大地电场铅电极的研制

张家口地震中心台经过多次试验,成功研制了大地电场铅电极,采用新型的电极孔成孔方法及埋设技术进行了试验观测,从实验数据中可以明显看到地电场的日变形态。该电极具有制作工艺合理、电极差较小、稳定性能较好、噪声低、使用寿命长、易于保存和使用方便等特点,不仅可以满足大地电场长期定点观测的要求,还可以用于地电阻率观测,亦可作为地震电磁扰动观测中的电极传感器。铅电极应用前景广阔。     

地电场电极故障判定及机理分析

分析总结近几年来河北省地电场台站地电场电极故障出现的数据变化,认为河北省地电场数据在无干扰情况下变化形态稳定,部分台站图像中可见“峰-谷”形态,且相关系数及差值良好。地电场电极故障时,共用该电极的两测道数据有同步干扰主要表现在:①两测道数据相关系数减小、差值变大。②图像上同步出现台阶、突跳、长趋势变化。根据数据变化的同步性可以初步判断电极故障及故障电极位置,另外还需非电极故障的排除,首先对观测环境、仪器、外线路、线路接头、配线板等进行检查,其次用对比试验法,即预埋新电极接入备用地电场仪器与故障电极并行观测,通过对比确定电极故障。最后运用化学及数学方法Butler-Volmer方程及Nernst方程对电极故障造成的数据现象进行分析解释。该研究结果为台站及时进行电极故障判断有一定参考意义。     

电极极化电位对地电场观测影响研究

在分析地电场测量电极的极化电位产生机理的基础上,通过同类电极组合试验和不同类电极对比试验,对极化电位在地电场观测中的影响形成几点认识：①由于电极和土壤介质之间的接触电位和扩散电位的影响,极化电位的存在具有普遍性;②当工作状态稳定后,电极极化电位可能使得观测结果产生固定偏差,但在误差允许的范围内;③正常情况下,电极极化电位的存在不影响对地电场变化特性的观测。     

电极类型及深埋对地电场观测精度的影响分析

精度的高低是考量地电场观测的一项重要指标,通过对阳原地震台近10年的观测精度进行分析(主要针对背景场项目改造后的观测数据),并对目前使用的JH-020型不极化电极观测及深埋处理进行研究,得出使用JH-020型不极化电极观测及电极深埋处理是有效提高观测精度的可行方法。同时,也为全省乃至全国台站提供地电场观测的有益借鉴。     

井下地电阻率观测的探测深度初步研究

对井下地电阻率观测的探测深度进行了研究,计算了均匀半空间和给定结构参数的水平层状介质模型在不同装置电极埋深下的探测深度,分析了探测深度与装置电极埋深和介质电阻率结构之间的关系,得到如下结果:①与地表观测相比,在供电极距为1 km左右时,探测深度随装置电极埋深的增大而增大,且增大的速度与装置电极埋深密切相关;当装置电极埋深h < 100 m时,探测深度的增大速度远小于装置电极埋深h≥100 m时. ②当装置电极埋深h < 50 m时,与地表观测相比探测深度增加很小,不超过10 m;当装置电极埋深相同时,供电极距越大,与地表观测相比探测深度增加得越小. ③对于水平层状电阻率均匀分层结构,在装置电极埋深相同的情况下,下伏低阻结构的探测深度显著大于下伏高阻结构.本文的研究结果表明,为了观测到深部电阻率的变化情况,首先需要查明测区电性结构,再进行综合分析,以确定井下地电阻率观测的装置电极埋深,其结果为深部电阻率变化研究提供了理论基础.      

呼和浩特地震台地电阻率观测系统改造

呼和浩特基准地震台地电阻率观测受环境干扰影响,N41°E无法观测;外线路和电极多处老化导致的漏电现象十分严重,直接影响观测数据的精度.为此,呼和浩特地震台于2005年4月开始对地电观测装置系统进行全面改造,包括外线路、电极和观测室内布线、电源和线路的避雷.本文用可靠的数据资料对此项改造工作的过程,和具体实施步骤进行分析,经过多次实验及深入细致的研究,总结出地电改造的成功经验,发现存在的问题,提出解决问题的办法及应采取的措施.     

偶极接地线对地电阻率影响的数值模拟

针对我国地震监测预报中地电阻率定点连续观测中存在的偶极接地线的干扰问题, 本文将台站区域地层简化为3层均匀介质模型, 将接地线等效为偶极接地的电阻体, 建立了接地线干扰地电阻率观测的耦合物理模型. 通过有限元分析软件ANSYS模拟分析不同电性断面情况下接地线对地电阻率观测的影响, 同时分析这种干扰的产生机理, 并结合实际观测中存在的干扰问题作了对比验证分析. 结果表明: ① 接地线使得供电电极产生的地下对称性电场分布发生局部调整, 从而影响地电阻率观测; ② 接地线对地电阻率观测的影响主要取决于线缆的位置及方位角的大小; ③ 适当增大电极埋深可以减小其对地电阻率观测的影响; ④ 电性结构的差异性决定干扰变化幅度的大小. 本文结果对相关台站地电阻率观测异常分析落实及干扰源避让和观测系统改造具有参考意义.      

井下地电阻率观测中地表电流干扰影响计算

本文把地电阻率台站地下介质简化为水平三层均匀介质模型,以点电流模拟地表干扰电流,针对对称四极观测装置,计算了在不同电性结构中的不同深度观测时,地表电流干扰源对对称四极装置地电阻率观测的影响,计算得到:地表干扰源对电阻率观测的影响取决于电性结构的类型和层参数、供电电极和测量电极的埋深以及避开干扰源的距离.本文研究结果对实施井下电阻率观测中台址电性结构的选择、电极埋深、干扰源避让距离等有参考意义.     

海安地震台深埋电极地电阻率观测分析

通过对海安地震台深埋电极和表层电极对比观测结果进行分析,发现相对表层电极观测,深埋电极观测能有效降低表层影响系数,对改善年变特征具有很好的效果,并且在避免表层干扰和提高观测精度上具有明显意义。深埋电极观测方式为解决地电阻率场地中的金属干扰、降雨影响等提供新的思路。     

菏泽5.9级地震前深埋电极的地电异常特征

1.前言笔者通过对大量地电资料的分析,发现深埋电极进行地电观测,能够排除表层干扰,突出地震异常。本文利用深埋电极的地电观测资料,总结了1983年菏泽5.9级地震前地电异常特征。2.菏泽5.9级地震前的地电异常菏泽5.9级地震前,震中周围300km范围内的地电异常反应是不同的(图1)。现分述     

Pb-PbCl_2不极化电极的设计与实现

长周期大地电磁测深需要观测最长周期为几万秒的大地电磁场信号,这要求用于测量电场信号的不极化电极具有很小的极差,以及至少长达1—2个月的稳定时间,普通的不极化电极不能满足要求。通过改进电极电解质配方和电极结构,试制出铅-氯化铅不极化电极。测量结果表明,该电极具有极差小、稳定时间长、使用寿命长、维护简单等优良特性。在山东菏泽等地的野外实验表明,该类不极化电极能够很好地观测几万秒的长周期信号。同等条件下,其性能优于国外同类产品,达到预期目标。     

Construction and Testing of a Durable Platinum Wire Eh Electrode for In Situ Redox Measurements in the Subsurface

We have developed a rugged, durable platinum wire Eh electrode for application in subsurface environments. The electrode design is described in detail and its performance under aerobic and anaerobic steady-state and transient conditions is assessed. The electrode consists of a 0.5-mm-diameter platinum wire (99.99% purity) cast in a glass fiber-reinforced epoxy jacket. The construction allowed installation through direct insertion into sandy media to depths up to several meters. Data collection was through connection to a datalogger with high impedance input; data points were collected every 10 seconds and averaged and stored once an hour. The electrodes functioned in situ for periods of more than three years and gave reliable readings during oxic, anoxic, and transitional conditions. Performance testing and examination of electrodes recovered after three years in situ indicated that they were not impacted by corrosion, dissolution, or poisoning.     

油井多相流电磁成像测量敏感场仿真

为了考察油井多相流电磁成像测量的敏感场分布,本文根据阵列电极结构和测量电磁场特性,应用有限元求解流体截面的电磁场问题,对于不同介质分布模型,计算电势分布,进而模拟测量敏感场.仿真结果表明,测量敏感场呈马鞍面状分布,在靠近发射电极和测量电极的区域敏感性较强,在弧形区域的中间敏感性较小.     

THE USE OF A SQUARE CONFIGURATION IN RESISTIVITY PROSPECTING *

Consideration is given to the use of a configuration of four electrodes set in a square array for resistivity measurements. It is found that, by passing current successively between different pairs of electrodes, an apparent resistivity can be determined which is both more sensitive to the position of the array centre and less dependent on orientation than the measures usually obtained with colinear arrays of electrodes. At the same time the observations made enable the degree of the departure of local conditions from conditions of lateral homogeneity to be assessed. Theoretical and practical examples of the use of this electrode system are given and the use of the system both as a tool in mapping and in depth investigations is considered. It is shown that provided electrode spacings are suitably arranged the results of a probe carried out using the square array can be interpreted by conventional methods. The system is shown to have particular advantages in the investigation of lateral resistivity variations and the reduced dependence on orientation makes possible the recasting of interpretation data in an orientationally invariant form with a consequent drastic reduction in the number of type curves required for a particular problem.     

深埋电极的地电阻率观测研究

首先研究了四极观测系统装置系数与电极埋深的关系;然后给出了点电流源在3层地壳模型的地表和第二层时,电源所在层的电位的解析表达式;最后将天津宝坻地区的电性结构简化成一个3层模型,计算给出了当地表层和基岩中的电阻率出现变化时,在地表和基岩上层开展四极地电阻率观测结果与供电极距和深度的关系.     

深井电极交叉供电对自然电位的影响

通过实验论证平凉地震台深井电阻率观测自然电位畸变由电极交叉供电造成,讨论分析不同电极供电对自然电位的影响。结果表明:对测量极供电,会影响自然电位,不会影响电阻率测值;单极供电对自然电位的影响表现为阶跃突跳,并以指数形态恢复,恢复时间约10 h,干扰峰值与供电电流、供电时间等有关;对观测数据进行校正,取得较好效果。     

电阻率测井响应的积分方程解法

从电流守恒条件出发,得到了两个积分方程.其中第一个和在1964年提出的相同,它的未知函数是边界面上的隐电流源分布密度;第二个积分方程的未知函数则是电位函数本身. 在的文章以及本文作者的另一篇文章中,供电电极和测量电极都被当成点电极处理.用这种方法来处理电位电极系和梯度电极系已不够准确,用来处理三侧向或双侧向等具有大电极的电极系则完全无能为力. 测井中所用的电极系是包着金属外皮的绝缘心棒,金属外皮就是电极.本文提出了处理这种电极系的方法.结果表明,第二个积分方程在处理这种电极系时有明显优点.     

Optimal Field Approaches for Electrokinetic In Situ Oxidation Remediation

Numerical simulations were used to identify and evaluate optimum electrode configurations and approaches for electrokinetic in situ chemical oxidation (EK‐ISCO) remediation of low‐permeability sediments. A newly developed groundwater and EK flow and reactive transport numerical model was used to conduct two‐dimensional scenario simulations of the coverage of an injected oxidant, permanganate, and the oxidation of a typical organic contaminant (tetrachloroethene, PCE). For linear configurations of vertical electrodes, the spacing of same‐polarity electrodes is recommended to be about one‐third to one‐quarter of the anode–cathode spacing. Greater coverage could also be achieved by locating additional oxidant injection wells at the divergence of the electric field in linear electrode configurations. Horizontal electrodes allowed greater contact between the injected permanganate and PCE and resulted in faster degradation of PCE compared to vertical electrodes. Pulsed oxidant injection, closer electrode spacing, and electric field reversal also resulted in faster EK‐ISCO remediation.     

Pilot‐scale field validation of the long electrode electrical resistivity tomography method

A validation experiment, carried out in a scaled field setting, was attempted for the long electrode electrical resistivity tomography method in order to demonstrate the performance of the technique in imaging a simple buried target. The experiment was an approximately 1/17 scale mock‐up of a region encompassing a buried nuclear waste tank on the Hanford site. The target of focus was constructed by manually forming a simulated plume within the vadose zone using a tank waste simulant. The long electrode results were compared to results from conventional point electrodes on the surface and buried within the survey domain. Using a pole‐pole array, both point and long electrode imaging techniques identified the lateral extents of the pre‐formed plume with reasonable fidelity but the long electrode method was handicapped in reconstructing vertical boundaries. The pole‐dipole and dipole‐dipole arrays were also tested with the long electrode method and were shown to have the least favourable target properties, including the position of the reconstructed plume relative to the known plume and the intensity of false positive targets. The poor performance of the pole‐dipole and dipole‐dipole arrays was attributed to an inexhaustive and non‐optimal coverage of data at key electrodes, as well as an increased noise for electrode combinations with high geometric factors. However, when comparing the model resolution matrix among the different acquisition strategies, the pole‐dipole and dipole‐dipole arrays using long electrodes were shown to have significantly higher average and maximum values within the matrix than any pole‐pole array. The model resolution describes how well the inversion model resolves the subsurface. Given the model resolution performance of the pole‐dipole and dipole‐dipole arrays, it may be worth investing in tools to understand the optimum subset of randomly distributed electrode pairs to produce maximum performance from the inversion model.     

Rapid inversion of data from 2D resistivity surveys with electrode displacements

Resistivity monitoring surveys are used to detect temporal changes in the subsurface using repeated measurements over the same site. The positions of the electrodes are typically measured at the start of the survey program and possibly at occasional later times. In areas with unstable ground, such as landslide‐prone slopes, the positions of the electrodes can be displaced by ground movements. If this occurs at times when the positions of the electrodes are not directly measured, they have to be estimated. This can be done by interpolation or, as in recent developments, from the resistivity data using new inverse methods. The smoothness‐constrained least squares optimisation method can be modified to include the electrode positions as additional unknown parameters. The Jacobian matrices with the sensitivity of the apparent resistivity measurements to changes in the electrode positions are then required by the optimisation method. In this paper, a fast adjoint‐equation method is used to calculate the Jacobian matrices required by the least squares method to reduce the calculation time. In areas with large near‐surface resistivity contrasts, the inversion routine sometimes cannot accurately distinguish between electrode displacements and subsurface resistivity variations. To overcome this problem, the model for the initial time‐lapse dataset (with accurately known electrode positions) is used as the starting model for the inversion of the later‐time dataset. This greatly improves the accuracy of the estimated electrode positions compared to the use of a homogeneous half‐space starting model. In areas where the movement of the electrodes is expected to occur in a fixed direction, the method of transformations can be used to include this information as an additional constraint in the optimisation routine.