Distribution Of Apparent Resistivity Research Articles

Simulation Monitoring for Rainfall Infiltration in Soil Based on High Density Electrical Method

Rainfall infiltration is a porous medium flow problem with variable saturation. Based on the theoretical analysis of the flow field, electrical conductivity of rocks, the electrical field, the paper simulates the coupling relationship between the water saturation in soil and the apparent resistivity distribution. It combines the Richards equation, the Archie formula and the Laplace equation. The experiment simulates the potential field data by the Wenner setting in electrical exploration on a two-layer geologic model with continuous rainfall during 5 days, which shows that the effective saturation in soil is increasing with the rainfall time, while the apparent resistivity is decreasing. This can provide a theoretical basis for the analyzing the rainfall infiltration and porosity of the soil by using high-density electrical method in the future.

Vector analysis of pole–pole array for determining the 3D boundary of object

ABSTRACTAn algorithm is proposed for the interpretation of resistivity data that allows the 3D parameters (the boundary in plan view and the depth range) of an anomalous resistivity object in a heterogeneous medium to be determined. The proposed method is based on a vector analysis of the apparent resistivity of soil obtained by a pole–pole survey within the measurement window. In the first stage of the algorithm, in each measurement window, the radius vector is calculated, and as a result, vector images of the main directions of change in the resistivity of the medium are constructed. This allows us to estimate the location of a local anomalous object and to correlate the resistivity of the object with that of the background medium. With a consistent variation in the effective depth of investigation, a set of vector images is formed that characterizes the apparent resistivity distribution in the soil layers. Mathematical analysis of the vector images by using the scalar product allows us to estimate the depth range of the anomalous object. The effectiveness of the proposed algorithm has been proven on synthetic models and in comprehensive investigations of archaeological sites. The proposed method does not allow the true resistivity of an anomalous object to be determined, which is a disadvantage. However, this simple algorithm for processing and analysing shallow electrical prospecting data can be directly used at the preliminary data processing stage during a field survey. First, a pole–pole array can be rapidly operated by a single person; second, the user does not need special knowledge in the field of electrical resistivity data processing. The estimated 3D boundaries of local objects will make it possible to determine the area of interest for further detailed surveying and to justify all the parameters of the measurement technique (distance between electrodes, depth range etc.).

Determination of Underground Structure and Migration of Hot Plumes Contaminating Fresh Water Using Vertical Electrical Survey (VES) and Magnetic Survey, A Case Study of Tattapani Thermal Spring, Azad Kashmir

A geophysical survey was carried out at Tattapani thermal spring Azad Kashmir to delineate structure,thickness, depth, lithology and migration of hot plumes contaminating fresh water. The study area was investigated byVertical Electrical Sounding (VES) using schlumberger array at 21 locations arranged in ten profiles to a maximumdepth of 500 m and 200 magnetic observations. The extension and tectonic setup of thermal spring was mapped bygeoelectrical litho sections, subsurface geological sections (20m, 20-100m and 100-500m) pseudo section, apparentresistivity map, geoelectrical parameters, statistical distribution of apparent resistivity, total magnetic intensity andanomaly map. The data show that Tattapani hot spring is concentrated along the fault line delineated by geoelectricallitho sections and magnetic section with value of -120 nT to -300 nT, total field intensity of 50000-50450 nT andconfirm by macro anisotropy (1.0 to 2.7). The geoelectrical lithological section portrays that study area compriseslithological fabric of dolomite (≥400 ohm.m), sandstone (150-200 ohm.m), clay (80-150 ohm.m), Shaley clay (50-80)and shale (≤ 50). The Thermal Plumes (10-70 ohm.m) were pictured by resistivity section and pseudo section ataverage depth of 30-60 m and showing migration of hot plumes in the North-Eastern direction contaminating freshwater (100-200 ohm.m). The longitudinal conductance (0.95-15 mhos), transverse resistance (20-300 ohm.m2) are seenhaving maximum value in the North-Eastern and North-Western side of the study area. The study also shows that freshground water is mostly concentrated in sandstone (150-200 ohm.m), dolomite (≥400 ohm.m) and lies above the thermalplumes and thus highly prone to contamination due to upwelling of thermal water.

Determination of Underground Structure and Migration of Hot Plumes Contaminating Fresh Water Using Vertical Electrical Survey (VES) and Magnetic Survey, A Case Study of Tattapani Thermal Spring, Azad Kashmir

A geophysical survey was carried out at Tattapani thermal spring Azad Kashmir to delineate structure,thickness, depth, lithology and migration of hot plumes contaminating fresh water. The study area was investigated byVertical Electrical Sounding (VES) using schlumberger array at 21 locations arranged in ten profiles to a maximumdepth of 500 m and 200 magnetic observations. The extension and tectonic setup of thermal spring was mapped bygeoelectrical litho sections, subsurface geological sections (20m, 20-100m and 100-500m) pseudo section, apparentresistivity map, geoelectrical parameters, statistical distribution of apparent resistivity, total magnetic intensity andanomaly map. The data show that Tattapani hot spring is concentrated along the fault line delineated by geoelectricallitho sections and magnetic section with value of -120 nT to -300 nT, total field intensity of 50000-50450 nT andconfirm by macro anisotropy (1.0 to 2.7). The geoelectrical lithological section portrays that study area compriseslithological fabric of dolomite (≥400 ohm.m), sandstone (150-200 ohm.m), clay (80-150 ohm.m), Shaley clay (50-80)and shale (≤ 50). The Thermal Plumes (10-70 ohm.m) were pictured by resistivity section and pseudo section ataverage depth of 30-60 m and showing migration of hot plumes in the North-Eastern direction contaminating freshwater (100-200 ohm.m). The longitudinal conductance (0.95-15 mhos), transverse resistance (20-300 ohm.m2) are seenhaving maximum value in the North-Eastern and North-Western side of the study area. The study also shows that freshground water is mostly concentrated in sandstone (150-200 ohm.m), dolomite (≥400 ohm.m) and lies above the thermalplumes and thus highly prone to contamination due to upwelling of thermal water.

Frequency domain soil parameters inversion of horizontally multilayered earth model with considering high‐frequency field

A method to estimate soil parameters of horizontally multilayered earth model in frequency domain is developed with considering high-frequency field. The theoretical formula of complex apparent resistivity with considering high-frequency field is derived from Green's function. To avoid time-consuming numerical integration, complex image method is introduced to solve Sommerfeld integral. Simulated annealing algorithm is applied to optimise soil parameters. The accuracy of this method is confirmed by interpreting field data under the DC field. As the inversion results of this method are different from other literature's results in a four-layer model, the posterior analysis is made. Then this method is applied to the inversion of frequency domain soil parameters under both quasi-static field and high-frequency field. The differences of complex apparent resistivity distribution between quasi-static field and high-frequency field are compared at different frequencies.

A64 Network-MT 法による雲仙火山周辺での見かけ比抵抗分布

A64 Network-MT 法による雲仙火山周辺での見かけ比抵抗分布

Three-dimensional numerical modeling of full-space transient electromagnetic responses of water in goaf

The full-space transient electromagnetic response of water-filled goaves in coal mines were numerically modeled. Traditional numerical modeling methods cannot be used to simulate the underground full-space transient electromagnetic field. We used multiple transmitting loops instead of the traditional single transmitting loop to load the transmitting loop into Cartesian grids. We improved the method for calculating the z-component of the magnetic field based on the characteristics of full space. Then, we established the fullspace 3D geoelectrical model using geological data for coalmines. In addition, the transient electromagnetic responses of water-filled goaves of variable shape at different locations were simulated by using the finite-difference time-domain (FDTD) method. Moreover, we evaluated the apparent resistivity results. The numerical modeling results suggested that the resistivity differences between the coal seam and its roof and floor greatly affect the distribution of apparent resistivity, resulting in nearly circular contours with the roadway head at the center. The actual distribution of apparent resistivity for different geoelectrical models of water in goaves was consistent with the models. However, when the goaf water was located in one side, a false low-resistivity anomaly would appear on the other side owing to the full-space effect but the response was much weaker. Finally, the modeling results were subsequently confirmed by drilling, suggesting that the proposed method was effective.

Local cell temperature monitoring for aluminum shell lithium-ion battery based on electrical resistance tomography

This paper presents an approach for the local the cell temperature monitoring of an aluminum shell lithium-ion battery cell by electrical resistance tomography, which has a great potential to analyze the correlation of apparent resistivity, local cell temperature and residual capacity. To determine this correlation, a flexible sensor was first designed, and the Wenner configuration was applied in the measurements. The investigated temperatures ranged from −20°C to 70°C. The results showed that the apparent resistivity had an exponentially increasing trend as the temperature increased. The effect of the residual capacity was further investigated. It is found that a lower residual capacity resulted in a lower apparent resistivity, which intensified as the temperature decreased. A comprehensive equation was developed to determine the local cell temperatures. Images of the apparent resistivity distribution under cell discharge further revealed the feasibility of the method. Finally, the proposed equation was applied to evaluate the cell core temperature which was compared with the surface temperatures from external sensors.

Characterization of geothermal reservoirs with electrical surveys: Beowawe geothermal field

The work reported here was undertaken to test the utility of electrical surveys for geothermal reservoir characterization using existing exploration and well data sets from the operating Beowawe geothermal field located in the Basin and Range Province of western USA. The STAR geothermal reservoir simulator was used to model the natural state of the system, and to compute the subsurface distributions of temperature and salinity, which were in turn utilized to calculate pore-fluid resistivity. Archie's law, which relates formation resistivity to porosity and pore-fluid resistivity, was adopted to infer the formation resistivity distribution. Subsequently, direct current (DC) resistivity, magnetotelluric (MT) and self-potential (SP) postprocessors were used to compute the expected response corresponding to available survey data. The measured apparent resistivity distribution from a dipole–dipole DC resistivity survey is in good agreement with the computed values. The calculated self-potential distribution agrees with the main features of an available SP survey. Although the computed MT apparent resistivity sounding curves reproduce the shapes of the measured MT sounding curves, an overall scale factor exists between the measured and calculated MT responses, and similarly with the computed dipole–dipole resistivity model. Possible reasons are static shifts in the coarsely sampled MT stations, and resistivity anisotropy due to the stratigraphy. Taken as a whole, the results of this study support the view that a suite of carefully designed electrical surveys (DC, MT, and SP) may be employed to infer favorable subsurface geothermal reservoir characteristics.

Subsurface structure exploration of wide landslide area by Aerial electromagnetic exploration

Aerial electromagnetic exploration obtains the ground resistivity of a wide area by measuring the intensity of a secondary magnetic field induced in the ground by a primary magnetic field. We conducted the AEM exploration in the Yamakoshi Village where was dameged by the Mid Niigata Prefecture Earthquake in 2004, for the landslide hazard assessment. The apparent resistivity distribution in the survey area differ between the Imogawa River Basin and the Asahigawa River Basin, and the former shows high resistivity and the later shows low resistivity with 30 Ω-m as the boundary. In the high resistivity zone that corresponds to the sandy rock distribution area, the large landslide blocks show lower resisitivity than in the surrounding ground. In sandy rock distribution areas, it is possible for the relatively low resistivity parts to be an index of the instability of slopes, even in landslide blocks where deformation has not yet appeared.

Combined application of dc and TEM to sea‐water intrusion mapping

A geoelectric survey using a dc resistivity method and a transient electromagnetic induction (TEM) method was carried out from 1986 to 1988. It was used to help map the lateral and vertical distributions of the freshwater/salt‐water interface in the Pei‐kang area on the west coast of Taiwan. The dc and TEM soundings were performed at 79 localities over an area of 240 km2 of Quaternary alluvium. Significant changes in pore‐water conductivity at some places were detected by these two methods. A low resistivity value (<1.5 ohm-m) implies salt‐water contamination of groundwater. The results of spatial distribution of apparent resistivity indicate the salt‐water‐affected aquifers are confined to the southwest part of the study area, and the affected aquifers are confined to the top of two aquifers. A geoelectric model with three to four layers is inferred from the joint inversion of dc and TEM data. Based on a modified Archie’s law suggested by the authors, an empirical relation between pore‐water resistivity of the stratum and formation resistivity can be obtained. It can be used to convert the computed resistivity of each geoelectric layer (aquifer) to the resistivity of the water contained in these layer, thus leading to the assessment of groundwater contamination. Repeated dc resistivity measurements have been carried out at selected locations once every year from 1986 to 1988. These data were used to monitor the temporal variation and a possible spreading of the salt‐water invasion. During 1995, a dc survey was conducted in the same area to compare with the dc sounding results obtained in 1988. The final results provide an evaluation of the efficiency of groundwater management in the study area.

Interpretation of resistivity sounding measurements in N-layer soil using electrostatic images

Geophysical inversion involves the estimation of soil parameters from a set of observations. Multilayer soils are modeled by N horizontal layers with distinct resistivities and depths. For known soil parameters, the apparent resistivity distribution can be computed efficiently from electrostatic images. Since the model responses are generally nonlinear functions of the model parameters, least-squared minimization techniques prove to be useful for evaluating layer resistivities and depths to agree with measurements. This paper demonstrates how electrostatic images can be combined for increasing efficiency in the computation of apparent resistivities and sensitivity factors such as the first and second gradient of the distance with respect to the model parameters. The factors are then used to solve the more demanding task of resistivity interpretation of measurements from Wenner, Schlumberger, Dipole or alternate electrode configurations. Results are presented for two-layer soil and for actual cases with three layer soil.

Numerical modelling of deep dipole-dipole MHD sounding

Distortion effects of surface geoelectrical inhomogeneities on deep MHD soundings must be taken into account in the interpretation of the measurements. Computer programs which calculate these effects for the steady-state part of the MHD pulses using the thin sheet approximation and which present the results graphically are used to study the distribution of apparent resistivity for various kinds of models in which the MHD generator is located off the coast of the Kola Peninsula.

Elimination of the regional coast effect an a local resistivity structure in the Noboribetsu geothermal area, southwestern Hokkaido.

Observations of electric and magnetic field variations were carried out in the Noboribetsu geothermal area, southwestern Hokkaido, in order to study a local three-dimensional behavior of electric and magnetic fields. Estimates of apparent resistivity and transfer functions are first examined for frequencies of 8-20Hz. The apparent resistivity distribution for this period range clearly shows a local zone of resistivity lower than 10ohm·m. Directions of induction vectors are generally perpendicular to the local gradient of apparent resistivity and hence no anomalous behavior is found. An attempt was made to pursue downward extension of this low resistivity zone by further analyzing the data at lower frequencies. Induction vectors at 0.03Hz all point toward the southeast and this trend is considered to be due to the regional coast effect. The result of two-dimensional model calculations of coast effect accounts for the overall distribution of induction vectors. The computed coast effect was subtracted to yield a local induction anomaly. Comparison of this local anomaly with the result of calculations for a model in which a three-dimensional block of low resistivity is embedded in a uniform half-space discloses the northward extension of the low resistivity zone. This feature is not clearly seen in the apparent resistivity distribution. It is thus concluded that induction vectors, if properly interpreted, provide important information on a local three-dimensional resistivity structure and hence they should be extensively used for geothermal exploration in addition to the conventional magnetotelluric method.