Electrical Sounding Method Research Articles

Constructing the Optimal Model of the Geoelectric Section Using Vertical Electrical Sounding Data: Case Study of the Central Part of the Garm Research Area

In geophysical studies, particularly when searching for precursors of earthquakes, there are problems of investigating the geoelectric structure of the medium at the observation point and its changes over time. This paper develops an approach to solving these problems based on the long-term medium monitoring data using the vertical electrical sounding (VES) method. The sounding was carried out daily for 12 years (from April 1979 to May 1992) in the central part of the Garm research area using a stationary multielectrode array. The data are used to construct about 4000 individual VES curves, which are then used to construct 36 10-day average curves for solving the inverse problem within a horizontally layered model using the IPI package. Four-, five-, six-, and seven-layer models of the geoelectric section are constructed based on the interpretation of the solutions. These models are compared by different criteria of their quality. As a result, a four-layer model is selected, which can be considered the best in the sense of minimizing the residual of the solution of the inverse problem, a horizontally layered approximation of the real (average for the seasons of the year) geoelectric section. A comparison of the available geological and geophysical data with each other and with the results of solving the VES inverse problem shows that the four-layer model of the section is in good agreement with the data of geological (drilling, geological mapping), geoelectric (transient electromagnetic sounding (TEM), profile VES), and other studies performed at the observation point.

Hydrogeological characterization of a carbonate aquifer using geophysical and geochemical approach: case of the Krachoua Formation in Tataouine area, Southern Tunisia

An integrated hydrogeological investigation involving geological surface data, well data (lithostratigraphical and piezometric data) and the vertical electrical sounding (VES) method was carried out in Tataouine area, Southern Tunisia to characterize the hydrogeology and the geochemistry of the Krachoua Formation aquifer. The electrical data were used to differentiate lithostratigraphic units and characterize their hydrogeological potentialities. Major elements contents within groundwater samples were assessed and some plots and diagrams have been established in order to investigate the hydrochemical properties of this aquifer and the origin of its mineralization. The Krachoua aquifer exhibits a general drawdown of the piezometric level from 2004 to 2015 reflecting a dramatic decrease in groundwater resources due to increased groundwater abstraction during the last decades. Flow directions shows that the recharge of this aquifer considered as a free aquifer is directly ensured by rainfalls over the outcropping fractured limestones. The geometry of the Krachoua Formation aquifer is tectonically controlled and structured in horst and graben features that impacted greatly the hydrogeology and the hydrodynamics of the area. Subsequent thickness and facies variations within this aquifer influenced the reservoir quality and the groundwater flows. The increased values of salinity to the northwest of the study area seems to be mainly related to the dissolution of the Upper Liassic gypsum of Mestaoua Formation which outcrops widely and can be dissolute easily by meteoric water and contaminate the Krachoua aquifer. This fact is also supported by the sulfated and calci-magnesian chloride facies of this aquifer related to the dissolution of evaporitic rocks (gypsum, anhydrite, and halite). However low salinity values are recorded within the zone where these evaporitic rocks are relatively deep.

A PRELIMINARY STUDY ON AQUIFER IDENTIFICATION BASED ON GEO-ELECTRICAL DATA IN BANDA ACEH, INDONESIA

The aquifers exploration has been conducted at the western part of Banda Aceh, Indonesia. This research aims to explore the aquifer layer beneath the surface and to obtain the cross-section model of the aquifer. The Vertical Electrical Sounding (VES) method was applied to investigate the aquifer layer. The VES method worked as the current penetrated into the ground using of two electrodes and the potential response due to its current being measured by another two electrodes. Ten grid points of VES has performed in western part of Krueng Aceh of Banda Aceh using the ARES (Automatic Resistivity Meter). The Res1Dinv and curve matching computer software used in VES data processing and analysis. The result shows the resistivity value of aquifer in Banda Aceh city at the range of 1 – 12 Ωm for freshwater, and 0.1 – 0.6 for brackish water layer. The first aquifer (water table) found at a depth of 0.5 to 2 meters beneath the surface. The 2-meters water table mostly located near the coastal zone or downstream zone of Krueng Aceh basin and shallow depth of 0.5 meters on the upstream. More than one aquifer layers were found beneath the surface, they were separated by aquitard layer consisting of silt to clay layers.

Perfecting the Advanced 2D Multi-electrode Electrical Exploration method

The Advanced Multi-electrode Electrical Sounding method (AMES) proposed by us was introduced at VNU. Journal of Mathematics-Physics, No. 31 (3), 2015. However, the published results are mostly focused on the symmetric MC array and tested on a theoretical model. In this paper, the authors continue systematically presenting and supplementing the results obtained after the study, namely the finalization and renaming of the AMES method into the Advanced 2D Multi-electrode Electrical Exploration (AMEE) method, including MC array, data collecting and processing, and testing on theoretical model and practical application to confirm the superiority of this method.

The use of Electromagnetic and Vertical Electrical Sounding Methods in Groundwater Exploration.

Electromagnetic (EM) profiling and Vertical Electrical Sounding (VES) studies were carried out for groundwater exploration in the Twifo – Hemang Lower Denkyira Districts of Ghana. These two geophysical methods were used for exploring the groundwater potentials beneath Achiase, Mbaa Mpe Hia Community and Moseaso Community. This paper seeks to encourage the use of inversion for interpreting electromagnetic data rather than the usual qualitative interpretation method using line graphs and also the use of apparent resistivity maps as 2D pseudo resistivity maps to support interpretations of the 1D inversion results (in cases where the available budget could not permit 2D and or 3D inversion). These would help in enhancement of obtained results, reduce ambiguity and help decision making. The EM results revealed that; the three communities are underlain by two layers with the first layer having the thickness range between 2 to 10 m and the second layer is a half space. The results from VES studies indicate that; Achiase Community and Mbaa Mpe Hia No. 2 community are underlain by three geoelectrical layers and Moseaso Community is underlain by four geoelectrical layers. On the basis of this study the Moseaso Community is ranked highest in terms of groundwater potential followed by the Achiase community and finally the Mbaa Mpe Hia No.2 Community. Several sites were recommended for drilling boreholes for water supply in these communities.

AQUIFER TRANSMISSIVITY VALUES FROM VES FOR PARTS OF PORT HARCOURT, RIVERS STATE, NIGERIA

This paper presents aquifer transmissivity values obtained from vertical electrical sounding method from some locations in Port Harcourt Local Government Area of Rivers State. Twelve (12) stations were occupied using the Schlumberger electrode configuration with maximum electrode spacing of 400 m. The data were interpreted using IPI2WIN software version 3.0.1 (2003).The results reveal four layer strata with transmissivity (Tr) values of between 145.53 and 18264.42 m2/day with average value of 7252.23 m2/day. These indicate high aquifer transmissivity values for the study area with high permeable and significant storability of the formations that enhances the migration and circulation of ground water within the region. The results indicate that the southern part of the study area is the most prolific in terms of groundwater exploitation and thus the most promising in sitting productive boreholes.

IDENTIFICATION OF AQUIFER USING RESISTIVITY GEOELECTRIC METHOD IN REGIONAL OF BEBANDEM, KARANG ASEM, BALI

Bungaya Kangin Village, Bebandem District, Karangasem Regency, Bali Province consists of paddy fields and settlements, required therefore a water source / aquifer that can meet all these needs. One of the Geophysical Methods that can identify the aquifer is the Geoelectric Method. Geoelectric method used in this research is Resistivity Method. Data acquisition using Vertical Electrical Sounding (VES) and Electrical Resistivity Tomography (ERT) Methods. VES method is a method of measurement to determine the variation of resistivity vertically at one point. Electrical Resistivity Tomography (ERT) method is a method of measuring resistivity on soil surface / rock by using many electrode (51 electrode), to obtain sub-surface resistivity variation lateraly and verticaly, to obtain sub-surface image. The equipment used for geoelectric measurements is Resistivity Meter of Naniura NRD 300 Hf which has been equipped with a switchbox to adjust the displacement of 51 electrodes. Based on the resistivity modeling results, the aquifers in the study area were found in rough sandstones with resistivity values : (49 - 100) Ohm.m.

Electrical resistivity mapping of oil spills in a coastal environment of Lagos, Nigeria

Three years after the oil spillage and pipeline explosion that claimed about 100 human lives at Ijegun Community of Lagos–Nigeria, a combination of carefully designed 2D Electrical Resistivity Profilling and Vertical Electrical Sounding methods was deployed to map and characterise the subsurface around the contaminated site. Data acquired were processed, forward modelled and tomographically inverted to obtain the multi-dimensional resistivity distribution of subsurface. The results of the study revealed high resistivity structures that indocate the presence of contaminant (oil plumes) of different sizes and shapes around the oil leakage site. These high resistivity structures are absent in the tomograms and resistivity-depth slices computed for Iyana—a linear settlement not affected by oil spillage. The five geo-electric layers and the resistivities delineated in the area are the top soil layer, 220–670 Ωm; clayey sand layer, 300–1072 Ωm; top sand layer, 120–328 Ωm; mudstone/shale layer, 25–116 Ωm and the bottom sand layer, 15–69 Ωm. The base of the first four geo-electric layers corresponds to 3.9, 8.4, 27.2 and 34.6 m respectively. The two groundwater aquifers delineated correspond to the third and fifth geo-electric layers. The top aquifer has been infiltrated by oil plumes. The depth penetrated by the oil plume decreases from 32 m to about 24 m across the survey profiles from the two ends. It was concluded that the contaminant plumes from the oil spillage are yet to be completely degraded as at the time of the study. It is recommended that the contaminated site be remediated to remove or reduce the contaminant oil in the subsurface.

An approach to estimate total dissolved solids in groundwater using electrical resistivity sounding and geochemical methods

Electrical resistivity method gives somewhat reliable results in hydrogeophysical deductions, in which the disposition of aquifers can be suitably deciphered. The present study was conducted to validate the use of geoelectric sounding in estimating total dissolved solids (TDS) in groundwater. Twenty (20) resistivity measurements obtained have been interpreted by curve matching and computer iteration and converted to formation resistivities and thicknesses. The resistivities of the aquifer delineated were subsequently used to estimate TDS in groundwater which was correlated with those derived from previous geochemical analyses of ten (10) groundwater samples taken near sounding locations. The result shows a strong correlation (R2 > 0.8) indicating that the TDS determined by geoelectric sounding and geochemical method give similar results.KEYWORDS: Total dissolved solid; groundwater; geoelectric; geochemical; aquifer

Identification of aquifer potential in Karanganyar city by using vertical electrical sounding method

The identification of aquifer was done by using Vertical Electrical Sounding (VES) method. This research aims to identify potential and depth of the aquifers. The locations of surveys are at ten points,namely TS1 (Alastuwo), TS2 (Wonorejo), TS3 (Kaling), TS4 (Kaling), TS5 (Buran), TS6 (Wonolopo), TS7 (Buran), TS8 (Ngijo), TS9 (Jati), and TS10 (Suruhkalang) where all located in Karanganyar regency. The survey path is about 500-600 meters length which can penetrate current to 100 – 200 meters in depth. The measurement was done by using OYO Mc OHM-EL Model 2119C. Geoelectrical data analysis was processed using Progress version 3.0 Software. The interpretation result shows that the locations of research area are included in Lawu-volcano rock formation which is breccias, lava, and tuff as the constituents. We found that unconfined aquifer in all of locations with different depth and confined aquifer just 7 locations start from 25.04 meters.

Prospecting for Groundwater Using the Continuous Vertical Electrical Sounding Method

2-D CVES surveys using the Wenner configuration was carried out in 22 communities in the Tain District, Ghana. This was done with the objectives of assessing the subsurface geology, identify high groundwater potential zones for drilling high-yielding boreholes that could yield sustainable amount of groundwater. The collected resistivity data were converted from the apparent resistivity to 2-D modelsection using the least-square inversion algorithm with the help of Res2DInv software. The 2-D resistivity model-sections produced a high quality structural resolution leading to the demarcation of the layering of various lithological units, weathered layers and identification of important structures such as joints, fractures and faults. Quantitatively, it can be observed that all the drilled wet wells have aquifer zones between 30 m and 60 m within sandstone, siltstone and phyllite granitic environments. The result of the borehole drill logs revealed that the aquifers were within weathered and fractured zones and is in agreement with the models. The results showed that the boreholes yield within the study area varied between a minimum of 15 litres/min to a maximum 800 litres/min and the mean depth for intercepting aquifer was at about 30 m and below. The study revealed that the potential aquifer zones in the study area are mostly as a result of weathering of the overburden and fracturing of the underlying bedrock. The results suggest that the hydrogeology of the study area is highly complex since the development of groundwater is generally due to secondary porosities.

Groundwater resources evaluation in calcareous limestone using geoelectrical and VLF-EM surveys (El Salloum Basin, Egypt)

Understanding and developing groundwater resources in arid regions such as El Salloum basin, along the northwestern coast of Egypt, remains a challenging issue. One-dimensional (1D) electrical sounding (ES), two-dimensional (2D) electrical resistivity imaging (ERI), and very low frequency electromagnetic (VLF-EM) measurements were used to investigate the hydrogeological framework of El Salloum basin with the aim of determining the potential for extraction of potable water. 1D resistivity sounding models were used to delineate geoelectric sections and water-bearing layers. 2D ERI highlighted decreases in resistivity with depth, attributed to clay-rich limestone combined with seawater intrusion towards the coast. A depth of investigation (DOI) index was used to constrain the information content of the images at depths up to 100 m. The VLF-EM survey identified likely faults/fractured zones across the study area. A combined analysis of the datasets of the 1D ES, 2D ERI, and VLF-EM methods identified potential zones of groundwater, the extent of seawater intrusion, and major hydrogeological structures (fracture zones) in El Salloum basin. The equivalent geologic layers suggest that the main aquifer in the basin is the fractured chalky limestone middle Miocene) south of the coastal plain of the study area. Sites likely to provide significant volumes of potable water were identified based on relatively high resistivity and thickness of laterally extensive layers. The most promising locations for drilling productive wells are in the south and southeastern parts of the region, where the potential for potable groundwater increases substantially.

Application of the Electrical (Geophysical) Method for the Identification of the Sealed Bevel in the Coastal Region of Walidia Province of el Jadida – Morocco

The Walidia area knows a great development of agricultural, industrial, maritime activities and a very great demographic expansion. This development is accompanied by a growing demand for water. On the other hand, any intense abstraction of fresh water at a coastal aquifer capture field causes a decrease in groundwater flow and a lowering of the piezometric surface. There is therefore a danger of advancing towards the land of the saltwater bevel and salinization of groundwater which is gradually loaded into mineral salts and can reach abnormally high levels. This work deals with the application of geophysics by electrical sounding method to the in-depth study of the freshwater-salt water interface (salted bevel) on the one hand and the study of the lateral and vertical evolution of the geometry of the different aquifers. The principle of the method is, when performing an electrical survey, to research how varies, at a given point on the surface, the resistivity of the subsoil vertically. For this one executes in a same place a succession of measurements, increasing each time the dimensions of the device and thus the depth of investigation which is proportional to them. At this site, we explore a slice of ground increasingly thick and thus highlights the changes in geological constitution along the vertical. The electrical soundings were carried out with the classic Schlumberger device. The interpretation and the exploitation of the data of the electric soundings carried out made it possible to : Follow the evolution of the salted bevel roof, Draw the upstream limit (marine invasion) of salted bevel Hauterivian, on the one hand, and Valanginian and Jurassic on the other hand, Follow the roof structure of Dridrat limestone (Hauterivien) and limestones of Valanginien and Upper Jurassic, Draw the map of the marl roof of Safi (Hauterivian) constituting the impermeable substratum of Dridrat limestones.

3D imaging of quarry materials using electrical soundings

In order to satisfy a need for aggregates required to build a section of the Algeria East–West Highway, a geophysical study was carried out. Seventy-five soundings were conducted in three different sectors, with twenty-five soundings per sector. The goal of the investigation is to study the deep limestone. The chosen method is sensitive to the formation types that characterize the area under investigation made of high-resistivity limestone and more conductive marls. The study site is located near Didouche Mourad city (eastern Algeria). Measurements were achieved using a Shlumberger device whose AB line length is equal to 650 m. Erroneous values were eliminated using the median filter. To invert the electrical sounding, the “smoothed model” technique was used. Based on the electrical sounding interpretation, we ended up with several conclusions. They can be summarized as follows: The electrical sounding method seems to have solved the problem raised from the beginning. Indeed, the electrical resistivity contrast between the limestone and the surrounding marl formations was very useful in precisely determining their geometry and evaluating their extension, depth and thickness. Sector 1 has an appreciable limestone thickness in its central part. Sector 2 indicates the presence of a substantially uniform limestone layer over almost the entire site. The layer’s small depth (a few meters) and its relative important thickness (50 m on average) make this sector very promising. Sector 3 is the least favorable in terms of limestone presence. Aggregate reserves in the first two sectors seem interesting.

EVALUATION OF GROUNDWATER POTENTIAL OF ODEDA LOCAL GOVERNMENT AREA, OGUN STATE, SOUTHWEST NIGERIA

Evaluation of groundwater potential in Odeda Local Government Area, Ogun State, Southwestern Nigeria, has been carried out in this study using Vertical Electrical Sounding method. The study area is underlain by Precambrian Basement Complex rocks of Southwestern Nigeria. These rocks are inher-ently characterized by low porosity and permeability. The interpretation of thirty (30) vertical electrical sounding (VES) conducted using the Schlumberger electrode array shows four geo-electric layers in the subsurface within the study area. The overburden thickness varies from 5.9 to 39 m across the study area. This was used to prepare the groundwater potential map which assisted in the zoning of the area into low, medium and high groundwater potential zones. The study showed that about 60% of the study area falls within the low/medium rated groundwater potential zone while the remaining 40% constituted the high groundwater potential zone. Hence, the groundwater potential rating of the area is generally low.

Groundwater Exploration in the Basement Complex Around Chibok Area in North- Eastern Nigeria Using Vertical Electrical Sounding Method

A geophysical survey employing Schlumberger electrode configuration using vertical electrical sounding (VES) method was carried out around Chibok area within the Basement Complex of north-eastern Nigeria using an ABEM SAS 300C Terrameter with a view to exploring groundwater within the study area. The overburden in the area ranges from about 15m to 58.5m thick. This overburden, based on geoelectrical interpretations, consists essentially of top soil, decomposed crystalline rock, highly weathered crystalline rock, weathered or fractured crystalline rock and weathered to fresh crystalline rock. The study suggest that the vicinities of all the VESs are best suited for the siting of boreholes apart from VES 1 and 5 due to the presence of fresh crystalline rock at shallow depth.Keywords: Hydrogeology, Basement Complex, Alluvium, Colluviums, Electric resistivity, Chibok

Controlled source radiomagnetotellurics: A tool for near surface investigations in remote regions

In the course of near surface measurements, we investigated the application of the controlled source radiomagnetotelluric (CSRMT) sounding method. The used equipment RMT-C includes a five-channel recorder (frequency range 1–1000kHz), two electric and three magnetic sensors, and a transmitter (1kW) with a horizontal electric dipole as a source. The electric field measurements are carried out with ungrounded lines thus enabling surveys in the wintertime on snow and ice, and in the summertime in conditions adverse to the groundings. The use of electric dipole as a source ensures operating in a wide frequency range at a significant distance (up to 3–4km) from the source. Measurements of basic signals and their odd sub harmonics raise the efficiency of the field surveys. For the covering of the full frequency range 1–1000kHz, three basic frequencies are usually transmitted; each one is accompanied by 8–12 sub harmonics. This provides a high rate of measurements, i.e. about 70 sounding stations per day - 10 times faster than by the vertical electric sounding (VES) method. The CSRMT method offers the possibility to work in the far-field zone of the controlled source where the plane wave approximation of the primary field can be used. For the analysis of the high-frequency field of the electric dipole, an approach is used considering quasi-stationary and wave zones of the source. Features of the electromagnetic field are analyzed by taking into account displacement currents in the air. In the wave zone, at a certain distance from the source (tens to hundreds of meters), field components are characterized by a number of differences compared to a quasi-stationary zone (slower drop of the field's amplitudes, change of the directional diagram of the source, appearance of the ellipticity of polarization of electric and magnetic fields). The CSRMT method is intended for the application in remote regions where surveys by the standard RMT method could only use Very Low Frequency (VLF) radio transmitter signals. Examples for the application of the CSRMT method are presented from the Arkhangelsk region (geophysical support of an onshore gas pipeline construction), and the Chukotka Peninsula (survey at a site of the ore-dressing factory construction). The CSRMT results were confirmed by the subsequent drilling.

Geophysical evaluation of groundwater potential in part of southwestern Basement Complex terrain of Nigeria

The geophysical assessment of groundwater in Awa-Ilaporu, near Ago Iwoye southwestern Nigeria was carried out with the aim of delineating probable areas of high groundwater potential. The area falls within the Crystalline Basement Complex of southwestern Nigeria which is predominantly underlain by banded gneiss, granite gneiss and pegmatite. The geophysical investigation involves the very low frequency electromagnetic (VLF-EM) and Vertical Electrical Sounding (VES) methods. The VLF-EM survey was at 10 m interval along eight traverses ranging between 290 and 700 m in length using ABEM WADI VLF-EM unit. The VLF-EM survey was used to delineate areas with conductive/fractured zones. Twenty-three VES surveys were carried out with the use of Campus Ohmega resistivity meter at different location and at locations areas delineated as high conductive areas by VLF-EM survey. The result of VLF-EM survey along its traverse was used in delineating high conductive/fractured zones, it is, however, in agreement with the delineation of the VES survey. The VES results showed 3–4 geoelectric layers inferred as sandy topsoil, sandy clay, clayey and fractured/fresh basement. The combination of these two methods, therefore, helped in resolving the prospecting location for the groundwater yield in the study area.

Integrated geophysical investigation of the causes of road pavement failure along Ibadan-Lagos dual-carriage, Southwestern, Nigeria

An integrated geophysical study has been conducted in a segment of Ibadan- Lagos Dual-carriage road to examine the geological factors responsible for highway failure. Schlumberger Vertical Electrical Sounding (VES) and Very Low Frequency Electromagnetic Method (VLF-EM) to evaluate the subsurface integrity, mapping out the subsurface structural features within the sub-grade soil and delineating the bedrock relief as a means of establishing the causes of road pavement failure of 1300 m stretch of road from Ibadan axis. Results from VLF-EM showed the presence of near surface linear geologic structures from the surface to a depth of 15 m which suggests probable conductive zones that have devastating effects to the foundation of the road pavement (g1, g2 and g3). VES results showed the presence of four geologic layers while fractured basement were observed with resistivity value generally less than 100 Ωm which indicates the presence of the water table. The unstable segment is characterized by low resistivity of the near surface materials and shallowness of the aquifer zone on which the road pavement was constructed. The failure of the road is caused mainly by geologic sequence and structures such as clayey subgrade soil under the road pavement and some suspected geological features such as faults and fractures. Keywords: Lithologic contacts, aquifferous zone, geoelectric section, linear contact, sub-grade soil

A MATLAB PROGRAM FOR THE ANALYSIS AND INTERPRETATION OF TRANSIENT ELECTROMAGNETIC SOUNDING DATA

Herein we present a software system, written in MATLAB, to interpret TEM sounding data. The program, dubbed maTEM, is designed to process, model and invert multiple soundings, either individually, or simultaneously along profiles. The latter capability allows for laterally constrained inversion, so as to generate pseudo-2D or 2D resistivity sections based on the program EM1DINV v2.13 by the Hydro-Geophysics Group of the University of Aarhus, Denmark. Using maTEM, the analyst may import and display data multiple data sets, denoise and smooth the data, perform approximate inversions, design 1-D model(s) graphically, perform forward modelling and inversion and generate/ update data base in which to store the results. Finally, the analyst may use the data base to create 2-D and 3-D displays of the geoelectric structure with built-in graphical functions. maTEM is highly modular so that additional functions can be added at any time, at minimal programming cost. Although the software presented herein is focused on the analysis of TEM data, the maTEM concept has been designed ready to incorporate additional electrical and EM geophysical sounding methods and to mutually constrained analysis of different geophysical data sets.