覆岩破坏进行了探测，分析了吸收系数、介电常数和电导率的关系及数值范围，根据地质资料进行了综合解释．所得结果较准确地重现了地下结构的形态、裂隙带的位置和煤层开采后的变化过程，指导了对破碎带的成功堵漏，解决了生产中的一个难题．     

基于逆重复m序列信号的岩矿石电性参数采集方法研究

归纳总结了岩矿石电性参数实验过程中激励场源性质与实验装置类型,提出基于伪随机逆重复m序列信号为激励场源的实验方案,进而设计了新的观测装置.发送机产生的伪随机信号序列采用恒流源形式输出,频带宽度为1.0×10-3～1.0×104 Hz;接收机采用FGPA+ARM架构进行数据记录,在对比变频法、2n 伪随机序列与逆重复m序...     

浅层直流电法探测隐伏断层可行性分析

通过讨论断层不同表现形式的电性特征,对高密度电法与联合剖面法在隐伏断层探测中的应用可行性进行研究,并通过实例探讨了测试中应注意的问题、测试与解译方法。研究表明高密度电法及联合剖面法可以应用在隐伏断层探测中,但有一定的限制,主要源于断层的地质表现形式。     

隐伏断层电性特征及浅层电法探测

探讨了不同类型隐伏断层的电性特征及其在浅层电法测试中可能的表现形式,并通过实例阐述了浅层电法探测隐伏断层的步骤及异常识别方法。研究表明浅层电法对某些类型的隐伏断层的探测是有效的,但先验知识非常重要,对于隐伏断层的探测效果与解译起关键作用。     

一种岩矿石密度测量的新方法

本文在分析常用固体密度测量方法的基础上,提出了一种基于阿基米德浮力定律测量岩矿石密度的测量方法,并完成了密度仪硬件电路设计工作,同时给出了密度仪的技术指标及测量结果的误差分析.密度仪由荷重传感器、放大器、模数转换器、单片机、显示部分及键盘等组成.该密度仪不仅可以用于测量岩矿石固体标本的密度,而且可以用于岩矿石标本的重量、体积、孔隙度和含油或水饱和度等多种参数的检测,同时实现了岩矿石密度值实时显示功能,提高了工作效率,减少了人为误差.本密度仪具有智能化程度高、自动显示密度值、可打印测试结果、测量精度高和操作简单等优点.现已在多家单位应用.     

The measurement and model construction of complex permittivity of vegetation

The complex permittivity of targeted objects is an important factor that influences its microwave radiation and scattering characteristics. In the quantitative research of microwave remote sensing, the study of the dielectric properties of the vegetation to establish the relationship between its specific physical parameters and complex permittivity is fundamental. In this study, six categories of vegetation samples were collected at the city of Zhangye, a key research area of the Heihe watershed allied telemetry experimental research. The vector network analyzer E8362B was used to measure the complex permittivity of these samples from 0.2 to 20 GHz by the coaxial probe technique. The research focused mainly on the corn leaves, and an empirical model was established between the gravimetric moisture and the real/imaginary parts of complex permittivity at the main frequency points of microwave sensors. Furthermore, the empirical model and the classical Debye-Cole model were compared and verified by the measured data collected from the Huailai County of Hebei Province. The results show that the newly-established empirical model is more accurate and more practical as compared to the traditional Debye-Cole model.     

低频含水岩石介电高值成因及改进测量方法

含水岩石在低频下常常呈现高达104以上的介电常数值,数值模拟和实测结果都表明这是由于岩石中存在着传导电流,其具有与外场同相和正交的实、虚部,这二者通过与频率成反比的关系叠加在介电常数上.提出在平行板电容器一极板与被测岩石样品间夹入不导电薄膜的办法来消除传导电流的不利影响.对标准件的测量表明该方法的最大误差在4%以内.用该方法测量淡水饱和岩石样品,结果得到合理适中的介电常数值及清晰明了的介电极化谱.除湿岩石外,该方法还适用于冰、生物肌体等固态导电介质的介电谱研究.     

基于二维图像的数字岩心电导率计算方法研究

电导率是表征岩石电学性质的重要物理参数,在地质资源勘查和测井解释等领域发挥着巨大作用.快速、准确地确定岩石电导率具有重要的理论和实践意义.作为近年来发展的一种岩石物理数值模拟工具,数字岩心技术在定量计算电导率等物性参数方面应用广泛.三维微观结构的准确获取是数字岩心技术计算岩石电导率的关键,但传统获取岩石三维微观结构的方法较为复杂费时.为了方便快速地通过数字岩心技术计算岩石的电导率,本文研究了岩石二维与三维数字岩心的电导率联系.我们基于微米级X射线CT扫描得到的三个砂岩样品的微观结构信息建立了三维数字岩心,并通过有限元法计算的三维数字岩心电导率与实验数据的对比验证数值计算方法的有效性.随后我们数字地扩展了岩石的孔隙,产生了较大孔隙度的三维数字岩心样本,在此基础上,计算了三维数字岩心和相应二维数字岩心的电导率,并通过Archie公式分别拟合了电导率与孔隙度之间的关系,得到了相应的胶结系数.结果表明,三维数字岩心的胶结系数小于二维数字岩心的胶结系数,且二者的比值与岩石实测孔隙度呈线性负相关关系.以该联系为纽带,通过二维图像快速计算得到的电导率与孔隙度关系,确定了三维数字岩心的电导率与孔隙度关系,并进一步通过三维数字岩心的孔隙度计算其电导率.该方法计算得到的人工砂岩样品的电导率与其三维数字岩心电导率相关系数高于96%,验证了基于二维图像的数字岩心电导率计算方法的有效性.本文的研究结果为快速、准确地计算岩石电导率提供了新的思路,在油气勘探开发中有广阔的应用前景.     

Calculation of elastic properties in lower part of the Kola borehole from bulk chemical compositions of core samples

In-situ elastic properties in deep boreholes are controlled by several factors, mainly by lithology, petrofabric, fluid-filled cracks and pores. In order to separate the effects of different factors it is useful to extract lithology-controlled part from observedin-situ velocities. For that purpose we calculated mineralogical composition and isotropic crack-free elastic properties in the lower part of the Kola borehole from bulk chemical compositions of core samples. We use a new technique of petrophysical modeling based on thermodynamic approach. The reasonable accuracy of the modeling is confirmed by comparison with the observations of mineralogical composition and laboratory measurements of density and elastic wave velocities in upper crustal crystalline rocks at high confining pressure. Calculations were carried out for 896 core samples from the depth segment of 6840–10535m. Using these results we estimate density and crack-free isotropic elastic properties of 554 lithology-defined layers composing this depth segment. Average synthetic P- wave velocity appears to be 2.7% higher than the velocity from Vertical Seismic Profiling (VSP), and 5% higher than sonic log velocity. Average synthetic S-wave velocity is 1.4 % higher than that from VSP. These differences can be explained by superposition of effects of fabric-related anisotropy, cracks aligned parallel to the foliation plain, and randomly oriented cracks, with the effect of cracks being the predominant control. Low sonic log velocities are likely caused by drilling-induced cracking (hydrofractures) in the borehole walls. The calculated synthetic density and velocity cross-sections can be used for much more detailed interpretations, for which, however, new, more detailed and reliable seismic data are required.     

Comparative experimental study on several methods for measuring elastic wave velocities in rocks at high pressure

To measure elastic wave velocities in rocks at high temperature and high pressure is an important way to acquire the mechanics and thermodynamics data of rocks in the earth's interior and also a substantial approach to studying the structure and composition of materials there. In recent years, a rapid progress has been made in methodology pertaining to the measurements of elastic wave velocities in rocks at high temperature and high pressure with solids as the pressure-transfer media. However, no strict comparisons have been made of the elastic wave velocity data of rocks measured at high temperature and high pressure by various laboratories. In order to compare the experimental results from various laboratories, we have conducted a comparative experimental study on three measuring methods and made a strict comparison with the results obtained by using the transmission method with fluid as the pressure-transfer medium. Our experimental results have shown that the measurements obtained by the three methods are comparable in the pressure ranges of their application. The cubic sample pulse transmission method used by Kern is applicable to measuring elastic wave velocities in crustal rocks at lower temperature and lower pressure. The prism sample pulse reflection-transmission method has some advantages in pressure range, heating temperature and measuring precision. Although the measurements obtained under relatively low pressure conditions by the prism sample pulse transmission method are relatively low in precision, the samples are large in length and their assemblage is simple. So this method is suitable to the experiments that require large quantities of samples and higher pressures. Therefore, in practical application the latter two methods are usually recommended because their measurements can be mutually corrected and supplemented.     

跨孔雷达全波形反演成像方法的研究

跨孔雷达全波形反演是一种使用全波形信息反演两钻孔之间地下信息的层析成像技术.常规的层析成像反演大部分采用射线追踪方法,其中基于初至时的射线追踪方法可以反演出速度剖面（介电常数剖面）,基于最大振幅的层析成像可以反演出衰减剖面（电导率剖面）.常规射线追踪方法有许多不足,究其原因是该方法仅使用了小部分的信号信息.为了进一步提高成像分辨率,本文全面推导了全波形跨孔雷达层析成像反演方法,该方法利用雷达波全幅度相位信息能够反演出地下高分辨率的介电常数和电导率图像.本文通过基于局域网的分布式并行算法,有效地解决了巨量数据正演计算问题.文中首先建立了基于单轴各向异性介质完全匹配层的时间域有限差分二维正演算法,进而通过应用包括时间维度在内的全波场信息与残场逆向传播的全波场信息乘积来计算梯度方向,通过求取以步长为自变量的目标函数的极值确定步长公式,并提出以第一次介电常数反演作为同步反演的初始模型,能够有效提高收敛速度.本文对多组模型进行成像实验,取得了较好的反演效果.     

Modelling of GPR waves for lossy media obeying a complex power law of frequency for dielectric permittivity

The attenuation of ground‐penetrating radar (GPR) energy in the subsurface decreases and shifts the amplitude spectrum of the radar pulse to lower frequencies (absorption) with increasing traveltime and causes also a distortion of wavelet phase (dispersion). The attenuation is often expressed by the quality factor Q. For GPR studies, Q can be estimated from the ratio of the real part to the imaginary part of the dielectric permittivity. We consider a complex power function of frequency for the dielectric permittivity, and show that this dielectric response corresponds to a frequency‐independent‐Q or simply a constant‐Q model. The phase velocity (dispersion relationship) and the absorption coefficient of electromagnetic waves also obey a frequency power law. This approach is easy to use in the frequency domain and the wave propagation can be described by two parameters only, for example Q and the phase velocity at an arbitrary reference frequency. This simplicity makes it practical for any inversion technique. Furthermore, by using the Hilbert transform relating the velocity and the absorption coefficient (which obeys a frequency power law), we find the same dispersion relationship for the phase velocity. Both approaches are valid for a constant value of Q over a restricted frequency‐bandwidth, and are applicable in a material that is assumed to have no instantaneous dielectric response. Many GPR profiles acquired in a dry aeolian environment have shown a strong reflectivity inside dunes. Changes in water content are believed to be the origin of this reflectivity. We model the radar reflections from the bottom of a dry aeolian dune using the 1D wavelet modelling method. We discuss the choice of the reference wavelet in this modelling approach. A trial‐and‐error match of modelled and observed data was performed to estimate the optimum set of parameters characterizing the materials composing the site. Additionally, by combining the complex refractive index method (CRIM) and/or Topp equations for the bulk permittivity (dielectric constant) of moist sandy soils with a frequency power law for the dielectric response, we introduce them into the expression for the reflection coefficient. Using this method, we can estimate the water content and explain its effect on the reflection coefficient and on wavelet modelling.     

数字岩石物理中弹性参数的有限差分计算方法

数字岩石物理利用三维成像技术和数学方法,建立数字岩心,开展多场物理响应模拟,计算岩石的等效弹性参数,为岩石物理学研究开拓了新的领域.本文发展了一种基于高阶有限差分的岩石模量数值计算的新方法,该方法便于理解,容易实现,占用内存相对较少,计算效率高,结果合理,弥补了常规岩石物理实验周期长,成本高,误差大等不足.该方法将三维数字岩心样本嵌入一个具有与岩心样本骨架颗粒相同弹性性质的区域中扩充成一个新模型,测量由数字岩石样本非均匀结构带来的纵波或横波峰值振幅的时间差,利用该时间差(相对参考模型)估算纵横波的等效速度,进而求取等效弹性模量.理论模型和实际岩心的计算结果表明,数值模拟结果与实验结果有较高的吻合度,验证了该方法的合理性.     

Coal top detection by conductively guided borehole radar wave imaging for open cut blast-hole drilling

Damage to the top of coal seams, caused by incorrect blast stand-off distances, results in coal losses of up to 10–15% to the Australian open cut coal mining operations. This is a serious issue to be addressed. Here we propose to use a new forward-looking imaging technique based on the borehole radar technology to predict the coal seam top in real time while drilling blast holes. This is achieved by coupling the conventional borehole radar waves on to a steel drill rod to induce a guided wave along the axial drill rod. The drill rod ahead of the borehole radar behaves as a forward-looking antenna for the guided waves. Both numerical modelling and field trials simulating a drill rod as an antenna are used to investigate the feasibility of the proposed technique for prediction of the coal top under typical open cut environments. Numerical modelling demonstrated that conductivity of the overburden is the most important factor affecting our ability to see coal seams ahead of the drill bit, the guided borehole radar waves could be used for top coal prediction and a theoretical prediction error less than 10 cm and a forward-looking capability of 4–6 m can be achieved. Field trials at Australian open cut coal mines also demonstrated that guided borehole radar waves can be observed and used for prediction of coal top ahead of drill bit during blast-hole drilling in resistive, open cut environments (the average resistivity should be higher than 75 Ωm).     

Recursive impedance inversion of ground-penetrating radar data in stochastic media

The travel time and amplitude of ground-penetrating radar (GPR) waves are closely related to medium parameters such as water content, porosity, and dielectric permittivity. However, conventional estimation methods, which are mostly based on wave velocity, are not suitable for real complex media because of limited resolution. Impedance inversion uses the reflection coefficient of radar waves to directly calculate GPR impedance and other parameters of subsurface media. We construct a 3D multiscale stochastic medium model and use the mixed Gaussian and exponential autocorrelation function to describe the distribution of parameters in real subsurface media. We introduce an elliptical Gaussian function to describe local random anomalies. The tapering function is also introduced to reduce calculation errors caused by the numerical simulation of discrete grids. We derive the impedance inversion workflow and test the calculation precision in complex media. Finally, we use impedance inversion to process GPR field data in a polluted site in Mongolia. The inversion results were constrained using borehole data and validated by resistivity data.