Calculation of all-time apparent resistivity of large loop transient electromagnetic method with very fast simulated annealing

In large loop transient electromagnetic method(TEM),the late time apparent resistivity formula cannot truly reflect the geoelectric model,thus it needs to define the all-time apparent resistivity with the position information of measuring point.Utilizing very fast simulated annealing(VFSA) to fit the theoretical electromagnetic force(EMF) and measured EMF could obtain the all-time apparent resistivity of the measuring points in rectangular transmitting loop.The selective cope of initial model of VFSA could be confirmed by taking the late time apparent resistivity of transient electromagnetic method as the prior information.For verifying the correctness,the all-time apparent resistivities of the geoelectric models were calculated by VFSA and dichotomy,respectively.The results indicate that the relative differences of apparent resistivities calculated by these two methods are within 3%.The change of measuring point position has little influence on the tracing pattern of all-time apparent resistivity.The first branch of the curve of all-time apparent resistivity is close to the resistivity of the first layer medium and the last branch is close to the resistivity of the last layer medium,which proves the correctness of the arithmetics proposed.

Pharmacoepidemiologic study of association between apparent treatment resistant hypertension, cardiovascular disease and interaction effect by sex and age

BACKGROUND A limited number of studies have been conducted to test the magnitudes of the association between apparent treatment resistant hypertension(aTRH)and risk of cardiovascular disease(CVD).AIM To investigate the association between aTRH and risk of CVD and examine whether sex and age modify this association.METHODS We applied an observational analysis study design using data from the United States Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial(ALLHAT).ALLHAT recruited participants(n=25516)from 625 primary care settings throughout the United States,Canada,Puerto Rico,and United States Virgin Islands,aged 55 and older with hypertension and at least one additional risk factor for heart disease.aTRH was assessed from the year 2 visit.CVD event was defined as one of the following from the year 2 follow-up visit:Fatal or non-fatal myocardial infarction,coronary revascularization,angina,stroke,heart failure,or peripheral artery disease.Cox proportional hazards regression was used to examine the effect of aTRH on CVD risk.Potential modifications of sex and age on this association were examined on the multiplicative scale by interaction term and additive scale by joint effects and relative excess risk for interaction.RESULTS Of the total study participants(n=25516),5030 experienced a CVD event during a mean of 4.7 years follow-up.aTRH was associated with a 30%increase in risk of CVD compared to non-aTRH[hazards ratio(HR)=1.3,95%CI:1.19-1.42].Sex and age modified this relationship on both multiplicative and additive scales independently.Stratified by sex,aTRH was associated with a 64%increase in risk of CVD(HR=1.64,95%CI:1.43–1.88)in women,and a 13%increase in risk of CVD(HR=1.13,95%CI:1.01–1.27)in men.Stratified by age,aTRH had a stronger impact on the risk of CVD in participants aged<65(HR=1.53,95%CI:1.32–1.77)than it did in those aged≥65(HR=1.18,95%CI:1.05–1.32).Significant two-way interactions of sex and aTRH,and age and aTRH on risk of CVD were observed(P<0.05).The observed joint effect of aTRH and ages≥65 years(HR=1.85,95%CI:1.22–2.48)in males was less than what was expected for both additive and multiplicative models(HR=4.10,95%CI:3.63–4.57 and 4.88,95%CI:3.66–6.31),although three-way interaction of sex,age,and aTRH on the risk of CVD and coronary heart disease did not reach a statistical significance(P>0.05).CONCLUSION aTRH was significantly associated with an increased risk of CVD and this association was modified by both sex and age.Further studies are warranted to test these mechanisms.

The Effects of Negative Values of Apparent Resistivity in TEM Surveys

The calculation of apparent resistivity in electrical methods is relatively simple and consolidated in the literature. Furthermore, in the case of DC methods, the apparent resistivity values are for the most part, intuitive and enable an initial interpretation of the results. On the other hand, in TEM method the apparent resistivity values are not very intuitive and interpretation based only on the apparent resistivity values cannot be done reasonably. In this way, this paper presents a discussion about the reasons and effects of the negatives values of apparent resistivity in TEM soundings. The main objective of this paper is to clarify the meanings of these negatives values and the possible effects in TEM inversion.

Electric potential and apparent resistivity in rocks containing non-uniformly distributed cracks

In this paper, the formula of electric field distribution and ground apparent resistivity of high resistance rock medium containing low resistance crack are deduced and simulated. The result shows that interstitial parameters, such as buried depth, scale, strike, and real resistivity, etc, have influence on observation and computing result of apparent resistivity. This study provided a useful foundation for earthquake prediction using apparent resistivity method.

Apparent resistivity of azimuthal anisotropy layered media

The electric field, equations of boundary conditions and calculation formula of apparent resistivity are derived for the azimuthal anisotropy layered media with the DC method based on the anisotropic Ohm's law. Taking the Schlumberger symmetric system as an example and using the recurrence formula of nuclear function, the paper theoretically simulates a model of four layers with the same anisotropy coefficient for each layer. The deep sounding curves of resistivity and the pattern of contours are obtained for the model. The results show that the theoretical formula is correct, and the deep sounding curves not only exhibit the difference of resistivity among layers but also indicate the anisotropy characteristics of layers.

A new approach for calculating the apparent resistivity tensor

The apparent resistivity tensor pB is an electromagnetic transfer function,which can be used to analyze and explain the underground electrical structure.Conventional method for obtaining the parameter requires controlled sources and can be easy to be disturbed by cultural noises.We present a new method for calculating the apparent resistivity tensor,the current density is first obtained by measuring the curl operator of the magnetic field on the Earth's surface.This approach is independent of the assumption of a plane wave,and may be used irrespective of source types and field areas.We derived the analytical expressions of the apparent resistivity tensor based on synthetic horizontally layered models with a vertical magnetic dipole source.We then calculate the responses of Pb through numerical modeling examples using both natural sources and controlled sources.Compared to traditional apparent resistivity definitions,our apparent resistivity tensor has the same amplitude value but with more sensitive phases in the far zone,and shows few distortions in the transition zone.And in the near-field zone,it is closer to the resistivity distribution under the ground.The simulation results have demonstrated the effectiveness of the proposed method for calculating the apparent resistivity tensor.

Inverse Spline Interpolation for All-time Resistivity of Central-Loop TEM

A convenient numerical calculation method (inverse spline interpolation) for all-time apparent resistivity intransient electromagnetic method (TEM) is proposed in this paper. Characteristic of early and late normalized inductiveelectromotive force was investigated. According to the turning point, the transient process is divided into the earlyphase, the turning point, and the late phase. Afterwards, apparent resistivity is obtained through inverse spline interpo-lation in the early and the late phases, respectively. Finally, the resistivities of the early-time and the late-time wereconnected together by the turning point. The result shows that the inverse spline method is feasible and the method alsolays a foundation for initial model construction in the TEM automatic inversion.

Analysis on Apparent Resistivity Variations of Garzê Station before the 2013 Lushan M_S 7. 0 Earthquake

A trend increase in apparent resistivity has been observed in the N30°E monitoring direction at Garzê Seismic Station since July 2011. This increase trend in geo-electric resistivity has been observed in the N60°W direction since 2012. During the period of the increase,the national highway No. 317 was expanded in the monitoring area,so the potential electrodes in the N30° E direction had to be moved 10 m towards the current electrodes. We interpreted the electric sounding data of Garzê Seismic Station with a horizontally layered model. Analysis based on this model showed that the shift of potential electrodes can cause a 4 Ω·m rise to the measurements in the N30°E direction. Therefore,apparent resistivity of the two directions increased in the same time in 2012 after offsetting the effects from electrodes shift. Sensitivity coefficients of the two observation directions were also obtained using the model. Sensitivity coefficients of both directions were negative for the shallow layers,which can well explain the unexpected annual variations of GarzêSeismic Station. In order to quantitatively analyze the effects from the expansion of the national highway on the observation,we constructed a finite element model based on the electrical structure. Analysis results also suggested that the expansion of the national highway could only cause a 0. 15 Ω·m decrease in the N60° W monitoring direction and0. 1Ω·m increase in the N30° E direction. Additionally,the valley values of annual variation of 2013 were distinctively higher than that of other years since 2008,meaning that there was an abnormal rise in apparent resistivity in the two observation directions at Garzê Seismic Station before the Lushan earthquake. However,the rise was contrary to the decline variation before the Wenchuan earthquake. Therefore, it is still unsure whether or not the rise variation is related to the Lushan earthquake.

AN EFFICIENT NUMERICAL MODELING OF THE DC RESISTIVITY LOGGING: THEORY AND APPLICATIONS

The numerical solution of Green’s function for the potential in 2-D arbitrary in-homogeneous media with axial symmetry has been given by use of efficient half-analytical, half-numerical hybrid method. Then the logging responses of various kinds of the DC resistivity log with axisymmetric excitation have been obtained by using surface integral equation method to match the boundary conditions on the electrodes of the logging sonde. Comparing the results with that obtained by other methods, one can see good precision and efficiency of the given method. Some applications of the numerical modeling have been also discussed.

Glass transition kinetics of La_(55)Al_(25)Ni_(10)Cu_(10) bulk metallic glass by electrical resistivity measurement

The glass transition behavior of La55A125-Ni10CU10 bulk metallic glass was investigated using elec-trical resistivity and differential-scanning calorimetry measurements. There are good agreements of the onset temperature （Tg-onset） and the end temperature （Tg-end） of the glass transition between the DSC curve and tempera-ture dependent electrical resistivity （TER） curve in the same heating rate. Kinetics of the glass transition is studied with the electrical resistivity data. The apparent activation energy of the glass transition （△Eg） is found to be 306.4 kJ.mol^-1. Fragility parameter D^＊ and VFT temper-ature To are 9.8 and 324.9 K, respectively.

Resistivity is used as a tool to evaluate the variability of soil water content

Resistivity is used to evaluate soil water content(SWC),which has the advantages of not causing soil disturbance and in low price.It is an effective way to assess the SWC variability.This paper aims to evaluate the variability of loess slope SWC through the change of resistivity.It provides a simple way for long term SWC monitoring to solve the expensive cost of deploying moisture sensors.In this context,geoelectric and environmental factors such as soil temperature and SWC were monitored for three years.The prediction model of apparent resistivity and SWC was calibrated.The post processing of geoelectric data was introduced.In addition,the SWC collected by Time-Domain Reflectometry(TDR)was used to verify the feasibility of electrical resistivity tomography(ERT)data.The SWC variability in the process of rainfall,the evolution of four seasons,and the alternation of drying and wetting were evaluated.The research results show that:i)the SWC monitored by ERT and TDR can reflect the response and hysteretic effect of water content at 0.5-3.0 m depth.ii)The moisture content monitored by ERT reflects that the soil is relatively wet in summer and autumn and dry in winter and spring.iii)From 2017 to 2020,the SWC increased in August,and the soil became dry in January.iv)Two areas with high SWC and three areas with low SWC on loess slope are reflected by resistivity.The outcome can provide the change information of SWC to a great extent without excavating boreholes.

Electrical Resistivity Sounding for Groundwater Investigation around Enugu Metropolis and the Environs, Southeast Nigeria

This report evaluates the use of electrical method and borehole data to investigate the subsurface to delineate the groundwater potential in Enugu metropolis and the environs, south-eastern Nigeria other than rely only on resistivity method which could lead to interpretation error. Integrating these 2 data sets is key in this study. The study area is located in the Anambra Basin and is underlain by Nkporo/Enugu Shale which is overlain by the Mamu Formation. It is bounded by Latitudes 6°2 0'00"N to 6°30'00"N and Longitudes 7°25'00"E to 7°35'00"E and covers surface area of about 342 m2. Thirty-one vertical electrical soundings (VES) were carried out across the area using the Schlumberger electrode array with current electrode separation from 2 to 500 m to identify the depths and resistivity values of the identified geo-electric layers. Through data analysis using WinResist software, the apparent resistivity, thicknesses and depths and the thicknesses of the aquifers were generated. The resistivity and depths were modelled to generate resistivity map and depth map. The resistivity of the aquiferous zone within the study area varied from 20.55 - 427.8 ohm-m at depths of between 10.7 - 40.05 m. Depth to the water table appears to be shallow at the south western part of the map. The interpreted geo-electric layers show a sequence of lateritic top soil, shale, sand and shale. The frequency distribution of the VES curves generated shows the presence of 3 to 5 layers with HK type as the highest. Also, a 2D model was generated using the correlation of VES to VES data and borehole data to VES data to show the underlying stratigraphy beneath the study area as well as the direction of ground water flow. Result of the VES curve analysis reveals that the sub-surface is underlain by three lithological layers namely: lateritic top soil, shale, sand and shales with NW direction of groundwater flow from the 2D model. Groundwater prospective zones can be seen along NW, SW and central parts of the study area which have low resistivity values.

断层虚位错模式揭示的2022年1月8日青海门源M_(S)6.9地震前的地电阻率变化

选取2022年1月8日青海门源M_(S)6.9地震震中400 km范围内四个地电阻率观测台站的观测精度高、具有稳态年变、震前无显著干扰的地电阻率ρ_(s)观测数据,结合ERA5同化数据集中的多层土壤温度和土壤水分含量,在利用多项式拟合获取各台站(或测道)地电阻率正常年动态的基础上,分析了门源地震前地电阻率的异常变化。结果显示:金银滩台EW测道、武威台NS测道和山丹台EW测道、N45°W测道震前存在超阈值的异常变化,并呈现各向异性特征。基于断层虚位错模式分析了地电阻率异常变化与孕震过程之间的联系,结果表明:金银滩台震前处于压缩区并受到NNE方向的挤压,与主压应变近似正交的EW测道于震前10个月出现负异常;同样位于压缩区的武威台,受到了ENE向的挤压,NS测道的地电阻率在孕震早期(震前13个月)以负异常为主,孕震中晚期(震前3个月)出现了正异常;山丹台,位于膨胀区,受到近似NS向的拉张,与主张应变平行的NS测道未发现异常,但EW测道震前一年地电阻率出现正异常,N45°W测道的地电阻率也在震前半年左右出现超阈值并呈正异常。此外,金银滩台、山丹台和武威台距离门源地震震中的距离分别为92 km,113 km和139 km,相应的地电阻率异常最大变化幅值分别为−3.0σ,2.2σ和−2.1σ。此外,门源地震前地电阻率异常变化的时空特征与岩石实验结果及理论模型一致,也符合震源区应力应变积累程度较高、向外围方向逐渐衰减的分布特征。由此推断,2022年门源M_(S)6.9地震前地电阻率的时空变化可能与区域介质变形及应力变化有关。

综合物探方法在碎屑岩地区找水中的应用——以云南宣威大路边村为例

为探索地球物理方法在碎屑地区找水应用的有效性,文章以云南宣威大路边村为研究对象,选取高密度电阻率法、联合剖面法、音频大地电磁法对碎屑岩层进行找水研究。结果表明:三叠系上统飞仙关组(T1f)碎屑岩富水性中等,含水性较均匀;受地面场地狭窄限制,高密度电法及联合剖面法测线长度有限,探测深度较浅,受碎屑岩电阻率小的影响,其找水应用效果不佳,在可探测的深度范围内较难识别基岩裂隙等找水有效异常,需结合其他物探方法甄别异常;音频大地电磁法找水应用效果相对较好,具有较高的横向分辨率,可有效识别碎屑岩中的断裂破碎带及构造裂隙带,表现为相对低阻异常特征;视电阻率单支测深曲线能有效分辨不同深度的岩土层结构,具有较高的纵向分辨率,对裂隙破碎带有较好指示意义。在地面场地较为狭窄的碎屑岩地区开展找水工作,音频大地电磁法结合视电阻单支测深曲线能取得较好效果,以音频大地电磁法确定碎屑岩地区中的裂隙发育带位置,以视电阻单支测深曲线确定裂隙发育带的深度。

成像测井解释评价方法及其地质应用

为了系统梳理成像测井解释评价存在的问题并拓展其在地质与工程领域中的应用范围,首先回顾了成像测井采集系列的发展历程及资料处理步骤与解释流程,然后提出了“四个层次”为约束(图像直接解释、常规测井约束、岩心约束以及地质理论约束)的成像测井精细解释方法。成像测井相模式可划分出具有地质意义的块状、条带状、线状、斑状、杂乱、递变模式和对称沟槽状模式七大类。成像测井可用于岩心定向、地层产状获取、裂缝评价、断层性质分析、地应力方向判别、沉积特征拾取以及古水流方向判别等领域中。通过阿尔奇公式反算,成像测井数据矩阵可以生成孔隙度频谱以及视地层水电阻率谱,并可分别运用于储层质量评价以及流体性质识别。成像测井切片处理可凸显沉积纹层等信息,可实现细粒沉积岩纹层结构拾取及非常规油气储层高分辨率测井评价。Poro Tex图像结构分析技术可用于拾取孔洞缝等储集空间特征,并定量计算孔隙度和裂缝孔隙度等参数,因此被广泛运用至非均质性较强的碳酸盐岩储层测井综合评价工作中。研究成果可规避成像测井解释中的误区同时可扩展成像测井应用领域。

基于深度学习SSD算法的高密度电法智能解译方法技术研究

高密度电法在探测灰岩区地下溶洞病害体方面得到广泛应用,但高密度电法反演结果依赖于初始模型,存在多解性,地质解译容易受专业人员主观因素影响。为此,本文从具有唯一性的视电阻率数据出发,研究了基于深度学习的SSD(Single Shot Multi-box Detector)目标检测算法的视电阻率异常智能解译方法技术。针对岩溶地质病害,设计了不同填充类型、形状、规模、数量的溶洞电性异常模型,利用Res2dmod软件进行视电阻率正演计算,构建了包含1400个样本的高密度电法视电阻率智能解译学习样本库(样本和标签)。基于TensorFlow框架,建立了基于深度学习SSD算法的高密度电法视电阻率异常智能解译方法技术,使用学习样本库训练网络权值,训练结束后对高密电法温纳装置视电阻率异常进行智能解译,单个视电阻率剖面异常智能解译耗时不到1 s,各类目标(填充型溶洞、未填充型溶洞)平均准确率为90.68%。研究结果表明:基于SSD算法的高密度电法视电阻率异常智能解译技术可显著提高高密度电法视电阻率解译效率,避免专业人员主观因素影响。

大定源回线装置瞬变电磁法在煤矿采空区探测中的应用

该文通过研究大定源回线装置瞬变电磁法在煤矿采空区探测中的应用,旨在提高煤矿采空区探测的效率和准确性。深入探讨大定源回线装置瞬变电磁法的原理和工作机制。在此基础上,设计并实施适用于煤矿采空区的探测方案,并通过试验进行验证。结果表明,大定源回线装置瞬变电磁法在煤矿采空区探测中取得显著的效果。大定源回线装置瞬变电磁法具有高效、准确、可靠的特点,能够快速识别采空区位置,为后续生产建设提供保障,同时也为其他煤矿采空区勘察提供参考。

基于等值反磁通装置频率域电磁法研究

人工源近区频率域电磁法具有轻便、分辨率高及抗干扰能力强等优点,但提取地质体二次场响应难题困扰了该方法推广应用。基于等值反磁通原理提取二次场响应,首先,推导出了基于等值反磁通原理的频率域近场垂直磁场响应的表达式;然后,采用层状介质与均匀半空间介质的垂向磁场同相分量的比值定义视电阻率,并计算了典型层状介质垂直磁场的频率响应;最后,通过试验对比时间域与频率域方法对浅埋藏铝板的异常响应。研究结果表明:基于等值反磁通原理能够有效提取近场频率域二次场信号,近场垂向磁场的同相分量与大地电导率的二次方成正比;垂向磁场同相分量的比值定义视电阻率能够清晰反映A型、Q型、H型及K型地电断面的特征。

时频电磁法频率域视电阻率求取方法研究

时频电磁法(TFEM)是一种应用于油气勘探领域,可同时实现时间域和频率域电磁一体化勘探的可控源电磁方法。本文引入水平电流场源定义的广义视电阻率,结合TFEM的发射源特征,实现TFEM频率域视电阻率的求取;分析不同偏移距、发设距水平电场振幅和视电阻率特征,验证了方法的可行性。TFEM频率域视电阻率的求取和基于模型的研究,为TFEM勘探采集参数的设计和采集数据的处理提供科学的借鉴和参考。

基于端到端深度学习的大坝渗漏电性异常识别研究

【目的】电法勘探中传统的电性异常判识方法计算复杂、效率低,且成果解译对初始模型依赖性强,难以满足海量数据快速处理的应用需求。【方法】对此,结合深度学习思想,提出了一种基于端到端的大坝视电阻率识别网络(Apparent Resistivity Network, ARNet)模型,将传统的渗漏判识方法转换为从输入视电阻率数据到输出异常体分布的非线性映射问题。利用pyGIMLi有限元工具建立2.2×104个不同形状、位置及电阻率值的大坝渗漏地电模型,计算视电阻率形态分布;通过对模拟数据进行批量提取、插值网格化处理,构建了网络训练数据集;采用相应的前端、后端及后处理方法完成网络模型搭建,并以“损失值”和“交并比”作为模型性能指标,采用随机梯度下降算法实现模型权重参数的迭代优化。【结果】结果表明:ARNet模型经过1 000次训练后,损失值降至0.068,交并比达到94.60%;在不同电阻率、位置、形状的单、双异常体对比测试中,模型匹配度达到97.66%,误差低于0.257 m。【结论】结合水库大坝的实测数据试验,ARNet模型具备良好的泛化性能,较传统反演可实现对异常体的高精度智能识别,研究成果拓宽了深度学习技术在大坝安全领域的应用研究。